How much of a mountain is below the surface? Is there some kind of math rule for how much does a mountain extend (depth) below the surface?

I found an article like this http://www.livescience.com/6595-depth-himalayan-mountain-roots-revealed.html says that subduction is rare, does this mean mountains don't usually extend below surface?

Is there some kind of math rule for how much does a mountain extends (depth) below the surface?

Definitely! It is called isostasy. When I was a student, the lecture about isostasy started with a slide asking "why don't the mountains fall over?" (it may sound better in my native language..)

First, some background:

Mountains, and in general the Earth's crust is part of the lithosphere. This lithosphere is the outermost layer of the Earth from a mechanical point of view. It is a relatively non-dense, solid and rigid piece of rock. The lithosphere lies on top of the asthenosphere, which is a more ductile layer composed of the upper mantle. In a sense, the lithosphere "floats" in the asthenosphere. You can think of ice cubes floating on water, or a better comparison would be solid cold chocolate floating on warm (but still solid) chocolate. There are two isostasy models: the Airy model and the Pratt model. The Airy model deals only with topography variations, so this is what I will consider here.

Let's take the following example:

(source: http://www.globalchange.umich.edu/globalchange1/current/lectures/topography/topography.html)

The two different settings, ocean and mountain, would be in equilibrium if the pressure at the bottom is equal: $$ P_1 = P_2 $$ Translating pressures to depth and density: $$\rho_1 g h_1 = \rho_2 g h_2 $$. You can either solve for the above example (hint: it is not exactly in equilibrium), or you can use this relationship to derive expressions for how much root would a mountain need in order to "not fall over". The Wikipedia article on isostasy has an excellent illustrated example that you can follow and understand. It also describes the Pratt model that I did not touch in this explanation.

You can also see a nice simulation of isostasy in the source link given below the drawing, where you can play with various settings and see how the cube (i.e. crust) responds.

What happens in the Himalaya?

  I found an article like this
  http://www.livescience.com/6595-depth-himalayan-mountain-roots-revealed.html
  that says that subduction is rare, does that mean that mountains don't
  usually extend below surface?

Not exactly. Mountains extend below the surface in any case. Subduction is also something that is very common. For example, the Pacific plate subducts under South America, precisely because it is oceanic crust denser than the continental crust of the Andes mountain range.

The article does not state that subduction is rare, it states that deep subduction of continental crust under continental crust is rare. This makes sense - in contrast to the Pacific and Andes example, here you have the continental crust of India colliding with the continental crust of Asia. Both are not dense and one is not supposed to subduct under the other. What you expect to see is that they both fold together. The article you linked to talks about a discovery in which the Indian plate is subducting below the Asian plate. This is not something you can easily describe with the Airy isostasy model since there are more forces involved - horizontal and not only vertical. Actually, this is why they need the computer simulations to figure it out.

This question might also be of interest:
What is the current theory about the formation of Tibet?

Also related is this article:
Researchers rule out a “tectonic aneurysm” in the Himalayas


How long would it take for earth's core to cool down and solidify? Would earth go the same way as Mars by first losing its magnetic field followed by its atmosphere as its core solidifies and cools down ?

At what rate is the earth's core cooling down?.

Is it slow enough that it would be past time when the sun's temperature rises as it starts its journey into the red giant phase and heat up earth at which point it doesn't matter if earth has its magnetic field or not, or is it fast enough to happen within the next few hundred million years?

At what rate is the earth's core cooling down?

The inner core is cooling at the rate of around $55^{\circ} C$ every billion years.

  Would earth go the same way as Mars by first losing its magnetic field followed by its atmosphere as its core solidifies and cools down ?

Given enough time, yes; But earth is constantly producing heat though multiple processes, the most important being the decay of radioactive elements with long half lives (for e.g., U-238 has a half life of around 4.5 billion years). As the present temperature of the inner core is estimated to be around  $5000^{\circ} C$, this is going to take tens of billions of years.

The magnetic fields are generated by eddy currents in the outer core, which is a liquid layer about 2,300 km thickness. The inner core is growing at the rate of about 1 mm per year, so it is going to 'freeze over' (i.e. solidify) in about 2.3 billion years. Without its liquid outer core, the Earth's magnetic field shuts down, and charged particles emanating from the Sun gradually deplete the atmosphere, like Mars.

  Is it slow enough?

Well, it is not slow enough for the sun to become a red giant and fry earth, which will happen in 4 billion years or so. But is certainly doesn't matter as we won't be around to witness it.


What is the fastest the Earth has ever spun? How fast can the Earth rotate and support life?

In prehistoric times, dinosaurs were so massive that archeologists wonder how they were not crushed under their own weight. Could a faster spinning Earth allow larger animals to exist?

Could the slowing of Earth's rotation cause extinction among the larger animals but not the smaller animals?

https://physics.stackexchange.com/questions/278117/how-fast-can-the-earth-spin-and-support-life

*Ignoring any environmental impacts

The speed of rotation of Earth is controlled by its angular momentum. And the conservation of angular momentum is a very serious law of physics (perhaps even stricter than conservation of mass). So in the same way that for the Earth to lose mass, that mass have to go somewhere. For the Earth to lose angular momentum, it'd have to go somewhere.

Earth's rotation can vary within a small range by rearranging the distribution of mass (changing the Moment of inertia). That's why on ice ages the day was a few seconds longer, because large amounts of water that used to be on the ocean was piled in large ice sheets, so like in the classic example of a rotating ice skater, by moving mass (ice on Earth or the arms of the skater) away from the rotation axis, slows down the rotation speed.

The only other way for the Earth to significantly change its rotation speed is by losing angular momentum, and any imaginable event that could change significantly Earth's angular momentum over a period of 15 years would be so catastrophic that the change in rotation speed would be secondary. Such event would have to be something like the collision with a massive asteroid, the fly-by of planet-size celestial body, or the ejection of large amounts of mass by the explosion of gigantic natural nuclear reactors (all things that might have happened very early in Earth's history).

There are however processes at work today that are slowly stealing Earth's angular momentum. The most important one is tides. Tides produce bulges of water around Earth that rotate slower than Earth, as in this picture (from Wikipedia):

Therefore, to keep the bulges in place the water have to be constantly flowing into those bulges moving against Earth's rotation and slowing it down by friction. The lost angular momentum goes mostly to the moon that accelerate on its orbit, therefore moving away from us 3.8 centimeters per year.

This process makes the day longer 1.7 milliseconds per century, something that is not a lot even at geological times scales. It is equivalent to 17 seconds per million of years. But even that small amount adds up to almost one full hour since the start of the Jurassic (201 Ma ago). But the change is so slow that animals would have plenty of time to adapt.

So I would say that any explanation of how the dinosaurs supported their own weight have nothing to do with changes in Earth rotation speed. Also, I think you are overestimating the impact of the rotation speed on the perceived weight. If we make the numbers, the centripetal acceleration due to rotation at the equator is
$$a_\mathrm c=\frac{v^2}r=\frac{(462\ \mathrm{m/s})^2}{6\,378\,100\ \mathrm m}=0.0336\ \mathrm{m/s^2}$$

Equivalent to a 0.3% of the acceleration of gravity. Therefore, even if the Earth were to stop completely, a dinosaur of 1000 kg would feel only ~3 kg heavier.

Said that, if we go to the very hypothetical case you say, a slow down wouldn't make much of a difference (ignoring any environmental impacts of having a one-year-long day).

And for how fast the can Earth spin and support life? I think nobody can really answer that question, as we don't know what conditions life can endure. But if you make the Earth spin faster, the centripetal acceleration grows as the speed squared, therefore it wouldn't take too much to make the centripetal acceleration equal to the acceleration of gravity, in which case objects in the equator would be weightless. In that case, Earth would lose its atmosphere and oceans, and further speed-up would start ejecting rocks into space. By rearranging the above equation we can get that critical speed, and it would be:
$$v_\mathrm c=\sqrt{rg}=\sqrt{6\,378\,100\mathrm m\times9.8\ \mathrm{m/s^2}}=7\,906\ \mathrm{m/s}$$

That is 17 times the current speed, equivalent to a day of one hour and 24 minutes.

Finally, for your  question: What is the fastest the Earth has ever spun? It depends. If we consider it after the main change in angular momentum associated to the formation of the Moon 4.51 billion years ago, we can just extrapolate those 17 seconds per million years (this is not the most precise as there were no oceans then, but it is a fair first approximation), and we get about 21 hours, so that the day at that time was only about three hours long.
Careful calculations for the length of the day in the proto-Earth before the formation of the moon lead to a day of 5.8 hours (see this paper, line 358)

As an anecdotal note, the fact that this number is quite close to the critical velocity, have made some people think that the explosion of a natural nuclear reactor could have been enough to give the extra kick to eject the whole Moon from the surface. Something that would explain why the composition of the Moon is so remarkably similar to that of Earth by recent analysis, challenging the theory of formation by a collision with "Theia" a hypothetical Mars-sized body. Although, there are other recent theories with an alternative solution to this problem, such as the synestia theory.

Finally, it would be wrong to restrict all possible changes of rotation speed only to surface processes or interactions to other celestial bodies. It could also be possible that mass redistribution in the Earth's interior could affect rotation speed. Events like the iron catastrophe would have increased the rotation speed, and other mass redistribution events could have happened or might be happening, but this is just speculation. Studying such processes is extremely difficult, we know very little about the dynamics of the Earth interior, and it will be extremely hard to prove or falsify theories concerning such internal mass redistribution events. This answers and and others in the same question have some ideas of how the angular velocity of a planet could change.


Why does it rain more at night than during the day? I'm living near a sea, and it rains mostly and heavily at night from 11 PM to 3 AM. The weather is mostly clear during daytime.

  Air is generally cooler at night, and cool air holds less moisture than warm air resulting in rainfall.

There is a similar Phys.SE question here which states the same thing.

Is this the only reason why it rains most at night, or are there any other factors which may affect the reason for raining more at night?

Note: I live in Chennai, India.

