How much does the productivity of modern agriculture depend on Glyphosate? Glyphosate is the most important herbicide in agriculture by quantity. A committee of the European Union just recently voted against a ban of the substance, after much debate around possible negative effects on human health. I now see a lot of petitions popping up on social media, calling for an immediate ban. This got me wondering: if Glyphosate would be banned in the near future, say in the course of next year, what problems would arise for farmers? Are there viable alternative weed killers, and would productivity be significantly reduced without using one?

Chemistry is not a bad thing; life depends on it. And just because a pesticide or herbicide is natural or synthetic has practically nothing to do with its toxicity. Many so-called natural or organic pesticides are many times more potent than widely-used synthetic ones, as this article mentions.As to whether or not Glyphosate is necessary, this article explains some of the economic impacts from an outright Glyphosate ban. Some of the effects include:...French research institute Arvalis suggested a ban would cost that country’s agriculture industry 976 million euros ($1.1 billion). And in Germany, the Kleffmann Group said restrictions could hurt barley and corn output—with profit margin shrinkage between 40 and 70 percent–as farmers start planting alternative, more profitable crops.

Meanwhile, in the United Kingdom, where in 2014 2.2 million hectares of farms—a third of arable land—was treated with glyphosate, Oxford Economics estimated the impact would reduce wheat yields by 12 percent, oilseed/rape yields by 14 percent, and cereal production by 15 percent. Agricultural contributions to the nation’s GDP would shrink by about £930 million ($1.23 billion).In another article I recall reading (but can't find the citation for), Glyphosate is applied at a rate of only one pint per acre. Farms are not drenched in it as many anti-Glyphosate advocates would have us believe.As to whether or not Glyphosate is a carcinogen, this article calls much of that into question. Apparently, there were individuals involved who might have benefited substantially by having Glyphosate declared a human carcinogen.Edit:Some other interesting articles:This article  from Factcheck.org had this interesting tidbitQ: Does the herbicide glyphosate cause cancer?

A: There is evidence to suggest it may cause cancer at very high doses, but not at the low doses typically found in foods.and
The European Chemicals Agency...concluded in March 2017 that “the available scientific evidence did not meet the criteria to classify glyphosate as a carcinogen.”And this article from the-scientist.com said A new study has found no conclusive link between exposure to glyphosate—the main ingredient in a popular weedkiller—and cancer.And Reuters in this piece  said:
The World Health Organization's cancer agency says a common weedkiller is "probably carcinogenic." The scientist leading that review knew of fresh data showing no cancer link - but he never mentioned it and the agency did not take it into account.


Intuition on overall effects from climate change under different levels of warming I am not a climate scientist, but I have been reading climate literature lately for my own education. Much of it discusses various effects that could be expected with different levels of warming, usually by 2050 or 2100, e.g. reductions in crop yield, flooding, etc. However, I find it very difficult to intuit what the effects of various scenarios would mean in aggregate. E.g. say we have 4 C warming by 2100. What is the overall level of economic damage globally? Even better, what is a way to get a grasp on the level of damage or suffering that results - is it a societal collapse, or something similar to WWII, or something similar to the Great Depression, or something much less?

Are there any good resources or papers that discuss overall (net amount of damage, net amount of suffering) range of possible effects in an intentionally intuitive manner like this, for different warming scenarios?

Note that I am not looking for predictions of temperature rise. Ideally, I am looking for predictions of damage that are stated in a way that is easy to get an intuitive global handle on, given specified temperature rises, by specified years (e.g., presumably 1 C by 2030 would cause more damage than 1 C by 2050 or even 2100).

The closest thing that I have found to this so far are the burning ember diagram in the IPCC reports, and the corresponding referenced papers. This is a step in the right direction as far as what I am looking for, and gives some references that may be helpful (I haven't explored them yet), but still doesn't quite hit the mark for me.

Anyway, this might be a broad and strange question, but an answer or partial answer to it would help me greatly to contextualize the subject as I study it.

I think you're asking about the sort of outputs that are obtained from climate-change integrated assessment models [IAMs] And now you've got the right search term, your quest will get a lot easier.

You're doing the right thing: start with the IPCC reports. The next step is to follow through on reading their references. And then use google scholar or any proper academic search engine you have access to, to find more recent papers that have also cited those papers that the IPCC cited.

Here's a pdf on the PAGE09 IAM, an updated version of the PAGE2002 model used for the Stern Review. Chris Hope makes his PAGE model available to other researchers, on request.

Here's the UK's Committee on Climate Change report on IAMs

Here's the London School of Economics' page on IAMs.

And the TIAM IAM from UCL.

Google Scholar claims to have 3000 results from the last five years on IAMs and climate change.

As you can probably imagine, there are uncertainties piled on top of uncertainties in this field. The scholarly work on them nevertheless represents the best available set of expert expectations on the sort of damages we are likely to experience with different increases in the concentrations of greenhouse gases.


What are the composition and pressure of the exosphere? I've read that the pressure and temperature are different - how different are they, and does that affect the atmosphere's composition?

Since this is the Earth Science stack exchange I assume you are talking about the Earth's exosphere, in which case the first issue to decide is how one defines the exosphere - there are several definitions. The lower boundary is straight forward - the thermosphere. However, the exosphere doesn't have a clearly defined upper boundary. You could argue that any gas molecule that is gravitationally bound to Earth is within the exosphere, but that depends upon the relative forces of solar wind and gravity, which is a variable. Some argue that the outer limit is defined by the geocorona at about 10,000 km, whereas the gravitational limit is more than 100,000 km, or arguably up to half the distance to the moon.

The exosphere's composition varies from oxygen, carbon dioxide, hydrogen and helium at its base, to just hydrogen and helium in the outer limits.

The exosphere's pressure is about 0.0007 atmospheres at its base to virtually nothing in the outer reaches. In fact 'pressure' is a meaningless concept in the outer exosphere because individual atoms and molecules are kilometers to hundreds of kilometers apart, so they almost never interact - and pressure is really the intensity of molecular physical interaction.

A comparable argument applies to the exosphere's temperature. In the outer regions of the exosphere the same hydrogen molecule could have a daytime temperature of nearly 2000 Kelvin, and a night-time temperature close to zero Kelvin. In both cases the space would feel cold because there is next to nothing there to transmit heat.

The Earth's atmosphere is still evolving by processes dominated by the lithosphere / biosphere. Only hydrogen and helium are light enough to shoot up to the top of the atmosphere (think helium weather balloons). At the height and temperature of the thermosphere, or higher, they can both gain sufficient thermal kinetic energy from sunlight to gain escape velocity, which is why there is very little helium or free hydrogen in our atmosphere.


Are the processes of the rock cycle currently in dynamic equilibrium? The standard representation of the rock cycle usually looks like this:

Does each stage of the rock cycle currently balance? That is, are the various processes in dynamic equilibrium, so that the proportions of the different rock types remain constant?

If the processes are not in equilibrium, which types of rock are currently increasing in overall prevalence, and which are decreasing?

It's an interesting question, but in practice I think it's impossible to answer. It's very difficult to measure the rates of many of those processes, and the divisions between rock types can be quite ill-defined (for example, in migmatites). There's no scientific instrument we can point at a chunk of the earth which will tell us "in this region, 29.4 megatons of sedimentary rock became metamorphic rock during the past year".

What we can say, at least, is that the global balance of these processes is not constant over time. For example, during the Deccan Traps eruptions there was an increase in the rate of formation of igneous rock through solidification of magma.

The classic rock cycle diagram you posted probably encourages this kind of question, because it makes it look like a neat, closed system with well-defined boundaries and comparable quantities of each rock type. It's a very useful simplification for many purposes, but remember that these processes are occurring at or near the earth's surface. This whole system sits on top of the mantle (which is vast compared to the volume of crustal rock), and material is continually being passed between the two, so it's far from being a closed system.


