Question:
Popular news has several articles linking back to the news article in Nature Earth’s magnetic field is acting up and geologists don’t know why which discusses the need for an early update to the World Geomagnetic Model.

However my question is about one line found in the Independent's Planet’s erratic magnetic field forces emergency update to global navigation system

The shift they observed was so large it was on the verge of exceeding the acceptable limit for navigation errors.

To account for this, scientists at the British Geological Survey and the US National Oceanic and Atmospheric Administration (NOAA) are issuing an unprecedented emergency update to the model.

They have fed in the latest data, including an unexpected geomagnetic pulse that took place beneath South America in 2016, to ensure the system is more accurate.

Question: What is the nature, and underlying cause of the "unexpected geomagnetic pulse that took place beneath South America in 2016"?

AKA geomagnetic jerk.

Explanation: the cause of the geomagnatic pulse is the magnetic field change.

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The "geomagnetic pulse" here refers to a series of academic works studying the
Earth's core such as [ this open access article
](https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2013JB010604)
(other related articles require scientific journal subscriptions to read).

Geomagnetic pulses have been associated with [ "geomagnetic jerks"
](https://en.wikipedia.org/wiki/Geomagnetic_jerk) . [ A jerk was reported (yay
for open access again) to have occurred in 2014
](https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2015GL065501) , the
2016 pulse under South America is believed to be related to this, both events
having been measured and identified after the fact.

The magnetic field is always changing - a "pulse" is a quicker-than-normal
(few year) acceleration of magnetic field change in time, in a region at the
surface of the Earth's outer core (magnetic field is generated within the
core).

A "jerk" is a quick change (few months) of the rate at which magnetic field
changes at Earth's surface, making something like a 'V' shape if you plot the
field against time at a given location.

The idea is that a pulse occurs at the core, and jerks are an effect seen at
the surface just before and after the peak of the pulse, as the field change
ramps up and down. _The underlying cause of this is not known_ , and we only
identify them after they've occurred, so they're currently unpredictable. That
said this behaviour is apparently part of the core's repertoire, and pulses
and jerks have been observed before.


Question: What parts of the fossil record are most lacking in specimens? That is, if you were to trace the evolution of a modern mammal (humans, for example) from abiogenesis to now, which periods are the most lacking in fossils? Where are the biggest gaps in our evolutionary history.

Explanation: The time period Precambrian, specifically pre-Ediacarian, is most lacking of specimans.

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The biggest temporal gap would be (IMO) the Precambrian, specifically pre-
Ediacarian. Accordingly the biggest gap in the evolutionary history is the
origin of eukaryots, both because of the paucity of pre-Ediacarian formations
but also because few of the early protists were likely to be fossilizable.

From the probable apparition of life ca. 3.8-3.5 Ga (e. g. **1** for a review
of Archean fossils) to the Ediacarian (ca. 600 Ma) in which metazoans (i. e.
"animals") are already diverse (e. g. **2** ), this is more than 3 Ga of life
history for which we have very little fossils (though our knowledge of this
fossil record increases currently thanks, in part, to our better understanding
of the "chemical" fossil record).

**1** : J. W. Schopf, 2006. [ Fossil evidence of Archaean life.
](http://rstb.royalsocietypublishing.org/content/361/1470/869) Philosophical
transactions of the Royal Society, B., 361: 869-885.
**2** : S.Conway Morris, 1993. [ The fossil record and the early evolution of
the Metazoa
](http://www.nature.com/nature/journal/v361/n6409/abs/361219a0.html) . Nature,
361: 219-225.


Question:
Okay, so I believe that most of the impact/collisions happen at oblique angles to the planet's radial direction. (I am not very sure about this, but since it is not a freefall, we can assume that the collision is oblique).

So why are most of the craters radially symmetric?

Why isn't the depression skewed?

I have almost never come across a photograph of a skewed crater.

Explanation: The post wants to find out why the impact craters are symmetric. It's due to the explosion when happening.

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The main reason why impact craters are close to symmetrically round is because
it's the explosion of the impactor, not its collision, that creates the impact
crater. The impactor is travelling so fast that, rather than simply exploding
on impact, it burrows deep into the collision site, heats up from compression
and friction, and explodes deep underground, thus creating a more-or-less
perfectly round crater.


Question:
I thought Auroras are only visible in the North Pole and South Pole, but recently, I found out that Auroras can be seen in areas of the world closer to the equator.

An example is that in the year 1909, a great storm of Auroras were seen in Japan and other countries.

This made me wonder: could an Aurora be seen in equatorial regions, too?

Explanation: The post wants to check if it's possible to see auroras in the equator. The anwser says that it's possible theoratically, but very little chance.

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Quoting from the Wikipedia article on the [ Solar Storm of 1859
](http://en.wikipedia.org/wiki/Solar_storm_of_1859) ;

> On September 1–2, 1859, the largest recorded geomagnetic storm occurred.
> Aurorae were seen around the world, those in the northern hemisphere even as
> far south as the Caribbean; those over the Rocky Mountains were so bright
> that their glow awoke gold miners, who began preparing breakfast because
> they thought it was morning.[2] People who happened to be awake in the
> northeastern US could read a newspaper by the aurora's light.[4] The aurora
> was visible as far from the poles as Cuba and Hawaii.

So, it didn't quite make it to the equator, but it came very close. There is
no physical reason why you can't get aurora at the equator, but it takes a lot
of very energetic particles being ejected by the sun over a brief period.

However, as I mentioned in my comment, a solar storm of that magnitude would
wipe out most of the Earth's electric grids. Even the telegraph systems of the
1800's couldn't survive. Another quote from the Wikipedia article;

> Telegraph systems all over Europe and North America failed, in some cases
> giving telegraph operators electric shocks.[6] Telegraph pylons threw
> sparks.[7] Some telegraph systems continued to send and receive messages
> despite having been disconnected from their power supplies.[8]


Question:
The Yellowstone National Park in Wyoming is unique for its large number of "thermal occurrences, of which there are some 30 geysers. This, in turn, appears to be the result of the presence of large quantities of molten rock, and the thinness of the earth's crust there, compared to the other spots on the earth.

To the best of my knowledge, there is no other (known) place on earth where so much thermal power is contained in a relatively small area. Is this in fact the case? If so, what made Yellowstone, Wyoming so unique in this regard?

Explanation: The post wonders if the yellowstone park is unique for geysers. Actually it's famous for being build above a mantle plume

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Yellowstone is thought to be above a [ mantle plume
](http://en.wikipedia.org/wiki/Mantle_plume) , of with there are tens to
hundreds on our planet, although there is plenty of [ debate on this matter
](http://geology.gsapubs.org/content/40/5/479.full) . The exact nature of
mantle plumes is a huge area of hotly contested research, but generally the
are thought to be large melts originally sourced from the D'' layer (core /
mantle boundary). Below the park, the plume is theorized to have resulted in
magmatic intrusions overlain by a hydrothermal system. The intrusions can also
be considered as magma chambers of a supervolcano, which has had several
ultraplinean caldera-forming events.

The Yellowstone hotspot is the only obvious expression of a mantle plume
beneath the continental United States, which may be why you consider it
"unique." The other major plume / hotspot in the US is Hawaii.

Yellowstone is certainly not the only major geothermal area in the world;
geothermal areas in New Zealand, Italy, Japan and Antarctica are comparable in
terms of heat flow. It's unclear what you mean by "thermal power" but
Yellowstone park does not have any geothermal electric power generation
plants. New Zealand, on the other hand, generates 13% of their national power
needs geothermally.


Question: In an area of frequent thunderstorms, I notice a 'crack or whoosh' sound if a strike is nearby but little or no thunder. Yet I can hear for 30 seconds or so after a distant flash when the thunder first is heard, the sound starts at a high frequency and then evolves into a deep rumble that can shake the walls. It approaches the sub-sonic. What is the relationship between the distance and the energy of the strike?

Explanation: The thunder origin's varying distances from the observer can generate a rolling or rumbling effect.

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Since the sound waves propagate not from a single point source but along the
length of the lightning's path, the sound origin's varying distances from the
observer can generate a rolling or rumbling effect. Perception of the sonic
characteristics is further complicated by factors such as the irregular and
possibly branching geometry of the lightning channel, by acoustic echoing from
terrain, and by the typically multiple-stroke characteristic of the lightning
strike.

In addition, thunder will sound louder when the air near the ground is colder
and the air higher in the atmosphere is warmer. This is because the acoustic
shock waves get "trapped" in the cold air. Such a temperature difference,
called an inversion, tends to happen at night, which is why thunder often
sounds louder at night.

See [ Wikipedia ](http://en.wikipedia.org/wiki/Lightning#Thunder) and [
wisegeek.org ](http://www.wisegeek.org/what-causes-thunder.htm)


Question:
I am working on a data visualisation of airline flight paths and their probability of forming contrails.

Given weather data for a specific area (location, time, temperature, pressure and humidity) and aircraft data (location, time, altitude, speed and engine efficiency)

Is there an equation that will give me a rough estimate of the probability contrails will form at this point?

Explanation: Schmidt-Appleman criterion (SAC) is used to model contrail formation, which gives a rough estimate of the probability contrails

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Schmidt-Appleman criterion (SAC) is used to model contrail formation. I advise
reading in full Ulrich Schumann's article "A contrail cirrus prediction model"
( [ http://www.geosci-model-dev.net/5/543/2012/gmd-5-543-2012.pdf
](http://www.geosci-model-dev.net/5/543/2012/gmd-5-543-2012.pdf) ) to get all
the relevant formulae and literature references.

While it is possible to transcribe the formulae here, the reference cited does
a better job of presenting state of the art (2012).


Question:
The Wikipedia article on the subject of the "Antarctic ice sheet" says that:

The icing of Antarctica began in the middle Eocene about 45.5 million years ago and escalated during the Eocene–Oligocene extinction event about 34 million years ago.

The article later says that:

Ice enters the sheet through precipitation as snow. This snow is then compacted to form glacier ice which moves under gravity towards the coast.

However it looks like, from the photos of Antarctica, that this transfer of ice to the coasts is not happening everywhere on Antarctica. Rather, many places seem to be under a perpetual ancient ice cover.

If the precipitation was recycled at a continuous rate everywhere, it shouldn't be possible to obtain a 1.5 million year old core sample (according to an article in Nature) or structures such as Vostok Station that covers an ancient lake.

A similar location is Dome F that according to Wikipedia has a yearly precipitation of about 25 mm (millimeters; approx. 0.98 inches).

So the question is, if we have a 25 mm precipitation per year for even just 10 million years, we should have an ice cover that's 250 kilometers thick. Or if we had it during just a 5 million year time span, it should give us an ice cover that's 125 kilometers thick.

Reasonably we could allow for some compression of the ice but still keeping in mind that we are not talking about a neutron star here.

How come the current Antarctic ice cover is just a couple of miles thick?

Explanation: The author wonders what determines the thinkness of ice cover. It's based on  accumulation, ablation and compaction.