First off, your observation that Tamil Nadu gets more rainfall in the evening is partially backed by records. Sahany, Venugopal, and Nanjundiah, 2010 provide data on diurnal scale rainfall distribution during the Southwest monsoon season shows that Tamil Nadu is dry from 0530-1430 each day, and likely to be wet from 1730-0230:

The Northeast monsoon is different. From Rajeevan et al, 2012 the NEMR (North East Monsoon Rainfall) peaks in the evening for most of Tamil Nadu but the coast facing the Bay of Bengal (including Chennai) peaks in early morning (0330-0630):

Regarding the reasons for this, here are some excerpts from Basu, 2007:

  In the Tropics most of the rainfall is from the tall clouds (Cu or Cb)
  formed by convection within a deep layer of the atmosphere. The usual
  forcing for such clouds to form is the heating from below by the solar
  radiation absorbed by the ground during the day. This forcing is
  maximum near the time of maximum surface temperature and the first of
  the thunderstorms caused by insolation start near 1430 local time

and

  Over the sea areas along the east coast (south of 15°N) too, the
  maximum in precipitation occurs in the early morning hours as the
  synoptic-scale westerly is weak over this region and the diurnal
  variation is dominated by the land–sea breeze.

Also worth noting, from Roy and Balling, 2007:

  The strength  of  the  diurnal  cycle  is  greatest  in  the
  peninsular region with close to 96% variance explained for stations
  located in Tamil Nadu.

My interpretation of this is that inland Tamil Nadu sees high surface temperatures from sunlight through clear skies striking the ground. The resulting heat is released in the late afternoon and evening, which causes cumulus or cumulonimbus cloud formation and rainfall. During this, the ground cools off at a rate faster than the nearby Bay of Bengal. This causes oncoming sea breezes laden with moisture and coastal rainfall peaks in the early morning hours. In Tamil Nadu especially, this pattern is very stable.


How do I derive the formula for lithostatic (overburden) pressure? The title pretty much says it. I have the formula: $P = \rho g h$ where $\rho$ is the density, $h$ is how deep the pressure is in the Earth and $g$ is the gravitational acceleration(?).

I don't get the units either. If I substitute the units for each term I get this:

$$P = \frac{\mathrm{kg}}{\mathrm{m}^3} \times \frac{\mathrm{m}}{\mathrm{s}^2} \times \mathrm{m} = \frac{\mathrm{kg}}{\mathrm{m}*\mathrm{s}^2}$$

Shouldn't it be something like $P = \dfrac{\mathrm{kg}}{\mathrm{m}^2}$? As far as I'm concerned that's the unit for pressure.

Where do I get this formula from and how do I derive the unit of measurement?

This isn't that difficult, but anything is if you start from the wrong place. Let's derive this thing:

$$P = \frac{F}{A}$$

Where $P$ is pressure, and $A$ is the area the force is pushing down on. Let's take a break and derive the units first, just so we know our end derivation is correct; $F$ is in Newtons, which comes out to $\mathrm{kg} \times \frac{\mathrm{m}}{\mathrm{s}^2}$ and $A$ is in $\mathrm{m}^2$. This means that pressure is $\frac{\mathrm{kg}}{\mathrm{m}\times\mathrm{s}^2}$. So your first substitution is correct.

Now that that is established, let's think about lithostatic pressure, and break up the original equation:

$$P = \frac{M \times a}{A} $$

We know that $a = g$, gravitational acceleration, but what we really want is to figure out how to get this equation in terms of density, so

$$\rho = \frac{M}{V}$$

where $\rho$ is density, $M$ is mass, and $V$ is volume. If we substitute this equation in for mass in the pressure equation, we get

$$P = \frac{\rho V \times g}{A}$$

let's now separate $V$ and $A$, $$V = \ell \times w \times h$$ $$A = \ell \times w$$

So canceling out $\ell$ and $w$, our final equation shows

$$P = \rho gh$$

or lithostatic pressure.


Phosphate in the oceans, does it tend to bond with sodium? Phosphate has a major role in biology and the biosphere. In its "abiotic" form, floating around in the oceans, lets say marine oceans to be specific, does it tend to be in the Na3PO4 form? If for example a cell floating around in the oceans were to absorb a phosphate from the oceans, would it be the acidic phase (bonded with hydrogen ions, like H3PO4) or, a sodium-phosphate (the completely disassociated anion phase seems unlikely.. )

The pH of ocean water is currently about 8.1, which lies between the second and third dissociation constants (7.20 and 12.37, respectively).  So most of the phosphate inthe ocean in its twice-dissociared form, as $\text {HPO}_4^{2-}$.  For comparison, our own blood is around pH 7.4, so phosphate in our blood would be a mixture of $\text {HPO}_4^{2-}$ and $\text {H}_2\text{PO}_4^-$.
In the EPA reference above, it is noted that the slightly lower pH today versus in the relatively past implies a larger increase in hydrogen ion concentration.  But it's worse than that.  Because of the way changing pH is coupled with changing dissociation of acids including phosphoric acid, a seemingly small change in pH could mean a lot more potentially acidic material (in the case of phosphate, $\text {H}_2\text{PO}_4^-$ versus $\text {HPO}_4^{2-}$) in the oceans.


What produces these amazing 3D structures in Tibet? A friend recommended I watch this Chinese language video 航拍西藏 2018 (Aerial photography in Tibet) and the HD drone video of scenery is stunning.

After about 37 minutes into the video, there are shots of these tall 3D structures that I don't understand at all. The shapes look familliar and remind me of something I think I saw in California, perhaps the Anza-Borrego desert in California, but it was nothing like this.

I'm told that the area is called 札达土林 in Chinese, and that seems to be Zanda County in Tibet

update: See for example 31.5230N, 79.6900E and this answer which recommends the name Zhada Earth Forest National Geopark

What is it exactly that produces these amazing 3D layered and ridged structures in China, and what are they called?

The terrain examples show some striking similarities to what is referred to in the United States as "Badlands" - a type of terrain formed by layered sedimentary strata of rock that is soft enough to be eroded by wind and water into recognizably similar features. For example, here is South Dakota Badlands National Park:

Anecdotally, I have seen similar terrain in numerous areas of the Western United States, some appearing almost identical to the examples in the question. Furthermore, as mentioned in the updated question, the terrain examples shown for Zanda County, Tibet, are also referred to as the "Earth Forest"; further research of this specific location indicates that it was likely formed by similar erosive processes acting on "sediment stratum [...] mainly composed by sandstone and clay", comparable to the processes forming the various areas of Badlands in the United States.


Seismic data spectral analysis The two images below correspond to two processed seismic cross-sections.
My question is this: why at/near 0 Hz is there "lots" of seismic energy still present? Most if not all of the lower end of the bandwidth stops at 10 - 15 Hz.

Typically seismic data should oscillate around 0 amplitude in the time domain, i.e. there should be just as much positive amplitude as there is negative (otherwise the ground would have had a net displacement in some direction). This is the energy at 0 Hz in the amp spectrum. It is like a bulk shift (DC shift) on the data.

So... unless the ground was permanently displaced by your seismic source, this is probably just an artifact. It could be as simple as: you used too few data to calculate your amplitude spectrum (e.g. small window, etc). Or it could be a super low frequency artifact coming from data processing.


Is the rainforest too wet to burn? I want to know if a living rainforest in the Amazon, completely untouched by humans, is too wet for the fire to spread, even in the dryer months around July?

I.e. if somebody dropped 5000 gallons of gasoline there, put it on fire, would the fire spread, or would it die out after the gas has burned, because it is still too wet there?

Or is it that the only areas that burn are those where the trees have been cut down (deforestation), the dead trees and remaining vegetation then have to dry out during the (relatively, for a rainforest) dryer months, and only then are they able to burn? Or does the fire spread into the actual living rainforest?

My personal experience of rainforest is confined to Malaysia, where it is too damp to burn unless it is first cut down and allowed to dry out in the sun. The fires on these ladangs, as they are called, never spread to nearby rainforest, and abandoned ladangs eventually become rainforest again.  I have some knowledge of other rainforests and have come to the conclusion that true rainforest is similar to Malaysia's. Throughout the wetter parts of the tropics, where there is not rainforest  there is a kind of forest called monsoon forest which is only wet for a few months of the year. After that it dries out and eventually loses it's leaves as though it were winter.

Often it is fairly close to real rainforest, so there is a gradual transition from monsoon forest to rain forest. Both kinds are found in Amazonia and Central America, Dropping 5,000 gallons of gasoline into a rainforest to see if it would burn would be regarded as very odd nowadays, but it frequently happened in WW2. Allied and Japanese aircraft were frequently shot down and crashed into the jungle, seldom with 5,000 gallons of fuel aboard but certainly enough to cause a fire. In Malaya and Borneo the jungle never caught fire, and although this happened all over S.E.Asia, surprisingly enough I have never heard of an incident where the jungle caught fire. There is some monsoon forest in India, but the fighting there was confined to Assam, where it is rainforest.

In modern times a large jet occasionally crashes into jungle, but again I have never heard of one setting he jungle alight. Jet fuel, of course, is not as inflammable as gasoline. Some of the fires in Brazil currently shown on TV look as though it is the sort of scrub which springs up on land which was once cultivated.


Are atmospheric halogen oxides "supposed to be" in the atmosphere? Where do they come from? I like to naively think of Earth's natural atmosphere as nitrogen, oxygen, argon, water, carbon dioxide and okay, some nitrogen and sulfur oxides, and again okay, a little hydrogen and methane from microorganisms. Everything else is pollution and shouldn't be there.

Just because I like to naively think that way doesn't meant it's so.

The excellent answers to Why are atmospheric BrO and ClO important to measure by satellite? talk about halogen oxides.

Are they a natural component of Earth's atmosphere, purely pollution, or a mixed bag?

Classifying the presence of halogen oxides in the atmosphere as either natural, pollution or mixed bag, would result in mixed bag.

Natural sources of halogen oxides include the ocean and volcanoes. In 1963, Duce et al,

  showed that bromine, like chlorine, was lost from the sea salt particles

Volcanoes are another source of halogen oxides,

  Halogens are emitted from volcanoes primarily as hydrogen halides (HCl, HF, HBr, and HI). Upon mixing with the atmosphere, chlorine and bromine species are partially converted to the halogen oxides OClO and BrO.

and

  Traditionally, emissions of volcanoes were regarded to be mainly of importance for the atmospheric sulfur cycle, acid deposition, and stratospheric effects from explosive eruptions. This view changed recently, mainly because of the observation of very high concentrations of bromine oxide, BrO, in the tropospheric, nonexplosive plume of Soufrière Hills, Montserrat.