Source of water for the Great Artesian Basin in Australia The Great Artesian Basin in Australia covers 23% of the continent and contains 64,900 cubic kilometres of water.

Many years ago it was claimed on a TV science show I saw that some of the water in the basin comes from Papua New Guinea (PNG) via an underground conduit.

Is it true that the Great Artesian Basin in Australia gets some of its water from PNG and how is the water transported from PNG to Australia under the Torres Strait?

Many studies, observations and measurements indicate that a great deal of the water recharges from the eastern highlands (Great Dividing Range).  This answer focuses on Governmental reports (including the CSIRO)

According to the CSIRO report Hydrostratigraphy, hydrogeology
and system conceptualisation of the Great Artesian Basin (2012), the Great Artsian Basin consists of complex geological and hydrogeological features.  This extensive study of the basin indicated no recharge from Papua New Guinea, stating that the recharge areas as being from folded Mesozoic rocks surrounding the basin in the central and southern parts, and Cenozoic aged recharge areas around the Gulf of Carpentaria in the north.

The recharge areas of the Great Artesian Basin are, according to the Australian Government Department of the Environment is mainly from rainfall on the highlands (near to the western margin of the Great Dividing Range) to the east of the Basin (with some from the western margin), as shown in the image below (from the Dept webpage):

Source:after Habermehl and Lau (1997). The shaded patterns broadly represent the
recharge area; arrows represent modelled flow lines after Welsh (2000). Dashed
lines represent spring clusters updated from Habermehl.

One major observation is that the top of Cape York is indicated as a recharge area, however, the CSIRO report details that this is recharge area is the Coen Inlier, just to the south of the shaded are.  Also noted is that there is discharge into the Gulf of Carpentaria in the north - according to the CSIRO, the basin extends into the Gulf of Carpentaria.  Although in all 3 reports there is no mention of recharge through the Torres Strait, the most any such discharge could influence, is the part of the basin in the Cape York/Carpentaria area.

A cross-section of a section of the basin is show in the image below (from the Queensland Government WetlandInfo webpage, clearly modelling the recharge areas (for the most part) being from the highlands on the eastern margin of the basin:

Additional References

Habermehl MA and Lau JE 1997, Hydrogeology of the Great Artesian Basin (Map at scale
1:2500000), Australian Geological Survey Organisation, Canberra

Welsh WD 2000, GABFLOW: A steady state groundwater flow model of the Great Artesian
Basin, Bureau of Rural Sciences, Canberra.


Why more matters appear in hot equator, when they should flow to the cold poles? I am reading a paper* about the application of the maximum entropy production (MEP) in Earth science (I'm new to MEP btw). The authors start with the system of gas molecules first. When the system is isolated, it has the maximum entropy and the molecules are distributed randomly. When it get contacted with the hot reservoir, nearby molecules will have higher energy, therefore moving faster and will tend to move to the other side, while colder molecules are not really active, so they will stay in their positions. As a consequence. the molecules will shift to the cold side.

When we replace the hot reservoir with the equator, and the cold reservoir with the pole, we will have the model of planetary system.

However, doesn't that mean that more matter will locate in the pole(s) than the equator? In Earth, this would mean that there will be more structured or ordered matters, including organisms in the poles than the equator. This doesn't look right to what we know.

How can this be explained?

*The Maximum Entropy Production Principle: Its Theoretical
Foundations and Applications to the Earth System

This is very simple to explain when we consider that the 'model' you have been presented with is a gross oversimplification - a one dimensional mechanism. But the Earth is a multi-phase (air water ice), three dimensional system in which convective currents circulate. Hence there is a counterflow of both air and ocean currents in addition to the basic entropy model. The entire thermal circulation is also massively influenced by considerations of conservation of mass, conservation of energy, and conservation of angular momentum. Its a pretty complex system, as climate modellers are only too aware, and cannot be reduced to any simple model.


How much faster are airmolecules going when the temperature raise from 15 to 25 degrees C? As far as I know the temperature of the air depends on how fast the airmolecules are moving. But what is the increase of speed (in km/h) of those are molecules?

User LTK 4 is correct. The air molecule is moving 1.7% faster at 25°C.
Marijn can calculate the absolute velocities from the simple equation given in http://www2.ignatius.edu/faculty/decarlo/surfacepower/pages/KineticTheoryOfGases.htm .

And yes, this is more physics than Earth Sciences.


Uranium Deposits in the Ocean? I was wondering whether there are any uranium deposits in the ocean floor, or in the rock walls of the continental shelf, etc.

I was hoping to have some deep sea uranium deposits accessible from the water, for fiction writing. So I would like to know if such has ever been found, or if it's possible to have uranium deposits so near to the ocean.

There are about 3 tonnes of uranium in every cubic kilometre of seawater, but in the general circulation there is no mechanism to concentrate the uranium, except perhaps low-level adsorption on manganese nodules in some parts of the sea bed. To concentrate the uranium you need some mechanism to transport it, and some other mechanism to make it precipitate. Both are pH-redox controlled, requiring substantial reducing conditions. The nearest plausible mechanism I can think of is a high concentration of uranium in groundwater, such as in the Aktau province of Kazakhstan, adjacent to the Caspian Sea. At present the Caspian is too oxygenated, and is likely to remain that way because of inflow from the Volga, but if climate change alters the rainfall-runoff relationship then that inflow to the Caspian would be reduced. Conceivably, it wouldn't take too much more pollution and reduced river inflow to make the deeper parts of the northern Caspian more reducing. Then maybe you could get uranium deposition at the groundwater-lakewater interface.


How are Earth's rotational changes due to large earthquakes calculated? According to NASA (and many other sources), Japan Quake May Have Shortened Earth Days, Moved Axis and in the answers to the question here What geophysical events can (temporarily) increase the Earth's rate of rotation?, that major earthquakes result in a slight shift in the length of the day, from NASA:

  calculations indicate that by changing the distribution of Earth's mass, the Japanese earthquake should have caused Earth to rotate a bit faster, shortening the length of the day by about 1.8 microseconds (a microsecond is one millionth of a second).

Past great earthquakes, such as the 8.8 in Chile in 2010 and the 9.1 Sumatra in 2004 have caused similar rotational 'wobbles'.  The NASA article states that the earthquake's magnitude, location and dynamics result in the orbital 'wobbles'.

How are Earth's rotational changes due to large earthquake calculated, and especially distinguished from oceanic and atmospheric effects?

Earthquakes, specially those at subduction zones, result in redistribution of mass (as one plate slides on top of the other). This change in distribution of mass causes changes in gravitational field that can be measured by satellites such as GRACE.

Now angular momentum is conserved. If we know the change in mass then we can calculate the change in moment of inertia and thus the change in the angular velocity.


What would the average temperature be if there were no greenhouse effect from water vapor? CO2, methane and other gases contribute to the greenhouse effect.

But most of the greenhouse effect is caused by water vapour in the atmosphere. There is always a lot average moisture present, but it is limited by precipitation. It causes most of the total greenhouse effect, without it, the surface would just radiate heat away from Earth.

If there were no moisture in the air, that should make the average surface temperature much lower. (It is not physically possible, of course.)

What would that temperature be?

As was pointed out in the question comments, there is no way to know what Earth's average temperature would do without water vapor in the atmosphere.  However, we can estimate the effects of the water, and remove them.  What follows is a rough approximation.

If there were no greenhouse effect, the average temperature of Earth would be about 0F (-18C) instead of 59F (15C). (https://www.giss.nasa.gov/research/briefs/ma_01/)

Water vapor roughly doubles the warming caused by carbon dioxide. (https://www.nasa.gov/topics/earth/features/vapor_warming.html)

Therefore I estimate that without water vapor, the average temperature would be about 30F (-1C).


Simplest formula of a calcium phosphate mineral? I had a homework question:

  Given the formula:

  $$\ce{Ca}_x\ce{(PO4)}_y\ce{OH}$$

  Find the lowest possible values of $x,y$ and state (look up) the mineral name.