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Ice floats with gravity towards lower elevation, the flow continues until the
base of the ice sheet becomes floating and the ice forms an ice shelf or
icebergs.

Due to the subglacial topography, basal melting and mass balance, the flow
velocities vary over a large range, faster outflows are glaciers. The pattern
is somehow similar to how rivers transport rainwater towards the coasts.

The thickness of the ice sheet is controlled by a complex relation between [
accumulation ](https://en.wikipedia.org/wiki/Accumulation_zone) , [ ablation
](https://en.wikipedia.org/wiki/Ablation_zone) and compaction.

[ ![Flow velocities MEaSUREs, plotted from
Quantarctica](https://i.sstatic.net/mC9rd.jpg)
](https://i.sstatic.net/mC9rd.jpg) _Flow velocities from[ MEaSUREs
](https://nsidc.org/data/docs/measures/nsidc0484_rignot/) (NASA), plotted from
[ Quantarctica ](http://quantarctica.npolar.no/) _

The ice velocity map shows, that some areas are unaffected by the flow towards
the coast. Some of these areas are ice-free. Also at some inland locations, as
Vostok, the velocity is very slow. Also, note that this is the surface
velocity. At the base, the ice flows slower or not at all.

To investigate the mass balance further, I recommended you to download [
Quantarctica ](http://quantarctica.npolar.no/) and look closer at the
datasets. [ Shepherd et al (2012)
](https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140006608.pdf) is a
good first read about the methods used to estimate changes in ice mass and the
present changes.


Question:
The line on the ground at the Greenwich Observatory is itself on a tectonic plate that is moving, so is the prime meridian still 0 degrees, 0 minutes, 0 seconds?

If not - what are the implications (if any)? For example, if my GPS says I am 100 km west of Greenwich Observatory, am I 100 km west of 0 0 0 or 100 km west of the line on the ground? Who (and what) decides this kind of thing?

Curious punter, not a scientist....

Explanation: The author wonders if the prime meridian moves as the land it on is moving. Answer is yes.

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Remember it is just an imaginary line on the Earth's surface used for
georeferencing purposes, so movement of the reference line has no implications
so long as we can still reference to it (hence the International Reference
Meridian).

In fact, the position of the Greenwich meridian has changed throughout
history, mainly due to the Airy Transit Observatory (the original location of
the Greenwich meridian) being built next door to the previous one (to maintain
the service to shipping). Such changes had no significant practical effect.
Historically, the average error in the determination of longitude was much
larger than the change in position. The adoption of WGS84 ("World Geodetic
System 84") as the positioning system has moved the geodetic prime meridian
102.478 metres east of its last astronomic position (measured at Greenwich).
The position of the current geodetic prime meridian is not identified at all
by any kind of sign or marking (as the older astronomic position was) in
Greenwich, but can be located using a GPS receiver. Due to the movement of
Earth's tectonic plates, the line of 0° longitude along the surface of the
Earth has slowly moved toward the west from this shifted position by a few
centimetres; that is, towards the Airy Transit Observatory (or the Airy
Transit Observatory has moved toward the east, depending on your point of
view) since 1984 (or the 1960s). With the introduction of satellite
technology, it became possible to create a more accurate and detailed global
map. With these advances there also arose the necessity to define a reference
meridian that, whilst being derived from the Airy Transit Circle, would also
take into account the effects of plate movement and variations in the way that
the Earth was spinning - the International Reference Meridian.

See:

Malys, S., Seago, J.H., Pavlis, N.K. et al. (2015) "Why the Greenwich meridian
moved" Journal of Geodesy. 89 (12) pp 1263–1272

Dolan, G (2013). "WGS84 and the Greenwich Meridian". The Greenwich Meridian.


Question: Why are tropical cyclones in the Bay of Bengal more frequent and stronger than those in the Arabian Sea?

Explanation: a low level jet covers the Arabian Sea during the indian sunner moonson, which cause tropical cycolones at the north india.

$\begingroup$

During the Indian Summer Monsoon, a low level jet covers the Arabian Sea. This
causes vertical wind shear to increase over the Arabian Sea and inhibits
cyclogenesis in the region. Hence, less tropical cyclone activity compared to
the Bay of Bengal.

[
http://www.meted.ucar.edu/tropical/textbook_2nd_edition/print_3.htm#page_5.3.0
](http://www.meted.ucar.edu/tropical/textbook_2nd_edition/print_3.htm#page_5.3.0)
(Need account to login) [
http://www.nature.com/nature/journal/v479/n7371/full/nature10552.html#ref1
](http://www.nature.com/nature/journal/v479/n7371/full/nature10552.html#ref1)
(First line)


Question:
I was reading this article about Zealandia and got excited that there could be an underwater continent. However, when viewing the image (below) it appears that Zealandia is much smaller than any other continent. The article says the bases considered were:

elevation above the surrounding area
distinctive geology
a well-defined area
a crust thicker than the regular ocean floor
Is there some criteria on size that should be met to be classified as a continent? If so, does Zealandia meet that criteria? Or, is it possible that Zealandia is a continental fragment?

Explanation: Zelandia meets the criteria of being a continent.

$\begingroup$

In the [ GSA Today article
](http://www.geosociety.org/gsatoday/archive/27/3/article/GSATG321A.1.htm)
that Michael linked to in the comments, it says:

> The Glossary of Geology defines a continent as “one of the Earth’s major
> land masses, including both dry land and continental shelves” (Neuendorf et
> al., 2005). It is generally agreed that continents have all the following
> attributes:
>
>   1. high elevation relative to regions floored by oceanic crust;
>   2. a broad range of siliceous igneous, metamorphic, and sedimentary rocks;
>   3. thicker crust and lower seismic velocity structure than oceanic crustal
> regions; and
>   4. **well-defined limits around a large enough area to be considered a
> continent rather than a microcontinent or continental fragment.**
>

>
> The first three points are defining elements of continental crust and are
> explained in many geoscience textbooks and reviews (e.g., Holmes, 1965;
> Christensen and Mooney, 1995; Levander et al., 2005; Kearey et al., 2009;
> Condie, 2015). **To our knowledge, the last point—how “major” a piece of
> continental crust has to be to be called a continent—is almost never
> discussed, Cogley (1984) being an exception** .

and goes on to mention:

> Furthermore, the 4.9 Mkm^2 area of continental crust is large and separate
> enough to be considered not just as a continental fragment or a
> microcontinent, but as an actual continent—Zealandia. This is not a sudden
> discovery but a gradual realization; as recently as 10 years ago we would
> not have had the accumulated data or confidence in interpretation to write
> this paper.

This part is important too:

> spatial and tectonic separation, along with intervening oceanic crust, means
> that the Zealandia continental crust is physically separate from that of
> Australia. If the Cato Trough did not exist, then the content of this paper
> would be describing the scientific advance that the Australian continent was
> 4.9 Mkm2 larger than previously thought.

So to wrap it up, they say:

> Being >1 Mkm^2 in area, and bounded by well-defined geologic and geographic
> limits, Zealandia is, by our definition, large enough to be termed a
> continent. At 4.9 Mkm^2, **Zealandia is substantially bigger than any
> features termed microcontinents and continental fragments, ~12× the area of
> Mauritia and ~6× the area of Madagascar** . It is also substantially larger
> than the area of the largest intraoceanic large igneous province, the Ontong
> Java Plateau (1.9 Mkm^2).


Question:
Tetens coefficients appear in a few meteorological/climatological models that I've been looking at,for example APSIM:

svp_A = 6.106
svp_B = 17.27
svp_C = 237.3
These same values appear in at least two other models, but I can't find any documentation about what they represent, or where they come from. What are these numbers?

$\begingroup$

The Tetens coefficents are the empirically derived coefficients of an equation
for calculating the saturation vapour pressure of water. From [ wikipedia
](https://en.wikipedia.org/wiki/Clausius%E2%80%93Clapeyron_relation#Meteorology_and_climatology)
:

> a very good approximation can usually be made using the August-Roche-Magnus
> formula (usually called the Magnus or Magnus-Tetens approximation, though
> this attribution is historically inaccurate):
>
> $e_s(T)= 6.1094 \exp \left( \frac{17.625T}{T+243.04} \right)$
>
> e_s(T) is the equilibrium or saturation vapor pressure in hPa as a function
> of temperature T on the Celsius scale. Since there is only a weak dependence
> on temperature of the denominator of the exponent, this equation shows that
> saturation water vapor pressure changes approximately exponentially with T.


Question:
According to the Mariana Trench Oceanography page is at a maximum depth of

is 11,033 meters (36,201 feet)

The 'Challenger Deep' being the name of the deepest point.

I understand that it is a subduction trench, but my question is, what geological mechanism result in the great depth of the Mariana Trench over other trenches?

Explanation: the supply of sediment, the age of the lithosphere at the time of subduction, narrow slabs sinking and rolling back more rapidly than broad plates, causing the great depth of the mariana trench.

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As taken from [ Wikipedia ](https://en.wikipedia.org/wiki/Oceanic_trench) :

> There are several factors that control the depth of trenches. The most
> important control is **the supply of sediment** , which fills the trench so
> that there is no bathymetric expression. It is therefore not surprising that
> the deepest trenches (deeper than 8,000 m (26,000 ft)) are all
> nonaccretionary. In contrast, all trenches with growing accretionary prisms
> are shallower than 8,000 m (26,000 ft).
>
> A second order control on trench depth is **the age of the lithosphere at
> the time of subduction** . Because oceanic lithosphere cools and thickens as
> it ages, it subsides. The older the seafloor, the deeper it lies and this
> determines a minimum depth from which seafloor begins its descent. This
> obvious correlation can be removed by looking at the relative depth, the
> difference between regional seafloor depth and maximum trench depth.
> Relative depth may be controlled by the age of the lithosphere at the
> trench, the convergence rate, and the dip of the subducted slab at
> intermediate depths.
>
> Finally, **narrow slabs can sink and roll back more rapidly than broad
> plates** , because it is easier for underlying asthenosphere to flow around
> the edges of the sinking plate. Such slabs may have steep dips at relatively
> shallow depths and so may be associated with unusually deep trenches, **such
> as the _Challenger Deep_ ** .

A simple picture for anyone who doesn't understand how these trenches form: [
![Oceanic trench](https://i.sstatic.net/oFeRh.gif)
](https://i.sstatic.net/oFeRh.gif)
(source: [ wikispaces.com
](https://sjesci.wikispaces.com/file/view/trench.gif/148041157/trench.gif) )

Also, the Mariana Trench isn't the only super deep trench in the ocean... [ 10
deepest parts of the ocean ](https://www.marineinsight.com/know-
more/10-deepest-parts-of-the-ocean/)


Question:
Bohrmann et al. 1989 advanced the idea that the silicate phase from some clinoptilolites come from the diagenetic degradation of biogenic opal (from radiolarians in that case but presumably also other siliceous microfossils).