The Sun is a requirement for the ocean source of halogen oxides.

Salt lakes, such as the Great Salt Lake in Utah are also sources of halogen oxides.

Forest fires can be a source of fluorine.

Pollution sources of halogen oxides includes: steel production, phosphate fertilizer production, burning coal, the manufacture of glass and ceramics.

Bromine and chlorine are used in cleaning products which are another source. Fire fighting chemicals such as PFAS (PolyFluoroAlkyl Substances) are another source.


Coupling recharge with 1D groundwater flow model Suppose we are modeling 1D groundwater flow in an aquifer of extent $x$ from $A(x=0)$ to $C$. Lets say for unsteady state conditions, the input is at $A(x=0)$, we can model piezometeric response at $B (x>0)$ by heat equation. If I want to couple recharge from unstutrated zone into aquifer, should it be simply added to head value at $B$ or should it be implemented as boundary condition. Lets suppose we have already calculated recharge at point $B$ with Richard's equation.  I have tried to illustrate problem here. The problem is equivilant to 1D heat transport in a rod.

If you are not interested in the vertical flow occurring in your aquifer (which I assume is the case) then one can indeed add the recharge to the existing head!

In groundwater issues, we often assume the recharge to be constant over time and equal over distances when considering such problems. This is mainly due to simplification as we are often interested in horizontal flow rather than vertical flow.

That being said, in general I would consider recharge (as this seems to happen outside the system we are interested in) as a constant rather than a boundary condition.

However, when going into details, considering boundary conditions there are several ways to go:

Dirichlet boundary conditions: Where we assume a constant head at a certain location. As we go from A to B, we could assume constant heads at these location(s), depending on your setup.

Neumann boundary conditions: Where we assume a constant input/output discharge at a certain location. This could also be your recharge but also dependent on your setup.

Cauchy boundary conditions: complex combination of the two where the input is related to a head. An example of this could be a river with head h_x feeding an adjacent confined aquifer with head h_x2

I hope this gives some insight in the application of appropriate boundary conditions. As you can see: it all depends on the characteristics of the system, the known values and your own considerations.

For further reading one might consider Fitts' Groundwater Science (fully available at ScienceDirect)


downloading ERA5 netCDF daily data for a decade, how to restrict location to reduce data size? I have download ERA5 netCDF file in order to get precipitation monthly/daily rates for 11 years. But I have realized, there is no option to select my area of interest. It seems it is a big file to handle.

However, I am currently using R language and but still in the basic level.

My question is about if there is anyway to extract precipitation values for a certain area?

There are two ways to get this done:

1- you can select the specific domain of interest when downloading the files. This is highly preferred when you have to download a large number of variables and years. ERA5 netCDF are offered in two different formats: either at hourly time steps, or at monthly averages (see this). If you need a sub-monthly time steps the global files for many variables for long time periods are extremely heavy in terms of disk space. You could set up a python script to download the data selecting only the domain by following a procedure like the one suggested in this nice post by Reto Stauffer (of course there are other ways to do this).

2- you can download the global netCDF of the variable and year under consideration ad use a software to extract your domain of interest.
One of the most efficient systems to do that is using the Climate Data Operator CDO. you could use the sellonlatbox with a command like

cdo sellonlatbox,LON1,LON2,LAT1,LAT2 Input_file_Name.nc Output_file_Name.nc

Or you could use R, as for your case, doing something like:

library(raster)
library(rgdal)

#load your area of interest
setwd("path_domain_shapefile")
domain_shp<-readOGR("shapefile.shp")

#read netCDF
setwd("path_to_ERA5_files_folder")
pr_data<-stack("ERA5_file.nc")

#extract the data for your area of interest
pr_data_domain<-extract(pr_data, domain_shp)

#then you can transform this in a data frame and write it as a csv

As reference for basic operations with spatial data in R, I would suggest this introduction guide.

Hope this helps.


How was the atmospheric/oceanic circulation different prior to the formation of the Isthmus of Panama? Did El Niño extend all the way to the West Coast of Africa? Did the meridional overturning circulation exist back then? Was there another overturning circulation that existed?

Concerning the thermohaline circulation: the defining part of it, I think, is the formation of bottom water in the polar regions.

The formation of Antarctic Bottom Water (AABW) in the Southern Ocean is strongly linked to the presence of the Antarctic Circumpolar current (ACC). The ACC was possible only after the opening of the Tasmanian Gateway and the Drake Passage (between Antarctica & South America) which both happened in the Late Eocene / earliest Oligocene. The ACC is thought to have been the deep, strong current it is today since the Late Oligocene at the very latest (Lyle et al. 2008), so the AABW is also thought to have existed since the Oligocene.

However as far as the North Atlantic Deep Water (NADW) formation is concerned: it is linked indeed in part to the Gulf Stream and the Northern Hemisphere glaciation. While the latter only occurred ca. 3.6Ma (e. g. Muddelsee & Raymo 2005), the Gulf Stream is a direct consequence of the closure of the isthmus of Panama: the shallowing (and therefore closure to deep current) of the Panama Seaway is thought to have happenned at ca. 4.6Ma (Haug & Tiedemann 1998) with a complete closure at 2.6Ma (Lunt et al. 2008).

So it is rather safe to say that the thermohaline circulation as we know it today settled probably around 3.6Ma (therefore mid-Pliocene).

Back in the Eocene (55 to 33Ma), the formation of bottom water is thought to have occurred in middle to low latitude (e. g. Kennett & Stott 1990) leading to a very completely different kind of global circulation.

The impact on the ENSO (if it existed at the time) is, as far as I know, unknown but since South America was still here to limit it eastward I don't think it ever reached Africa.

References:
Haug, G. H. & R. Tiedemann. 1998. Effect of the formation of the Isthmus of Panama on Atlantic Ocean thermohaline circulation. Nature, 393: 673-676.
Kennett, J. P. & L. D. Stott. 1990. Proteus and Proto-oceanus: ancestral Paleogene oceans as revealed from Antarctic stable isotopic results; ODP Leg 113. In P. F. Barker et al. (Eds), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 113: 865-880.
Lunt, D. J., P. J. Valdes, A. Haywood & I. C. Rutt. 2008. Closure of the Panama Seaway during the Pliocene: implications for climate and Northern Hemisphere glaciation. Climate Dynamics, 30: 1-18.
Lyle, M., Gibbs, S., Moore T. C., Rea, D. K., 2007. Late Oligocene initiation of the Antarctic Circumpolar Current: evidence from the South Pacific. Geology, 35(8): 691-694.
Mudelsee, M. & M. E. Raymo. 2005. Slow dynamics of the Northern Hemisphere glaciation. Paleoceanography, 20: PA4022.


Why is it always rainy in Addis Ababa? I watch the news and in the weather forecast it's always rainy in central Africa, especially in Addis Ababa. Why is that?

Addis Ababa lies 9 degrees north of the equator at about 2300 metres in altitude. Its' mean annual rainfall is about 1090 mm, with an average daily  probability of rain of about 41%. The inter-tropical convergence zone in this part of East Africa is a little anomalous, but sufficient to bring long rains in July-August, and short rains in March-April. Given the altitude, latitude and synoptic climatology, there is nothing unusual about this rainfall, though as Kwinkunks points out, if you happen to hit an unusually wet 'long rainy season' it might seem unusually wet.


Confused about whether physical impact is 'erosion' When I dropped a stone or a crystal onto the floor, can it be considered as erosion? What is the difference between rocks breaking due to natural disturbances vs human action?

Here is the stone/crystal I dropped

I'm assuming here that you're asking whether you can apply the term ‘erosion’ to the damage your stone suffered, rather than the damage your floor suffered. In this case, the applicability of the term hinges not so much on who's doing it as on what it's happening to. In geology, the term ‘erosion’ is usually applied to land surfaces rather than individual, loose bits of rock. For instance, the Oxford English Dictionary has:

  erode, v.
  2. Geol. Of the action of currents, glaciers, etc.:
  a. To wear away; to eat out.
  b. To form (a channel, etc.) by gradual wearing away.

Nichols (2009), more concisely, says

  ... erosion is the removal of regolith material.

Once your stone is picked up and taken into your house, it's no longer part of the regolith material, although the surface you took it from was itself eroded by the stone's removal.

In the literature, human influences aren't usually excluded when discussing ‘erosion’. For example, the term is often applied when discussing how footpaths are worn down by human use (see e.g. Coleman, 1981).

So, if your dropped stone chipped a bit out of your floor, you might try to claim that as erosion, but only if you're prepared to argue that your floor constitutes regolith!

If you want a geologically appropriate term for what happened to your stone, abrasion would probably cover it. Allaby (2008) has this definition:

  abrasion (corrasion): The erosive action that occurs when rock particles of varying size are dragged over or hurled against a surface.

The use of ‘erosive’ in the definition perhaps doesn't make it entirely clear that this can apply to the particles as well as the surface itself, but it's easy to check that ‘abrasion’ is indeed used in this way in the literature. For example, again from Nichols (2009):

  ... sharp edges tend to be chipped off first, the abrasion smoothing the surface of the clast.

Responses to comments

  Does this mean that when my stone suffers abrasion, it is now destroyed?

No, not at all. ‘Abrasion’ just means that some material has been removed from your stone by mechanical action. Of course it would be possible to abrade your stone so much that it was completely destroyed, but this isn't implied by the term ‘abrasion’ itself.

  What would happen to the damage over time? Will weathering try to repair it?

In general, material removed from a piece of rock will not be repaired by natural processes. In some natural environments, new minerals may precipitate in a crack left by abrasive damage, but this won't happen to a piece of rock sitting on a shelf in your house :). In the natural course of the rock cycle, an abraded fragment of rock may eventually be ‘recycled’ rather than being ‘repaired’ -- for example, it may be incorporated into a conglomerate, or buried, melted, and recrystallized as a new igneous rock.

