Why the Indian Monsoon doesn't start in the north? The usual explanation for the Indian Monsoon that I read everywhere is that it is generated by winds from the Arabic Sea, moving to India mainland because of the low pressure there. These winds are stopped by the Himalayan mountains, the air rises and cools down, giving heavy rains. But if this is true I would expect rains starting next to the Himalayas, and then eventually travel south to complete a cycle. Why is the monsoon starting in the south instead? The Himalayas are clearly a barrier, and that's why in Tibet they don't experience the monsoon, but to me it doesn't make sense that they are the reason for the south-west monsoon, I would say more the Western Ghats.

Summarizing what I wrote in the comments

1) The monsoon does not start off in the Arabian Sea. There is actually a cross equatorial gradient that drives winds from the Southern Indian Ocean into the Northern Indian Ocean and then into the Arabian Sea.

2) There is also a second branch of the Indian monsoonal winds and that is the Bay of Bengal branch. This branch also receives winds from the Southern Indian Ocean. This branch ends up contributing easterlies and south easterlies to the Indian monsoon.

3) The crucial aspect that you left out in the question is the role of the Monsoon trough. The monsoon is not just made of winds alone converging rather it is the north to south movement and sometimes south to north movement of the monsoon trough along the Indian subcontinent that researchers and forecasters track. Why is that ? It is because systems form within the monsoon trough. What governs the movement of the monsoon trough up and down the Indian subcontinent ? Well that is a topic beyond the scope of this question.

4) So the monsoon trough includes westerly winds in the equatorward section and in the poleward section you have trade winds. The Himalayan branch from that definition contains easterly winds and not westerly winds from the Arabian Sea.Actually Arabian Sea winds  only have a secondary role in providing moisture for systems to form in the Himalayan side.

5) Finally the Indian Himalayas only receive rainfall when the monsoon trough is located along those latitudes. This condition is known as a "break monsoon" condition and it happens when sub tropical westerlies are present aloft. This usually happens after the monsoon has provided rain to the southern parts of the country including the western ghats.

I would recommend going through this free e-book - sw monsoon e-book for a thorough description of what I have mentioned above.


Why would channelizing a river reduce any nearby wetlands? Channelization is when you straighten a river to make a shorter path from A to B. This makes the water flow faster, since the path is shorter but the volumetric flow rate of water must be the same (because it's receiving the same rate of water from the watershed).
However, that wikipedia article also says,

Channelization has several predictable and negative effects. One of them is loss of wetlands.

No citation and no explanation. I don't get it. Why would nearby wetlands be lost from this process? How could that happen?

Channelizing a river keeps it from overflowing its banks as often, which prevents flooding.  However, wetlands need a certain degree of said flooding to function as a biome.


How is sea level measured? In comments on Earth changes due to global climate change, sea level changes is a common topic. I hear quotes about sea level changes in the centimeter and even millimeter range and wonder how such precision is even possible. The sea moves a lot; way more than a centimeter in a given day. I have no understanding how the sea level is measured, and I also can't even imagine how to do it with that kind of precision. How exactly to oceanographers measure sea level?

Perhaps a different question, I also can't envision a way that a measurement of 1 cm change is pragmatically meaningful, even for just a single beach, never mind a global average. A 1 cm higher tide I don't think would be noticed at most places. Even 10 cm could go unnoticed at many places. Does a 1 cm global average change mean anything useful? I guess rates of change can be alarming. 1 cm per year would add up over the decades.

There are two main approaches to measuring sea level (and thus its change): local and satellite-based.

To measure local sea level we can set up gauges on the coast that record the water level every so often - hourly is common. These use various methods, which have evolved over time, all aimed at having a very precise (sometimes down to millimetres) long-term record at that location. In the UK, the UK Tide Gauge network has records going back (in some locations) to 1915.

The mechanisms of tide gauges vary, and have improved over time. Early ones used floats inside a "stilling well" (a column of water that protects the gauge from waves). Some modern gauges work by sensing water pressure. If we have good measurements of temperature and salinity we can calculate density, and if we know density and the pressure at a location, we can calculate the amount of water above that location. Other modern gauges use ultrasound or radar transceivers located at a known vertical position above the water, and thus measure the distance to the water surface with very high accuracy.

These records of water level include the tides, of course, as well as other influences such as the effects of changing air pressure, wind driven currents, and so forth. They are also affected by the rising and falling of land over time. These effects can all be accounted for, and removed from the signal, and effort goes into doing this. You might some interesting reading on the topic from the National Tidal and Sea Level Facility.

However, no matter how good the record from fixed tide gauges, they can only tell us what is happening on the coast. While that's arguably the most important for mankind, it's hardly a global picture.

The other approach that we can take is satellite observations. Radar altimeters on satellites can, and do, measure sea level worldwide to a precision of a few centimetres or better. This is a recent mission for this purpose (there may have been others since - I'm not an expert). The level of accuracy here is not as good, but it can be improved statistically through a large number of measurements.

The greater difficulty with satellite altimetry is removing the tides, because the satellites are always moving over the earth's surface and so can only measure any one location at relatively infrequent intervals. Consequently, some sophisticated global tidal models are used with data provided by the satellites to (a) improve the models, for people who want to predict tides, and (b) use the tides from the models to remove the tides from the satellite measurements, leaving just longer-term changes in sea level.

I think part of the intent of your question is "people quote changes in sea level of millimetres or centimetres per year, yet surely the measurements are not this accurate?". Well, satellite measurements aren't, though local ones might be, but remember that we're measuring for more than just one year. One approach might be to look at a ten- or twenty-year trend, and work out the average change per year from that.


How can we measure the thickness of the Earth's mantle? According to Wikipedia the earth's mantle is approximately 2900 km (1,800 miles) thick.

How is it possible to achieve such measurements?

Obviously we haven't sent anything down that far to check.

You are right...noone ever was able to make a borehole that deep. The two deepest boreholes are about. 12.300 m (40.400 ft) - those are the Kola Superdeep Borehole in Russia and the Al Shaheen oil well in Qatar.

So how do we measure the thickness of our subsurface? Think of the earth as an onion with different layers. Each of those layers (lithosphere, asthenosphere, mesospheric mantle, outer core, inner core) contain different mechanical (and chemical) properties. Due to this it is possible to infer indirectly the depth of each layer by using the travel time of refracted/reflected seismic waves (those come from earthquakes).

As mentioned before, each layer contains different mechanical properties, thus making the seismic velocity different in each layer. So on the border of each layer, those changes cause refraction or reflection if large increases in seismic velocity are involved.

Conclusion: no direct measurements possible, only indirectly derived measurements by the speed of travel from seismic waves.


Converting grid resolution from degrees to kilometers I am curious how can one have an idea of grid resolution. How much is the distance resolution in km of a grid with resolution of 0.5 deg x 0.666 deg?

Assuming spherical shape, Earth's circumference is about $40,000\mathrm{km}$. These are split into $360^\circ$, so one degree is a bit more than $100\mathrm{km}$. This is true for latitudes. For longitudes, the circles of constant latitude are shorter as you move away from the equator. Therefore you need to multiply that number by $\cos(latitude)$. To summarize, if $R_e$ is Earth's radius, we got

$$\Delta y=2\pi R_e\frac{\Delta lat}{360^\circ}$$

and

$$\Delta x=2\pi R_e\cos(lat)\frac{\Delta lon}{360^\circ}.$$
Note that here I am using $\Delta x$ and $\Delta y$ for the resolution in a cartesian frame with $y$ pointing south-north and $x$ pointing west-east. For your numbers, think about it as around $50\mathrm{km}$ resolution.


Effective Temperature of a Planet and Surface Temperature due to Greenhouse Effect The effective temperature of the Earth is roughly 12 °F (- 11 °C), which means that in thermal equilibrium when it is emitting as much radiation as it is absorbing, the distribution of wavelengths and intensities of electromagnetic radiation an observer in outer space would measure would correspond to the temperature of a blackbody object at 12 °F (- 11 °C)

Of course, the surface of the Earth is actually much warmer than 12 °F (- 11 °C) due to the greenhouse effect. If there are greenhouse gases in an atmosphere then some fraction of infrared radiation from the terrestrial surface is absorbed by the atmosphere and re-emitted toward the ground. This re-emission of infrared radiation to the ground is like a trap for energy and over time it will cause the surface temperature of the planet to rise. This is right about where I have actual questions:

If the terrestrial surface is warming it will have to emit even more infrared radiation back to space. Is the atmosphere (and greenhouse gases) now absorbing the same fraction of a now larger amount of infrared radiation? in order to eventually rebalance incoming and outgoing radiation? I was thinking that the surface will grow warmer and emit more radiation until the amount exiting equals the amount incoming, establishing the new thermal equilibrium.

I often get confused because most diagrams for the Earth energy budget and net radiation balance show more infrared leaving the surface than is ever supplied by solar radiation at the top of the atmosphere in the first place. Is this because they count percentages or units of radiation twice? because some is re-emitted back?

I have included a photo showing how the electromagnetic wave types are partitioned in the radiation balance. It is from NASA's CERES page. As you can see, more infrared is leaving Earth than enters as solar radiation and yet this is still a picture of equilibrium where the net radiation is zero.

I think you’re not far off with your understanding, but maybe I can put in a few comments to make things clearer.

  I often get confused because most diagrams for the Earth energy budget and net radiation balance show more infrared leaving the surface than is ever supplied by solar radiation at the top of the atmosphere in the first place… As you can see, more infrared is leaving Earth than enters as solar radiation and yet this is still a picture of equilibrium where the net radiation is zero.

These types of diagrams only show the fluxes, but you have to remember that the surface (mainly the ocean) and the atmosphere are reservoirs of energy that have built up over time.  In that diagram the top-of-atmosphere net radiation balance for the Earth system is,

67 (absorbed by atmosphere) + 168 (absorbed by surface) = 235 (outgoing longwave radiation)

and all the other much larger components are just different pathways for energy transfer between those two internal reservoirs.  The sun only has to top-up the amount of energy that the reservoirs are leaking to space (235 W/m2) to maintain the equilibrium.