If this hypothesis is still regarded as valid, is clinoptilolite the only kind of authigenic zeolite that can be traced to biogenic opal?

Has any work been done in that domain since this paper?

Explanation: clinoptilolite is the only kind of authigenic zeolite that can be traced to biogenic opal. clinoptilote and heulandite occur in Si-rich diagenetic environments.

$\begingroup$

Yes, there have been recent research in this field.

In the article [ Oceanic minerals: Their origin, nature of their environment,
and significance ](http://www.pnas.org/content/96/7/3380.full.pdf) (Kastner,
1999), who asserts that

> The zeolites phillipsite and analcime mostly reflect on diagenesis of
> volcanic matter; **clinoptilote and heulandite occur in Si-rich diagenetic
> environments.**

and confirm that

> In addition to diagenetic opal-CT and quartz that form from the dissolution
> of biogenic opal-A, other common authigenic alumino-silicate minerals are
> smectites and zeolites.

This is further confirmed by a 2007 paper [ Clinoptilolite as a new proxy of
enhanced biogenic silica productivity in lower Miocene carbonate sediments of
the Bahamas platform: Isotopic and thermodynamic evidence
](http://www.sciencedirect.com/science/article/pii/S0009254107003804) (Karpoff
et al) which determined that

> Seawater–rock modeling specifies that clinoptilolite precipitates from the
> dissolution of biogenic silica, which reacts with clay minerals. The amount
> of silica (opal-A) involved in the reaction has to be significant enough, at
> least 10 wt.%, to account for the observed content of clinoptilolite
> occurring at the most zeolite-rich level. Modeling also shows that the
> observed amount of clinoptilolite (∼ 19%) reflects an in situ and short-term
> reaction due to the high reactivity of primary biogenic silica (opal-A)
> until its complete depletion.


Question: Currently it is winter in Antarctica. According to news I read, Antarctica has set a new record high temperature, above 18 °C. How did this temperature records occur?

Explanation: The author says that in the winter the hottedt weather in Antarctica is 18 celsius degree. But the fact is that that's the hottest temperature of summer there.

$\begingroup$

You just read the news too fast. WMO [ announced
](https://public.wmo.int/en/media/press-release/wmo-verifies-one-temperature-
record-antarctic-continent-and-rejects-another) that, after evaluation by a
committee, they have validated the 18.3°C temperature recorded _in February_
(i.e., in summer) last year:

> GENEVA, 1 July 2021 (WMO) - The World Meteorological Organization (WMO) has
> recognized a new record high temperature for the Antarctic continent of
> 18.3° Celsius on 6 February 2020 at the Esperanza station (Argentina).


Question:
What causes the typical red, pink or orange colors seen in sun-rises and sun-sets?

How come the sky doesn't just turn a darker blue?

Explanation: The reason why the sky is red or other colors during the sunset is the phenomenon called  Rayleigh scattering.

$\begingroup$

There are many references about this on the web, such as [ Wikipedia
](https://en.wikipedia.org/wiki/Sunset) and the [ NOAA
](http://www.spc.noaa.gov/publications/corfidi/sunset/) site.

At sunrise and sunset the angle the Sun's light makes with the Earth at those
locations is low compared with angle the light makes at midday. Because of the
low angle, the light has to travel through more of the atmosphere before it
reaches the Earth's surface and the eyes of anyone watching either the Sun
rise or the Sun set.

The colour of the Sun's light is white, being composed of the colours of the
light spectrum: red, orange, yellow, green, blue, indigo and violet. The [
wavelength ](http://science-
edu.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html) of these component
colours are all different. Red has the longest wavelength at 650 nm. Each of
the other colours have shorter wavelengths with violet having the shortest at
400 nm.

As the Sun's light passes through the atmosphere it get scattered by the air
molecules and particles in the air such as dust and aerosols.

Due to a phenomenon known as [ Rayleigh scattering
](https://en.wikipedia.org/wiki/Rayleigh_scattering) the shorter wavelengths
of light (greens, blues, violets) are scattered first, leaving the shorter
wavelengths (yellows, oranges and reds) to travel further.

The greater the amount of particles in the air, dust and aerosols, the greater
the degree of scattering and the more red the sunrises and sunsets will
appear. This is particularly evident after large amounts of ash have been
ejected by [ volcanoes ](http://www.livescience.com/12834-iceland-volcano-
fiery-sunsets.html) , after large forest fires and in locations where [ air
pollution ](http://www.economist.com/blogs/babbage/2014/04/air-pollution) ,
particularly from industrial chimney stacks and internal combustion engines
from road vehicles is a major source of airborne [ particulate
](http://www.scientificamerican.com/article/fact-or-fiction-smog-creates-
beautiful-sunsets/) matter such as soot or ash and other very small products
of combustion


Question:
If I wanted to make an air shield around the earth to contain exactly half the planet's atmosphere (by mass), how far above sea level would I have to build it?

It's slightly complicated to me because you have to take into consideration the change in pressure as well as the geometric growth of the volume of a sphere as you increase the radius.

Thank you.

Explanation: The author wants to find out the distance to cross the atmosphere, which can be solved through hydrostatic function.

$\begingroup$

Roughly 5.5 km, although the exact value depends on the weather. All you need
to do is to [ solve the hydrostatic equation
](https://en.wikipedia.org/wiki/Vertical_pressure_variation) and find the
height at which the pressure is 50% of the height at sea level (or perhaps
average elevation of Earth surface instead of sea level). Any answer actually
performing the calculation deserves upvotes more than I do ;-)

See, for example, [ Thickness of Earth's Atmosphere
](http://www.pdas.com/atmthick.html) :

> Using boundary layer theory as an example, we can define the thickness of
> the atmosphere to be the altitude that encloses 99 percent of the total mass
> of the atmosphere. Looking at the chart, we can see that this seems to be
> about 31 kilometers. The halfway point, where half the mass of the
> atmosphere is below and half above occurs at 5.5 kilometers. Another
> interesting fact is that when you are cruising in a modern jet transport at
> 11 kilometers, you are above 77.5 percent of the atmosphere. The total mass
> of the atmosphere turns out to be 5.3 zettagrams (5.3 Zg).

I'm not entirely sure how the calculations in the linked article are
performed, but I recall calculating this as a student and ending up somewhere
around 5 km, so it sounds right. Simple calculations often assume an
isothermal atmosphere, which is of course not accurate, but good enough if you
don't need to know the answer more precisely than within several hundred
metre.

[ This page at Stanford reaches the same number.
](http://nova.stanford.edu/projects/mod-x/id-pres.html)


Question: I would like to calculate the latitude values of a Gaussian Grid of a size of my choosing. Unfortunately, I didn't find a method or a formula to do so. Where can I find this information? Alternatively, is there a function publicly available that can do the job?

Explanation: NCL gaus fuction is  a good way for calculating latitudes of gaussian grid.

$\begingroup$

I believe the NCL function [ NCL gaus
](http://www.ncl.ucar.edu/Document/Functions/Built-in/gaus.shtml) should be
able to give you the solution you are looking for. From the API documentation
you are requested to provide - the number of latitude points per hemisphere
and you should get Gaussian latitudes and Gaussian weights.

Here is a code sample from their website

    nlat = 64  ; for globe
    gau_info = gaus(nlat/2)   ; divide by 2 to get "per hemisphere"
    glat     = gau_info(:,0)  ; gaussian latitudes ( 1st dimension of gau_info)
    gwgt     = gau_info(:,1)  ; gaussian weights   ( 2nd dimension of gau_info)


Question:
I'm confused by what exactly a CDL file is and what its purpose is. Unidata specifies the syntax of such a CDL file in its netCDF documentation.

Questions:
Are CDL files designed to be opened by a simple text editor like Notepad or gedit? Or should I use some other tool to open it?

What is its purpose and how is it used?

$\begingroup$

A CDL file is basically a text output from a netcdf file. If you want to know
the contents of a netcdf file but don't have the time (or ability) to use
programs built to read/write netcdf, you can use the simple text output of
"ncdump" and then read/write it with a basic text editor. You can also use
"ncgen" to regenerate a netcdf file based on the new CDL file. I've used this
process to make simple changes to netcdf files, and it works very quickly
compared to generating a netcdf file using programming methods.

See [ http://www.atmos.washington.edu/ive/ive_help/writing_netCDF_files.html
](http://www.atmos.washington.edu/ive/ive_help/writing_netCDF_files.html) ,
quoted below:

> A CDL (network Common data form Description Language) file is an ASCII
> descripton of the binary data in a netCDF file that is designed to be easily
> read by humans. CDL files can be generated from netCDF files via the
> `ncdump', command. For example,
>
> ncdump -c sample.nc generates the file `sample.cdl' that contains the file
> name, the dimensions, the specification of the variables, any attributes and
> the data for any "coordinate variables." A CDL file of this type is shown
> below. Note that the double slash indicates a comment in the CDL file.
>
> netcdf implicit_grid{
>
> dimensions: lon = 101; lat = 101; level = 5; time = UNLIMITED ; //(7
> currently) variables:
>
> float A(time,level,lat,lon); A:units = "meters/second"; float level(level);
>
> level:units = "millibars"; float time(time);
>
> time:units = "hours"; //global attributes:
>
> :x_min = -180.f; :x_max = 180.f; :x_units = "degrees_east"; :x_label =
> "longitude"; :y_min = -90.f; :y_max = 90.f; :y_units = "degrees_north";
> :y_label = "latitude";
>
> :z_label = "level"; :t_label = "time";
>
> data: level = 1000, 850, 700, 500, 300 ; time = 0, 2, 4, 6, 8, 10, 12 ;
>
> The command ` ncgen' is the inverse of ` ncdump'; it converts an ASCII CDL
> file to a binary netCDF file. For example
>
> ncgen -o sample.nc sample.cdl converts the CDL file ` sample.cdl' to the
> netCDF file ` sample.nc'. The easiest way to create a netCDF file is to (1)
> write all the header data (the name, dimensions, variable and attribute
> specifications, and the values of any coordinate variables) to a CDL file,
> (2) convert the CDL file to a netCDF file using ncgen, and (3) continue
> writing the main data arrays to this netCDF file.


Question: I know volcanologists study volcanoes. Is there a subdiscipline that only studies maga or lava? A magmatologist?

Explanation: Igneous Petrologists is a subdiscipline that only studies maga or lava of volcanology.

$\begingroup$

Perhaps they are called [ Igneous Petrologists
](http://en.wikipedia.org/wiki/Igneous_petrology) ?

Someone who studies magma/lava flows tends to go by Geophysicist because they
inherently study continuum mechanics and fluid flow.


Question:
Someone I know posted a question about climate change that I do not know how to answer. While I do believe (for lack of better word) in climate change, I do not know how to answer this persons question. The tl;dr of the question is:

If climate change is not a natural phenomenon, then how did the last ice age end?

The person is implying that warming/cooling reoccurs periodically on the Earth, and that the current climate change threat is overblown.