References

Allaby, M. (2008). Oxford Dictionary of Earth Science. Oxford University Press.

Coleman, R. (1981). Footpath erosion in the English Lake District. Applied Geography, 1(2), 121-131.

Nichols, G. (2009). Sedimentology and stratigraphy. John Wiley & Sons.


Are AO-GCMs sensitive enough to take large lakes into account? Of course atmospheric-ocean-coupled global climate models are, by their nature, very strong on ocean-atmosphere interaction, but what about large lakes? Lake Victoria in East Africa, the N American Great Lakes, and Lake Nasser, and maybe some others are of comparable size to the average grid cell size of the AO-GCM. Hence wind, humidity and evaporation should affect adjacent grid cells. Is this taken into account?

The resolution of AO-GCM are not high enough to include lake model in their code, at least as far as I can remember (looking at google scholar, I have not found anything related to lake model in AOGCM).

However, lake model are implemented (and operational) in regional climate model (RCM), such as CRCM5 (Canadian Regional Climate Model v5). See for example Martynov et al. (2012), where they describe the results of implementing lake model in a 45km resolution simulations. On that note, I think that until AOGCM (and now the Earth System Models, which implement carbone cycle) goes to resolution close to 50km, they won't adopt massively such lake models.

From Martynov et al. (2012)

"The  presence  of  lakes  influences  mostly  the  lake-rich region of the Canadian Shield by altering the low-level  air  temperature,  humidity  and  precipitation.  The influence of lakes on the precipitation is most significant over   the   Laurentian   Great   Lakes   and   within   the distance  of  200-300  km  downstream  of  these  lakes,
especially  with  open  water  on  lakes  in  wintertime.  The patterns of enhanced precipitation correspond to regions of the well-known lake effect snow on downwind coasts of  the  Great  Lakes."

Since the effect is rather regional, I suspect that other climate processes are more important for the AOGCM modellers.

Citations

Martynov, Andrey, Laxmi Sushama, René Laprise, Katja Winger, and Bernard Dugas. 2012. “Interactive Lakes in the Canadian Regional Climate Model, Version 5: The Role of Lakes in the Regional Climate of North America.” Tellus A; Vol 64 (2012), February. http://www.tellusa.net/index.php/tellusa/article/view/16226.

On ResearchGate: https://www.researchgate.net/publication/234872039_Interactive_Lakes_in_the_Canadian_Regional_Climate_Model_version_5_The_Role_of_Lakes_in_the_Regional_Climate_of_North_America


How will air quality, weather and climate improve because of the containment, social distancing and lockdown during the COVID-19 outbreak? The actions taken to contain the corona-virus epidemic is closing any form of human activities in the world. Schools are closed in most cities of the world, people are told to stay at home and it seems industries are also partially closed. So, chemical emissions from industries and cars will lower significantly. How does this affect the air quality, weather and climate?

This is a topic of almost continual discussion in the South China Morning Post, scmp.com , an English language newspaper in Hong Kong. This is both because air quality is a major problem in China (but one to which they are paying a good deal of attention) and because massive economic interruptions are relatively frequent. The Olympics were a big one, national festivals like Spring Festival, 春节, Chūn jié, give readers a chance to mourn or hope, the current trade war modulates the scale of industry, and now we have Covid-19.

Obviously the virus crisis is bringing about great improvement in current air quality almost everywhere. I doubt that any climatic effects are known yet.

Here's an article which introduces the topic in China -- which is, after all, the major live experiment going on: https://www.scmp.com/news/china/society/article/3044747/beijings-air-quality-shows-significant-improvements-war


Does this optical phenomenon have a name? Last summer, I snuck out with a row boat around 4am. Eventually with the sun risen but still quite low in the horizon, I was rowing in the middle of the absolutely still lake when I witnessed an optical phenomenon unlike anything that I've ever seen before: I found myself enclosed in a triangle in which, the sun was in one corner, and in the other corners, the surface of the lake had turned rainbow-colored.

As a photographer I technically understand what happens there, i.e. even though it looked clear to the eye, there obviously must've been some nocturnal mist left on the water surface to act as a medium, and, had there been more moisture particles higher up in the air, I should've seen an entire rainbow connecting these two reflections. But due to the conditions, apparently all I saw was the ends of the rainbow, on their own.

I tried to search for instances or info on this, but found none. Does this specific phenomenon have a name? Under what conditions might one expect to possibly witness this phenomenon?

Here's a quick illustration of the setting, as perceived subjectively.
I made a quick simulation of the sun in that time and location using Stellarium , and the sun was about 11° above the horizon (actual bald horizon, not including trees, hills etc.)

It appears from your picture that there is some mist above the lake surface. The phenomenon will be due to the same mechanism that causes conventional rainbows. The angles between the sun, the mist/cloud, and the observer will be identical but you will only see this with the sun low in the sky since the mist is near the water. That will also make the rainbow appear to be floating on the water surface (great photo, btw). I think the dark background of the trees helps make the colours more intense. The low sun means that the spectrum can be seen on either side and behind the observer. So you are correct that it will form a triangle around you. If I'm visualizing things properly, in your photo the sun would be to your right - on the violet side of the rainbow.

I am not aware of any distinct name for this, possibly because it is not really different from a rainbow from a scientific perspective or because too few scientists are awake at 4 AM.


IPCC digital references I'm tidying my citations for my thesis, and I'm facing the task of sorting out the references for the IPCC reports (all of which have very long lists of authors).
Does anybody know where there are any existing online .bib files or similar for these references? I'd really prefer to avoid adding them all manually if I can help it. For some reason the IPCC doesn't seem to do this as standard, which seems kind of odd.
Edit. OK I clearly didn't describe this very well. I'm after the references for chapters within the reports (as many as I can) not the references for information cited in the chapters. So AR5 WG1 CH1, Ch2 etc. etc.

Some of the IPCC AR5 reports were written in LaTeX, some in MS Word. You will not be able to get the .bib files for those reports written using MS Word because Word does not use BibTeX.
Working Group I did use LaTeX, and you can get the .bib files for their report, on a chapter by chapter basis, here.
Working Group II apparently used Word, but they have released a set of bibliographies in both .csv and .xml format. I used "apparently" because I am getting errors galore for any page under ipcc-wg2.org. Apparently IPCC Working Group II has not updated their subscription, and some expletive deleted online gambling company has bought rights to that domain.


What impact on climate did 2011 earthquake and tsunami have? The 2011 Tōhoku earthquake and tsunami was one of the biggest in modern history; the earthquake even moved Earth's axis for a very small, but measurable bit. The four years since then is not enough for hard climate data, but enough to have some insight to how the weather was influenced. So did it influence weather in any way that could be seen as "impact on climate"? If yes, how?

Local effects are definitely possible, mainly from the tsunami itself - turbulence in the air from the waves and increased evaporation from flooded areas after.  However, it appears that the earthquake and tsunami has had no significant effect on the world's weather, particularly in the long term.  According to the Lamont-Doherty Earth Observatory, Columbia University web-article, Can Big Earthquakes Disrupt World Weather?, a key point is that although the earthquake released a massive amount of energy, it is not enough to disrupt the energy balance of the atmosphere.

A particular point is that one of the significant effects - the axial shift from the earthquake, is, according to the article, minimal compared to natural cyclical axial fluctuations.  The article also mentions that other major earthquake and tsunami events have the same minimal effects.

Although, some studies such as what gansub mentioned in comments, Impact of tsunami on Tamil Nadu Monsoon Rainfall, suggest that the tsunami itself can cause disruptions to local and regional climatic systems  -particularly with rainfall patterns.  This is an ongoing study by the University of Canterbury's Dr Iman Soltanzadeh research "The Atmospheric Impacts of Volcano and Large Tsunamis" where land use modifications due to a tsunami would affect local and regional climate and weather patterns.

However, the effects on the thinner upper atmosphere were a bit more pronounced according to NASA observations reported in the web-article Quake and Tsunami make waves in the Atmosphere, causing ripples in the ionosphere (~85km above the surface), as can be seen in the image below:

The quake caused acoustic and Rayleigh waves that reached the ionosphere in about 10 minutes, and the rolling motion of the tsunami caused gravity waves to propogate to the ionosphere in about 30-40 minutes, continuing westward even after the tsunami was stopped by the east coast of Japan.

The most significant aspect of NASA's findings can be interpreted that as the waves (all types) propogate through the atmosphere from the earthquake rupture and tsunami to the ionosphere, they appear to cause no significant climatic disruption to the lower near-surface and even the middle layers of the atmosphere, further emphasising the conclusions made by the Lamont-Doherty Earth Observatory that large earthquakes and associated tsunami do not cause any long term affects on weather patterns.


At the ocean surface, why do large amplitude waves travel faster than small amplitude waves? I understand the mathematics behind it but I am looking for an intuitive description.

Higher amplitude waves, on water, are caused by larger disturbances and longer durations of energy input, in the form of wind, than smaller ones. Quite simply in order to build a big ocean wave you need to put in a lot of acceleration of surface waters over an extended period of time. So it's not just that the wave itself is travelling that much faster, the whole surface that the wave is moving on is itself moving in the same direction as the wave on the surface. The larger amplitude of the waves is in fact partly due to them going faster rather than the other way around.

NB: This doesn't apply with Tsunami waves as those are full column disruptions involving the water column from seabed to wave crest.


What are the causes of lower UV radiation at lower elevations? After recently visiting the Dead Sea in Israel and not getting any skin burns, I was wondering about the reasons for that. Searching the literature, it seems that the UV radiation is indeed lower in the Dead Sea (ca. -400 m) compared to Beer Sheva (a nearby city at ca. +300 m): 1 2 3. Both UVA and UVB rays are lower, but UVB rays are attenuated the most.

These sources give mostly measurements, but hardly discuss the reasons for the lower radiation. I always thought that the ozone layer blocks most of the UV radiation, but here it seems that just a few hundred meters of atmosphere can greatly reduce the amount of incident UV.

What are the reasons for that? Is it simply because there are more air molecules that absorb the radiation?

You are almost totally correct when you asked:

  What are the reasons for that? Is it simply because there are more air molecules that absorb the radiation?