  This re-emission of infrared radiation to the ground is like a trap for energy and over time it will cause the surface temperature of the planet to rise… If the terrestrial surface is warming it will have to emit even more infrared radiation back to space... I was thinking that the surface will grow warmer and emit more radiation until the amount exiting equals the amount incoming, establishing the new thermal equilibrium.

Broadly yes, but remember that the diagram you posted describes a long-term steady state (“thermal equilibrium”), so all that “warming” has already occurred and is built into those numbers.  It may just be your phrasing, but note that surface doesn’t emit the bulk of its thermal radiation directly back to space.  In your diagram this is the 40 W/m2 “atmospheric window”, which is much smaller than the 350 W/m2 of surface emission that’s absorbed by the atmosphere.

It might be better to think of the atmosphere less as trapping energy at the surface and more as slowing the net transfer of energy from the surface through the atmosphere to space.  Atmospheric science text books often include a cartoon to demonstrate how energy is absorbed and re-emitted as it passes through the atmosphere:

Here each arrow is 1 arbitrary unit of energy.  Things to note are that (1) each layer emits as much as it receives, (2) there's a lot more than 1 unit of flux within the atmosphere, (3) there's a steady 1 unit of net flux through the atmosphere and (4) this equilibrium is maintained by 1 unit in and 1 unit out at the top of atmosphere.


What started the US Dust Bowl of the 1930s, and could it happen again? Most of us know about the Dust Bowl: the huge storms of dirt and dust that swept across America in the 1930's. But what I'm wondering is...

What actually triggered the start of the Dust Bowl?
Is it very likely that it will occur again?

I've often heard that it was the farmers plowing up to much soil, but that doesn't make any sense to me because we're definitely plowing up more soil now than we were then.

The Dustbowl occurred during the 1930s because of a combination of man-induced drought and the (mis)use of relatively new farming practices.

In the 1920s, the spread of automotive (and tractor) technologies made it possible to "plow up" the Great Plains. This resulted in the loss of a lot of natural moisture and the creation of drought conditions in lands that had been marginal to begin with regarding the adequacy of the water supply.

Even by the 1930s we still had not learned our lesson. There were conservation techniques using the new technologies, but we weren't using them. For example, the tractors would still plow up and down slopes (the "easy" way) making it easy for topsoil to run down hills and into the rivers. More to the point, the newly dry and loosened topsoil would then go into the air and create a "Dust Bowl" when the winds kicked up. There was a real fear that the agricultural Midwest (basically the Plains states) would turn into a desert.

It was only after an additional half a decade of bitter trial and error (and a new generation of better educated farmers) that things changed. By the mid 1930s, it was a relatively new technique called contour farming, which consisted of using motor vehicles to plow horizontally around hills instead of vertically, that saved the day. Also, farmers started planting trees as "windbreaks" in strategic locations.

IMHO, it could happen again, probably in a developing country like China, which is trying to "catch up" to the United States, and has been prone to adopting our bad habits of an earlier era.

Bottom line, the Dust Bowl was (largely) a man-made, not a natural phenomenon. And the operative principle was attributed to Confucius:

  "Men are the same everywhere. Only their habits are different."


How to identify a landslide area early? We know that this natural disaster can cause a big damage. I have heard that we can identify such areas by some geographical signs, such as curved trees. Do we have any stronger detectable signs which we can observe easily?

Curved trees are a sure sign of movement of surface. Special geomorphic shapes are also present in a slowly developing landslide. At the top of the landslide cracks can start to show, at the foot you can find "bumps" in the soil. Water will have difficulties to drain at the foot of the landslide.

Here are a few examples of literature that should be something to start with:

http://ny.water.usgs.gov/pubs/jrn/ny0155/jrn02-r20500g.pdf
http://www.ags-hk.org/notes/09/Geomorphology_and_Landslide_Hazard_Models_Steve_Parry.pdf
http://www.adpc.net/casita/pdf/01-Geomorphic-mapping.pdf


Is there a correlation between hot springs and earthquakes? Is there a correlation between how many hot springs an area has, and how frequent or severe the area's earthquakes are?

Yes, there is a correlation.

In other words: places with hot springs are more likely to experience earthquakes than places without hot springs. The relationship is scale-dependent in time and space (your house might not sit on a hot spring but still get earthquakes).

Ideally I'd dig around and find actual data to quantify this spatial correlation (and I hope someone does!), but for now I will settle for qualitative evidence at the continental scale. I offer a visual correlation between the two datasets in question. First, geothermal springs:

Now earthquakes:

Like any correlation in geoscience, it's not perfect. But, broadly speaking, there is one.

Footnote: Actually, there are at least two correlations. As with fracking for shale gas, well stimulations and other industrial activity in geothermal fields has recently been blamed for induced seismicity in places like the Imperial Valley of southern California. Sometimes correlation does imply causation!


Odd Inuksuk-like objects I found some huge objects that are way too big to be inuksuks, in my opinion.

The object on the right is very odd because the arms are not straight like they are in most images of inuksuks. and there are huge piles of rocks that look so unnatural. Can any geologist or anyone explain this?

These are the coordinates: left: 68°41'52.47"N 124°53'41.18"W
right: 68°45'59.09"N 125°10'6.76"W

I can engage in some educated speculation about what you think you see, but I'm confident you were fooled by the shadows in the image, which are caused by a low sun angle and distorted by the terrain. These are not inuksuit (which is the correct plural of inuksuk). They are all natural, not man-made.

Let's point out a few things we know and can see on the imagery:

It's in the Low Arctic.
The uplands away from the river are snow-free, except in a few pockets. There is even some greening of new tundra vegetation.
There is broken-up ice along the sides of the river.
The trees in the uplands all have very long shadows, so other shadows are likely to be elongated.

Together, #1, #2, and #3 tell us that it's probably early summer just after the river ice has broken up.

The tooth-like features in the left image are simply erosional remnants sticking out of the riverbank. They could be bedrock (not likely), ice wedges, unmelted permafrost, or simply dirt. They are on the outside of a meander, so the river is actively cutting into them, and so the river-facing faces are quite sheer and high compared to the slopes in between. The right side might be white because the conditions there had left the snow unmelted when the image was taken. And of course their shadows are longer because the river channel is at the bottom of the bluff.

If you use Google Maps or Earth to go downriver a bit (up and to the left), you will see similar features sticking out of the riverbank, but because they're at a different angle from the features in your image, the fact that they're natural is more readily apparent.

Although the terrain is much less regular on the right side of the image, again the long shadows tell the tale. There are some round lumps that may be pingoes.  The shadow that looks like a man is just a coincidental jumble of shadows from the broken terrain. If you look closely at the lump that is supposed to be the "man" (which would technically be an inunnguaq) does not have any protrusions that correspond to the "arms". The "arms" are the shadow of a little cliff or shelf past the lump, which is overlapped by the lump's larger shadow.

It's similar in effect to the infamous misinterpretation of a Viking orbiter image of a natural feature on Mars as a "Face on Mars".

This is a good example of the complications of image interpretation, specifically, understanding the conditions under which the image was taken. It's also a good time to emphasize the importance of doing ground truth when interpreting images. So when you go there, let us know what you find.


How does the ozone layer "stay in place"? It is said about ozone:

a layer in the earth's stratosphere at an altitude of about 10 km (6.2 miles) containing a high concentration of ozone

Over the Earth’s surface, the ozone layer’s average thickness is about 300 Dobson Units or a layer that is 3 millimetres thick. (nasa)

So, how does the Ozone gas stays in that altitude without dissolving?

For the ozone layer to dissolve, it would need something to bind to. Chloroflurocarbons are one very notable thing that it can bind to, but that doesn't exactly answer the question.
While the ozone layer would be 3 mm thick if it was compressed down to the pressure of earth's surface, since it is further up in the atmosphere, it can take up a larger volume (like 20 km thick). The ozone layer is maintained by the Chapman cycle.
That is, the oxygen molecule ($\ce{O_2}$) is dissociated by UV radiation (photolysis) to oxygen atoms ($\ce{2O}$). Then the photolyzed oxygen atoms ($\ce{2O}$) can bond with two oxygen molecules ($\ce{2O_2}$) to make an two ozone molecules ($\ce{2O_3}$), provided another molecule can take away some excess energy.
Since it is a cycle, there has to be a way for the ozone to return to oxygen. One ozone molecule ($\ce{O_3}$) can photolyze to make an oxygen atom ($\ce{O}$) and oxygen molecule ($\ce{O_2}$). The oxygen atom ($\ce{O}$) can react with another ozone molecule ($\ce{O_3}$) to make two oxygen molecules ($\ce{2O_2}$).
To just answer your question directly, the ozone layer is replenished by the sun's UV energy reacting with the oxygen in the atmosphere.


How do I find the temperature of the air mass, and how do I use a t-skew chart? So the first problem I'm stuck on is this one:

An airmass is moving down a mountain from point A to B. At A the temperature is -10 Celsius and the pressure is 890hPa. At point B the pressure is 1010 hPa. What is the temperature to the air when reaching point B (assuming the airmass is isolated)?

So I thought about using the ideal gas law and $P_1/P_2=T_1/T_2$, but I'm not sure if that is correct. The numbers I get don't look right.

The pilot on an airplane thinks it's time to get some fresh air in the cabin. The airpressure outside is 350 hPa and the temperature is -40 Celsius, and the pressure needs to be increased to 850 hPa before being brought into the cabin. This is an adiabatic process. After being compressed what is the temperature of the air?

My teacher says that we need to use the following t-skew diagram.
But I don't understand how to use it in the problem, and which of the lines that represent an adiabatic process.