I have searched online for answers, but cannot find anything concise on this specific subject. According to this wikipedia article,

There is evidence that greenhouse gas levels fell at the start of ice ages and rose during the retreat of the ice sheets, but it is difficult to establish cause and effect (see the notes above on the role of weathering). Greenhouse gas levels may also have been affected by other factors which have been proposed as causes of ice ages, such as the movement of continents and volcanism.

In short, how and why did the last ice ages end? I am assuming that the carbon dioxide concentration during these ice ages is much lower than the current estimate of ~410 ppm. Aside from the difference in carbon dioxide levels, what evidence suggests that the climate change of today is different than the climate change that ended the ice age(s)?

Explanation: There are two ways that the climate change today is different from the ice age: speed and civilization

$\begingroup$

Difference #1: **Speed** . The warming at the end of the ice ages went much,
much slower than what we are currently experiencing.

Estimates of the amount of warming since the beginning of the industrial
revolution are [ in the order or 1 degree Celsius
](https://www.ipcc.ch/site/assets/uploads/sites/2/2018/12/SR15_FAQ_Low_Res.pdf)
*  \- that's in 100-150 years time.

* Page 7

> When the Earth moved out of ice ages over the past million years, the global
> temperature rose a total of 4 to 7 degrees Celsius over about 5,000 years.

(NASA Source: [ How is Today’s Warming Different from the Past?
](https://earthobservatory.nasa.gov/features/GlobalWarming/page3.php) )

The article [ Earth is warming 50x faster than when it comes out of an ice age
](https://www.theguardian.com/environment/climate-consensus-97-per-
cent/2016/feb/24/earth-is-warming-is-50x-faster-than-when-it-comes-out-of-an-
ice-age) sums it up nicely:

> What humans are in the process of doing to the climate makes the transition
> out of the last ice age look like a casual stroll through the park. We’re
> already warming the Earth about 20 times faster than during the ice age
> transition, and over the next century that rate could increase to 50 times
> faster or more. We’re in the process of destabilizing the global climate far
> more quickly than happens even in some of the most severe natural climate
> change events.
>
> That rapid climate destabilization is what has climate scientists worried.
> It’s faster than many species can adapt to, and could therefore cause
> widespread extinctions, among other dangerous climate change consequences.
> Coastal flooding in places like Florida has already become much more common
> than it was just 50 years ago, and sea level rise is expected to keep
> accelerating.

Difference #2: **Civilization** . At the end of the ice ages we did not have [
3 billion people living within 200 km from a coast line
](https://www.prb.org/rippleeffectspopulationandcoastalregions/)
That is not an difference in the _cause_ of the warming, but definitely in the
_effect_ .

One could argue that that same civilization will make us able to deal with the
consequences, but looking at thing that already exists several centuries
without change, surely raises doubts to our ability to deal with the current
rate of climate change. Think (1) unequal global wealth distribution or (2)
the psychology of our behavior (denial, politics).

* * *

BTW The question asked to you

> If climate change is not a natural phenomenon, then how did the last ice age
> end?

is based on a false premise - it's a bit of a word game.
The current warming is _still_ a natural phenomenon, but it's now [ primarily
driven by _our_ input, and not other 'natural' phenomena
](https://www.britannica.com/science/climate-change/Evidence-for-climate-
change) .


Question:
I've heard long ago that the rock material deeply below surface are checked by a device that acts like radar - it sends radiowaves into the ground, and geologists find out from reflections that what type of rock can be found there.

What's the name of this device or method, and how is it possible to differentiate rocks from radiowave reflection?

Explanation: The post wants to know how detect different rocks with radio waves. Ground panetrating radar can solve this problem.

$\begingroup$

Do you mean [ Ground Penetrating Radar ](http://en.wikipedia.org/wiki/Ground-
penetrating_radar) ? This is typically limited to very shallow depths though -
eg. archaeological investigations, police forensics (finding graves), and
civil engineering site investigations. The latter can go to tens of meters and
would be used for planning foundations, excavations, etc (I know of an example
where it was used for site characterization for a planned rowing lake). The
depth limit is typically due to attenuation in brackish groundwaters. Ice
applications can typically go further due to the lack of conducting liquid
water.

Or are you thinking of [ Reflection ('Active') Seismic Surveys
](http://principles.ou.edu/seismic_explo/reflect/reflect.html) , which work on
a similar principle but using sound waves. Sound waves can travel to the far
side of the Earth (cf. large earthquake 'P' waves), but reflection surveys are
typically looking at the upper crust (few km) and rarely go beyond the base of
the crust (aka the 'Moho') which is a strong seismic reflector. Reflection
seismic surveys are widely used in the oil business.


Question:
Are there any resources (books/links) that discuss the mathematical tools and methods used to forecast the aurora borealis activity in a particular location?

I see many websites that claim to predict aurora, but are there any open source code that lets you have an idea of the models?

Explanation: OVATION is a model to predict the aurora.

$\begingroup$

**One model is the[ OVATION auroral precipitation model ](http://sd-
www.jhuapl.edu/Aurora/ovation/) . **

OVATION [ stands for ](https://en.wikipedia.org/wiki/Backronym) Oval
Variation, Assessment, Tracking, Intensity, and Online Nowcasting.

The [ NOAA Space Weather Prediction Center ](http://www.swpc.noaa.gov/) uses
the OVATION Prime model for their 30-minute aurora forecast. They use a
modified version of the model for their [ 3-day forecast
](http://www.swpc.noaa.gov/products/aurora-3-day-forecast) . It was devised by
Newell et al. (2010) at Johns Hopkins University.

You can read all about it in Machol et al. (2013). [ The paper
](http://onlinelibrary.wiley.com/doi/10.1029/2011SW000746/full) is open access
and contains several equations and a description of the method. They explain:

> The OVATION Prime model is derived from electron and proton flux
> measurements from the SSJ4 detectors on the [ DMSP satellites
> ](https://en.wikipedia.org/wiki/Defense_Meteorological_Satellite_Program) .

SSJ4 sensors, according to [ one source
](http://www.ferzkopp.net/Personal/Thesis/node28.html) :

> [...consist] of an array of four cylindrical, curved plate, electrostatic
> analyzers configured into two pairs; one pair each to measure electrons and
> ions. Each pair covers the energy range from 30 eV to 30 keV in 20 channels
> spaced at equal intervals in energy on a logarithmic scale.

###  References

Machol, J. L., J. C. Green, R. J. Redmon, R. A. Viereck, and P. T. Newell
(2012), Evaluation of OVATION Prime as a forecast model for visible aurorae,
Space Weather, 10, S03005, [ doi:10.1029/2011SW000746
](http://onlinelibrary.wiley.com/doi/10.1029/2011SW000746/full) .

Newell, P. T., T. Sotirelis, and S. Wing (2010a), Seasonal variations in
diffuse, monoenergetic, and broadband aurora, J. Geophys. Res., 115, A03216, [
doi:10.1029/2009JA014805
](http://onlinelibrary.wiley.com/doi/10.1029/2009JA014805/full) .


Question:
I got caught in a downpour while climbing a mountain and was amazed to see, as I climbed down, the tiny trickles of water combine to form mini-streams, the dry rocks I had climbed up now hosted sizable waterfalls, and the path which I had followed to the mountain had become a small river.

But it got me wondering about my question, which is the reverse of this. Why, after a long period of dry weather, are many rivers still flowing? I live near a river and it seems that it takes over a week of dry weather before there's any noticeable drop in its level. How does it not simply run out of water? Is it simply that it takes very a long time for the water at its source and the sources of all its tributaries to reach the point I'm observing from?

It seems there's a constant supply of water when I would have expected the network of rivers to start draining, and the drying up starting from the source the moment the rain stopped.

Explanation: The rivers are generally fed by water that percolated into the ground, which helps it last during the dry season.

$\begingroup$

The rivers are generally fed by water that percolated into the ground, it
takes longer for that water to work its way down to the stream so the streams
and rivers keep flowing long after the initial rain. [
https://water.usgs.gov/edu/rivers-contain-groundwater.html
](https://water.usgs.gov/edu/rivers-contain-groundwater.html)


Question:
I am trying to understand the concrete process of how a meteorologist at a weather forecast office produces the different types of weather forecasts. I understand how numerical weather models work, but I would like to learn how the model output is turned into a forecast and to what extend it is improved by a skilled meteorologist.

I have found an older reference from 1993 that has some information on the workflow, https://esrl.noaa.gov/gsd/eds/gfesuite/pubs/AWIPS-Forecast-Preparation-System.pdf but this is probably outdated and doesn't talk about the meteorological side.

There are a lot of different forecast products from text to graphical products, so my question might be an overly broad one, but I haven't found much information so far, so I don't want to be too restrictive.

What concrete model outputs do forecasters look at and to what extend do they use local observations and experience?

Explanation: Scientists review observations using radar, satellites, and other instruments. Forecasters analyze this data, create graphical representations, and use various models to predict changes. They review model output daily, selecting the most accurate or blending different models for optimal results.

$\begingroup$

The Virtual tour is good, and I don't know why that wasn't an accepted answer.
So I'll throw my answer into the ring. I'll recommend you try the [ NWP and
Forecasting Comet module ](https://www.meted.ucar.edu/bom/intro_nwp/index.htm)
(it's free if to get an account). That'll probably help more than my answer,
which is based around the forecasting classes that I took and my experience as
a forecaster in the university's student-run weather service.

From the outside, the forecast process is a very mysterious thing. But in
reality it is not. Though, it is highly a subjective task and is subject to
some degree of variation per person (hence some people are better forecasters
than others). It also takes a lot of time to do it right. Here is my pattern
if I want to be rigorous.

  1. Know where I am forecasting for.

Location is important. What do I know about the climatology. Climatology can
give a "first guess" on the range of values that can be reasonably considered.
The previous day's weather can also be a good first guess. If I am well
acquainted with the area, then this becomes a shorter and shorter step.

  2. Start with observations.

What is happening now? What is reality saying? The amount of space that is
looked at needs to be proportionate to the forecast time.

  3. Make inferences on the current state and causes of weather features.

What patterns are seen? Was map analysis done? Are there certain areas that
are colder than others? Are there places that have clouds and others that
don't have clouds? What does the radar say? Why, why why why why? If you know
the mechanisms that are generating weather now, then you can understand how
they might evolve.

  4. Examine how the weather models have started.

Before you use a weather model, you should understand it. Garbage in=garbage
out, _sometimes_ . How well did the model do today? If it is overpredicting
temperature right now, will it continue overpredicting the temperature? Will
the errors that occurred upstream yesterday occur today?

  5. Look at how the weather models progress. Question if it aligns with my knowledge and experience.

Taking a model at face value might work for research purposes (unless you are
researching the model itself), but shouldn't be done on a practical level or
in a rush. What does Model Output Statistics (MOS) say?