The Ozone Layer blocks most of UVB, but does not affect the amount UVA entering the atmosphere (as seen in the illustration below):

(Image source)

But there is a little more to it than that. From NASA's Earth Observatory's webpage What Determines How Much Ultraviolet Radiation Reaches the Earth’s Surface?, elevation's role in attenuating UVB (and by similar processes, UVA):

  high elevations UV-B radiation travels through less atmosphere before it reaches the ground, and so it has fewer chances of encountering radiation-absorbing aerosols or chemical substances (such as ozone and sulfur dioxide) than it does at lower elevations.

The aerosols absorb and scatter incident UV radiation.  So nearer to the surface, there is a greater concentration that the light must pass through - and as the altitude decreases, the UV radiation path is therefore increased, so the further 'down' in altitude, the more the air mass and an increased presence of aerosols absorb and scatter solar UV radiation.

In respect to the aerosols in area you have specified (the Dead Sea), according to the first link in your question, The Analysis of the Ultraviolet Radiation in the Dead Sea Basin, Israel (Kudish et al. 1997), they state

  the air above the Dead Sea is characterized by a
  relatively high aerosol content due to the very high salt content of the Dead Sea

Their results indicate that

  The relative attenuation in the ultraviolet range as a function of wavelength, i.e.
  site-specific spectral selectivity, decreases with increasing wavelength.

thus, indicating that the attenuation is also wavelength dependent.


How should I start studying about 'successful transitions in post-drought economies'? Accept my apologies for weak formulation of my question. I do not have any background in environmental sciences, but since recently a lot of coverage in the media has been devoted to future droughts in Iran and their socio-economical effects, I got curious enough to investigate the depth of the matter. My main question is that when a drought in a region plagues an agriculture-based economy, what are the options for a fast and flexible transition in the economy of that region? By transition, I mainly mean providing a new source of income for the individuals, such that the drought does not translate to unemployment and/or relocation of people.

I assume that this has been studied, and maybe best practices already exist. However, since I'm not even remotely familiar with environment science, I don't even know which keywords I should search for.

Is there a dedicated field of research investigating this question? Is there a definitive book on this topic? It looks like a question on which a UN-related organization has already published some reports. If I want to find these hypothetical reports, what should I exactly search for?

There isn't a lot written on this yet. A search of FAO, UNESCO, World Bank and Asia Development Bank should turn up answers for specific regions. Keep in mind that climatic modelling is generally quite accurate for temperature, but woefully inaccurate in terms of regional water resources assessment. One should rely as much upon instrumental evidence-based historic trends as upon global climatic models and their down-scaled derivatives. In terms of temperature the important issue is to develop higher temperature tolerant crop cultivars, and maybe totally new crops. For example, fruit orchards that require so many days of frost will not do well under global warming, but new genetically engineered crops might do spectacularly better. The main issue is increased crop-water demand combined with diminishing irrigation water availability. In this, improving the irrigation efficiency is crucial, and requires massive reforms in almost every country. Apart from rising sea level, efficient irrigation combined with an upgrade to modern farming practices is by far the most important climate change adaptation.


Should I worry about copper pipe outside attracting lightning strikes? I used some copper pipe outside to string some decorative lights up higher in my yard. I used the copper because I thought it would be pretty and patina nice.

Then I remembered that copper is a good conductor, and there's a lightning storm outside. Should I be concerned about attracting lightning strikes? It's not grounded.

Any build up of static electricity in the ground will seek to connect with opposite charge in a storm cloud, and will spark through the line of least resistance. Any high metal structure, whether it is copper or not, is a candidate for the line of least electrical resistance. You may be able to protect your copper support by a higher lightning conductor (sharp spikey, high, pointing up, and well earthed, preferably to the local water table). Also bear in mind that the lightning can jump over short distances possibly to your copper support.

I once observed a lightning strike on a house close to where I live in South Australia. The lightning hit a TV aerial, jumped to the metal guttering around the roof, jumped to metal window frames, and made contact with the house's internal wiring. It was like a bomb had gone off. Every electrical appliance that was plugged in was fried. The guttering kind of exploded, and a sour smell of 'charred house' lingered for weeks.

So yes, you should be concerned!


Has an entire plate ever subducted? We know that plates can subduct, causing one plate to be pushed into the core by another.  As the plates move, the subduction continues, pushing one plate under the other.

If this process continues, logic says, the entire plate could be subducted under the other.

Has this ever happened?  How would we know?

Excellent question!  Indeed, entire plates have subducted before.

One example is the Intermontane Plate (Wikipedia).  This plate sat west of North America around 195 million years ago.  The plate contained a chain of volcanic islands on its western edge (known as the Intermontane Islands).  As the plate subducted under the North American plate, that island chain stood too tall and merged with the North American plate.

An illustration of the plate:

Source: Black Tusk, Wikimedia Commons

The entire Intermontane Plate was subducted under the North American plate.  However, we are able to see the remnants of the plate in the volcanic islands it left behind.

Once this Intermontane Plate was subducted, the Insular Plate became the new subduction zone.

This entire process was actually repeated with the Insular Plate, subducting the entire plate, leaving behind yet another chain of volcanic islands that fused to the western coast of the North American Plate.

The Burke Museum has an excellent article that describes the subduction of both the Intermontane Plate and the Insular Plate.  Well worth the read.


How can the Simpson Desert be the largest sand dune desert in the world? In the Wikipedia article for the Simpsons Desert in Australia in the first paragraph it says:

  It is the fourth-largest Australian desert, with an area of $\small\mathsf{176,500}$ $\small\mathsf{km^2}$ ($\small\mathsf{68,100}$ sq mi) and is the world's largest sand dune desert.
  Simpson Desert - Wikipedia

I know that the Rub' al Khali Desert is the largest sand desert in the world, and as seen in this photo it has sand dunes:

This is the Rub' al Khali. The caption for this picture on the article says "Sand dunes to the east of Liwa Oasis".

Here is another photo of the Rub' al Khali

Is it the case that although the largest sand desert is in southern Arabia and contains sand dunes nevertheless there is another larger "sand dune desert" in Australia? How is this classified? I'm assuming if this is true it means that the  Rub' al Khali Desert doesn't fall into the category of a "sand dune desert", whatever that is.

I've seen photos of both and both look very sandy and duney to me.

The linked Wikipedia article has been edited after the OP's question was posted. It now says:

  The Simpson Desert is a large area of dry, red sandy plain and dunes in Northern Territory, South Australia and Queensland in central Australia.1,2 It is the fourth-largest Australian desert, with an area of 176,500 km2 (68,100 sq mi).

  The desert is underlain by the Great Artesian Basin, one of the largest inland drainage areas in the world. Water from the basin rises to the surface at numerous natural springs, including Dalhousie Springs, and at bores drilled along stock routes, or during petroleum exploration. As a result of exploitation by such bores, the flow of water to springs has been steadily decreasing in recent years. It is also part of the Lake Eyre basin.

  The Simpson Desert is an erg that contains the world's longest parallel sand dunes.3 These north-south oriented dunes are static, held in position by vegetation. They vary in height from 3 metres (9.8 ft) in the west to around 30 metres (98 ft) on the eastern side. The largest dune, Nappanerica or Big Red, is 40 metres (130 ft) in height.4

  1Twidale, C.R. (1980). "The Simpson Desert, central Australia". South African Geographical Journal. 65: 3–17.

  2"Desert Parks of South Australia" (PDF). Department of Environment and Heritage, South Australia. Archived from the original (PDF) on 29 July 2008. Retrieved 23 October 2008. "Simpson Desert". Britannica Encyclopedia Inc. Retrieved 23 October 2008.

  3Madigan, C.T. 1936. The Australian sand-ridge deserts. The Geographical Review 26(2):205-227.

  4Rachel Dixon (2018). Deserts & Savannahs in Australia. Redback Publishing. p. 23. ISBN 9781925630206.

It seems that the article has been corrected on 13:13, 2 September 2019 by user Casu Marzu per the article's history page

Considering the timing, this is likely to be a direct result of your question. Good work!


Why confined aquifers have low storage? Identical drop in head in unconfined and confined aquifers releases different amounts of water. The confined aquifer releases less water and thus has less specific storage. When both aquifers are fully saturated then what makes storage in confined aquifer lower as compared to unconfined?

In an unconfined aquifer the 'storage' is that fraction of the saturated void space that can be drained. In a confined aquifer, what you are effectively measuring is the compressibility of the aquifer - that is, the water released by depressurizing the aquifer per unit head. They are really two different things.
In an unconfined aquifer, the water that is drained comes from a narrow cone of depression. In a confined aquifer, although the numerical storativity is very much less, the cone of depression extends very much further because it is a general pressure release which propagates far into the aquifer, in all directions, so the yield can still be very high.


What would happen if the same soil received waste water contaminants for a long time? I know that soil is used to filter septic systems within our treatment system, however what happens to this soil that is used in filtration, I know it would be changed every once in a while but what really happens when acidic and basic waste flows through this soil?

Like many things in Earth Science, the answer is, "It depends."

In this case it depends on the composition of the soil and the contaminant you are talking about. Climate, particularly the amount of precipitation, can also have an effect.

Septic systems are primarily designed to promote aerobic conditions and aerobic bacteria to degrade organic compounds and pathogens. In a well designed and maintained system, that will be effective for a long time. One of the important considerations is to be sure the soil will allow enough infiltration that it doesn't become waterlogged. Some places need a sand mound because the natural soil isn't suitable.

Some contaminants aren't treated by the septic system. Some are transported down in the infiltrating water with little or no interaction with the soil. These can quite easily contaminate the groundwater if concentrations are too high. Salt,  (NaCl), for example, is transported with practically no retardation. Many positively charged cations with charges of 2+ or more will be adsorbed onto the surface of (mainly) clay minerals or in between layers in the clay crystals. They do that because the surface favours them more than the cations that are already present so the new cations replace the old. But the minerals only have a finite ability to exchange the new ions for old. With time the new ions will flow deeper into the unsaturated soils (the vadose zone) until they breakthrough to the groundwater. How fast this happens depends on the soil properties, the concentration and properties of ions in the waste, and the amount of infiltration.