Based on the anion charges I know, and trying to balance them, I would expect

$$\ce{2Ca^{2+} + (PO_{4})^{3-} + OH^{-} -> Ca_{2}(PO_{4})OH}$$

But I couldn't find a mineral with this formula, and the closest I could find was hydroxyapatite with the formula:

$$\ce{Ca_{5}(PO_{4})_{3}OH}$$

which is still balanced based on the charges I had initially used, but isn't the same. Can anyone explain why this mineral doesn't form as I had expected?

Yes, you are correct in your calculation. However, the most common hydrated calcium phosphate in nature is indeed hydroxyapatite. Note that industrially, there are several other calcium phosphates (see link, note that none of them is your calcium phosphate) The reason that it forms instead of the "simpler" mineral is that it is more stable thermodynamically. I'm not certain about the exact reasons for that.

Apatite is so stable that in nature and rocks, almost whenever you have phosphate, it binds with calcium to form apatite. The only way to not have apatite is to not have calcium, not have phosphate, or have some really exotic system that suppresses its formation.

This is also known experimentally. In experiments that simulated calcium phosphate systems as early as the 60s, it was hard to crystallise anything but apatite.


Is there any video evidence of animals raining from the sky? I image most people have heard stories of fish, frogs, or other small animals raining from the sky.  I found quite a few articles on line with many instances of such occurrences but they were mostly from historic times and often from second or third person accounts.  Then I came across this article from National Geographic which mentions two more recent accounts.  The first they mention is a fish drizzle which occurred in Lajamanu, Australia in 2010 and the second is a frog fall which occurred in Odzaci, Serbia in 2005.  Both of these events seemed to be backed up by meteorological claims of either tornadoes in the Australia case or waterspouts in the Serbia case.

What I'm curious about is:

If this is somewhat relatively common, with the abundance of video cameras
now, why hasn't something like this been recorded.  I've had no luck
finding anything on line.
Why does it seem like it's always one type of animal?

Brian Dunning already went into this extensively in episode 4170 of Skeptoid: It's Raining Frogs and Fish

  In 1901, a rainstorm in Minneapolis, MN produced frogs to a depth of several inches, so that travel was said to be impossible. Fish famously fell from the sky in Singapore in 1861, and again over a century later in Ipswich, Australia in 1989. Residents in southern Greece awoke one morning in 1981 to find that a shower of frogs had blanketed their village. Golfers in Bournemouth, England found herring all over their course after a light shower in 1948. In 1901, a huge rainstorm doused Tiller's Ferry, SC, and covered it with catfish as well as water, to the point that fish were found swimming between the rows of a cotton field. In 1953, Leicester, MA was hit with a downpour of frogs and toads of all sorts, even choking the rain gutters on the roofs of houses. The stories go on and on: More frogs in Missouri in 1873 and Sheffield, England in 1995, and more fish in Alabama in 1956.

From everything he read, waterspouts seem unlikely:

  Not once in a single case of several dozen that I read was there ever a report of a tornado or waterspout in the vicinity, or even at all, no matter how far away. I conclude that waterspouts have no connection, either hypothetical or evidentiary, to the phenomenon of frogs, fish, or any other animals, falling out of the sky.

For frogs it seem to be coincidences of bad weather and frog migration.Well, not really coincidence: they probably migrate more (often) when it's wet.
And for fish:

  You don't find mass migrations of fish crossing overland, do you? Well, maybe not mass migrations, but believe it or not, there are fish species that occasionally take to the ground in search of better waters. There are many species of "walking fish" in the world.

The main reason that they did not fall from the sky is simple:

  Drop a fish off a building, and that's a dead fish

That's why you won't find actual videos.

Brian concludes:

  Go back and read any story you've ever seen about frogs and fish falling from the sky, this time allowing for the possibility that the animals were already naturally on the ground when the witnesses first discovered them. Allow for the possibility that some elements of the report, like the falling part, could be based originally on witness conjecture or assumption.

Which is more or less what Stephan also writes in his answer.


What is the status of meteorological data exchange standards? How do the web services exchange meteorological data?

One method is transferring NetCDF and GRIB data and hooking them up to your software.

I read here about the possibility of using WFS and WCS. Here, I read about the proposal of using calls like dataQuery, similar to getCapabilities of WMS servers. I also note that NASA uses JSON output, e.g. for the DCP-30 dataset. In Europe, the INSIPRE committee publishes very complex guidelines . DWD, UK Met office and others recently held a conference on that.

Is there a global standard and what is it? I know the OGC-DWG is working on that since 2009. What are the latest updates?

Addendum (Full forms of Abbreviations)

WMS : Web Mapping Service, a Server that responds with a map image of
a spacific area, or about its ability to serve.
WCS : Web Coverage
Service, similar to above, but serves gridded data, e.g. temperature,
covering a continuous area.
WFS : Web Feature Service, similar to
WCS, but serves features on an around a given point (or points) -
thus discreet, not continuous.
DCP : Downsized Climate Projection, a
low resolution dataset projecting the future global climate. 30
indicates 30 years in future and so on.
OGC : Open Geospatial
Consortium , a non profit organization standardizing geospatial data.
DWG : Domain working Group, a workgroup in OGC specializing in a
particular field, one in this case for standardizing meteorological
and oceanographic data exchange.

I don't think there can be "the single standard" for a range of technical and organisational reasons.

Probably the biggest thing to note is that different formats serve different purposes. For example, comparing WFS, WMS and WCS. WFS is a feature concept - the sort of data you might get as observations from a set of irregularly distributed sites (e.g. automated weather stations at airports).  WMS is a picture (e.g. PNG image or JPEG) - the sort of data you might get as an IR image from a satellite, or some particular styling of a gridded forecast such as wave heights (turned into colour bands). WCS is a coverage (so no particular visual representation) - in the gridded forecast of wave heights example, it would be a floating point number of the height (average, peak, whatever is defined) for that "grid area".

Note that these OGC protocols weren't really designed to handle multiple parameters at a time, nor were they designed to handle data represented in more than two dimensions at a time (e.g. you can ask for an elevation and a time, but you can't ask for multiple elevations and times in a single output without some custom (i.e. not standard) approach.

So you'll see observations and forecasts in specialist formats (like BUFR, GRIB and NetCDF). Those formats can be transmitted (e.g. raw files), but they're also able to be subsetted. THREDDS is a particularly good tool for this purpose. Note that GRIB and NetCDF have some overlap in scope. There are also multiple versions of GRIB, and there are non-standard parts to GRIB (e.g. forecast centre specific tables). Adding new standards doesn't help.

Changing formats isn't easy - there are often massive collections of data and complex tools (like numerical forecasting models) that need to be updated or reworked to handle new formats. Not everyone can do that (e.g. for financial reasons, or organisational expertise reasons, or some programmatic reason like there is already another upgrade going on) at the same time.

So you can expect to need to handle lots of formats for a long time to come.

If you have options and need to exchange data, I'd start with NetCDF, mainly because it has a lot of pretty good tools.


Does the feel of temperature change, when you're in two different places I'm from Baltimore Maryland. And our summers can be very intense sometimes a heatwave could put us at 100 degrees and with humidity it could feel like 110 degrees. Now, I have friends from the U.S. Territory of Guam with the same temp or even lower. And some of them say its hotter there and some say it's hotter here. Where's the science to deal with this.

Opinions are often very subjective and can't make accurate assessments, especially in matters like this where the two things being compared are vey much alike. The only objective way of doing it is to have accurate temperature and humidity readings over a period of several years for both places. Someone has probably already done that, but I don't know where the best place would be to see their results. Being a relatively small island, Guam should have a marine climate, which is less extreme than continental climates. We have a marine climate here in Britain, and though we often complain about the weather it is less extreme than weather in Europe. A marine climate gives us cooler summers and milder winters, as the temperature is moderated by the sea, which also gives us a damp climate. Guam is nearer the equator than Maryland and is rainforest country, so I would expect it to be fairly humid but not so extreme and variable as Maryland.