  6. Choose the right numbers or features.

This is probably the step that requires the least amount of explanation.
Though the more intricate the type of forecast, the harder and harder this
becomes. Does it actually require numbers, or is there some sort of GIS
software (like for hurricane trajectory or lightning forecast)?

  7. Verify

This can't be stated enough. You must verify how well you did. Decisions need
to be made on how the forecast will be verified. What data sources do you know
of for verification? If I could move this up to number 1 and still have this
make sense, I would. Because this is what you should start off with. This
actually goes part and parcel with starting with observations, since
observations are what you start a forecast with. Understand the processes of
why your forecast was off. This will serve you in the future and in the next
forecast.


Question:
In Pangaea, northern Africa would have had humid onshore winds from the Tethys Ocean, making dense vegetation/rainforest biome likely.

Consequently, would we be likely to find coal underneath the Sahara desert?

Explanation: Much of the Sahara is covered with limestone, the possibility that there are coal mines under sahara desert is small.

$\begingroup$

The older rocks underlying the [ Sahara ](https://geography.name/the-geology-
of-the-sahara/)

> are mostly granite, schist, or gneiss, all mixtures of igneous and
> metamorphic rocks forged deep beneath the surface
>
> This stable mass of rock has been covered over with younger sediments, laid
> down in horizontal, largely unaltered layers. **Much of the Sahara is
> covered with limestone** , made mostly of the skeletons of microscopic sea
> creatures raining down onto the bottom of a vanished sea.
>
> Most of the limestone and sandstone covering the surface of the Sahara were
> deposited in the Mesozoic era (245–65 million years ago).

From the [ picture below
](https://pubs.usgs.gov/of/2008/1258/graphics/Africa_Coal.png) , produced by
the US Geological Survey, most of Africa's coal deposits are in the southern
part of the continent. There appears to be a very minor coal deposit in
western Algeria with other similar sized deposits in Niger, Mali and Sudan.
Egypt's Sinai appears to have an exceedingly small deposit of coal from the
Jurassic period.

[ ![enter image description
here](https://pubs.usgs.gov/of/2008/1258/graphics/Africa_Coal.png)
](https://pubs.usgs.gov/of/2008/1258/graphics/Africa_Coal.png)

In terms of hydrocarbon resources, the Sahara contains about [ 4 percent of
the worlds current reserves of oil and gas
](https://www.sciencedirect.com/topics/earth-and-planetary-sciences/african-
plate) . In terms of energy resources, " [ North Africa is dominant in oil and
gas ](https://en.wikipedia.org/wiki/Energy_in_Africa) ".

[ ![enter image description here](https://i.sstatic.net/ttPR1.png)
](https://i.sstatic.net/ttPR1.png)


Question: I was reading many articles about estimates of the age of the Earth throughout the ages. I was dumbfounded when I read that Newton, arguably one of the greatest scientists ever to have ‘calculated’ the age of the earth, estimated that the Earth was created in 4000 BCE. Johannes Kepler arrived at a similar result. Which methods did these scientists use to arrive at such conclusions?

Explanation: Newton's estimation of the age of the earth actually is consider bible as a historical documentation.

$\begingroup$

The estimates of Newton and Kepler, and the similar estimates of [ dozens of
their contemporaries ](http://en.wikipedia.org/wiki/Dating_creation#Masoretic)
, were produced by treating the Bible as [ a historically accurate document
](http://en.wikipedia.org/wiki/Chronology_of_the_Bible) and deriving a
chronology from it. I think that a detailed explanation of their techniques
would be off-topic for Earth Science, but the Wikipedia page on the [ Ussher
Chronology ](http://en.wikipedia.org/wiki/Ussher_chronology) (which provides
probably the most famous biblically-based estimate of the Earth's age) goes
into reasonable detail about the methods used for such calculations.


Question:
How is/was continental drift monitored?
I am curious about current technology but I am particularly interested in what techniques were employed prior to the advent of satellite technology.

Explanation: We now use GPS or SLR to observe contenental drift, but before they were invented, we use paleomagnetism.

$\begingroup$

Scientific [ GPS ](http://www.pocketgpsworld.com/howgpsworks.php) and [ SLR
](https://en.wikipedia.org/wiki/Satellite_laser_ranging) have been used for [
some time ](http://onlinelibrary.wiley.com/doi/10.1029/2003JB002944/full) now,
and the [ measurements
](http://onlinelibrary.wiley.com/doi/10.1029/97JB00514/pdf) are rather
accurate. Not only do we measure horizontal movements of tectonic plates, but
also uplift as e.g. in the Tibetan and Colorado plateaus.

Before the GPS was introduced, [ paleomagnetism
](https://en.wikipedia.org/wiki/Paleomagnetism) were used in some studies to
estimate the velocities; The age of oceanic crust are estimated by various
methods and the travel distance is estimated from the width of the magnetic
polarized bands in the ocean floor. To understand [ paleogeography
](http://www.scotese.com/earth.htm) and make good models we need to
incorporate all branches of geology. E.g. [ fossil records
](https://en.wikipedia.org/wiki/Biostratigraphy) , paleomagnetism, [
radiometric age estimation ](https://en.wikipedia.org/wiki/Radiometric_dating)
of rocks.

Some active faults (E.g. San Andreas) can also be directly measured with laser
ranging or, in some cases, with a measurement tape to measure deformation of
trenches or railway tracks.

Still, scientists are trying to understand the exact driving forces behind
plate tectonics. [ Modelling ](http://www.earthbyte.org/Resources/Pdf/Ghosh-
Holt-2012-Science-PlateMotionsStressesGlobalDynamicModels.pdf) of [ mantel
dynamics ](https://en.wikipedia.org/wiki/Mantle_convection) is an interesting
field of research and many questions remains.


Question: This is more of a terminological question, but I think it fits here. I've been reading a book by Rachel Carson, from the early 50s, and she uses the phrase "Archaeozic period". I haven't seen this used elsewhere - is it just an archaic (pardon the pun) form of "Archean", or does it describe a different period? Etymologically, it seems like it's more oriented around "life", but that may just be a semantic distinction.

Explanation: Archaeozoic is just a formal name of Archean, basically they mean the same thing.

$\begingroup$

The [ Archaen ](https://en.wikipedia.org/wiki/Archean) was named by American
geologist [ James Dwight Dana
](https://en.wikipedia.org/wiki/James_Dwight_Dana) in 1872, to refer to the
entire span of time before the Cambrian Period. A synonym was "Azoic" as this
period was considered lifeless. Later, it was found that the carbon isotope
ratios changed in rocks about 3.8 billion years old between ones that
indicated no life present to ones that indicated life. So "Azoic" began to
refer to the "lifeless" period before 3.8 billion years and "Archaeozoic" for
the "earliest life" after that point.

That's the way it stood when Rachel Carson wrote her book. The 1969 World Book
Encyclopedia which sat on my parents' bookshelf divided the Precambrian into
the [ Proterozoic ](https://en.wikipedia.org/wiki/Proterozoic) , Archaeozioc,
and Azoic eras.

By 1972 this wasn't working, so Preston Cloud suggested the term " [ Hadean
](https://en.wikipedia.org/wiki/Hadean) " to refer to the time between the
formation of the Earth/Solar System and 4 billion years ago. At the same time,
the boundary adjustment caused "Archean" to be preferred to "Archaeozoic".

But "Archaeozoic" matches up enough to be considered a synonym for "Archean"
these days.

[ Here's a rabbit hole ](https://pubs.usgs.gov/bul/0769/report.pdf) (PDF) to
dive down.


Question:
I'm currently doing research for a paper in school where we need to research on a university-like level. When I read the paper Causes and impacts of the 2014 warm anomaly in the NE Pacific, I found the sentence:

The wind stress curl was negative, which has precedence but is still quite unusual.

The wind stress curl was given as −0.5∗106 N∗m−3
. I neither know what wind stress curl is, nor what the negative sign is, nor what the unit of it exactly describes (of course, pressure per meter, but what does that mean?).

Can anyone explain what it is?

Explanation: Wind over water creates movement in the upper layers, which transfers to lower layers. Water movement is influenced by the Coriolis force, generally moving to the right of the wind in the northern hemisphere. Divergence and convergence of water occur when there's a difference in wind strength and direction. Negative wind stress curl pushes water downward, suppressing ocean mixing and maintaining warmer upper ocean conditions.

$\begingroup$

Skimming the paper, I believe the relevance of the wind stress curl is its
relation to "Ekman pumping". I haven't found a simple, concise reference for
this, but [ this page ](http://paoc.mit.edu/labguide/ekpump.html) might be a
good start, and [ this page
](https://marine.rutgers.edu/dmcs/ms501/2004/Notes/Wilkin20041028.htm) has a
couple of formulas about wind stress curl. I'll try to summarize here.

When wind blows over water, the top of the water starts moving. It shears
against the water below it, so that water starts moving too. The momentum from
the wind is transferred down into lower layers of the water. This water also
feels the Coriolis force. The direction it ends up moving in depends on the
balance of friction/drag and Coriolis force. On average, the water moves to
the right of the wind in the northern hemisphere; if the wind is blowing
northward, the water moves eastward.

Now imagine you have strong wind blowing northward at one location and weaker
wind to the right of it. The water at the first location moves to the right,
and it does so faster than the water at the second location (because the wind
forcing the water is stronger at the first location). The water converges at
the second location, pushing the water downward. This is how the curl of the
wind stress (the northward wind changing in the east-west direction) is
related to the water convergence (the eastward current changing in the east-
west direction) and hence to water being pushed down or pulled up. Positive
wind stress curl pulls water up; negative wind stress curl pushes it down.

The last relevant part here is that this kind of motion suppresses ocean
mixing. The relevant sentence from that paper is

> The wind stress curl and hence Ekman pumping anomalies were negative, which
> also is consistent with relatively weak entrainment.

"Entrainment" is how much of the deep, cold ocean water mixes with the
relatively warm upper ocean water, cooling it. The negative wind stress curl
leads to water being pushed down and less deep water mixing with the upper
ocean. The upper ocean stayed warmer, so the whole heat blob lasted longer.


Question:
I read that the acidic character, or, better, persilicic character of a rock is determined by a content of more than 65% SiO2
.

A rock is defined, by the texts available to me, as mesosilicic (or intermediate) when its SiO2
 content is contained in the interval 52%−65%
, while it is called hyposilicic (or basic) when SiO2<52%
.

If I correctly understand the SiO2
 contained in the rock as a part of a mineral other than pure SiO2
, for example, the Si2O4
 part of anorthite CaAl2Si2O8
, is calculated into the quantity of total silica. What I cannot understand at all, is whether mass or volume is taken into account.

Explanation:
The website from Tulane University provides a general classification of igneous rocks based on their silica (SiO2) content. According to the classification:

- Rocks with a silica content above 66 wt. % are classified as "acid."
- Rocks with a silica content ranging from 52 to 66 wt. % are classified as "intermediate."
- Rocks with a silica content ranging from 45 to 52 wt. % are classified as "basic."
- Rocks with a silica content below 45 wt. % are classified as "ultrabasic."