Negatively charged anions are interesting. They are generally poorly adsorbed by mineral surfaces so they are quite mobile in the subsurface compared to cations. Compounds of oxygen and other elements can form important anions like nitrate (NO3-) and sulfate (SO42-). My favourite is pertechnetate (TcO4-), which makes this man-made radioactive element quite mobile under oxidizing conditions. Since many elements have several valence states, changing the oxidation-reduction conditions can change their mobility.

You mention acidic and basic wastes. These can do several things. First, they can exchange for adsorbed ions on the sediments and compete with others ions, increasing the mobility of the others, Secondly, they can affect the chemical form of the ions in solution. Thirdly, they can react with the minerals and alter them to ones with different properties. Finally, they can affect the microbiology in the sediments and change the ability to degrade contaminants.

It is important to inspect and maintain household septic systems by pumping out the tank and checking the leach field for problems. Some places require that you define the location for a replacement leach field before building in case it is needed. Be careful not to put contaminants down your system - especially things like pesticides and herbicides.


How would a particle travel in a hurricane? How would a particle other then water travel in a hurricane? At what buoyancy or height would a small air born life preserver be safe from the ground in a hurricane? How fun would that be?

You can find diagrams of air flow in hurricanes. If your balloon has neutral buoyancy it will go with the flow. Good luck in the complicated currents in the rainbands and eyewall.


Why is ferret giving me error that the region is not 2D while plotting I have downloaded ERA5 data and am trying to plot temperature variable. The problem I am facing is that even after providing a 2D area for plotting, ferret is giving an error saying that the region must be 2D

yes? fill t[k=1,l=1]
 **ERROR: dimensions improperly specified: must be a 2D region
      CONTOUR/FILL t[k=1,l=1]

You need to use the following syntax

yes? fill 't'[k=1,l=1]

This is because ferret treats t variable name as time and to distinguish your variable name (if it is the same in the file), you have to provide it in double quotes.


How do you calculate the elevation at which clouds will form (lifting condensation level)? I have a parcel of air at 30°C with a dew point temp of 15°C.  It goes up and then back down a mountain 4km in height. Assuming the normal and dry adiabatic lapse rates apply, and an ELR=7.5°C/km, with the environment also at 30°C.

From Wikipedia it says that to find cloud base I:

(1). Start at the initial temperature (T) and pressure of the air parcel and follow the dry adiabatic lapse rate line upward (provided that the RH in the air parcel is less than 100%, otherwise it is already at or above LCL).

So then the initial temp is 30*C not sure what it means to follow the dry adiabatic lapse rate line upwards.

I know that lapse rate is the rate at which Earths atmosphere increases and decreases in conguence with the altitude. So the temperature increases when the altitude decreases and the temperature decreases when the altitude increases. So a dry unsaturated lapse rate is one where the parcel lacks water content, and the saturated lapse rate is one where the parcel is moist and contains water content. I understand that when they warm or cool both types move in up and down in direction.

(2). From the initial dew point temperature (Td) of the parcel at its starting pressure, follow the line for the constant equilibrium mixing ratio (or "saturation mixing ratio") upward.

Not sure what this means

(3). The intersection of these two lines is the LCL.

Not sure what this is asking me to do.

Things I have been asked to provide include:

  a) the elevation at which clouds will occur (the lifting condensation
  level);

  b) the temperature of the parcel at the top of the mountain;

  c) the temperature the parcel will have when it descends to the bottom
  on the far side of the mountain;

  d) the portions of its journey where it follows the wet and dry rates

  e) explain why the parcel is warmer/cooler/same temperature on the
  back side of the mountain as compared to when it started.

ANSWER:
$h={\Delta}t/{\Delta}l$
$h=$ height of LCL (unit depends on unit height of lapse rates)
${\Delta}t=T-T_d$
${\Delta}l=l_t-l_d$
$T$ is surface temp (deg)
$T_d$ is surface dewpoint temp (deg)
${\Delta}l=$ difference between lapse rates (deg)
$l_t=$ dry adiabatic lapse rate of temperature (deg/unit height)
$l_d=$ lapse rate of the saturation mixing ratio corresponding to the surface dewpoint (deg/unit height)


Why do tropical cyclones around Australia have erratic paths? According to the Australia Bureau of Meterology:

  Research has shown that cyclones in the Australian region exhibit more
  erratic paths than cyclones in other parts of the world. A tropical
  cyclone can last for a few days or up to two or three weeks. Movement
  in any direction is possible including sharp turns and even loops.

Why do they change directions so radically?  Does this occur in other parts of the world or are North American hurricanes the anomaly in their typically smooth tracks?

The paths of cyclones in the Australian Basin are no more erratic than cyclones, hurricanes or typhoons elsewhere. Conditions at the time of a cyclone's existence determine its path.

Sinuosity of Cyclone Tracks - SW Indian Ocean states that over the past three decades the sinuosity of cyclone paths in the SW Indian Ocean has a high degree of variability. It appears that in that part of the world, cyclones can make more abrupt changes in their paths during January than in other months of the cyclone season. It also goes on the state there are marked periods when the paths of cyclones are less sinuous and other periods when they are more sinuous when compared with long term averages.

The following picture, from Wikipedia, shows the paths of the cyclone tracks for the 1988-89 south west Indian Ocean cyclone season. A number of the paths are erratic.

Paths of other cyclones can be seen on the following Wikipedia pages:

1988-89 SW Indian Ocean Cyclone Season

1988-89 Australian Cyclone Season

2013-2014 SW Indian Ocean Cyclone Season

1985-1990 Southern Hemisphere Cyclone Paths

Paths of the World Hurricanes, Cyclones & Typhoons for the past 170 Years

NOAA Site displaying the paths of past cyclones, hurricanes & typhoons

Tracking paths for current cyclones in the Indian Ocean & Western Pacific


Why silicon is abundant in earth surface? What is the reason for having silicon in so large quantity on earth surface?

Silicon, in the form of silica (oxidised silicon: Si4+ or SiO2), is indeed very common on Earth's surface.

This answer has two parts: why is silicon common in the Earth as a whole, and why it is concentrated particularly in the crust (therefore the surface).

Why is silicon common in the Earth

Silicon forms in nucleosynthesis processes in large stars (larger than our suns) and in supernovae. Turns out that quite a lot of silicon can be formed this way. When our solar system was still a hot molecular gas cloud, our region in place was rich in silicon (among other elements) so eventually Earth has lots of silicon in it. This is slightly beyond my field of expertise, so I will refer to the link daniel.neumann gave in his comment and to this good explanation at UCSB Science Line.

Why is silicon extremely rich in the Earth's crust?

Now we know there's quite a lot of silicon in the Earth to begin with. How do you end up with even more silicon in the crust (outermost layer) than in the mantle (middle layer, between the crust and the iron metallic core)?

The answer lies in what happens to rocks when they melt. You have a rocky mantle, with let's say 35% to 45% of SiO2. When this rock gets heated or decompressed (or wet, but nevermind this for now), it melts. But it doesn't melt completely, it melts only partially. This will always be richer in SiO2 than the original rock, and the residue of the melting now has even less SiO2. Once SiO2-rich melt moves upwards in the Earth (sometimes even erupting as volcanoes), it moves more SiO2-rich material to the crust. Over billions of year and large successive partial melting events, you end up having quite a lot of SiO2 in the crust.

This gets even better, because in those SiO2-rich rocks, you also have lots of quartz - which is a mineral composed of pure SiO2: 100% SiO2. This is a very resistant mineral to alteration and weathering. So if you have a granite that has only a third of quartz, with time the other two thirds (mostly feldspars) will decay and turn into clays (aka dust, mud). Only the quartz will be left behind, and the rest will wash away with water to the oceans (eventually). This is why you have impressive sand dunes which are "seas" of almost pure SiO2:

Some other questions on this website you might be interested in:

What was the likely composition of Earth's early crust (how did crustal composition evolve)?

Why do felsic materials have lower melting points than mafic?


There is soil in Archean? Following a mobilista approach over geological time, and considering the Earth's internal heat as responsible for tectonic regime, which was involved in the "Permobile type" during the early times of the Archean, what would be the pedogenesis in this context?

I don't totally understand what you are asking but yes there was soil in the Archean. In some locations around the world, these soils were buried and preserved as paleosols. The Archean paleosols are very important in studying the origin of the atmosphere because the oxidation state of the minerals is an indicator of the presence or absence oxygen and other gases in the atmosphere (Mukhopadhyay et al., 2014)


Projecting rectangular stereography centred on 42°N, 10°E I am reposting from GIS Stack Exchange as here might also be someone who might help:

I have a precipitation GRIB2 file obtained at EUMETSAT H-SAF I am able to decode it to ascii but the software I am using (gdal, ArcMap,...) does not recognize the projection (in the title) so I am not able to properly project to Web Mercator for example.
So can anyone please suggest software that preferably works on Ubuntu and projects either grib2 files to other projections or is able to recognise the projection from decoded ascii.

The product (H-SAF 05) manual stated the datasets are in the projection mentioned in the title. EUMETSAT user support answered me the datasets use a polar stereographic projection with 25-75°N lat, 25°W- 45°E long.


How can I specifiy a substance in AERMOD? Since I use OTHER as a pollutant ID, are there some parameters I could specify in order to get better results for dispersion of substance I am trying to model? eg. molecular weight or density?

The POLLUTID key is used to specify some regular options.
Some examples:

PM2.5 can only evaluate averages greater than 24 hours (if you try to generate hourly averages it throws an error).
NO2 forces the use of options to simulate the conversion of NOx to NO2.
SO2 triggers the use of a 4-hour half-life for SO2 decay in urban zones.

All pollutants (gases and particles) are treated similarly, regardless of their weight or molecular density.


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

I don't know who voted down your question. I'm guessing those who voted it down thought that prior to asking your question you could have searched on the internet to find out how the Sun and the solar system, including Earth formed.

I've just found the following two links by doing just that. The following quote is from one of them and it explains the current theory/model for the formation of the solar system:

From Birth of the Earth

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

Read this article from Wikipedia as well.

https://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System#Formation_of_planets


What would the geology and climate of a supposed landmass near the pole be like, assuming a thoroughly warmer planet? I am designing a fantasy setting for pen-and-paper role-playing (and potential novel) purposes. I have decided that a continent be situated right on a Pole of some imaginary planet with axial tilt comparable to Earth. My question is: is it possible to achieve environmental conditions in the Continent at least somewhat similar to those of current-day Europe?