Land to ocean ratio in jurassic era In todays world, 71% of the surface is covered in water. But was this always the case, far prehistoric times?
Id guess you can estimate pretty precisely where the prehistoric oceans were based on sediments, but i cant find a single answer to the question - even though you can see detailed maps of Laurassia, Gondwana and Pangaea.

Britannica says:

  ... because of the significant tectonic activity occurring around the world, it is not clear which of these local changes can be correlated
  to global sea level change. Because there is no evidence of major
  glaciations in the Jurassic, any global sea level change must have
  been due to thermal expansion of seawater or plate tectonic activity
  (such as major activity at seafloor ridges). Some geologists have
  proposed that average sea levels increased from Early to Late Jurassic time.

Notice, that we have no information about the change of the mass of water from Jurassic till now.

Even the articles https://www.sciencedirect.com/science/article/pii/S2095383615000267 that shows, how the sea level changed, touch only relative changes in the sea level. As we don't know the statistics for depths and heights for these times, we can guess, that the ocean/land area ratio was greater than now, but the guess is very wild. Any number of percents could be only a sheer speculation.


Meaning of Coupling in Modelling The Community Earth System Model (CESM) is described as a

  fully-coupled, global climate model that provides state-of-the-art
  computer simulations of the Earth's past, present, and future climate
  states

I've come across "coupling" and "coupled model" many times but still have trouble with the term. What does "coupling" and "fully coupled" mean? Does refer to the physics or numerical aspects?

In Earth-system models, the term "coupling" is often used in two ways.  The first is "offline" coupling, where output from one model is passed to another model for computation of some variable.  The second is "online" coupling, where the feedbacks are allowed to pass between the two models.  Online coupling is synonymous with "fully coupled".

A good example is when wildfires are modeled with coupled meteorology-chemistry models.  Historically, the aerosol emissions from the fire would be modeled by a separate chemistry model that only used the meteorology model as an input (e.g. offline coupling).  However, now you can fully couple (e.g. online coupling) the chemistry with the weather such that the heat and aerosol released from the fire perturbs the meteorological/radiation calculations in the next iterated time step.


Is it possible to prevent high magnitude earthquakes by induced earthquakes? As we know, earthquakes can be induced by human activities. Can we induce earthquakes around faults regularly so that the energy releases regularly, and hence prevent high magnitude earthquakes by stopping large amount of energy releases at one time?

The idea of trying to limit energy released by earthquakes and the damage that may result via the use of controlled smaller blast induced quakes is an interesting idea.

One of the problems with this is that we don't know enough about the snags along faults that cause stresses to accumulate during the normal movements along a fault. We also don't know enough about fault surfaces (shapes, undulations and friction factors) of individual fault surfaces. The other thing we don't know is where the snags are located on fault surfaces: along and down the fault surface.

The strength of snags is one factor which determines how much energy accumulates and is eventually released suddenly when the snag fails.

The other factor is the type of movement at the fault zone. Do the fault surfaces slide past one another laterally, does one sub-duct beneath the other, or are they spreading apart.

With some faults, wedge failures may produce large blocks that act a snags. Other snags can be very hard, strong protrusions of rock firmly cemented in the fault surface. Corrugations can also act as snags.

Another possible mechanism by which quakes can happen, particularly in the subduction zone is that part of the fault surface that is riding over a subduction zone might hang with no support, due to undulations or point support. If the overhanging rock is not strong enough it can fail and drop. The impact of the dropping block then causes an earthquake.

The ways in which earthquakes occur are varied and sometimes complex.


What is the age of the Gamburtsev Mountains? The mechanism for the formation of the Gamburtsev Subglacial Mountains in East Antarctica seems to be a combination of old volcanism and Cretaceous rifting (Ferraccioli et al., 2011). While the modeling results seem to match the available geophysical observations, have there been any dating studies that looked at age through the analysis of rock samples?

The Lamont-Doherty Earth Observatory describes the Gamburtsev Subglacial Mountains (GSM) as being like:

  opening the door of an Egyptian pyramid and finding an astronaut inside.  There is no good reason for an astronaut to be inside an Egyptian pyramid just as there is no good reason for a major mountain range in the middle of East Antarctica.

Despite being buried under a considerable amount of ice and observed to have had slow erosion rates since at least the Permian (Cox et al. 2010), accessible detrital material has been determined to have been deposited as fluvio-deltaic deposits in Prydz Bay (Cox et al. 2010; Flierdt et al. 2008).

$\ce{U-Pb}$ dating of dertital zircons and $\ce{^40Ar/^39Ar}%edit$ dating of detrital hornblendes age them as ~530 Ma and ~519 Ma respectively, with no evidence of any yonger volcanic contributions (Flierdt et al. 2008).  These dates led Cox et al. (2010) to postulate that the GSM formed during the Pan-African Orogeny.

Veevers and Saeed (2013) suggest that detrital zircons found in the Ellsworth Land–Antarctic Peninsula–Weddell Sea–Dronning Maud Land sector of ages 1.4-1.7 Ga, 1.9-2.1 Ga and 3-3.35 Ga possibly have their provenance from the GSM.

In summary, in the absence of direct measurements of GSM petrology, detrital material from pre-glacial erosion has suggested that the youngest tectonothermal evidence is for a Cambrian age of the GSM.

References

Cox et al. 2010 Extremely low long-term erosion rates around the Gamburtsev
Mountains in interior East Antarctica, Geophysical Research Letters

Flierdt et al. 2008 Evidence against a young volcanic origin of the Gamburtsev Subglacial Mountains, Antarctica Geophysical Research Letters

Veevers and Saeed, 2013 Age and composition of Antarctic sub-glacial bedrock reflected by detrital zircons, erratics, and recycled microfossils in the Ellsworth Land–Antarctic Peninsula–Weddell Sea–Dronning Maud Land sector (240°E–0°–015°E) Gondwana Research


What is the earliest tropical cyclone in record? The question is simple: what is the earliest tropical cyclone (hurricane or typhoon) described in the historical record?

Japanese legend claims that typhoons twice save Japan from attempted invasions by Kublai Khan, once in 1274 and seven years later 1281. These divine winds ("kamikaze") are mixed in Japanese mysticism and are perhaps apocryphal.

The Chinese were meticulous record keepers and recorded disasters of all kinds. Liu et al. scoured written Chinese history for records of typhoons. T earliest unequivocal report of a typhoon they found was in the “Official History” of the Song Dynasty:

  In the tenth lunar month of the eighth year of the reign of Kai Bao [i.e., November AD 975], the city of Guangzhou was struck by a jufeng [typhoon]. Two zhang [a traditional Chinese measurement unit that equals about three meters] of rain fell within a day and night. The sea rose. Some boats were blown away and lost.

The Mayans were also meticulous record keepers and their homeland, the Yucatan, suffers a high rate of hurricane landfalls. There are two problems, however. One is that the Spanish conquistadors and the priests they brought with them were extremely meticulous about hunting down and destroying Mesoamerican writings. The other issue is that those writings were inextricably interwoven with the bizarre religion of the Mayans.

The Popol Vuh, written by the Dominican priest Francisco Ximénez around the turn of the 18th century, records some aspects of Mayan mythologies. The translations are a bit challenging. The Popol Vuh describes the ball court (which was very important to the Mayans), describes many of the Mayan deities, describes the Mayan creation story. One translation of this creation story follows.