$\begingroup$

According the website [
http://www.tulane.edu/~sanelson/eens212/igrockclassif.htm
](http://www.tulane.edu/~sanelson/eens212/igrockclassif.htm) from Tulane
University silica content in igneous rock is based on mass. Below is copy of
the relevant part of the web page where it states **wt %** , weight percent.

General Chemical Classifications

$\ce{SiO2}$ (Silica) Content

    > 66 wt. % - Acid

    52-66 wt% - Intermediate

    45-52 wt% - Basic

    < 45 wt % - Ultrabasic


Question: Taiga is the Russian word for big areas of forest wilderness in high latitude regions. What about forests in the mountains? What is the name for the forested areas in mountains which are below the treeline?

Explanation: Forests directly below the alpine tree line are high-elevation or Montane forests.

$\begingroup$

Forests directly below the [ alpine tree line
](https://en.wikipedia.org/wiki/Tree_line#Alpine) are high-elevation or
Montane forests. See more about [ Montane ecology here
](https://en.wikipedia.org/wiki/Montane_ecology) .

[ ![treeline image](https://i.sstatic.net/9AjVQ.jpg)
](https://i.sstatic.net/9AjVQ.jpg) Image from [
http://www.nature.com/scitable/knowledge/library/global-treeline-
position-15897370 ](http://www.nature.com/scitable/knowledge/library/global-
treeline-position-15897370)


Question:
I have downloaded the sea surface temperature data from the Ocean Color website, the file is in NetCDF format and contains no of geophysical_data variables like sst, qual_sst, flag_sst, bias_sst, etc. I used the following MATLAB code for file read and it is giving me an error:

temp=ncread('A2014213085500.L2_LAC_SST.x.nc','sst')
Error:

Error using internal.matlab.imagesci.nc/getGroupAndVarid (line 2075)
Could not find variable or group 'sst' in file.

Error in internal.matlab.imagesci.nc/read (line 593)
        [gid, varid] = getGroupAndVarid(this, location);

Error in ncread (line 58)
vardata = ncObj.read(varName, varargin{:});
Can someone tell me what is the cause of the error?

Explanation: use ncgeodataset can read a netCD4 file in Matlab.

$\begingroup$

These days I use: [ ncgeodataset
](https://code.google.com/p/nctoolbox/wiki/ncgeodataset) . The routine allows
for the extraction of a subset of data without having to load the entire file
or even an array into Matlab. It is great for large datasets.


Question:
In ocean spectra such as the Pierson Moskowitz or the JONSWAP models, the units of S(ω)
 are m2/(rad/s)
 (or whatever unit of measurement you are working in). Where does the m2
 come from and what does it mean physically?
I understand that the integral of the spectrum over all frequencies, i.e. ∫S(ω)dω
, is the variance which means that the integral should have m2
 units? Please correct me if I am wrong.

Explanation: the units of S(w) is m^2, which comes from integral of ∫S(ω)dω

$\begingroup$

> I understand that the integral of the spectrum over all frequencies is the
> variance which means that the integral should have $m^2$ units? Please
> correct me if I am wrong.

You are correct. If elevation $\eta(t)$ is the measured quantity (units of
$m$), the Fourier transform of wave variance $\eta^2$ yields spectrum $S(f)$
with the units of $m^2/Hz$, or if you are working with angular frequency
$\omega = 2\pi f$, it yields $S(\omega)$ with the units of $m^2/rad/Hz$.

More details can be found in the answer to [ this question
](https://earthscience.stackexchange.com/questions/4521/is-wave-spectrum-
always-positive-and-why/4522) .


Question:
I'm trying to solve the following problem. The sea level in the past was 200 m higher than today. The seawater became in isostatic equilibrium with the ocean basin. what is the increase in the depth x
 of the ocean basins? Water density is ρw=1000 kg m−3
, and mantle density is 3300 kg m−3
.

Using the compensation column, I reach:

x=(ρw∗200 m)/3300=60.60 m
but normally I expected to find 290 m.

Can someone explain to me what's wrong?

Explanation: by making use of Airy's isostasy model, we can calculate hydrostatic equilibrium in the situation when sea level being 200m higher and in isostatic equilibrium.

$\begingroup$

I am assuming you are asking for the case of sea level being 200m higher
**and** in isostatic equilibrium. In that case we can make use of Airy's
isostasy model: [ https://en.wikipedia.org/wiki/Isostasy#Airy
](https://en.wikipedia.org/wiki/Isostasy#Airy)

Applied to a water column over the mantle, you have to replace $\rho_c$ with
your $\rho_w$. The total increase in ocean depth is $x = b_1 + h_1$, where
$h_1$ are the 200 m extra sea level and $b_1$ is the depth increase to
isostasy. Using the equation given in the link: $$ x = \frac{h_1
\rho_w}{\rho_m - \rho_w} + h_1, $$

giving $x =$ 287 m


Question:
I am following the paper to calculate UTCI using ERA5 meteorological variables.

https://link.springer.com/article/10.1007/s00484-020-01900-5?shared-article-renderer

In the paper, the authors have mentioned that they are using ERA5 product. And specifically mentioned to use the direct and diffuse component of shortwave (SW) radiation.

The problem is, ERA5 data does not provide the direct and diffuse SW separately. Rather it only provides Surface solar radiation downwards which includes both the direct and diffuse component.

My question would be, is there a way to calculate the direct and diffuse component of SW from ERA5. The dataset I have is similar to ERA5 and has the Downward SW and Net SW. I have no problem in obtaining the Long waves BTW.

Any help would be much appreciated. TIA

Explanation: A clearness index approximation can be used to partition direct and diffuse from ERA-Interim.

$\begingroup$

[ This paper
](https://gmd.copernicus.org/articles/7/387/2014/gmd-7-387-2014.pdf) By Fiddes
& Gruber ( _TopoSCALE: downscaling gridded climate data in complex terrain_ )
provides a method to partition direct and diffuse from ERA-Interim. The
results could easily be applied to ERA5.

It uses a clearness index approximation from Ruiz-Arias et al. (2010)

$k_t = SW / SW_{toa}$  (eq C11) where  $ SW_{toa} $  is the shortwave at the
top-of-atmosphere.

then,

$SW_{diffuse} = 0.952 - 1.041 e^{-exp(2.3 - 4.702k_t)}$  (eq C12)

You should be able to get top-of-atmosphere SW from ERA5, or possibly
calculate it based on solar geometry.


Question: Given the fact that industries emit about 1.5 billion metric tons of carbon dioxide each year just in the US, why is it still such a small part of the atmosphere's composition (0.04%)?

Explanation: The mass of the atmosphere is 5.1 × 1018 kg, which is 5.1 × 1015 t. As stated in the edited question, industries emits 1.5 billion metric tons of carbon dioxide each year, that's 1.5 × 109 t, which is super small compared to the whole.

$\begingroup$

The [ mass of the atmosphere
](https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html) is 5.1 × 10
18  kg, which is 5.1 × 10  15  t.

As stated in the edited question,

> industries emits 1.5 billion metric tons of carbon dioxide each year,

That's 1.5 × 10  9  t.

The mass of Earth's atmosphere is 3,400,000 times the mass of CO  2  that
industries produces each year in the US.


Question: The question is clear enough in my opinion but, I've found out that if you redraw this picture, you'll notice that the Sun is as big as the Earth. But if you scale up the Sun to it's real size compared to the Earth, you would realize that the Earth would covered in daylight ALL THE TIME. So what's going on here?

Explanation: The reason why the 'total daytime' will never happen is that, the sun is super farwaway from the earth, the light thus become almost parallel, which will not 'cover' the earth's surface.

$\begingroup$

The sun is [ really far away
](https://en.wikipedia.org/wiki/Astronomical_unit) . Thus its rays are [
essentially parallel
](https://physics.stackexchange.com/questions/155075/what-makes-suns-light-
travel-as-parallel-beams-towards-earth) at the earth's orbit. So, while the
diagram you posted is clearly a bit off in terms of the relative size and
distance between the sun and the earth, the parallel rays are about right.

[ ![Sun and Earth - public domain image](https://i.sstatic.net/L4pXa.png)
](https://i.sstatic.net/L4pXa.png)


Question:
Natural gas:

...is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, but commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxide, nitrogen, hydrogen sulfide, or helium.

I saw the graphic below in the BBC News article Trump climate: Challenges loom after Obama policies scrapped. It lists natural gas as the source of about 33% of the US electricity generation in 2015, but also lists "Other gases" as the source of less than 1%. Presumably it is a meaningful fraction of that 1% or else the BBC would not have included it. While the source of the data is listed as the US Energy Information Agency, the graphic itself was prepared by the BBC if I understand correctly.

Are thee other gases available from the Earth that could account for this fraction of 1%? I don't mean gases that are produced during an industrial refinement process, but perhaps gases that were simply separated. Just for example could it be natural propane? The same Wikipedia article mentions heavier hydrocarbons, but I don't understand if these are already present in the Earth and just being separated, or if they are produced primarily as reaction products.

Explanation: By retrive the data from US resources, the 'other gases' accounts more than 1%

$\begingroup$

The category "other gases" may not solely include other naturally occurring
gases extracted from the Earth.

As you state [ natural gas ](https://en.wikipedia.org/wiki/Natural_gas) is
predominantly methane, extracted from the Earth.

Another type of gas commonly used is [ petroleum gas
](https://en.wikipedia.org/wiki/Liquefied_petroleum_gas) , which is prepared
by refining petroleum of wet natural gas. Petroleum gas is [ propane
](https://en.wikipedia.org/wiki/Propane) or [ butane
](https://en.wikipedia.org/wiki/Butane) .

[ Coal gas ](https://en.wikipedia.org/wiki/Coal_gas) , which was manufactured
from coal and largely consists of hydrogen, carbon monoxide and methane, is no
longer manufactured or used.

Another type of gas that could be included in the category is [ biogas
](https://en.wikipedia.org/wiki/Biogas) , which is a manufactured gas made
from biological waste products, such as: manure, sewage, food waste and green
waste. Biogas is predominantly methane.


Question:
What is a temperature inversion and can it trap smog/pollution?
Just as the title says, I heard about this term but am not sure how it works.

Explanation: A temperature inversion is where the air temperature rises with altitude. Since pollution is generally produced at ground level, temperature inversions can trap the pollution (e.g. smog) at ground level.

$\begingroup$

Normally, temperature broadly [ decreases with altitude
](https://en.wikipedia.org/wiki/Lapse_rate) , and convection is effective:
locally warmer air will rise, and cooler air will fall. A [ temperature
inversion ](https://en.wikipedia.org/wiki/Inversion_\(meteorology\)) is where
the air temperature **rises** with altitude. This means that convection is
less effective because the air above is already warmer, and so there is less
mixing of air between altitudes.

Since pollution is generally produced at ground level, temperature inversions
can trap the pollution (e.g. smog) at ground level.