I don't want to answer your question explicitly because it will ruin your education. Instead, I will guide you by asking three questions:

Where on the Skew-T are you?
Where on the Skew-T do you want to go?
What type of process do you want to undergo to get there? If it is dry and adiabatic, follow the dry adiabat ($\theta=T\left(\frac{P_0}{P}\right)^{\frac{R_d}{c_p}}$)

I recommend drawing the process out. Does the result make sense?


What are the criteria that make a planet (in)habitable? Recently, I realized a lot of factors must contribute toward making a planet habitable, other than just the ones that come to mind like having oxygen, the right temperature, and so on.

What makes a planet habitable? Is there an official set of criteria? I don't see how one could say we have $x$ number of official potentially habitable exoplanets unless there was a standard set of criteria.

EDIT:
I'm not sure if the correct term is "habitable" or "inhabitable", but what I am obviously asking is what factors determine whether humans and other organisms could live on a given planet.

Circumstellar habitable zone

There are a few pages that explain the concept in detail, but the gist is that the circumstellar habitable zone is (my definition)

  The region around a star inside which a planet similar to Earth can have liquid water on it surface.

However, with more detailed observations of Europa, with its possible underground ocean, and Titan, with its hydrocarbon lakes, the definition may be modified:

  The region around a star inside which a body can have liquid water, or where other compounds suited for the formation of life can arise; alternatively, the region around a gas giant where moons can be heated by tidal forces such that the compounds can exist.

The latter section, of course applies to moons only. The galactic habitable zone (see here and here) is another - slightly less-well-defined - area where a habitable planet should lie.

You can calculate the habitable zone around a star based off of what defines it: the luminosity of the star, primarily. There's a poorly-explained formula here, although Planetary Biology gives a much more explicit derivation. The two important equations are these:
$$r_i = \sqrt{\frac{L_{\text{star}}}{1.1}}$$
$$r_o = \sqrt{\frac{L_{\text{star}}}{0.53}}$$
where $r_i$ and $r_o$ are the inner and outer radii, and $L_{\text{star}}$ is the luminosity of the star. Note, though, that these are for the conventional definition of the habitable zone, neglecting non-$\ce{H2O}$-based compounds and tidal heating of moons orbiting gas giants. This pre-print, by Kopparapu et al., does give another interesting formula:
$$d=\left(\frac{L/L_{\odot}}{S_{eff}} \right)^{0.5} \text{ AU}$$
where $S_{eff}$ is a parameter determined by the effective temperature $T_{eff}$ of a planet at that distance and some coefficients, as well as the Sun's $S_{eff}$. But those findings are rather new, so I'd stick with the older formulas.

So the habitable zone is determined primarily by the star's luminosity.

Mass

An atmosphere is generally considered a must for planets with Earth-like lifeforms. Low-mass bodies, such as the Moon, can't hold on to one, and that's one of the reasons that moons have not been of as much interest as planets have been. Atmospheres, among other things, can keep the planet at a nice temperature and allow distinct climates to form. As this site elaborates on, they also help protect the planet from radiation like UV rays. Our ozone layer is really helpful in that regard.

Mass isn't the only thing that helps a body keep its atmosphere. For example, Titan is relatively low-mass (although relatively high-mass for moons), yet it still has an atmosphere. This is because the solar wind - which can hurt atmospheres - is so weak at Titan's distance from the Sun.

To expand on what gansub mentioned: Magnetic fields are important because they are extremely useful when it comes to helping a planet retain its atmosphere. As Luhmann and Russell explain in "Mars: Magnetic Field and Magnetosphere", Mars lost its magnetic field long ago, and so the solar wind is gradually stripping it away, albeit at a really slow rate.

Rotation

This section is based a lot on this paper, by Yang et al. It, too is recent, so keep that in mind.

Before I get into the paper, I'll say this: Rotation helps because it keeps one side of the planet from being baked while the other side freezes. Tidally-locked planets aren't the greatest places for life. A decently-fast rotation can really help.

Anyway, Yang et al. came to this conclusion (as voiced in their opening sentence):

  Planetary rotation rate is a key parameter in determining atmospheric circulation and hence the spatial pattern of clouds. Since clouds can exert a dominant control on planetary radiation balance, rotation rate could be critical for determining mean planetary climate.

In other words, rotation helps clouds, and since clouds help govern the climate of the planet, a proper rotation rate can make the climate less extreme.


How does composition change if you extend an Earthlike atmosphere 50km below sea level? I'm working to design the atmosphere of a fictional planet inspired by Venus (let's call it Cael).

Cael's atmosphere at an altitude of 50 km is essentially identical to Earth's atmosphere at sea level, and parallels Earth's atmosphere as altitude increases beyond that. I want to figure out what needs to happen in the lower 50 kilometers in order to keep the Earth-like atmosphere where it is. My problem is that I can't find resources on what happens when an Earth-like atmosphere is extended downward by any significant distance.

The atmospheres of Venus, Jupiter, and Saturn all contain distinct layers of varying composition caused by the changes in temperature and pressure with increasing depth. While none of them have a layer of Earth-like composition to use as a convenient reference, it seems logical that this would hold also hold true in the case of Cael. So my question is,

What kind of layers would form beneath a complete Earth-like atmosphere?

For the purposes of this question, the Earth-like atmosphere starts at the imaginary surface where the temperature and pressure of Cael's atmosphere are functionally identical to Earth's atmosphere at sea level, 50 km above the true rocky surface. I'll call this the Sea-Level Equivalent altitude, or SLE.

Just like on Earth, Cael has a tropopause roughly 10-20 km above the SLE that marks the beginning of the stratosphere. Above that is the mesosphere, thermosphere, and exosphere. As on Earth, atmospheric composition is effectively constant all the way up to the lowest part of the thermosphere due to turbulent mixing dominating its molecular interactions.

A very rough estimate for the air pressure at Cael's surface is 50 atm, according to this "Air Pressure at Altitude Calculator" from Mide Technology Corp. That pressure is well above the critical pressure for nitrogen (33.5 atm) and right around the critical pressure for oxygen (49.8).

Even if we assume that temperature remains constant rather than increase as you descend beneath the Earth-temperature SLE, the critical temperatures of both gasses are below -100°C, a temperature that has never been recorded at Earth's surface.

Thus, I would expect to find a very high volume of supercritical nitrogen as well as a bit of supercritical oxygen at Cael's rocky surface. Argon, neon, and methane would all be supercritical under those conditions as well.

I also expect liquid water oceans, because Cael needs to have enough water to experience water clouds and precipitation above the SLE, and my guesstimates for temperature and pressure are within the liquid section of water's phase diagram.

More information about Cael:

Mass: 6 × 10²⁴ kg
Average radius of planet surface: 6,450 km
Average gravity at planet surface: 9.65 m/s²
Average altitude of SLE: 50 km
Average gravity at SLE: 9.5  m/s²
Average air pressure at SLE: 1 atm
Solar intensity and spectral makeup at SLE is the same as on Earth

This seems like a World Building question. I presume that on your imaginary planet something, perhaps an asteroid strike, has created a huge bowl 50 km deep. On the rim of the bowl, the atmospheric pressure and composition are the same as at sea level on Earth. You want to know what conditions would be like at the bottom.

In some respects a bit like Venus. Very hot, but exactly how hot would depend on whereabouts on the planet this deep bowl had formed. The composition of the atmosphere would be the same as at sea level (I assume the lip of the bowl is not close to a sea). The pressure at the bottom would be many atmospheres, but not as many as the 90 atmospheres on Venus. It would seldom rain down there because of the heat and high pressure. Rain falling in from high altitude would usually evaporate before reaching the bottom. As explorers ascended the sides, conditions would become more normal

Would it be habitable? Yes, but how habitable depends on where on the planet this bowl occurred. There would be habitats on the slopes, where conditions were less extreme than at the bottom. If this bowl or basin were in the tropics, the bottom would probably be too hot to sustain life. A water supply would also be problematic. Pressure is less of a problem; there are life forms 12 km down or deeper in Earth's ocean trenches.


What's the default meaning of "Valid" in NOAA weather map? NOAA weather forecast maps often include a valid time period, e.g:  "valid from time1 thru time2."  However, many maps only indicate a single time, e.g: "valid time1."  In the absence of other information, does this typically (or officially) mean valid up until time1, or valid after time1?

EDIT:
Link to example map and source

Short answer: Valid just means the expected conditions at that certain time.

In your example the map shows a forecast of 00 hours which is valid for 0600 UTC. Basically it means that the forecast/simulation is initialized on 0600 UTC and because the forecast time is 00 hours this forecast is also valid for 0600 UTC.

NOAA also provides forecasts for several hours (or days depending on the product). In this case, your simulation may be initialized on 0600 UTC but if you want to see what the conditions on 1500 UTC are you have a forecast of 09 hours which is valid for 1500 UTC. See this example.


Why are there places where trees don't grow? I can understand places like a desert where it's too dry or tundra where it's too cold, but why are there places like meadows or fields in the middle of the forest where trees don't grow? Or even large areas like prairies?

A non-conclusive list:

frequent wildfires
not enough water
too much water
bad soil conditions
average temperatures too high or low
not enough sunlight
animals
human intervention
other vegetation is better adapted to local conditions and thus suppress growing trees


Why do clouds have ceilings and bases? What is the point called when water can not rise above or visually seem to have a ceiling in the atmosphere? What makes that point ideal?

Clouds have ceilings and bases because the atmosphere is stratified.
Atmosphere is stratified due to earth's rotation and variance of composition, humidity, density,  temperature, and pressure from surface of the earth to the edge of the orbital space.

Clouds form under specific conditions of composition, humidity, density,  temperature, and pressure.  These conditions are often persisted within specific layers in the atmosphere.  Complex fluid flow of air is also a contributing factor for layering within the atmosphere between air masses for varying density.