  Heart of Sky arrived here with Sovereign and Quetzal Serpent in the darkness, in the night. He spoke with Sovereign and Quetzal Serpent. They talked together then. They thought and they pondered. They reached an accord, bringing together their words and their thoughts. Then they gave birth, heartening one another. Beneath the light, they gave birth to humanity. Then they arranged for the germination and creation of the trees and the bushes, the germination of all life and creation, in the darkness and in the night, by Heart of Sky, who is called Huracan. First is Thunderbolt Huracan, second is Youngest Thunderbolt, and third is Sudden Thunderbolt. These three together are Heart of Sky.

Note the name of the Heart of Sky, Hurucan. Others translate that name as Juracán, yet others, Hurricane. That Mayan god may well be the source of the word "hurricane". Then again, that god might have been given that name based on an already existing word. Similar sounding words were used throughout Mesoamaerica and the Caribbean to describe what we now call hurricanes, and also to describe the god of the sky.

Heart of Sky was a blood-thirsty god (many of the Mayan gods were blood-thirsty.) Two surviving Mayan stelae (carved stone monuments) depict a destructive event dated on one of the stelae as having occurred on June 3, 544 that depict whirling winds and pools of blood. That might well have been a hurricane. Then again, it might have been the ascension of a powerful king who aligned himself with Heart of Sky.

Stephen Houston, "Hurricane!", http://www.mesoweb.com/articles/houston/hurricane.pdf

Kam‐biu Liu, Caiming Shen, and Kin‐sheun Louie. "A 1,000‐Year History of Typhoon Landfalls in Guangdong, Southern China, Reconstructed from Chinese Historical Documentary Records." Annals of the Association of American Geographers 91.3 (2001): 453-464.


Are volcanoes formed from earthquakes? I know that some earthquakes are caused by volcanoes and that some earthquakes can trigger volcanic eruptions close to where the earthquake is.

But what if a great earthquake(8.0 or above) occurs and causes there to be a fault line? If more earthquakes of any magnitude occur in the same area the fault line would get deeper and deeper until the mantle is exposed. Then the pressure in the mantle is released and lava starts flowing out of the fault line. Over years this would form a ridge whether that is underwater or inland.

But are any volcanoes actually formed from earthquakes?

From what you wrote, you are assuming several things:

The mantle is made up of molten rock,
Faults can go deep enough to reach the mantle.

Both are not exactly accurate.

  lava starts flowing out

The mantle of the Earth is mostly solid. It has areas where it's partially molten, and that's where the lava in some volcanic eruptions comes from. But mostly, it's solid. Even if you did get a fault line deep down there, it would not release any lava because it's not there to begin with.

  ...fault line would get deeper and deeper...

Faults can not go too deep. As you go deeper in the earth, rocks stop being brittle and become ductile. They don't break, the flow. Think of chocolate - if you take out chocolate from the freezer you can shatter it to pieces. If you put it in the sun, it bends instead of breaking. Same thing with rocks.

  I know that some earthquakes are caused by volcanoes

The movement of molten rock (magma) underground is the cause of volcanos and earthquakes associated with volcanos. Note that these kinds of earthquakes are usually very weak and their destructive power is very small, at least compared to the actual volcanic eruption.

  some earthquakes can trigger volcanic eruptions

Not really - only if it's a big earthquake you had molten rock around. Which brings me to the next point...

Having said that - actually most of the volcanic eruptions on Earth in fault lines where decompression of mantle occurs. These are the mid ocean ridges that look like this:

Source: Pearson Prentice Hall (?)

And are located here:

Source: USGS

In the case of mid ocean ridges, you basically have mantle rock melting because of decompression, and this is occurring at fault lines with earthquakes. However, the location where all of this is known and it's all pretty expected. It's also in mid ocean ridges (except Iceland) so the danger to us humans is negligible.

Other than those cases, the chances of having a surprise magnitude 8 earthquake with a volcano erupting after it are very low.


Why is the concentration of highly siderophile elements so uniform in the mantle? The plot above is about the concentration of siderophile elements in the terrestrial mantle.
From the logarithmic plot, we can deduce that the concentration of highly siderophile elements is quite uniform.
Why ?

First, note that this plot is normalized to a reference, here the composition of CI chondrites (your version lacks the Y axis label, it's figure 2.1 from Walker 2016). So if the concentration of highly siderophile elements (HSE) seems uniform, it's partly because it is a relative concentration, not an absolute one. If you look at the raw data (Table 1.1), you'll see that the absolute concentrations vary by more than one order of magnitude depending on the element (from 0.35 ppb for Re to 7.6 for Pt). Also, as you noted the scale is logarithmic, which tends to flatten the differences.

Now, why do HSE have the same relative abundance in the mantle compared to chondrites? Because elements from the same family show the same behavior—actually it's why they form a family in the first place. HSE all are, well, highly siderophile, so they all went into the core during the core segregation, and now they all are highly depleted in the mantle compared to chondrites.

Note that despite this depletion, HSE are actually still too abundant in the mantle: there should be even less of them. Geochemists have long debated this issue. This nice paper (Walker 2009) reviews the different hypotheses that might explain this HSE "enrichment": incomplete core segregation, lower metal/silicate partitioning, late accretion of chondritic material after core segregation...


What is meant by controlling and reacting factor? I'm interested in issues related to Global warming and therefore started to read about it from this website --> Link

As I was reading I got stuck in the third paragraph of What are Greenhouse gas ? section. It says

  Secondly, CO2 tends to remain in the atmosphere for a very long time (time scales in the hundreds of years). Water vapor, on the other hand, can easily condense or evaporate, depending on local conditions. Water vapor levels therefore tend to adjust quickly to the prevailing conditions, such that the energy flows from the Sun and re-radiation from the Earth achieve a balance. CO2 tends to remain fairly constant and therefore behave as a controlling factor, rather than a reacting factor. More CO2 means that the balance occurs at higher temperatures and water vapor levels.

I do not understand the whole paragraph and also specially the controlling and reacting factor. Please help .Thankyou in advance.

A controlling factor is a factor that acts as a cause for others.  A reactive factor is rather the consequence: that which reacts to the controlling factor.

For example, the Sun is certainly a controlling factor.  Nothing we do influences what happens on the Sun, but what happens on the Sun certainly influences us very strongly.  Fortunately, its total power output is quite stable so as far as climate is concerned, we don't need to worry about it too much as far as the next couple of million years are concerned (although eventually, in hundreds of millions to billions of years, increasing power from the Sun will render the Earth uninhabitable).

CO₂ is both a controlling and a reactive factor.  We add CO₂ to the atmosphere, so the CO₂ concentration reacts to our emissions (reactive factor).  But CO₂ levels are also a cause.  If you were to make a simple climate model, you would put in the CO₂ concentration as a fixed value or perhaps an increasing value as a function of time: in such a model, it would be a boundary condition.  If you instead made a model of a single factory or car and modelled how changes in the fuel cycle would affect CO₂ emissions, then those would instead be a reactive factor.  It all depends on the context.

For H₂O, however, it makes no sense to put in a fixed version as a boundary condition.  Its concentration varies rapidly on short timescales: today may be dry and tomorrow a wet airmass may get in.  Of course, physically, H₂O causes even more of the greenhouse effect than CO₂, but the increase of H₂O is not what is causing anthropogenic climate change; if anything, an increase in H₂O is one of the effects.

So, think of it as a system: you add CO₂ (cause), many things happen, including an increase in H₂O in some places (effect).  The cause is the controlling factor.  The effect is the reactive factor, even though physically, both CO₂ and H₂O are strongly contributing greenhouse gases.


Yes, they are. It's not the sills or dykes that "jump", it's the magma. Depending on the various parameters such as viscosity, stress, temperature, pressure, and local conditions and availability of joints, the magma will flow either as a sill or a dyke (or some other intrusive body).

Notice that your two sketches are basically the same thing - it's just the in one case the sill is the dominant structure whereas the dyke is more dominant in the second sketch.

The flow regime can definitely change from a "dyke" to a "sill" and vice versa. Here's a schematic diagram:

 (source: USGS)

I also had a quick Internet search and came up with this great example from nature:

You can read more about it at Geotripper blog by Garry Hayes.