My understanding of Earth climate is that the poles, while extremely cold, are also very dry in terms of precipitation. I have understood that this is mostly due to the axial tilt but I'm not sure. I have heard that in a warmer part of Earth's history the poles had vegetation - is this possible even with the ever-present high-pressure zone?

I guess one way the continent could be habitable is to be full of freshwater rivers, originating from glaciers high atop of some mountains. I guess such mountains are plausible near the pole (I don't think the movement and mutual interaction of continental plates are somehow dependent of the latitude, are they?)

Thank's in advance for your great contributions!

For a very basic explanation of why poles are the way they are, note that the amount of solar radiation coming from the sun is spread over a larger area at the pole. Therefore you get less radiation per square meter. As a result it is colder.

Cold air can hold less water vapour. As such it is very dry (in terms of water mass per air volume) in cold regions. Dry air obviously can provide less precipitation. If your polar continent is warmer, you'll see more precipitation.

Large-scale weather phenomena are indeed mostly driven by Earth's rotation. As such you have somewhat more stable conditions along the poles. However, complex topography (i.e. mountains) can severely interfere with these conditions. This is the reason why the stratospheric ozone hole is much smaller in the northern hemisphere than in the southern hemisphere: There is much more mixing between differnt air regions in the north. In the troposphere this effect is even more pronounced.


If storms form above low pressure regions, why doesn't the eye of a hurricane, a low pressure region, have any storms? If this is due to the Coriolis Effect, my other question would be how does the wind go upwards to form the storm clouds?

While hurricanes are low pressure systems, their structure, determined by the Coriolis Effect as you mentioned, is determined by winds getting deflected slightly from rushing directly into the center of the storm.  This deflection causes the characteristic rotation of large scale low pressure systems, including hurricanes.  When a hurricane forms and surface low pressure deepens, a balancing anticyclonic high pressure system actualy forms in the upper troposphere, above the budding storm.

Air at this altitude actually spirals out and away from the center of the cyclone, pulling more air below in toward the eye (causing a positive feedback loop).  However, some of this high pressure, high altitude air "leaks" inward towards the center of the storm instead of outward, and pressure eventually increases enough that it counteracts the strength of any updrafts in the center/eyewall of the storm. This air begins to descend (subsidence) in the center of the eye, stifling any convection and causing clearing at the mid and lower levels - creating the famous stadium effect.

The convection/rising motion in the storm is caused by air converging as it approaches the center of the hurricane.  Essentially, when there is a bunch of air rushing toward the center of low pressure, it has nowhere to go when it arrives but up, thus forming updrafts!


Can the atmosphere affect the composition of igneous rocks? Recently I was reading 'How to build a habitable planet' by Langmuir and Broecker and in chapter 15 they speak about how Life has led to a difference in oxidation potential in the atmosphere, essentially leading to the earth becoming a fuel cell. They also spoke about how this led to certain ions being oxidized - ie uraninite to uranyl oxide, iron to hematite.

I was wondering if this could mean that as atmospheric composition would affect the sea floor, when this subducted it would affect the melt of the mantle - as far as I'm aware, it is the dehydration of the subducting slab which allows for the hydration, and therefore melt, of the mantle in regions such as Japan. If the subducting slab's composition is affected by the atmosphere, could this have any effect on the composition of the igneous rocks formed? Would this be detectable?

Thank you.

I figure you're looking for more exotic examples, and some geologists may well have some offhand, but I want to say "yes" because of the example of carbonatite rocks described in this geology page from San Diego State University:

  Carbonatites are perhaps the most unusual of all lavas. They are
  defined, when crystalline, by having more than 50% carbonate
  (CO3-bearing) minerals, and typically they are composed of less than
  10% SiO2.

Which would rely on the carbon cycle and the deposition of atmospheric CO2 onto the seafloor by biological processes.

However:

  Some scientists believe that the Ca-carbonatites are generated by
  fractional melting of crustal carbonate rocks. However, others believe
  that the Ca-carbonatites are not primary magmas at all, but rather
  derived from the alteration of Na-rich natrocarbonatite lavas.

There is an interesting paper in GeoScienceWorld titled Atmospheric K-feldspar as a potential climate modulating agent through geologic time that addresses your topic as the author tries to estimate K-feldspar (Kfs) flux through geologic time -- which addresses your question from the other direction: assessing atmospheric content (in some cases simple dust deposition) over billions of years by evaluating its traces in the geological record.


Average Snowfall for Snowy Places? I just moved to Wisconsin, so my family is throwing snow statistics at me. But it seems to me that the most meaningful average US snowfall statistic isn't available (or easy to find).

The average snowfall in the US is 28 inches.  But that includes places that never or rarely get snow.  A better stat would limit to places that get some modicum of snow annually.

So, what is the average snowfall for places (perhaps cities) that get at least an inch of snow annually?

Here are some cities and locations

Average Annual Snowfall for the Following Cities and Locations (in inches)

Asheville, North Carolina: 9.9”

Waynesville, North Carolina: 14.1”

Milwaukee, Wisconsin: 46.9”

Madison, Wisconsin: 50.9”

Syracuse, New York: 123.8”

Buffalo, New York: 94.7”

Smugglers Notch, Vermont: 59.8”

Burlington, Vermont: 59.8”

Mount Washington, New Hampshire: 281.2”

Morristown, New Jersey: 14.1”

New York City, New York: 25.8”

Montpellier, Vermont: 94.2”

Ogden, Utah: 22.1”

Salt Lake City, Utah: 56.2”

Barrow, Alaska: 37.7”

Seattle, Washington: 6.8”

Alta, Utah: 549”


What is the origin of oil? Most people may believe that oil comes from dead plants and animals, but there are alternative theories that are known as Abiogenic Petroleum Origin. If oil in generated in this manner it could mean we could find oil on other planets or moons as well.

As far as we can tell, almost all crude oil (petroleum) is biogenic, and specifically comes from marine organisms. That's the only theory that is supported by the geological record, by the thermodynamics, and by what we know of the biology and the chemistry.

That's not to exclude the possibility of abiogenic petroleum: indeed, we know that abiogenic liquid hydrocarbons are possible, because we can synthesise them ourselves. So finding hydrocarbons that cannot be biogenic does not show that most fossil fuels are abiogenic: it merely shows that some abiogenic hydrocarbons exist.

However, the quack theory, popular in Soviet Russia and with other fringe pseudo-scientists, is that almost all oil discovered in the ground comes from abiogenic sources. Geoff Glasby looked at how the pseudo-science came about, in his article Abiogenic Origin of Hydrocarbons: An Historical Overview (Resource Geology, vol. 56, no. 1, 85–98, 2006) DOI:10.1111/j.1751-3928.2006.tb00271.x


Online resources for geographical distribution of minerals I'm trying to find the geographical distribution and availability of mineral Brannerite. Is there a resource online to know or query where a certain mineral is found?

On the link page, they mention certain types of geophysical deposits where this mineral is usually found:

"In granite pegmatites and in granitic gneisses; in silicified pebble conglomerates; in hydrothermal quartz and calcite veins; detrital in placers"

If the answer to the former question is negative; Would there be online information about geographical distribution of these geological features?

You did not mention why you are interested in brannerite, so I am assuming you want it as a collector's specimen and not a microscopic crystal.

Unfortunately, there is no definite source. However, there are some possibilities:

Try the Handbook of Mineralogy: http://handbookofmineralogy.org and more specifically the brannerite page. You will fine there a more detailed list of localities for that mineral.
Another option is to run a Google Scholar search for brannerite. You can find scholarly papers dealing with brannerite, and occasionally they also mention where they found the mineral or how they obtained it. Notice that in the specific case of brannerite, there are many articles dealing with brannerite structure. This may not be what you're looking for. There is also the problem of accessibility - unless you have an institutional or personal subscription to these journals, you may not be able to access the full article. However, sometimes this information can be found in the freely available abstract.
Go to Rocks & Minerals magazine and run a search there for brannerite. They may have some articles dealing with localities.

Regarding your second question about geological features, the features may be mapped if they are big enough. This is probably true for granitic gneisses, may be true for pegmatites and conglomerates and unlikely for veins and placers. This will not help you though. Even though the mineral appears in let's say gneisses, 99.9% of gneisses will not contain this mineral. Of those 0.1% that do contain it, only a fraction will have it big enough so you will be able to see with without a microscope, or any larger than a speck of sand.

Finding rare minerals is indeed hard. If however you do indeed come across brannerite, I would like to remind you that it contains quite a lot of radioactive elements so don't make jewelry or good luck charms out of it, and washing your hands after dealing with it is usually a good idea.

Good luck!


Have there ever been simultaneous cyclones in the same ocean but different hemispheres? I'm teaching a physics class, and I'm getting to the point where we are talking about the Coriolis effect.  I usually show a couple of photos/videos showing a storm in the Northern Hemisphere and a storm in the Southern Hemisphere, and talk about why they rotate different directions.

However, it occurred to me that at some point in history, there could well have been two storms occurring in the same ocean but in different hemispheres.  Has this ever occurred?  This would most likely have to be in the Pacific or Indian Oceans (probably the Pacific, since from what I've gathered the Northern Indian Ocean is less active than most other cyclone basins.)  Ideally, a photo/video of this event would exist that I could show my students.

It does occasionally happen. Not often, because to kick-start a hurricane there has to be some rotation to start with, from the Coriolis effect, together with a sea surface temperature of >27 °C (+ some other requirements such as lack of horizontal shear). This combination is best met during summer when one or other hemisphere is tilted towards the sun, so the hurricane seasons in both hemispheres tend to be 6 months out of synchronization. But there are occasional overlaps, as in this vector composite, found at http://www.wunderground.com/blog/JeffMasters/archive.html?year=2015&month=06&MR=1


Can living where magnets are abundant provide a mini-magnetoshere? Are there a mini-magnetosphere within the magnetosphere similar to mini-magnetosphere found on the Moon? Is there a map of these areas that would resemble the white swirls in the picture below?