The answer is probably best summed up as the result of the physics of fluid dynamics.


Equatorial bulge and tectonic plates It is well known that the Earth is not a sphere, but rather it bulges at the equator. Also it is well known that the Earth's crust is composed of 7 or 8 (depending on definition) major tectonic plates, which are able to move on top of the asthenosphere, the upper layer of the Earth's mantle.

Due to the equatorial bulge, it would seem as though plates near the equator should not be able to drift away from the equator, and plates away from the equator should not be able to drift near the equator, since they will not be of the right shape to fit over these portions of the Earth. So how are the plates able to drift to and from the equator when the surface of the Earth is shaped differently there?

The plates are not as rigid as you think. You seem to be imagining the situation as something like this: I boil an egg and take the shell off in pieces, but I can't take a piece of shell from the end and make it lay flat on the side of the egg. However, rock is not that rigid on scales of thousands of kilometres and millions of years (I don't think there exists any material which would be that rigid). Also, Earth's equatorial bulge is tiny relative to its diameter -- less than 50km. Tectonic plates move very slowly, and there is plenty of time for them to deform as they move.


Book Introduction to Climate Change The question might be in an opinion-based grey zone. If it is, I apologize.
My wife and I want to get informed about climate change.
We want to read a book (no online course etc.) and it should be either in English or available in Portuguese and German. It is supposed to "start from the beginning" e.g. treating us as people that almost don't know anything about it.
We wish a rather scientific approach (for example with references to papers) and it should of course talk about the strongest evidences of the existence of the climate problem and its causes.
After some short internet research we thought of "The Rough Guide to Climate Change of Robert Henson.
The question is: Would this be a good choice?
Does it fulfill our requirements? And since it is (at least) 9 years old, is it maybe too old?
Maybe some significant findings were added in this time.
And if it isn't a good choice can you recommend other books?
Thanks in advance

I highly recommend Climate: A Very Short Introduction and Climate Change: A Very Short Introduction, both by Mark Maslin and published through Oxford U Press's highly-regarded VSI series. I use both books when teaching college-level classes where an understanding of climate and climate change are important to the subject matter but are not the sole focus of the class.


What is the relevance of Arctic coastal erosion to the Earth's climate? Due to global warming and Arctic amplification, Northern Hemispheric permafrost is thawing and becoming a source of carbon and many greenhouse gases, which then positively feedback to global warming again.

More specifically, severe Arctic coastal erosion of permafrost material has taken place in recent years. How relevant is this specific process, alone, to Earth's climate in general, or at least to the Arctic climate?

If we consider only the climatic impacts of Arctic coastal erosion, there are still two sides of the question of how relevant is Arctic coastal erosion of permafrost.

The first side is how big is its current role as a ${CO}_2$ source, and the second is how much of risk it posses for future climate change.

It term of current contribution the answers is that it is not very relevant. According to the "The Arctic Coastal Dynamics Database: A New Classification
Scheme and Statistics on Arctic Permafrost Coastlines" from 2011, there are 101,447 km of coastline in the Artic, and the mean coastal erosion rate is 0.5 m/yr with a mean backshore elevation of 8.3 m. Multiplying all those numbers we get that 421,005,050 $\text{m}^3$ of Arctic soil are lost to the sea every year.

That paper is behind a paywall so I'll copy here Table 2 (where most of above numbers come from) and figure 6 that are relevant here.

Table 2 also indicates that ~2% of the weight of that lost soil corresponds to carbon, so using a bulk density of 1,900 $\text{kg}/\text{m}^3$ (source) you get that the lost corresponds to 0.00002 Pg C (peta grams of carbon) per year, a very small number compared with the ~7.8 Pg C that burning fossil fuels put into the atmosphere every year.

Now, it is more concerning the potential of permafrost lost. Scientist have studied Arctic ocean sediments and found that during the period of fast sea level rise at the end of the last ice age, a huge amount of organic carbon stored in permafrost was released (source), perhaps close to 1,000 Pg (source). Carbon that was then available for microorganism to metabolize and transform into greenhouse gases as carbon dioxide and methane. This greenhouse gases helped warming the Earth and melting the ice caps that covered it at that time.

There are still about 1,300 Pg of carbon stored in permafrost (source). Thawing of permafrost is increasing rapidly. As well as coastal erosion rates. In coastal Alaska for example it have increased from 6.8 m/yr in 1955-1979, to 8.7 m/y in 1979-2002, to 13.6 m/yr on 2002-2007 (source).
Arctic warming, sea level rise and release of permafrost organic carbon form part of a dangerous positive feedback cycle that we don't know how far or how fast it can go. And it have the potential to release massive, and this time, VERY considerable quantities of greenhouse gases into the atmosphere.


How does one create petroleum/crude oil for future generations? I am a geological novice so maybe this is a wrong question. But the idea is to create a thought experiment. How does one "create" petroleum or crude oil for future generations? Is it enough to bury a lot of trees underneath the earth at great depths and eventually thousands (maybe hundreds of thousands years) later crude oil is formed?

Geological processes are just too slow. Although, given how quickly we are pumping greenhouse gases into the atmosphere, humanity may well (in a generation or two) be growing biological material as fast as possible and throwing it into deep holes in the ground, which will give another fossil-fuel resource in a few million years. But we'll be doing that just to sequester carbon dioxide from out of the atmosphere, not to invest in future hydrocarbon supplies.

Hydrocarbons are useful because they have very high energy density: the energy stored per unit weight and unit volume is extremely high. Furthermore, that energy can be harnessed with very primitive technology - just burn it. Because we've been relying on them for nearly two centuries now, we've got very good at safely transporting them globally, and safely storing them in a form ready for immediate use.

So, hydrocarbons have two uses: one, they act as storage, as a time-buffer for time-sensitive energy demands such as electricity consumption. And two, their energy density makes them very suitable for powering transport on irregular or changeable routes.

However, as a means of energy storage, they're not very efficient: even the best CCGT gas-powered electricity generators are only 60% efficient; and internal combustion engines tend to give an efficiency of about 20-25%, tank-to-wheel. And that's without the losses involved in creating the hydrocarbons in the first place

So whether hydrocarbons have a future as a source of energy is very dubious, because for almost all applications, we now have superior options.

And the future for fossil hydrocarbons must, for the sake of human civilisation, be short and quickly-tapering, because of the risk of catastrophic global warming.

For some transport applications, the energy density is still a winning attribute of hydrocarbons: most notably, powered flight for freight and travel.

We already have two routes to non-fossil hydrocarbons: biological sources, and direct chemical synthesis. Each involves capturing atmospheric CO2, and combining with water, to generate a blend of hydrocarbons.

Now, we already have means of creating hydrocarbons suitable for flight (e.g. Jet-A and Jet-A1 fuels). And there are already demonstration plants that have closed-loop generation of synthetic hydrocarbons, for use in electricity-grid-balancing, by using surplus electricity to synthesise methane, which is then burnt in gas turbines when required. Similarly, Tony Marmont's team have been synthesising petrol (gasoline) from air, water, and electricity.

However, none of those things mean that hydrocarbons necessarily have much of a future, beyond plastics production. Because hydrocarbon-powered aviation has a lot of environmental problems beyond just CO2 emissions, in particular it makes other contributions to exacerbating global warming. And there are lots of options for energy storage within the electricity supply chain.


Why does computation cost increase 24 times when the spatial resolution doubles? In a Chinese book, I read about the relationship between the numerical model spatial resolution and the computation cost.

It states: when the spatial resolution of model is finer, the result will be preciser. But to achieve a fine grid resolution, the computation cost will increase. For example, when the grid resolution in a 3-D model framework halves (e.g. from 10 km to 5 km), the computation cost will increase by a factor 24.

Why is this? How can I determine the increase of computation costs when the spatial grid resolution changes?

Update

The model here is a 3-d numerical model for weather forcasting like WRF, MM5, etc.

Update 2

Here is an schematic representation of the impact of model resolution
on the calculation of chemical oxidants

I can't answer why there's a 24x increase, according to the textbook - but it may well be the case for a specific model. In general,

If you double the resolution of a 3D model in each dimension, you are multiplying the number of cells (or elements) in the model by $2^3 = 8$.

Typically the maximum length of the time step that a model may be run at and remain stable is proportional to $\frac{\Delta x}{u}$, where $\Delta x$ is the size of a grid cell and $u$ is the speed of the flow in that cell (see info on the CFL condition) (for simplicity I'm assuming that the flow is parallel to one grid axis, which makes this one-dimensional; but the same result applies if not). This means that if you double the spatial resolution, you will probably also have to halve the timestep to maintain numerical stability. This gives an extra factor of two on the computation time, taking us to $2^4 = 16$ times.

This will vary in its details from model to model, and it is entirely feasible that additional non-linear processes in a given model push that to 24 times.


Is climate change homogenous globally When searching for continental trends in climate I could not find clear sources broken down to regions or continents.

My question is: is it proper to talk of global warming as a homogenous trend or is there actually a difference between trends when the data is broken down per continent or region for example. Can anyone point me to clear sources on climate change trends per region or continent?

A hypothetical example would be: while the south-American climate remains stable polar climates warm up. Or, the poles warm up faster than south-American climate.

Is climate change homogenous globally?

Not at all. The Arctic (both the Arctic Ocean and far northern land masses) has and will continue to experience greater temperature changes than other parts of the Earth. Other than the Arctic, land masses have and will continue to experience greater temperature changes than the oceans.

The warming seen to date is a portrayed below. This image portrays annual temperature anomalies averaged over the last ten years, with anomalies relative to a 1951 to 1980 baseline.

Source: https://data.giss.nasa.gov/gistemp/maps

  Can anyone point me to clear sources on climate change trends per region or continent?