Why are minerals found in "large" quantities and not scattered throughout the earth as individual atoms? Heavier elements are created in stars.  After stars die they scatter these heavier elements throughout the universe.  These elements eventually gather to form planets.  But why do we find "chunks" of gold, silver, etc. and not scattered atoms throughout the earth.  In other words, how do the atoms of these elements come together to form chunks of the same element involving billions and billions of atoms?

First of all, Earth is not a random assortment of atoms. While it probably formed along like that in the beginning, somewhere along the way it differentiated into distinct core, mantle and crust, which are not chemically the same. That's a story for another question though, and there is an excellent answer to it on this site.

Back to your question, Why are there ore deposits?

So in addition to the Wikipedia quote given by farrenthorpe, here are some more (hopefully easily digestible) points:

Chemical elements posses differing properties. Even if you take a random mix of all elements in the periodic table, each and every one of them will have different properties.

Imagine a homogenous pile of gold and salt. Now, start pouring water over it, let it flow to a specific place and wait until the water dries and evaporates. Exploiting the different chemical properties of Au and NaCl, you've created two "ore deposits", one of gold and the other of salt. In the Earth, there are a multitude of processes resulting from all kinds of combinations of temperature, pressure, fluid chemistry, magma processes and more, that facilitate selective concentration of certain elements over other elements.

If you are interested, here are some answers regarding the deposit formation of gold and rare earth elements.


Is it possible to convert carbon dioxide into a solid at low cost? Is it possible to reduce the level of carbon dioxide (CO2) in the atmosphere by converting it into a solid, thus reducing the level of greenhouse gases?

This article in the press cites CO2 has been converted  into Carbon at relative low temperature.

The research team led by RMIT University in Melbourne, Australia, have developed a new technique that can efficiently convert CO2 from a gas into solid particles of carbon.

To date, CO2 has only been converted into a solid at extremely high temperatures, making it industrially unviable.
By using liquid metals as a catalyst, we’ve shown it’s possible to turn the gas back into carbon at room temperature, in a process that’s efficient and scalable.
While more research needs to be done, it’s a crucial first step to delivering solid storage of carbon.

The study is published in Nature Communications. They used cerium oxyde as catalyst to reduce the temperature of the reaction.

... which facilitates the electrochemical reduction of CO2 to layered
solid carbonaceous species, at a low onset potential of −310 mV vs
CO2/C

All these CO2 sequestration issues are under investigation and will be implemented in the coming years by energy companies.

Esrafilzadeh, D., Zavabeti, A., Jalili, R. et al. (2019): "Room temperature CO2 reduction to solid carbon species on liquid metals featuring atomically thin ceria interfaces." Nat Commun 10, 865. https://doi.org/10.1038/s41467-019-08824-8


Magnetic rocks no magnetite I got some sand out of a river bed and moved a magnet through it. Some of the particles I picked up were definitely small crystals of magnetite, but a lot of others were small, round brown rocks that did not look like magnetite at all.

I thought the only thing commonly found in country rock that was magnetic was magnetite. Does this mean the small brown rocks have magnetite crystals somewhere inside of them?

Broadly speaking you are correct on both counts: magnetite is the most magnetic mineral, and it can oxidize, first to the matastable phase maghemite, and ultimately to the fully oxidized haemetite. This process can yield grains with a zoned appearance, both in hand specimen and more clearly under the microscope, with brown on the outside and residual black magnetite in the core. Maghemite, as the name suggests, is also magnetic. There are several other moderately to strongly magnetic minerals, closely related to magnetite, and with a similar molecular structure. For example ilmenite, a very common mineral that sometimes occurs with magnetite, is the double oxide of iron and titanium. Tantalite / columbite, or manganotantalite $(Fe, Mn)(Ta, Nb)_2O_6$ is not as magnetic as magnetite but may still be magnetic enough to swing a compass needle. It looks identical to magnetite, but can have a slightly purplish brown sheen. Similarly, chromite, the double oxide of chromium and iron, can be very magnetic, but I don't recall ever seeing anything other than black chromite. Franklinite, which is reddish purple, is another mineral of the magnetite group, and is a complex oxide of zinc,iron and manganese. There are several other weakly magnetic minerals of the magnetite group, most of which are quite rare. As a rough rule of thumb, the more oxidized or the more iron is replaced with some other metal, the less magnetic it is.

PS, if you ever find metallic looking sand that is magnetic, stake a claim! Platinum is also weakly magnetic.


How did the intensity of Earth's magnetic field change through geological time? Looking at the wikipedia article on the Earth's magnetic field, I see that its strength varies through time. How did Earth's magnetic field change throughout its history, from the beginning of the Archean period (~4 billions years ago) to today?

My current attempt

All I found so far is this graph from wikipedia (which is on a too short time scale) and this kind of text (not a science paper) reporting an estimate for a given time point (3.2 billions years ago) reporting a field of about 25 microTeslas.

The Earth's initial accretion was about 4.5 billion years ago, and there is good Hf-W isotopic evidence that an iron core started to form within about 10 M years, and may have been largely complete within 30 M years. However, the Earth's dynamo, which is driven by isotopic heating and core rotation/convection, didn't switch on strait away. It must have built up over hundreds of millions of years, possibly kick-started by a the magnetic field of a stronger solar wind at that time. The evidence from 3.5 Bn year old dacites suggest that the magnetic field at that time was only 30 to 50% of the current value. There is no magnetic data for 4.4 to 3.5 Bn years, (the time period you are interested in), but current models lean towards lower rather than higher values. There appears to be no mechanism for strong magnetism in the early Earth. Geomagnetic evidence from about 2.5 Bn years ago seems to indicate that the Earths magnetism was more stable then than now, with few if any peaks of high or low magnetism. Probably the Earth's early magnetic field will always be imprecisely known because nearly all the early rocks have been 'cooked' in such a way as to extinguish the early magnetic evidence.


Is there any correlation between Australia's uranium deposits and the unique animals? Australian animals are very different than the rest of the world. I wonder if the radiation of Australia's Uranium deposits have anything to do with why animals uniquely evolved? For instance, marsupials have three vaginas and platypus are one of the only mammals that lay eggs.

If not Uranium what makes them so different?

https://list25.com/25-outrageous-kangaroo-facts-to-keep-your-mind-hopping/

No. The reason for Australia’s unique evolution is that it was relatively isolated from the rest of the world.

Australia isn’t too radioactive either. The fact that it has more uranium deposits than other countries is that it’s huge.


Can anyone recommend a good college level meteorology textbook? I am trying to learn meteorology through self-study.  I have found quite a few lectures on YouTube, but they tend to be for non-scientists.

I have a strong engineering and physics background and am looking for a text that presumes you can think through thermodynamics.  Many of the ones I can see a sample of online at Amazon sort of hide the real depth to help the reader not need to understand that sort of background.

Does anyone know of a good textbook that one would use at the undergrad level if you were trying to major in meterology, as opposed to a survey type course?

So meteorology is unique in that it changes depending on the scale and process. For a general taste of meteorology, I suggest Wallace and Hobbes. You may note similarities among most of my recommendations, but that may just be a bias from my personal experience.

One of the most problematic elements of meteorology is atmospheric dynamics. A common resource is Holton's book.

For thermodynamics, a common book used in my undergraduate studies was Bohren and Albrecht. Although you may have experience in thermodynamics, atmospheric thermodynamics is often treated differently, with different quantities. You may recognize some of the equations used, but the variables derived are used throughout atmospheric science.

For mesoscale (medium-sized) meteorology, Markowski and Richardson have a good book.

For atmospheric radiation, Petty has a basic book.

In my synoptic meteorology class, we were assigned this book, but I don't recall ever really using it. This book looks more comprehensive (in fact, I might get it for myself).

For boundary layer meteorology, try Roland Stull's book.