Question:
In meteorology the seasons always start at the beginning of the month the astronomical seasons start.
The astronomical seasons start around the 21st in a month so I guess it would make more sense to start the meteorological season at the first day of the month following the start of the astronomical season.
Another more logical reason to do this: for example the meteorological winter start at December 1 and ends at February 28 (or 29) in the next year so meteorology actually measures in broken years. Should the meteorological winter start at January 1 and end at March 31 then all seasons do exactly fit in the same year.
So is there a reason why meteorologists do it this way or is it just arbitrarily chosen?

$\begingroup$

Meteorological seasons are based on temperature, whereas astronomical seasons
are based on the position of the earth in relation to the sun. So
meteorological winter is the three coldest months of the year (December,
January, and February) and meteorological summer is the three warmest months
of the year (June, July, and August). More information can be found on this [
NOAA web site ](https://www.ncei.noaa.gov/news/meteorological-versus-
astronomical-seasons) .


Question: I'm slightly confused by how thermohaline circulation works in the Earth's oceans. Is it different for surface water as opposed to deep water? I thought that warm water from the equator is transported to the poles, cools down, and then returns to lower latitudes. Is my thinking incorrect? Isn't water denser near the equator because of higher salinity? How does this impact the ocean circulation?

Explanation: Salinity and temperature affect the density of seawater. Cooling water with fixed salinity makes it heavier and sink, while removing water through evaporation or ice formation increases salinity and density. This process, known as thermohaline circulation, causes surface water in the tropics to become saline but less dense due to high temperatures, while in colder climates, the water cools down and the high salinity causes it to sink. In polar regions, ice formation increases the density of surface water by leaving salt behind in the sea.

$\begingroup$

Salinity and temperature both affects the density of sea water. When water
with a fixed salinity cools down, it becomes heavier and sinks. In the same
way, when vapor or ice removes water from sea water, the remains is more
saline and heavier. Thermohaline circulation can work as you describe. Surface
water in the tropics is saline, due to evaporation, but warm due to high
temperature in the atmosphere and therefor low density. As it reach colder
climate (less solar energy per area), it cools down and the high salinity
makes it sink. Surface water in polar regions also get heavier as ice is
formed of water and leave the salt behind in the sea.

This is very simplified model, you can read more on the topic [ here
](http://oceanmotion.org/html/background/ocean-conveyor-belt.htm) and [ here
](http://oceanservice.noaa.gov/education/tutorial_currents/05conveyor1.html) .


Question:
Where do I find the documentation of different VARIANT-IDs for the CMIP6 dataset? A VARIANT-ID is of the format r<k>i<l>p<m>f<n>, where the characters r, i, p and f denote:

r-realisation
i-initialisation method
p-physics
f-forcing

I checked the overview paper Eyring et al. (2016), but it doesn't mention anything about VARIANT-ID. I have also checked other documents provided at ESGF, but couldn't find any information.

Explanation:
The variant_labels are defined in the CMIP6 Data Reference Syntax (DRS) document and are made up of the realization_index, initialization_index, physics_index and forcing_index.

A link to this DRS document can for example be found in the CMIP6 Participation Guide for Modelers.

$\begingroup$

The variant_labels are defined in the [ CMIP6 Data Reference Syntax (DRS)
](https://docs.google.com/document/d/1h0r8RZr_f3-8egBMMh7aqLwy3snpD6_MrDz1q8n5XUk/edit)
document and are made up of the realization_index, initialization_index,
physics_index and forcing_index.

A link to this DRS document can for example be found in the [ CMIP6
Participation Guide for Modelers
](https://pcmdi.llnl.gov/CMIP6/Guide/modelers.html) .

Edit: Following up Deditos' comment, I quote the respective section of the DRS
document below:

> For a given experiment, the realization_index, initialization_index,
> physics_index, and forcing_index are used to uniquely identify each
> simulation of an ensemble of runs contributed by a single model. These
> indices are defined as follows:

>   * realization_index = an integer (≥1) distinguishing among members of an
> ensemble of simulations that differ only in their initial conditions (e.g.,
> initialized from different points in a control run). Note that if two
> different simulations were started from the same initial conditions, the
> same realization number should be used for both simulations. For example if
> a historical run with “natural forcing” only and another historical run that
> includes anthropogenic forcing were both spawned at the same point in a
> control run, both should be assigned the same realization. Also, each so-
> called RCP (future scenario) simulation should normally be assigned the same
> realization integer as the historical run from which it was initiated. This
> will allow users to easily splice together the appropriate historical and
> future runs.
>   * initialization_index = an integer (≥1), which should be assigned a value
> of 1 except to distinguish simulations performed under the same conditions
> but with different initialization procedures. In CMIP6 this index should
> invariably be assigned the value “1” except for some hindcast and forecast
> experiments called for by the DCPP activity. The initialization_index can be
> used either to distinguish between different algorithms used to impose
> initial conditions on a forecast or to distinguish between different
> observational datasets used to initialize a forecast.
>   * physics_index = an integer (≥1) identifying the physics version used by
> the model. In the usual case of a single physics version of a model, this
> argument should normally be assigned the value 1, but it is essential that a
> consistent assignment of physics_index be used across all simulations
> performed by a particular model. Use of “physics_index” is reserved for
> closely-related model versions (e.g., as in a “perturbed physics” ensemble)
> or for the same model run with slightly different parameterizations (e.g.,
> of cloud physics). Model versions that are substantially different from one
> another should be given a different source_id” (rather than simply assigning
> a different value of the physics_index).
>   * forcing_index = an integer (≥1) used to distinguish runs conforming to
> the protocol of a single CMIP6 experiment, but with different variants of
> forcing applied. One can, for example, distinguish between two historical
> simulations, one forced with the CMIP6-recommended forcing data sets and
> another forced by a different dataset, which might yield information about
> how forcing uncertainty affects the simulation.
>

> Each data provider can assign whatever positive integers they like for the
> realization_index, intialization_index, physics_index, and forcing index.
> For each source/experiment pair, however, consistency (in these indices)
> should be maintained across each parent/child pair whenever sensible (so
> that, for example, both the ScenarioMIP child and its “historical” parent
> simulation would be assigned the same set of index values for realization,
> initialization, and physics); the integer 1 should normally be chosen for
> each of these in the case of a single variant or for the primary variant (if
> there is one). This is only a suggestion, however; there should be no
> expectation on the part of users that every model will have a value of 1
> assigned to any of the r, i, p, f indices, and even if a 1 is assigned it
> does not imply that it is the primary variant. Note also that a child
> spawned by a control run will not necessarily have the same “ripf” value as
> the control, since, for example, multiple realizations of an experiment will
> branch from the same control.
>
> Note that none of the “ripf” indices can be omitted.
>
> Example of a variant_label: if realization_index=2, initialization_index=1,
> physics_index=3, and forcing_index=233, then variant_label = “r2i1p3f233”.


Question: Has anyone ever found or gone looking for similar locations, i.e. volcanic eruption sites in which unfortunate victims – human and non-human – have been entombed in the volcanic ash, with the possibility of revealing their forms by producing casts from the voids? Such sites, if they exist, could reveal exciting new knowledge about ancient peoples and animals.

Explanation: Volcanic eruption sites have been explored to uncover preserved victims entombed in volcanic ash, offering insights into ancient peoples and animals. The 1902 eruption of Mt. Pelée in Martinique, which claimed 30,000 lives, is a well-known example, though the extent of burial and preservation varies.

$\begingroup$

Probably the best known is more recent, the 1902 eruption of [ Mt. Pelée on
Martinique ](https://en.wikipedia.org/wiki/Mount_Pel%C3%A9e) , where 30,000
people were killed by pyroclastic flows. I don't know the extent of burial -
it appears that the city may have been destroyed more by the ash cloud than
the dense part of the flow.


Question:
For my research related to coastal Odisha, India I am mapping the coastal boundary. I have downloaded available Landsat images which date back to 1972. But I want to map the same for before 1972.

I am interested in old topographic maps showing the coastal boundary of Odisha, preferably before 1970.

Does anyone know from where can I get the scanned map of the same?

Explanation: The old topographic maps can be found at a Texas-Austin's website, especially India's

$\begingroup$

The [ PCL Map Collection ](https://maps.lib.utexas.edu/maps/index.html)
(University of Texas at Austin) is a huge online collection of maps. For
India, they have [ a series from the U.S. Army Map Service
](https://maps.lib.utexas.edu/maps/ams/india/) which might be of interest, as
it dates from the 50's and has a decent scale (1:250,000). They also have
older maps from the British era, but the series doesn't seem to be complete.
It might be worth looking for those at the Royal Geographical Society
archives.


Question: Atmospheric mixing ratios of the hydroxyl radical have relatively short lifespans (on the order of microseconds). When modeling air quality or the weather, the time step is usually much larger than the the half life of hydroxyl. How is this computation numerically stable? Is the problem of numerical stability simply ignored?

Explanation: air quality models like CMAQ assume a pseudo-steady-state for the hydroxyl radical (OH) due to its catalytic nature and rapid reactions. This simplification is made to ensure numerical stability, as explicitly modeling OH can be challenging. For more detailed OH chemistry, specialized box models like MECCA are typically employed.

$\begingroup$

The hydroxyl radical chemistry is not modeled explicitly in air quality
models, so numerical stability is not an issue. Instead, OH is held in pseudo-
steady-state. For instance, see [ CMAQ's documentation
](https://www.cmascenter.org/cmaq/documentation/4.7.1/AQCHEM_NOTES.txt) which
states:

> In CMAQ's gas phase, OH is assumed to be in pseudo-steady state, and it is
> not a transported species. This is because hydroxyl radical reactions tend
> to be catalytic (e.g., consumption and production). In the aqueous phase
> chemistry, OH is absorbed by cloud water and in an open cloud model (i.e.,
> the design approach currently employed), absorbed species (e.g., OH) would
> be replenished via gas-to-cloud partitioning. However, due to operator
> splitting, aqueous and gas-phase chemistry are not solved simultaneously. To
> account for this and other uncertainties in predicted OH aqueous phase
> concentrations (e.g., neglect of production reactions (H2O2 + hv -> 2 OH)
> not currently implemented in aqchem), a steady-state assumption for OH is
> adopted in the aqueous chemistry routine.

Typically, if you are trying to model something like the hydroxyl radical, you
would use a [ box-model like MECCA ](http://www.atmos-chem-
phys.net/10/9705/2010/) , not a chemical transport model.


Question:
The image below is included in the BBC article Amazing white rainbow snapped over Scottish moor. Apparently this phenomenon is sometimes called a "fog-bow" and is characterized by the washing out of perceived color relative to a conventional rainbow.
Is this related to the geometry (fog being far closer to the viewer) or properties of the droplets themselves? If so, which properties and why?

Explanation: Fog bows lack color compared to rainbows because the tiny water droplets in fog (less than 0.05 mm diameter) cause diffraction effects that smear out the colors, unlike the larger droplets in rainbows.