The IPCC reports is always a good start. The most recent is the fifth assessment report. The site I used to make the above map, Global Maps from GHCN v3 Data is also a good source.


research question for modelling extreme rainfall event with coupled 2D surface and 1D sewersystem model I would like to write my thesis on modelling extreme rainfall events in urban areas coupling a 2D surface model with an 1D sewer channel model. I have access to a good software which models hydrodynamically and offers me 3 different modelling approaches. My basic idea was to apply all three approaches and compare them and see what happens but my prof. is not convinced yet. He is happy with the model but he wants me to formulate a clear research question and ideally a hypothesis. Further, I can apply the model but I have no data to verify the results.

I'm stuck here, I don't know how to come up with a good research question and hypothesis. Maybe you can give me some ideas of what I could do?

It sounds as though you have ideas on the tools you'd like to use, but not on an actual question that you want to use them to answer.

You probably need to either come up with such a question, or focus instead on methodology - in studying the tools and the effectiveness of using them in a given scenario.

For nearly any modelling project, its viability will be affected by whether data are available to validate the model. If no appropriate data are available for the area you're looking at, you probably don't have a project (because what use is a model if you have no idea whether it's right?).

Bear in mind that these comments are all generalisations based on very limited information. The best advice is still "talk to your advisor".


Why Earth's magnetic poles are (and were) in their positions? This is a sort of a follow-up question to What causes the Earth to have magnetic poles?

The Earth has magnetic fields, and according to dynamo theory I roughly understand why. If the Earth's rotation influences the Earth's magnetic field, it also seems natural that the poles will be orthogonal to the plane of rotation.

But I still don't understand few things:

Why are the magnetic poles positioned near, but not exactly at, the geographic poles?
Why do they drift over time?
Why does the Earth's magnetic field sometimes change polarity?
Are the changes in polarity based on some cycle? Can they be predicted?

Actually, all of the three questions are directly related.

As you noted, the Earth's magnetic field is generated by flow of molten conductive materials (probably mostly iron) in the outer core. (Contrary to popular belief, only the outer core and the oceans are liquid. The crust, mantle, and inner core are all solid. Solids can flow, but they have a shear strength. Liquids have no shear strength.)

However, this flow is turbulent.

Therefore, Earth's magnetic field can be described by having two poles, but in reality, it's much more complex.  Part of this is due to crustal structure (i.e. the magnetic anomalies we typically work with in geophysics to, say, locate an igneous intrusion or understand the evolution of the oceanic crust). However, the part that's due to crustal structure doesn't change rapidly and only influences a very small region.  The "longer wavelength" (i.e. broader) differences are due to variations in the flow of the outer core.

Every "eddy" (i.e. any vorticity) in the flow produces its own magnetic field.  The sum of these is what produces the global magnetic field.  At the surface, we're a significant distance from the flow that produces the magnetic field.  Therefore, it gets "smoothed out" and these small perturbations are less apparent. It looks fairly close to a single magnetic dipole because the bulk of the flow is approximately around Earth's rotational axes.

This is the answer to your first and second questions.

The magnetic field is not the result of a single "current" of laminar flow, but rather the sum of much more complex turbulent flow.  Therefore, it doesn't exactly match the rotation axes, and the position of the magnetic poles changes over human timescales.

I'll hold off on answer the third question, as you split it into a separate question, but basically, the flow tends to self-organize, producing a strong magnetic field that's close to a single dipole.  Then, for reasons that aren't entirely clear, it episodically de-stabilizes (basically, you'd have multiple equally strong poles that somewhat cancel each other out), and then re-stabilizes (sometimes in the opposite direction).

If you're interested in a "pop-sci" style writeup, there was a very nice Scientific American piece on this awhile back written by Glatzmaier (a very big name in the field).  Unfortunately, the web version is missing  the figures that were in the print version, but they're mostly from Glatzmaier & Roberts, 1995 or one of the follow-up papers by the same authors.


Why are temperatures within a few degrees of the all-time high actually pretty common? I see from a news report that the all-time high temperature, anywhere on Earth, is 129 F. But temperatures within 10 degrees of that record are not rare, and temperatures within 20 degrees are pretty widespread. Why does there seem to be a ceiling on the high temperature, such that a lot of places approach that temperature and don't exceed it? A related question -- why isn't the high temperature much higher, such as, I don't know, 150 degrees?
In contrast, the coldest temperature is -129 F, and few places ever get anywhere near that. Why is there such a disparity between high temperatures and low temperatures in that way?
EDIT: By the way, I apologize for the US-centric temperature measurements. I hope I got the point across nonetheless.

the coldest temperature is -129 F, and few places ever get anywhere near that.

This is at high altitudes in Antarctica. There are very few places with weather stations (geographically) near there.
There are more places with weather stations near the hottest places, so (because mathematical statistics theorem) there are more record max readings near the global max.


What causes periodic floods? I am trying to determine what could cause periodic flooding of the type that might generate a savannah or plain with low growing plants and grasses. Where does the water come from, and how or why is it consistently periodic?

This question refers to no specific area. It is asked with a worldbuilding mindset, and I'm just trying to figure out how periodic flooding works in general.

The causes vary around the world, but we can make some generalizations. Seasonal floods mean that there's more water coming in than going out for only part of the year. If it's annual, the changes are probably related to annual weather patterns in precipitation, temperature, or both. Some big sub-cases are:

(a) in Mediterranean climates, e.g. California, almost all the rain falls in winter in cool weather when evapotranspiration is relatively low. The Central Valley has regions that develop standing water from the rain that falls directly on them because the soil has impermeable clay or hardpan (the vernal pools prairies); and other regions that develop standing water because they're the confluence of several drainages and in wet years the water literally can't flow out to the sea as fast as it comes in (the Yolo Bypass).

(b) If annual precipitation includes a lot of snow and it melts in a hurry, it's common for the downstream rivers to flood at the confluences. There may be years in which the surface snow is melted while the ground is still impermeably frozen, which would turn anyplace level swampy. Parts of Minnesota have bedrock not far under the soil surface and they get this kind of inundation relatively easily.

(c) Where rivers meet the ocean in a long, nearly level bench, high tide (spring tide or storm tide especially) can raise the river level enough that the fields flood. I believe this is the case in the Somerset Levels and in the Netherlands. Some of these are watermeadows and can be quite productive if farmed carefully.

These don't all develop the same kinds of vegetation. For instance, I think I've forgotten a tropical or semitropical case where monsoon rains overwhelm the drainage (possibly the entire Amazon, where the hardwoods are adapted to having their roots underwater even though they aren't flooded all year).


How much cheaper is it to mount oceanographic sensors on elephant seals and other animals, compared using Argo floats and other abiotic sensors? This article says that mounting sensors on animals is relatively cheap compared with the alternatives.

  Seals, in other words, were filling in the blind spots on oceanographer’s maps. And they were doing it relatively cheaply—at least compared to the cost of ships or Argo floats, the international network of probes that transmit real-time measurements of the Earth’s oceans.

But how much cheaper?

Each float costs around US$15,000 and communication, deployment and calibrations costs approximately double the through-life cost of each float.

(from http://www.argo.ucsd.edu/Argoflyer_final.pdf)
One can roughly estimate from this source, given a life-span of four years, an Argo float costs slightly over \$3.5k/yr (float only) or \$7k/yr (including deployment and calibration etc.).

...by June 2007, over 95 percent of the goal of 3,000 floats had been deployed...
...With a four-year life span per float ...
...The annual cost of the worldwide Argo program is about $20 million...

(from http://celebrating200years.noaa.gov/magazine/argo/welcome.html#float)
Based on this source all inclusive number will be in the ball park of slightly less than \$7k/yr.
So, without getting into details of whether one can be an alternative to another technically, a primitive cost comparison based on the yearly cost derived from the mentioned article and the links below it is ~7k\$/yr (including deployment and calibration etc.) or ~3.5k/yr (only the float) vs versus \$4k per tag with Tarpon fish. So if one can assume the deployment/retrieval/calibration costs are similar they will cost about the same by the end of first year. After one year the annual cost of a fish tag will keep getting cheaper and cheaper than a float until the end of its life-span.


ERA Interim problem with Waves Has anyone had a problem with significant wave height (swh) and mean wave period (mwp) from ERA-Interim not matching very well with either a time series of measurements or a different model? Or does anyone know if the formulas in the model (the way they made it) have changed from one period to another? (In my case they seem to correlate better/worse at either side of 1991).

I haven't looked into ERA-Interim wave data a huge amount but I know around 1991 it started to assimilate ocean wave data from satellite altimeters (ERS-1).
See the first figure here
https://climatedataguide.ucar.edu/climate-data/era-interim

I remember Jean-Raymond Bidlot who runs WAM at ECWMF showing me so experiments with and without the assimilation into the wave. I think the Hs differed by ~1m in large events so not insignificant.


How do scientists confirm iron core at the centre of the earth? How do scientists confirm iron core at the centre of the earth?
We know scientists couldn’t yet drill to the core of our planet earth. Yet we know they confirmed there is a core of iron at the centre of it. How did they confirm that? Is it yet in hypothetical state or it’s already confirmed? What are the test approaches we know?