First to Sail the Jet Stream Around the World My questions are related to a scenario discussed on Earth Science: A huge (heavier-than-air) kite sailing in and out of the jet streams.
The kite:

The scenario:

The assumptions:

Such an airship exists and there is a person aboard, with an oxygen mask.
The person is thermally insulated to keep the heat inside.
The jet streams are at an altitude around 9–12 km (30,000–39,000 ft) .

The Questions:

Can a kite like the one in the picture be built to hold a person?
Does the human body require pressurization as well as oxygen and insulation? ANSWER
Is it possible using the jet stream systems to go around the world?
Can the kite fly at speeds around 80-150 km/h related to the ground?
Can it sustain a free fall from its cruising altitude around 9–12 km so that the pilot can land maybe using a parachute?

Possible Solutions:
Launch Considering the altitude is up around 9–12 km then air would be thinner the size of it will have to be much larger to compensate. Use a cable and boat to lift the UltraKite into the Jet Stream. At preferred altitude cable then can be mechanically released from connected drag section of the kite. A drone or balloons could replace boat and then dropped. Maybe the person could ride in the drag section.
Long Term Altitude with Ultralights Gliders on Record.
The current 15460-meter glider height record was made with pressurized suits. But it is only 500 meters higher than Harris' previous record from 1986, which was done with just an oxygen mask. – Martin Argerami in a comment in Turbulent Jet Streams on Ultralights
As commented by @Jan Hudec: This is supposed to be a kite, but instead of being fixed to the ground as normal kite, it would have just a cabin with a braking parachute flying below the jet stream and the kite flying in the jet stream, so the whole thing would move at some speed between the slow speed of the wind at low altitude and the high speed of the jet stream.

As your diagram shows, the jet stream actually has two circulating components: one is "around the earth" (which is why the transatlantic crossing is so much faster going East than going West), while the second is more like a vortex, with a circulating flow "around" the main direction. This circulating flow is vertical in two places: North of the jet stream it is downwards, and South of the jet stream it is upwards.

That makes for an "almost endless" lift - and you could in principle hover there. It would be very uncomfortable, as the winds in that region are quite strong and turbulent.

It reminds me of something I have seen near the beach: when the wind comes in from the sea, it is lifted up by the dunes; and people with hanggliders can jump off the dune, catch the wind, and literally stay in the air as long as they want (and as long as the wind stays up). If they "miss" the updraft when they first jump off the top of the dune, they are on the beach within five seconds; if they succeed, they fly for an hour or more. Right alongside the sea gulls who discovered the same trick many years ago. Example source:

I don't think you can prevent yourself from traveling around the globe when you do this - in other words, you would have to be content to travel in a mostly Easterly direction. I suspect (but do not know for sure) that the currents are too strong to allow you to traverse in the Westerly direction by ducking in and out of the Jet.


Travel Times for Seismic Wave Types - Why reflected t-x plot curves I do not understand how the reflected wave in a seismic survey has a steepening slope (slows down)  Please bear with me as I lay out my thoughts because I feel like I can grasp all of this except this one thing and I am struggling to reconcile it.

If a wave source produces waves at a point, as in a seismic geophysical survey there are 3 types of waves which we consider. There is the direct wave, the reflected wave, and the refracted wave. The reflected wave is never a first arrival. The refracted wave is first lagging behind the direct wave before reaching it at the crossover point and overtaking it. This makes sense because the refracted wave has a higher speed but it does not register its propagation at the first geophone until a certain time has elapsed since the initial pulse at the wave source; and the direct wave has been traveling from the source all the while.

On an arrival time plot where time is the vertical y-axis and where distance is the horizontal x-axis we see that the refracted wave has an unphysical beginning at the y intercept and the direct wave begins normally from the origin. Where the intersect the refracted wave overtakes the direct wave. On this type of diagram the smaller the slope, the faster the wave. The slope of the refracted wave is 1/v2 and the slope of the direct wave is simply 1/v1.

What I do not understand is why the reflected wave has a hyperbolic or curved trajectory on this plot. The slope steepens as it asymptotically approaches the direct wave. It makes sense that over long distances that the direct wave and the reflected wave should merge to almost being indistinguishable, but how is it possible that the reflected wave plot as a steepening slope i.e. is slowing down?  The reflected wave travels less  surface distance per unit time the smaller its angle of incidence ( meaning closer to the source) because it is more vertical than horizontal. Over time it becomes more horizontal and therefore more like a direct wave which takes a shorter and quicker path across the surface.  What am I missing? Why does the reflection plot curve as it does?

This is conceptually relatively simple if you look at where the reflection (and refraction) happen, and in fact you have articulated the key concept in your question:

  The reflected wave ...Over time it becomes more horizontal and therefore more like a direct wave which takes a shorter and quicker path across the surface.

This is absolutely correct. So if you are close to the seismic source (distance a, where a is small), the direct wave is quickest, as the reflected wave has to first travel down to the boundary before being reflected back. It travels a little over 2b, where b is the depth of the boundary layer. That "little over" depends on the angle, which is related to the distance a.

As an example, look at the image below, from this presentation on reflected, refracted and diffracted waves. The 2nd of the reflected waves is not much larger than the first, however the direct wave has travelled 4 times as far.

If a is much larger than b, then that 2b portion becomes less and less significant, and in fact you can say the distance travelled by the reflected wave tends towards a.

So the graph does not show that the velocity of the wave is slowing down, more that the distance relationship with the angle of reflection tends to an asymptote.


Can an aurora australis be bright enough to illuminate someone's face? If two people are standing next to each other during a polar night, and the brightest possible aurora is occurring overhead, could one person see the other person's face clearly?

If your eyes are fully adapted to the darkness you will be able to see a persons face in the light from the auroras.

By fully adapted to darkness means sitting in a totally dark room for 20+ minutes before you start looking at the night sky. The time you will need to adapt depends on your age.

Any bright light will destroy your night vision. As we get older our night vision will get poorer so young people will see better at night than older people do.


Does subduction of continental crust happen at continental-continental convergent boundaries? What exactly happens at a continental-continental (cc) convergent boundary? I read myself through the web for the last few days and what I came up with is that such a boundary will start as an oceanic-continental (oc) one until the continental plates meet and then a huge falt mountain range like the Himalaja, Alps or Appalacian Mountains is formed.

At this point the sources I found gave me conflicting information. Either no subduction of the continental plate occurs or the continental plate is subducted and melts somewhere around 90 to 140 km down. Apparently rockes which where once part of the continental plate melt and resurface. I also heard that this is an area of ongoing research and it isn't fully understood what happens at cc convergent boundaries. So...

Does no subduction of the continental plate occur?
Does only a bit of subduction of the continental plate occur, as some of it is pulled down into the deep by the rest of the oceanic plate?
Does subduction occur at cc boundaries as on oo and oc boundaries, just slower and in a more quiet manner and cc boundaries usually don't last long enough?

Both of the processes you describe occur; in some cases such as the Himalayas the plates are not subducted and a moving plate, in this case the Indian plate, bulldozes the continental crust ahead of it into a high mountain range. In most cases, such as the Pacific rim for example, subduction is the norm. Where there is subduction there are usually many volcanoes, and this is certainly the case on the Pacific rim. The subducted crust carries rock and water down into the hot mantle, where the friction,heat and water content tend to liquefy it,and it rises to the surface to form volcanoes. To answer your specific question, no. there is no subduction when continental crust meets continental crust, as is the case with the Indian plate meeting the Eurasian plate. Subduction occurs when sea floor spreading forces a plate underneath the lighter and more buoyant continental crust.


Direct measurments of vertical ocean mixing? What kinds of vertical ocean mixing measuring instruments are available? This answer How to measure ocean vertical velocity? tells about the measurement of vertical velocity by ADCP, but they give very noisy vertical velocities and hence almost unusable (at least in my case in the Bay of Bengal in India). Also I am interested in vertical velocities in the upper ocean with mixed layer depths of 30 to 50 meters and this is where many different things happen (e.g. fish, air bubbles etc.). Has anyone done direct vertical speed measurements in the upper ocean? I am unable to find a good lead.