$\begingroup$

The reason why [ fog bows ](https://en.wikipedia.org/wiki/Fog_bow) lack
colour, compared to rainbows, is due to the size of the drops of water.

Fog is composed of very small drops of water - less than 0.05 mm diameter.
Because of this the wavelength of light is critical, with diffraction smearing
out colours that the larger drops of water in a rainbow would make.


Question:
I have recently bought a medium sized plot of wood/scrub land. Half of this plot was once used to dump shale from coal mines, which means I have a lot of shale.

I have been wondering/looking for possible uses for the stuff. One thought I've had is to make "mud bricks" however I can't find any mention of whether it is possible or not. I know the traditional method uses loamy soil but would it work with shale?

I don't have a kiln or any way of baking the bricks, so would be reliant on the sun. I was thinking maybe adding water and maybe some loam?

Aside: there are no suitable tags for my question and I do not have the reputation to add any, I'm thinking I could be on the wrong site for this question, if I am, please advise me of a more suitable one.

Explanation: shale can be used to make sun-dried mud bricks. Being a type of mudstone composed of clay and silt, shale can be crushed and mixed with water, potentially with some added loam, to produce an effective material for making simple unfired mud bricks.

$\begingroup$

Your idea has merit. Shale is classified by geologists as being a mudstone. It
is composed of silt and clay sized minerals.

According to this [ geology website ](http://geology.com/rocks/shale.shtml) ,
shales can be crushed to produce a clay and then mixed with water. These days,
items that were once made from natural clay, such as terracotta pots and tiles
for roofs, are now made from crushed shale.

* * *

Extra Information

One thing to be mindful of is that clays expand when wet and contract when
dry. Anything you make from it, such as bricks, that isn't baked or protected
from water by a sealed coating will expand and contract according to it
moisture content.

Another application which you may want to consider is to supply crushed shale
as a garden mulch or other such landscaping product.


Question:
I was wondering if we could possibly reduce the severity of, or steer a hurricane by changing albedo (e.g. dying the part ocean with a temporary light colored dye)? My thought would be to put this dye well in front of the path of a hurricane, with enough time to reflect the sunlight back off the ocean and cool the ocean surface. When the hurricane arrives there, the ocean surface should then be cooler, leading to the hurricane being less powerful. I am also wondering if this could be used to steer the hurricane somehow (e.g. if a hurricane would be drawn to or repelled away from cool ocean surface). If so, could we use that to steer a hurricane away from populated areas?

Some potential methods (there may be others):

Use light colored dye injected into the ocean

Use light colored smoke to block the sun from reaching the ocean

Possibly use "cloud seeding" ahead of the hurricane and form clouds to block the sun light from warming the ocean. - Covered in the alternate question

Perhaps a "surface film" could also be applied temporarily to part of the ocean (sort of like a "light colored oil spill", hopefully with something safer for the environment than oil). - Covered in the alternate question

If this experiment were to be conducted, I would think it should be done far from inhabited land. Environmental impacts would need to be thought out too, e.g. would a film block the carbon dioxide / oxygen exchange in that area and cause severe environmental impact? Could the experiment actually strengthen instead of weaken a hurricane?

Explanation: Changing the ocean's albedo (reflectivity) just before a hurricane passes is unlikely to have a significant cooling effect due to water's high heat capacity and the short timeframe. More promising approaches being explored include pumping up cold water from deeper ocean layers to cool the surface, or injecting aerosols into the atmosphere to reflect sunlight and encourage rainfall, though these methods have challenges and potential side effects that need further study.

$\begingroup$

Water has a large [ thermal capacity ](https://water.usgs.gov/edu/heat-
capacity.html) .

> which is why the temperature change between seasons is gradual rather than
> sudden, especially near the oceans.

For water to lose heat time is required. By changing the albedo of the ocean
just prior to a hurricane/cyclone/typhoon passing over a section of water will
not give the water enough time to cool down to have any significant effect.

If it were possible to change the temperature of water to minimize the
strength of hurricanes/typhoons/cyclones, large sections of ocean would need
to have their albedos changed for a long period of time.

* * *

Edit 10 August 2023

[ Newly discovered information
](https://www.abc.net.au/news/2023-08-10/cyclone-risks-of-controlling-weather-
hurricane-typhoon/102706094) reveals that hurricanes could be influence by
other means - cooling the surface reaches of a region on ocean by pumping cold
water from at least 200 m below the ocean surface.

> there's been renewed interest in Cold War era experiments in weather
> control. While early efforts had little success, our new research evaluates
> other methods of weakening these storms by pumping up cold water from the
> depths or spreading particles in the lower atmosphere to reduce incoming
> heat and encourage early rainfall.
>
> In the 1960s, the United States explored the use of cloud seeding to stop
> hurricanes from forming.
>
> During Project STORMFURY, planes flew high above cyclones out at sea and
> sprayed them with silver iodide, a chemical which could encourage water
> droplets to clump together and fall as rain. This, the theory ran, would
> disrupt the hurricane from forming. While some seedings seemed to correlate
> with weaker hurricanes, the link was never adequately found and the project
> was eventually abandoned.
>
> Instead, researchers are exploring two new options.
>
> Cyclones need hot sea surfaces to form. If we could cool the surface – such
> as by piping chilled water from depths below 200 metres – we could prevent
> the cyclone from ever forming.
>
> The problem is it's expensive. Norwegian cyclone-busting startup OceanTherm
> estimates it would cost about AUD750 million to develop the technology, and
> another AUD105 million every year to keep it going.

> And worse, cooling one area of the sea does nothing to stop cyclones from
> forming elsewhere. Models suggest ocean cooling will, at best, have only a
> limited dampening effect on cyclones.
>
> There's a more likely option – aerosol injection. Scientists already know
> that dust blown from the Sahara into the Atlantic reduces cyclone formation.
> We could use planes or drones to inject hygroscopic (water-attracting)
> particles into the lower atmosphere, where they would reflect and scatter
> sunlight and trigger rainfall and energy release.
>
> This method has a stronger scientific pedigree, given it already occurs
> naturally. But we don't know what side-effects it would have and we still
> aren't sure what happens to energy redistributed by the intervention.


Question: What events took place in our Solar System which led to formation of the Earth? I have heard from sources that a big giant star exploded and the Earth was formed. Is this true ?

Explanation: A supernova explosion about 5 billion years ago deposited heavy elements into a nearby cloud of hydrogen gas and dust. The cloud collapsed under gravity, forming a new star at its center (the Sun) surrounded by a white-hot disk. The disk eventually formed Earth and the other planets in our solar system. Similar processes are observed in other parts of the universe.

$\begingroup$

The following quote from [ Birth of the Earth
](http://geology.about.com/od/nutshells/a/aa_earthbirth.htm) explains the
current theory/model for the formation of the Solar System:

> Long, long ago (some 5 billion years ago) in a perfectly ordinary place in
> the galaxy, a supernova exploded, pushing a lot of its heavy-element
> wreckage into a nearby cloud of hydrogen gas and interstellar dust. The
> mixture grew hot and compressed under its own gravity, and at its center a
> new star began to form. Around it swirled a disk of the same material, which
> grew white-hot from the great compressive forces. That new star became our
> Sun, and the glowing disk gave rise to Earth and its sister planets. We can
> see just this sort of thing happening elsewhere in the universe.

Read this article from Wikipedia as well.

[
https://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System#Formation_of_planets
](https://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System#Formation_of_planets)


Question: Seems like the Earth Day related crowd sourcing project to create the first global soundscape by encouraging smartphone owners around the world to download and use an app developed to record the sounds around them is interesting, though it's unclear what scientific value it would have. Is there any scientific value to understanding soundscapes on a global basis?

Explanation: Remote sensing uses signals like passive sonar and seismograms to indirectly measure objects or phenomena through related variables. Soundscape ecology studies the impact of sound on organisms, including biophony, geophony, and anthrophony. Soundscapes play a crucial role in ecological processes, but anthropogenic noise pollution negatively affects organisms. Preserving natural soundscapes is an important conservation goal.

$\begingroup$

> Remote sensing using [ passive sonar and seismograms
> ](http://en.wikipedia.org/wiki/Remote_sensing#Acoustic_and_near-acoustic) ,
> which are acoustic or near-acoustic signals, works on the principle of the
> inverse problem. While the object or phenomenon of interest (the state) may
> not be directly measured, there exists some other variable that can be
> detected and measured (the observation), which may be related to the object
> of interest through the use of a data-derived computer model.
>
> [ Soundscape ecology ](http://en.wikipedia.org/wiki/Soundscape_ecology) is
> the study of sound within a landscape and its effect on organisms. Sounds
> may be generated by organisms (biophony), by the physical environment
> (geophony), or by humans (anthrophony). Soundscape ecologists seek to
> understand how these different sound sources interact across spatial scales
> and through time. Variation in soundscapes may have wide-ranging ecological
> effects as organisms often obtain information from environmental sounds.
> Soundscape ecologists use recording devices, audio tools, and elements of
> traditional ecological analyses to study soundscape structure. Increasingly,
> anthrophony, sometimes referred to in older, more archaic terminology as
> anthropogenic noise dominates soundscapes, and this type of noise pollution
> or disturbance has a negative impact on a wide range of organisms. The
> preservation of natural soundscapes is now a recognized conservation goal.
>
> Source: Wikipedia links referenced above.


Question: What percentage of Earth's surface is arid?Is there available information on how much of Earth surface is arid climate?

Explanation:
The four arid climates, add up to 4.401×107km2
 of a total of 1.527×108km2.

$\begingroup$

It will depend on the exact definition of "arid" and the period of time. But
using the widely used and accepted [ Köppen climate classification
](https://en.wikipedia.org/wiki/K%C3%B6ppen_climate_classification) , "arid"
would correspond to the four climates in [ climatic group B
](https://en.wikipedia.org/wiki/K%C3%B6ppen_climate_classification#Group_B:_Dry_\(desert_and_semi-
arid\)_climates) : " **Dry (desert and semi-arid) climates** ". Using [ the
most up-to-date present climate data (2006) ](http://koeppen-geiger.vu-
wien.ac.at/present.htm) provided by the [ WORLD MAPS OF KÖPPEN-GEIGER CLIMATE
CLASSIFICATION ](http://koeppen-geiger.vu-wien.ac.at/) at 0.5° of resolution,
that looks like this (in an equal area projection):

[ ![enter image description here](https://i.sstatic.net/sLj6J.png)
](https://i.sstatic.net/sLj6J.png)

We get that the four arid climates (group B), add up to $4.401 \times 10^7
{km}^2$ of a total of $1.527 \times 10^8 {km}^2$ inventoried in the dataset (A
good match for the figure of of [ global land area of $1.489 \times 10^8 km^2$
listed by wikipedia ](https://en.wikipedia.org/wiki/Earth) ), leading to a
grand total of **28.8% of Earth's land surface corresponding to arid
climates** .