This is more a geophysics than an astronomy question—and thus the available methods of investigation are greatly increased. An Earth model also is not a one-person-show based on one measurement, but requires many different measurements from different fields with greatly different methods which form a unique picture which leaves only few possibile explanations which fit all observations.
One of the easiest methods to investigate the interior of the Earth is seismic sounding. Investigations of the deep interior of the Earth use teleseismic, which means we scan the seismic velocity of Earth by using the seismic waves generated by an Earthquake. The time-of-arrival of the different direct but also reflected waves at the different seismometers all over the world—or the absence of any arrival at all—allows to get a quite detailed mapping of the interior structure in terms of seismic velocities as function of depth and also whether the material is liquid or not. This already gives you the principle structure of Earth with a mantle with many of its different layers and the existence of an outer, liquid core and an inner solid core, e.g. see the 40 year old preliminary Earth reference model. See also the outstanding answer to this question about seismics and the video by the answerer or a newerver version of it.
Measuring density is much more complicated and needs a detailed analysis of Earth's rotation, deriving the moments of inertia to as many degrees as you can get. However from that you get a good indication that the center has to be much denser than the crust and mantle. There's a lot of work on that, as a random paper the one by Kennet (1998) might give some overview.
This paragraph is now extremely abridged, yet still: With knowledge about density and seismic velocity you already have a very good handle and constraint on the mineralogy or chemistry. Especially with some knowledge about equations-of-state of the materials the choice becomes very limited. In laboratory setups you can create high-pressure and high-temperature configurations and measure the properties of the materials—including their seismic velocity, be that directly or indirectly via their Young modulus and poisson number etc (some links in this answer by user20217 to a similar question). Assuming that the whole solar system formed from one primordal cloud, the chemistry should be pretty uniform—and that also means that iron is missing in the materials on the Crust and mantle—and iron incidentially fits magnetic observations (we have a magnetic field!) and the requirement for a heavy core very nicely. It also is logical as heavy elements tend to sediment towards the centre in a differentiated body.
As such to answer your question: it's not a hypothesis, it's a well-established theory backed by a multitude of greatly different observations which require the existence of a a liquid outer core and a solid inner core, which both consist of a iron with some nickel and traces of other heavy elements mixed into it.


What are the basic rules of how light and seasons affect landscape and objects lighting? It would probably be a strange question for here but i will shoot it.

I want to modify the shaders for Prepar3d the next version of MS flight simulator game.

I have ways of interfering with ambient/diffuse ratios on objects terrain e.t.c Also you can control saturation of clouds sky terrain and objects. You can also use expressions and affect the above based on altitude,season,cloud coverage e.t.c

What i am searching for is real life rules that i should apply to the above.

Examples:

Should i reduce saturation when the weather is full of clouds and light is not enough? What happens to the sky color as the altitude rises?

I know that the rules are infinite but i would appreciate some starting points that will help me adjust:

Terrain lighting and saturation based on season and cloud coverage
Object reflection lighting and saturation based on season cloud
coverage and altitude
Water lighting reflection and saturation based on cloud coverage.

I know that all the above depend on which part of the world you are in and many other factors. , so i need just an average for all in order to try to adjust the settings of the simulator close to a real world appearence.

I suspect that the answers you seek lie as much in computer graphics and human perception as they do in physics or earth science - for example, colours on a cloudy day won't actually be significantly less saturated than on a sunny one - it's still white light to most intents and purposes - but we may perceive them that way due to the differences in contrast, illuminance, and colour.

There are three components to natural light :

You can calculate the angle of the sun according to time of year, time of day, and latitude. From this angle, and the altitude of your viewpoint, you can estimate the colour of the direct sunlight. The more air it has to travel through, the lower the colour temperature and the intensity.

Then you need to consider the blue sky. This will be lighter at low altitude and darker at high. You'll need to do something about the sunwards sky not being blue at low sun angles. The blue sky casts light on things, but this is mostly only evident by shadows appearing a bit bluer than their surrounds.

Then you need to consider cloud cover. For a flight sim this is complicated by the fact that it may be above or below the camera, or you might be in it. One approach might be to treat clouds as large diffusers that act on the light from the sun and from the blue sky. Whether this is feasible is beyond my ken, and definitely lies in the realm of computer graphics, not earth science.


How does salinity and density affects sea surface temperature? I was reading Planning Commission report of Five Year plan (2012-2017) of India, and in the context of Inter-linking of rivers it is mentioned that :

  The presence of a low salinity layer of water with low density is a reason for maintenance of high sea-surface temperatures (greater than
  28 degrees C) in the Bay of Bengal, creating low-pressure areas and
  intensification of monsoon activity.

So how does salinity and density affects SST?

A low salinity layer that is associated with low density (assuming the same temperature) will remain on top of the water column. As such the water will be able to get warmer and the difference in salinity and temperature will make it even more difficult to mix it down with the rest of the water column. So the combination of high temperature and low salinity results in even lower densities. You can play with the relationship using http://www.mt-oceanography.info/Utilities/density.html


How are chenier ridges and strand plains formed at wave dominated coastlines? In the attached image, we can see chenier ridges and strand plains. How are they formed and what is the involvement of rip and longshore currents in their formation?

The following sources helped me understand these landforms - hopefully they can help you too :)

From the Miranda Shorebird Centre: The Miranda-Kaiaua cheniers are first formed as sand and cockle-shell bars on the foreshore or intertidal flats. The bars are then moved landward by wave action. Eventually the bars attain sufficient height to withstand such wave action.

From NASA's Earth Observatory: Strandplains are built by successive additions of beach sand, usually from some nearby source. Each ridge shows the position of a prior shoreline.


The origin of permafrost Old permafrost is loaded with frozen vegetation.  As it now melts, it is rotting and releasing methane.

Doesn't that mean that it froze quickly, centuries ago, and stayed frozen until now?

What process caused such a sudden, centuries-long freeze? Don't we need to know this before we understand why it's reversing now? Presumably we humans had nothing to do with the freeze!

What caused a centuries long freeze, the beginning of the current ice age. Yes we are in an ice age, as long as greenland and antarctica have large ice sheets we are technically in an ice age) Which in turn was caused by the movement of continents close enough to the poles to create permanent ice caps. the freezing of organic matter into permafrost is not a fast occurrence, it is a slow build up of organics as soil is built and added too, as long as it remains cold enough for permafrost to persist.

The strange thing about the warming now is every major natural factor and most minor factors point towards cooling conditions yet we have warming. Human activity however is producing strong warming factors that are overriding the natural prevailing conditions, which makes you wonder what will happen when some of the natural factors stary cycling back to warming.


Have fossils ever been found in the asphalt lakes of Trinidad and Venezuela? La Brea tar pits in California are the result of ancient oil seepages and famous for the fossils of extinct animals which were trapped in the tar. The asphalt lakes in Trinidad and Venezuela are also the result of ancient oil seepages. Have fossils of any kind been found in either of them, and if not, why not?

Trinidad

Quote from https://www.smithsonianmag.com/travel/trinidad-and-tobago-nature-and-scientific-wonders-18329129/

  Quite an oddity sits in La Brea in South Trinidad—the world's largest asphalt lake. Pitch Lake, while perhaps not the most beautiful of nature's creations, is certainly an intriguing one. The 100-acre lake is believed to be 250 feet deep in the center and contains some 10 million tons of pitch. As the lake replenishes itself and turns over, artifacts both peculiar and historically significant such as a mastodon tooth, fossil remains of the giant sloth, and Amerindian artifacts have been uncovered. Mineral pools on the lake are purported to have healing properties because of their high sulphur content.

Venezuela

One example from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6097493/ is an article with the title

  Fossil snakes (Squamata, Serpentes) from the tar pits of Venezuela: taxonomic, palaeoenvironmental, and palaeobiogeographical implications for the North of South America during the Cenozoic/Quaternary boundary

Summary:

yes, fossils have been found


Estimating the permeability tensor of an oil field by remote sensing I work a lot with numerical methods to solve multiphase flow in porous media for oil applications.  In our field, we often use Darcy's law which states that the flux is negatively proportional to the pressure gradient by a factor called the permeability.  In general, permeability is not a constant, but a tensor.  This implies that a pressure gradient in one direction may induce flow in an orthogonal direction as well.

In a laboratory, permeability tensors are obtained by inducing controlled pressure gradients and measuring the resulting flow.  In an oil field, we can certainly induce pressure gradients, but it is much more difficult to control all the parameters.  Is there a way to sense a permeability field using remote sensors and geophysical inversion?

I remember a comment on this by Rodney Calvert in the video lecture version of his SEG Distinguished Instructor Lecture "Insights and Methods for 4D Reservoir Monitoring and Characterization":
http://shop.seg.org/OnlineStore/ProductDetail/tabid/177/Default.aspx?ProductId=1842

The comment was referring to the possibility of observing a pressure change front moving through the reservoir (as opposed to a fluid staturation change front) if one were to perform very closely repeated time lapse seismic surveys (down to probably days instead of months between surveys) AND in the very early stages of development. Costly of course but it would allow far superior well placement in complex reservoirs.

There's some reference to this in Chapter 2 of the book:
http://library.seg.org/doi/book/10.1190/1.9781560801696

but if I recall, the comment in the video lecture was far more specific. It is worht a try, the course is great to take anyways.

UPDATE

Following comments below and a review of some reference material.
The problem of permeability is that this is a multiscale property. You get different estimates (and different relationships, for example to porosity) at different scales (e.g. pore, lamina, bed, geobody, formation, and reservoir scales). The challenge is to link permeability at all scales and it is compound mainly by two facts: 1) at some scales you measure permeability statically, at other scales dynamically; and 2) at some scales permeability is not well captured/represented by any measurement (for example bedset scale, which is larger than core scale but often not well captured by wireline log data).

My advice to you would be to get this book by Patrick Corbett, the go-to guy in the field: http://library.seg.org/doi/book/10.1190/1.9781560801597. It is about 90 pages and it guides you through the whole process, with measurements, modeling, testing at all scales, topped by an excellent example of integration at all scales in chapter 6. I worked through the book and several of the reference papers 3 years ago, for personal knowledge, and it was great.