The white areas extending up to 360 km and are the safer areas where one could be protected to a degree.

Are there areas on Earth that could have this magnetic crustal properties as the moon has and would it add or supplement the protection of Earth's magnetosphere?

Source: http://lunarnetworks.blogspot.com/2010/10/grand-lunar-swirls-yielding-to-lro-mini.html

Near to the Earth's surface there are small variations in the Earth's magnetic field, but these don't play a role in providing the magnetosphere which protects the Earth from charged particles emanating chiefly from the solar wind.


Derivation of Geomagnetic field lines (after interaction with solar wind) I understand that without the solar wind, the Geomagnetic field would essentially be that of a dipole.
With the presence of the solar wind, this field is distorted, as can be seen in many images that a quick online search will show.
However, I am looking for the early mathematical descriptions of this model (with the solar wind distortion). I have found several papers from Tsyganenko (links attached below). I am curious to know if:
a) this is the first attempt to describe this mathematically, or
b) if not, is there any other information out there which would show how this model was developed?
Thanks!
Link to Tsyganenko material : https://ccmc.gsfc.nasa.gov/modelweb/magnetos/tsygan.html

Short answer: Tsyganenko was not the first to attempt an observation based mathematical model, and older purely theoretical models also exist.
The first mathematical magnetic field model was created from measurements made on Earth's surface by Carl Friedrich Gauss in the 1830s, when he derived the mathematical techniques we still use. For the solar wind and interactions between the Earth's field and the solar wind, we're talking the advent of the space age when we were first able to make measurements out in space and begin to mathematically describe them, though the idea of the solar wind had been suggested (not by that name) in the early 1900s, and theoretical models exist from the 1960s at least.
Wikipedia has a brief summary of the history of major magnetospheric and solar wind discoveries, that suggests things kicked off with satellite measurements made in 1958/9. Tsyganenko cites a NASA study from 1975 as the first empirical model of Earth's magnetosphere and its interaction with the solar wind, though direct measurements apparently weren't made in the magneto-tail until 1983 (from the first Wiki page).
An aside for clarity: the dipolar nature of Earth's magnetic field isn't due to the interaction with the solar wind - the field generated by the geodynamo in Earth's outer core contributes the bulk of Earth's magnetosphere and has a more complicated shape when considered at the Earth's surface, for example.
Magnetic fields have a strong dependence on distance from their source, and smaller spatial features attenuate more rapidly (think like with sound waves - you hear low frequencies far away, but the high frequencies attenuate more quickly), so the approximation as a dipole gets more accurate as you move further away from the source of the field.
So when considering the interaction between the solar wind and Earth's field, which occurs at several Earth radii out in space (the exact distance changes as it depends on the strength of Earth's field pushing out, and the strength of the solar wind pushing back) the Earth's field is roughly dipolar, and then gets distorted with a squashed bow-shock and elongated magneto-tail by the action of the solar wind.


Why do we say Earth rotates from west to east? It is said that Earth rotates from west to east. I take this as

  Earth's western hemisphere moves towards the Eastern hemisphere when seen from the frame of reference of pole star.

Now I can also say that,

  Earth's Eastern hemisphere moves towards the western hemisphere when seen from the frame of reference of pole star

So can't I say then Earth rotates from east to west?

When we say Earth rotates from west to east we don't say a point on earth moves from its west to its east. We just say Earth moves from west to East. Now what is west and East for Earth? My knee-jerk is that Earth's west means the western hemisphere. Then it is not wrong to say Earth moves from East to west as the Eastern hemisphere always move towards the western hemisphere.

P.S: The question was originally asked at https://gis.stackexchange.com/q/178685/66197 The discussion in comments over there might be useful.

Your confusion arise from the definition of East and West hemispheres. That's an arbitrary and confusing definition. Because East and West are relative directions. Meaning they depend on the position were they are specified.

East and West come from the proto-germanic languages, where East means dawn and West means evening. Therefore, East from any given point is roughly the direction at which the sunrise happen. And West is where the sunset happens.

That's why the east/west hemispheres definition is confusing, because if you are in the middle of the pacific, the Western hemisphere is towards the East... confusing.

So let's forget about East/West hemispheres, and consider the East/West cardinal directions. Where East is 90° to the right of North and West 90° to the left of North. These directions keep the original spirit, on which East points roughly to the sunrise, and West to the sunset.
Let's also forget about clockwise and counterclockwise, because that depends on where are you looking from. If you are on top of the North pole it will look like Earth is rotating counterclockwise, but from the top of the South pole it will be clockwise.

Now, when we say that Earth rotates to the East, we mean that each point on the surface is moving to the East of that point.

The following figure taken from pulauubinstories.com will help clarifying the point:

In the figure is clear that the fact that sunrise happens to the East is because we are moving in that direction. At dawn, as we move Eastwards we enter in the sunlit side of Earth, producing the sunrise. And as we keep moving Eastwards during the day, we enter in the night side of Earth, leaving the sunshine and the sunset to the West.

Therefore, as East means "dawn" it follows (basically by definition) that Earth rotates to the East.


What is the primary cause of the "Norwester" winds that affect parts of India & Bangladesh? I am primarily interested to know:

What is Norwester (localy called Kalboishaku as because in occurs during the Bengali Month Boishak which falls between Mid April to Mid May).
What causes  Norwester.
Why does it occur during the month of April and May.
Characteristics of Norwesters (What I have personally seen is, it happens during late afternoon with a sudden onset of Cumulonimbus cloud spreading across within few minutes followed by heavy thunderstorm and rain which persists for an hour followed by clear sky)
What are the areas affected by Norwesters. (I am only aware of the east Gangetic plane)
Why it is called Norwesters (My guess is its because the wind blows from North West)

Note

There are very little information around currently on Norwesters and even the wiki page is a stub. Most of my contextual answers are based on my experience with Norwesters but I couldn't find any studies or articles in this regard. I am possibly looking for answers drawn from credible source (possible links to journals/ books / papers), as this would be a nice opportunity to build a credible wiki on this subject.

Though you have divided your question up into 6 parts, I am combining the information in the answer, as they all link together.  Also, as can be seen in the reference list (below), the resources come from the same primary author, but from different aspects of his studies of this phenomena (these are all paywalled, so university access would be required - but I'll paraphrase the main points).

Firstly, a bit of terminology, a Nor'wester are storm gusts between 11 ms$^{-1}$ and 42 ms$^{-1}$, above which are referred to locally as being 'tornadoes' (2).  These are collectively known as Severe Low Convective Storms (SLCS) by Yamana et al. (1),(2),(3). The main areas affected are across Bangladesh and north-east India (3).

SLCS generally seasonal, usually occurring during the pre-monsoon months of March to May, peaking in April, usually in the evenings (as you have observed). Although rare, SLCS can actually occur at any time of the day and at any time of the year (2). Records over several years do not show any particular obvious trend in occurrence and frequency of events that occur each year - though they average at around 145 occurring each year (2).

Yamane et al. 2010 (2) note that the most frequent occurrence is in the Dhaka district (north-central Bangladesh) and trends in a northerly direction during the pre-monsoon.  However, the authors caution this observation as being the result of the amount of people recording these occurrences in other districts.

Yamana and Hayashi (2006) (3) explain that the SLCS are a result of regional atmospheric thermal instability, where the convective available potential energy (CAPE) is high (greater than 2000 Jkg$^{-1}$) and the shear is moderate (greater than 10 ms$^{-1}$, and that the phenomena also coincides with severe local storms across the Indian Subcontinent.

Yamana et al. (2012) (1) elaborates further on what causes the atmospheric thermal instability, with a synoptic analysis of a SLCS, describing the phenomena as a confluence of  (note, the authors use AGL = 'above ground level' for the following information):

Moisture inflow (increase in humidity) from the Bay of Bengal, enhanced by a south-west wind intensification at 950 hPa (approx. 500 m AGL). This increases the amount of water vapour available.
A temperature increase, due to westerly winds, across the region at 800 hPa (approx. 2 km AGL), leading to
A trough leading to an enhancement of cold advection at 550 hPa (approx. 5 km AGL) from the north west.

This, in part, gives a reason for its name and confirms your 6th point, that it blows in from the north-west.

References

(1) Yamana Y. et al. 2012, Synoptic situations of severe local convective storms during the pre-monsoon season in Bangladesh, International Journal of Climatology

(2) Yamana Y. et al. 2010, Severe local convective storms in Bangladesh: Part I. Climatology, Atmospheric Research

(3) Yamana Y. and Hayashi, T. 2006, Evaluation of environmental conditions for the formation of severe local storms across the Indian subcontinent, Geophysical Research Letters


Is it possible that water (H2O) was made on earth? Most theories suggest that water was already on earth at the beginning but due to temperature most of it evaporated. Others theories suggested that water was brought to earth with komets or asteroids.

But if there was hydrogen available could it be created by combining with the oxygen into H2O?

This is more Astronomy than Earth Science, but the Young Earth, while forming, would have had a hard time retaining Hydrogen.   There's two reasons for this.   One is the Frost Line which means there was relatively little hydrogen and relatively little water and other gases present when the Earth formed.

And the other is Atmospheric Escape.  The Earth doesn't have enough gravity to retain Hydrogen.  In fact, the Earth is still losing Hydrogen, by this estimate, about 95,000 tons per year.

Precisely how much hydrogen and water the Earth contained at formation vs how much it acquired by solar wind (Hydrogen nuclei) and comet and asteroid impacts (water and other gases) isn't known.  I think it's likely that the majority came from impacts and I think that's where the consensus leans, but an precise answer isn't known.

As far as the Earth combining Hydrogen with Oxygen, there's relatively little free Oxygen in the solar-system.  Oxygen binds easily with many elements, so it's abundant but not in it's elemental/gaseous state.  The Earth also tends to lose gaseous hydrogen and not having Oxygen until about 2 billion years ago, it's unlikely that much water was formed in that way.

When we learn more about exoplanets, we might find that larger/super Earths might retain more hydrogen and form abundant water in that way if they have photosynthesis to create Oxygen, but that's just theoretical.  Earth is too small to have retained enough hydrogen to do that in large amounts.