From a quick review last night I'd say one very important tool is Petrotyping, as defined in the book. The full work is in reference paper Corbett and Potter, 2004, Society of Core Analysts paper SCA2004-30. This paper defines Hydraulic Units as representative volume elements where geological, petrophysical, hydraulic properties are predictable and different from those in other units. Each unit is defined by a Flow Zone Indicator (FZI) (defined in the paper). A relationship is intorduced in the paper relating permeability to porosity via FZI. With this relationship a set of lines of constant FZI can be used as a template in a porosity (decimal) - permeability (log) plot to assess Global Hydraulic Elements in the reservoir. A Global Hydraulic Element is an element where the relationship between porosity and permeability is unique. If you are lucky your reservoir (for example a chalk reservoir, one of the examples in Corbett's book) has a single Global Hydraulic Element, in essence a single rock type of uniform properties. In this case you could go relatively easily from a static geomodel of reservoir facies modeled at the reservoir scale (and constrained with seismic inversion for acoustic impedance or porosity, ideally stochastically) to permeability at the scale of your lab measurements - you would be using also well tests (drill stem tests, production tests) and Lorentz plots. In the case of a developed field you may also integrate dynamic simulations and time laps (4D) seismic data (linekd to saturation and/or geomechanic changes introduced  in the reservoir by production).

If there are multiple GHEs, then the work of predicting at core plug scale, upscaling, validating with dynamic testing, and extending to the reservoir scale is more complicated (but still possible).

I really recommend the book.


Why do most opal deposits occur in Australia? According to the Wikipedia page about opals, this hydrated amorphous silica based gemstone is most commonly found in Australia, with according to the page, over 90% from Australia.

Opal from Coober Pedy, South Australia (source: Wikipedia)

What geological conditions resulted in most opal deposits occurring in Australia?

A recent study published in the Australian Journal of Earth Sciences, Opalisation of the Great Artesian Basin (central Australia): an Australian story with a Martian twist (Rey, 2013). The study makes the assertion that a unique set of geological conditions existed during the Cretaceous era that led to the relative abundance of opals in Central Australia. Rey proposes a 'redox model' of opal formation to account for the great relative abundance of the precious stone in Australia.

An important aspect to note is that just about all opal deposits occur either in or on the periphery of the Great Artesian Basin, as can be seen in the map below:

Image Source and brief information of opal mining centres: The National Opal Collection

The conditions around the opal field part of the Artesian Basin during the Cretaceous, according to Rey (2013) were:

From about 130 to 93 million years ago, The Great Artesian Basin was flooded by what is known as the Eromanga Sea, this was a cold, shallow, largely stagnant waterway that was poorly connected to the open ocean.
The Eromanga Sea served as a 'sink' for volcaniclastic sediments eroded from orogenic volcanic sources on the Pacific margin of Gondwana.

Rey describes how the iron- and organic- rich sediments contributed to an anoxic seafloor environment that became rich in pyrite, ferrous iron, feldspar and volcaniclasts, but virtually no carbonates.

At the end of the Cretaceous and into the early Palaeogene (from about 93 to 60 million ears ago), the region experienced slow uplift, erosion and denudation, as well as subsequent sea regression; this, according to Rey, caused an acidic oxidation of the Eromanga Sea deposits as oxic fluids perculated through faults, some trapped by clay deposits - these are where the opal deposits have been found.  Further deposition in the Palaeocene and Eocene provided protection from further erosion.

In summary, Rey notes 5 aspects unique to the geological history of the Great Artesian Basin that has resulted in the great relative abundance of opal:

Large scale organic matter-rich, iron-rich volcaniclastic sediments
The depositional environment to be anoxic
negligible carbonates
sea regression driving oxidative weathering
stable landscape to preserve opal from erosion and to prevent its transformation into quartz via burial

The connection to Mars in the title is based on recent observations by NASA of opaline minerals found on the Martian surface, Rey suggests that there could be a link with the conditions with the dehydration of Eromanga Sea in the Cretaceous and processes that may have occurred on Mars.


When can taste be used to help identify rocks? Taste can be used to distinguish halite (ordinary salt) from sylvite (which has some bitterness) and siltstone from mudstone (the latter has a creamy texture while the grains of the former can be felt). Are there other uses of taste for identification?

You are correct about halite and sylvite. I might add that carnallite also has an extremely bitter taste. These three minerals are chlorides and dissolve very easily, so that may be a part of the issue here.
Differentiating mudstone (clay) from siltstone is actually not about taste, but rather about texture. Note that this can be misleading. If you have a rock with 70% clays and 30% sand (or silt), you are going to feel the silt, giving it a higher proportion in your estimate, unless you have enough experience to consider this bias.

I would also like to note the dangers in tasting rocks. Although not common, some minerals are radioactive. Also some minerals contain lead, mercury and other hazardous elements. Some minerals may also be contaminated by anthropogenic pollution. So be careful with tasting rocks.


Where do bad smells eventually go? Suppose that I haven't taken a shower for a while, or haven't disposed of my trash, or something, and the room I've been in now stinks. Then, to remove the smell from the room (presumably after first throwing me out of it), you can just open a window or door, and let in the fresh air. Intuitively, the reason this doesn't leave a permanent stench outside, is because there's a lot more atmosphere outside than inside, thus diluting the smell so much it becomes unnoticeable.

But wait! There are billions of people on the planet, and life has existed on the planet for billions of years. And surely, most of the lifeforms that have existed here have made lots of bad smells, perhaps especially after they're dead. (And I sure don't think dogs smell good when they're alive either, for that matter.)

And yet, we call the air fresh, for the most part. So I suppose that, over time, the bad smells must have been destroyed or absorbed somewhere, and now I'm curious as to where. Would you have any ideas?

If you are smelling something, you are inhaling gases, particles, or a combination of the two.  They don't normally build up in the atmosphere because of three reasons:  transport/dilution (which you mentioned), chemistry, and deposition.  Yes there is plenty of fresh air out there but as you say, over billions of years there would be a lot of accumulation of odorous compounds if it weren't going somewhere.  Though, stinky air does get trapped near the ground sometimes during stagnation events, caused by a temperature inversion close to the surface which prevents mixing with the upper air.

Atmospheric chemistry usually involves the hydroxyl radical (OH) in some way.  Rapid chemical conversions of gases often depends on OH, which is cycling and replenished thanks to the abundance of oxygen and water vapor in the atmosphere.  Many gaseous pollutants will go through a series of chemical reactions with OH, other chemicals, and/or sunlight.  They are then converted to simpler chemicals that we don't really smell.  Most odorous pollutants are chemically converted quickly (e.g. hours, days).  Some pollutants do take years to convert (e.g. methane) and so accumulate in the atmosphere.  We don't smell them, though, because our ability to "smell" things is limited to organic compounds and other molecules like hydrogen sulfide and ammonia (see here).

Deposition of air pollutants is dominated by precipitation, whereby rain can scavenge particles and chemically react with gases.  The rain deposits the pollutants (usually in a modified form) onto the surface of the Earth.  Dry deposition also occurs, especially with "sticky" compounds like ammonia.  However, dry deposition is not nearly as efficient as wet deposition.  Though, if particles are large enough, they will settle out of the atmosphere relatively quickly and deposit on the surface.

I suggest you read up a little on the topic here to get you more familiar with the different factors that affect air pollutants.


What is the maximum grain size of a sediment that can be point counted using a standard thin section? Point counting is an extremely useful tool for determining the composition of a clastic sedimentary rock. It is also very useful in provenance studies to determine the sediment source of a sedimentary rock (see, for example, the classic paper by Dickenson and Suczek, 1979). The theory behind point counting is straight forward. For me, putting it into practice has been challenging because I cannot find the "definitive guide to point counting". I know the general rule is 300-500 points per slide and that the step size should be 1.5 x grain size (although this company says otherwise).  But what is the maximum grain size one can analyse on thin section before the counting becomes statistically unrepresentative?

you might have guessed: There is no such an easy answer as a precise, always valid maximum grain size.

Point counting is an upscaling technique. It works when the sample area you inspect is >= to the so-called representative elementary area (REA) of the rock facies. The larger your grains, the larger needs the REA to be. Same holds true for increasing heterogeniety and increasing number of mineral phases.
So check if your point count analysis is changing when you increase the inspection area. Once the analysis comes to a stable ratio of analysed items, you found the REA of the rock facies. This REA is a material property and not depending on the step size you choosed (as long as you make sure to obey the law of large numbers for each area).

-> look for "REA"

Best,
Ben


What is the origin of the Montmartre mountain in Paris? I have always wondered what is the origin of Montmartre mountain in Paris. What surprises me is that the whole area seems quite flat, and yet there's a very steep hill in the middle. How has that happen? Is it an instance of some common geological phenomenon?

A clue is in the full name of the hill: 'Butte Montmartre'. A butte is an erosional feature in which a block of resistant rock overlies a less resistant layer. Erosion of the soft layer below causes the more resistant rock to erode as well by undercutting. This can lead to an isolated hill in a relatively flat surrounding.

The Montmartre hill itself consists of relatively resistant sedimentary rocks (can't find what exactly, although Deffontaines (2005) and De Wever (2002) hint at sandstones and shales) overlying soft marls and gypsum, which was mined until 1860, also contributing to instability of the butte (Deffontaines, 2005). Evaporite-diapirism, as mentioned by Spießbürger, might therefore have played a role as well.

Deffontaines, B., B. Fruneau, A. Prunier-Leparmentier, A. Arnaud, R. Cojean, E. Pajot, J. Rudant (2005) Urban instability revealed by DINSAR and SPN Interferometry: The Montmartre "Funiculaire" case example (Paris, France). Géoline 2005
De Wever, P., F. Guillocheau, J. Reynaud, E. Vennin, C. Robin, A. Cornée, D. Rouby (2002) Deux siècles de stratigraphie dans le bassin de Paris. Comptes Rendus Palevol


Timeline of atmospheric model resolution I'm looking for a graph of improvements in spatial resolution for any atmospheric model (such as the UK Met Office Unified Model or ECMWF IFS).  Ideally it would include a range of historical model versions and perhaps forecasts for future model resolutions.

Europe is looking nicer and nicer every year (source):

This is a little bit out of date, since AR5 is already out - the dates for the first 4 IPCC reports were:

IPCC First Assessment Report, 1990
IPCC Second Assessment Report, 1995
IPCC Third Assessment Report, 2001
IPCC Fourth Assessment Report, 2007
IPCC Fifth Assessment Report, 2014

And an updated image for AR5 looks like this (both of these are AR5 model resolutions) (source, p145):

And that same PDF has another representation of increasing complexity, where cylinder height indicates complexity (source, p144):


What tidal databases are available to be used as model boundary conditions? I am trying to set up a coastal ocean model simulation. I am looking for different ways to force the tidal boundary condition in the model to study how uncertainty in the tidal forcing in the boundary affects the model solution. What are the different tidal databases that people are currently using?

The boundaries to coastal models are frequently forced using information on water level (or, less commonly, velocities) predicted from databases of tidal constituents. These databases may be global or regional, and typically they offer a grid of points with constituents available at any of these points.

The products listed below are all produced by global tide models informed by satellite altimetry. All will give water levels, and some will also give depth-averaged velocities. As with any global tide model, caution should be exercised when applying them in coastal and/or shallow water regions, as they are unlikely to have the resolution (of bathymetry or computational mesh) to resolve coastal effects.

OTIS

One source is the outputs of the Oregon State University Tidal Inversion Software (OTIS). OSU host a number of different data sets which are accessible from this page, along with the software required to extract constituents in FORTRAN or MATLAB. Both global and regional grids are available. The data here are based on TOPEX/POSEIDON satellite altimetry, combined through data assimilation techniques with a basic global tidal model and, in some cases, coastal tide gauges. The various grids have varying resolutions and varying numbers of tidal constituents.

DTU10

Another source is the DTU10 model from the Technical University of Denmark. This information is produced from a global tidal model combined with TOPEX/POSEIDON data and also Jason-1 and Jason-2 satellite altimetry. The model is described in a poster here. This model has a resolution of ${\frac{1}{8}}^{\circ}$ and includes twelve tidal constituents. Use of it is likely to be widespread in industry because it is included in the commercial modelling package MIKE by DHI.

FES2012

The newest dataset listed here is FES2012. More satellite data was used in its building than the other two models listed, and an improved model was used. The authors claim especially good performance in coastal and shelf regions.
Data are available on a ${\frac{1}{16}}^{\circ}$ grid with 32 tidal constituents.

NB: this description is based on the linked web page. I have not personally used this dataset yet.

Regional databases

In order to minimize the effect of applying a global tide model solution to coastal and/or shallow water regions, regional tidal databases are available. Some examples are:

As mentioned above, OTIS provides a number of regional databases around the world with varying resolution (from 1/12 to 1/60 degrees).
ADCIRC tidal databases: One encompasses the Western North Atlantic, Caribbean and Gulf of Mexico (up to 60W); and another one the Eastern Pacific (from Alaska to Mexico).
Many examples of local tidal model simulations are available for many specific locations, but the solutions are rarely available online.

Other sources of boundary data

All of the above data sources provide surface elevations from models. In the near future it may become feasible to produce velocity boundary conditions from land-based radar measurements of surface velocities in some areas.


Energy Density of Porous Rocks It's very long, I know. But please, don't be discouraged from going through this question if you can help me. The question is at the second to the last paragraph, but you need to read through to understand where I am coming from. Thank you.

I am currently doing some simulations in digital rock physics (using Comsol Multiphysics software). The compression energy density in the solid can be calculated from $\frac{1}{2}K\Delta^2$; where $\Delta$ is the total dilatation (or fractional change in volume), and $K$ is the bulk modulus parameter of the solid. When I integrate this equation over the volume of the solid, I get the energy. And when I divide the result by the total volume, I get the energy density.

Naturally, if the total volume is changed, the result of the energy density should remain the same, provided the porosity and the material parameters (like the bulk and shear moduli) are the same for both rock volumes. However, I find that this is not so with my models. I have tried using simple 3D models; e.g. I built concentric spheres having the inner sphere as the fluid region and the outer sphere as the solid region. Then I ran the simulation and compared the energy density result with that of another model, which I set up in the same way, but having a different volume. Mind you, these two models both have the same porosity.

My question then is, why am I not getting the same result? Is my energy density equation wrong in the first place (although I doubt that, as that has been of old from Hooke's law for isotropic media).

Thank you for your time. And, if you can, please suggest possible solutions I can try in order to fix this. I have tried everything in my knowledge base.

Eureka! I and my prof figured it out. We found something interesting - that the energy density actually depends on a number of internal variables, namely, the displacements of the outer and inner walls, and porosity (which we already knew). So, when we specified the outer displacement to always be a fraction of the radius of the outer sphere, that seemed to fix the problem.

Thanks to all who attempted to help me out! :)


Correlation and causation Linear correlation (Pearson's) is vastly applied in meteorology/climatology to assess the relationship between two variables, say precipitation and SST, for example.

However, we know that correlation does not necessarily imply causation, mainly for two factors: there may be external factors acting on both series or spurious coincidences may also happen.

What are possible and comprehensible ways, that have been used and are possible to reproduce in the Earth Sciences (Meteorology, Oceanography, Clmatology...), to go further and make a point to show that correlation does imply causation in some situations?

EDIT to make it more specific:

Imagine correlation is found between sea surface temperature (SST) in some region and rainfall in another. How to test if the variability of the two series are not being externally forced by a third party?

Thank you.

Convergent cross mapping (CCM) is a recently developed tool to answer the question you've asked. It's based on tools developed in nonlinear time series analysis and dynamical systems theory. It allows you to:
1) determine if a causal relationship between two variables is present
2) establish the direction of causality
3) do so even in the presence of noise.

As for an interesting application, check out the paper Causal feedbacks in climate change [van Nes et al., 2015], where CCM is applied to co2 and temperature based on the Vostok data sets.

EDIT: Below I've added a more detailed explanation of CCM to show the original poster that this technique does indeed answer their question, as well as to show it has a rigorous mathematical underpinning.

The general idea of convergent cross mapping is based on phase space reconstruction [F. Takens, 1981],[H. Abarbanel, 1996]. Numbers 1 through 5 explain the idea behind phase space reconstruction, which is needed to understand CCM. Numbers 6 through 8 very briefly explain CCM. References are listed at the bottom for more depth.

1) A physical system that is described by a set of equations (e.g. conservation of mass, momentum, etc) has a phase space. The solution to the system of equations is a trajectory through (or subset of) the phase space.

2) An attractor is a subset of the phase space that the trajectories/solutions evolve toward.

3) If you know the governing attractor, then you have all solutions of the system for all time.

4) Taken’s theorem says that one can reconstruct the attractor of the system based on a single observable. For example, if temperature, pressure, and velocity are the three variables of the system, then you only need measurements from one of these variables to reconstruct the attractor of the system. State space reconstruction

5) The reconstructed attractor is not exactly the “true” attractor, but it has a direct 1:1 mapping to the true attractor. Taken's theorem

6) If two observables belong to the same system, then they each have a reconstructed attractor with a direct mapping to the true attractor. The reconstructed attractors also have a direct mapping to one another. Convergent cross mapping

7) It is then possible to make predictions on one observable, based on the reconstructed attractor of the other observable, if they are in fact from the same attractor (causally related). Time series and attractors

8) Last, a series of tests/predictions with the data help to establish the direction of, strength of, and linearity of the interactions between the two variables. This is detailed in the papers [sugihara et al., 2012] and [van Nes et al., 2015].

To answer your question "given two observed variables, how do you tell if an third variable is simply forcing the two observed variables, making them appear correlated? First, the process of phase space reconstruction would yield an estimate of the "embedding dimension", which is an estimate of the dimension of the phase space (how many variables there). In the CCM framework, a one-way forcing relationship between the two known variables (v1 and v2) would be attractor for v1 can make skillful predictions of v2, but attractor v2 can not make skillful predictions for v1. Contingent upon the situation where you have an idea of what the third variable is (v3), I think what you could do is the following, take the reconstructed attractor of v3 and make predictions on both v1 and v2, and show that v3 has more predictive power on v1 (compared to v2), and that v3 has more predictive power on v2 (compared to v1). I'm not sure about this though.

Also, if the forcing (v3) is thought to be linear, you could simply remove/detrend v3 from v1 and v2, as is done when you remove seasonality from temperature data.

Note: There is MATLAB code available to mess around with this technique. I believe you can find similar codes in R as well.

References

Sugihara et al., 2012, Detecting causality in complex ecosystems.
van Nes et al., 2015, Causal feedbacks in climate change.
Abarbanel, Analysis of Observed Chaotic Data,1996, Springer publishing.
Takens, 1981, Detecting strange attractors in turbulence


Arabian Desert rock formation I'm interested about this rock formation in Arabian desert. The rock looks like melting chocolate.

Not sure where the exact Location, the source says it around Al-Ula, Saudi Arabia. Here the image source: https://www.instagram.com/p/CKAGbRcoa1r / https://www.instagram.com/p/CKAZR1yohtM
What this formation called?
what is the cause and how was this rock formed?
I made a little research on google, some says this was fomed by water and/or wind. I know, there was water and rarely snowfall in Arabian desert (obviously wind too). My presumptuous opinion, it doesn't look like was formed by fast flowing water like river or flood or wind. Sorry for that, i'm not geologist.
If the rock was eroded by water, how was it? By flood, river Or by glacial snow?
I need more scientific detail from the people in geology field. Can somebody please explain to me and provide me some scientific literature about this rock formation. Thank you..
Regards.

There are two water-related erosional process at work here:

The exhumation of main sandstone blocks caused by heavy rainfall, incising channels and carrying away the loose debris for deposition elsewhere as "sand".

Formation of weather resistant surfaces caused by dissolution and re-precipation of iron-rich minerals.

You often see this process at work in any desert environment bearing iron-rich sandstones. The morphology, however, will differ based on the internal structure of the rock. Where high winds can carry sand, these iron-rich surfaces can become highly polished into a varnish-like surface.