I am assuming you know how to get to mixing from velocity field since you are talking about the noise in the ADCP data. The way people get the small fluctuation and vertical mixing profiles that are highly trusted are with "micro-structure" sampling technique.

Please follow this link for more detail on that technique.
https://earthobservatory.nasa.gov/blogs/fromthefield/2012/10/04/what-is-ocean-microstructure-and-why-study-it/


What causes this striped rock formation? I was hiking a very popular trail in Akamina-Kishnena Provincial Park, and noticed these strange lines in the rocks on top of the mountain:

The lines were parallel to each other, and were on both sides of the trail covering quite a large area of the mountain face. My best guess is that run off from snow melt could cause this, but they look almost like they were raked. The picture was take at around 2,400m in elevation. What causes this?

This is the ridge we were on:

The lines were on the southern face of the mountain.

Frost heaving of the striped variety

As soil freezes it expands, this slowly pushes coarser material outwards, (since no ice forms in the stones just between them). This forms in bands of coarse and fine material like you see in your image.

The effect only becomes more exaggerated as the soil gets more and more sorted, since the finer material holds more water and thus expands more. This also means that even the smallest variation in particle size can get the process started.

A variety of patterns can form; sloped ground is especially prone to this sort of striped frost sorting.

B and C in this image are examples from this paper.

Additional source


Is Mississippi and parts of Alabama, Tennessee, and Kentucky one giant island? Apologies if this is a poorly written question, I'm writing this on my phone.

I noticed that there were a lot of rather long rivers in the region in question, and I began to wonder just how connected they are. I came up with the following path:

Start in Mobile, Alabama, and head north along the Tombigbee River past the Mississippi-Alabama border and into Mississippi. It seems to go through some name changes, but near the Tennessee-Alabama-Mississippi border, it connects with the Tennessee River. Follow the Tennessee River north through Kentucky and Kentucky Lake, where it will eventually meet the Ohio River. That, in turn, feeds into the Mississippi River, which flows back to the Gulf of Mexico.

It seems to me that it makes the region enclosed an island, since it is impossible to reach it without crossing a body of water. But is this significant in any other way? I can tell that not all the rivers flow in the same direction, and it's possible that some portions of the water around it were artificially created, is there anything else that comes as a result of this?

Rhetorical questions:

Does the Erie Canal, which connects the Hudson River with Lake Erie make northern New York, southern Quebec, all of New England, all of New Brunswick, and the non-island parts of Nova Scotia an island?
Does the Chicago Sanitary and Ship Canal make all of the eastern part of the US an island?
Does Russia's Unified Deep Water System make Finland, Scandinavia, and Estonia an island, and mainland Europe another island?

Humankind has learned to connect waterways with canals, locks, and dams. The sudden appearance of those canals, locks, and dams does not suddenly make those now disconnected lands into islands. The connection between the Tombigbee and the Tennessee rivers involves manmade canyons, manmade canals, and several manmade locks and dams.

What about naturally narrow waterway connections? As an extreme example, consider the Committee's Punch Bowl in Alberta, Canada. This little lake has two little outlets. One of the outlets eventually joins the MacKenzie River, which flows into the Arctic Ocean. The other eventually joins the Columbia River, which flows into the Pacific Ocean.

This leads to one last rhetorical question: Does the natural existence of the Committee's Punch Bowl make most of Washington state, most of British Columbia, almost all of the Yukon, and all of mainland Alaska into a very large "island"? Most geographers would say no.


Climate change research and policy How impactful is climate change scientific research on climate change policy?
Are there any statistics which help to visualise the effectiveness of new scientific findings or new technology innovation inducing a change in government policy to help kerb climate change?
Even any papers regarding this will be appreciated.

Climate change is a complicated subject which is difficult to predict with accuracy.   The IPCC's predictions at least since their 3rd report (TAR) appear to be quite good, but good over the first few years or decade and a half vs good for predictions up to 2100 remains inexact and perhaps unclear.

Governments (many not all) do rely in the scientific research of the IPCC both to anticipate coming changes and determine action, but these are difficult questions, as a global effort is required to reduce the greenhouse gas footprint, and individual nations can only control their own policies.   Even if we know, 100%, the future effects of climate change, it would still be a difficult transition away from fossil fuels towards a more climate neutral approach because (If I may borrow the word from Al Gore), fossil fuels are convenient.   They're relatively easy, especially for nations that don't need to import them and they're economically viable.

That's a general outline.   The scientific predictions are important because without them, government leaders would be making policy decisions blind (as opposed to making them based on imperfect projections), and imperfect is better than blind.

There are similar predictions/estimates made across the gamut in political policy decisions.  Estimates are made on future costs of government programs and on tax policies and national debt, or trade.   We're always trying to make mathematical or scientific estimates which, in theory, help leaders make predictions for the future.

Ofcourse, sometimes, you get leaders who don't care, who don't listen to the forecasts, climate change or economic indicators.  Politics is a messy game.

  Are there any statistics which help to visualise the effectiveness of
  new scientific findings or new technology innovation inducing a change
  in government policy to help kerb climate change?

I don't know where you'd find such statistics and I've never seen any.    Statistics can be a tricky business with a long game approach like this one.   There's a lot of factors.


Is this article self-contradictory, or am I missing something? This article:

Anderson, C. H., C. J. Behrens, G. A. Floyd, and M. R. Vining. 1998. “Crater Firn Caves of Mount St. Helens, Washington.” Journal of Cave and Karst Studies 60: 44–50.

discusses, among other things, density of the ice that forms the walls of the fumarolic ice caves in the crater of Mt St Helens.

It says:

  The [St Helens summit crater] caves are called firn caves because their density ranges from 0.55 to 0.82 g/cm3...

but also:

  The ice density in September 1994 at the base of this crevasse was 0.85 g/cm3. The ice density in the lowest cave passage was 0.86 g/cm3.

As far as I know, 0.86 is greater than 0.82. Right!?

There's no contradiction. Firn is an intermediate form between snow and ice, with a density between that of snow and ice.

The frozen fluffy stuff that falls from the sky -- that's not ice, it's not firn. It's snow. It's also not very dense, typically less than 0.5 grams/cm3. As the snow sits and gets compressed by snow atop it, some of the gas gets squeezed out. The snow changes from ice to firn. The authors are using density between 0.55 and 0.82 grams/cm3 as the definition of firn. As the firn sits even longer, it changes from firn to ice. Note that solid frozen water (no air pockets whatsoever) has a density of about 0.934 grams/cm3. Compressed former snow with a density of 0.82 or higher acts a lot like ice. It is ice, not firn.


Mechanism for Pluto's young surface According to recent reports (e.g. in Nature), Pluto is geologically active. It has some mechanism by which it has "recycled" its surface. I originally thought we had a similar case to Jupiter's moon Europa: tidal energy causes the moon to flex up and down and all that energy is then released as friction and heat, keeping the theoretical underwater ocean in Europa.

We can't use this mechanism for Pluto, because it is locked with Charon, which is also geologically active. If the dwarf planet has some internal heat, its density is way too small for it to have lasted billions of years; in that case, Mars should still be geologically active.

Does anyone have any idea what keeps Pluto active or are scientists still trying to find out?

Prior to the New Horizons flyby, a popular model for Pluto’s surface involved frost migration. Delsanti & Jewitt (2006) explain that at different points during the year, there should be seasonal pressure variations in the atmosphere. This then causes changes in the extent of nitrogen and methane ices on the surface, which over long periods of time - remember, Pluto has a very long period of revolution - alters local geography. The authors also mention cryovolcanism as a potential source for replenishment of methane that is destroyed by cosmic rays.

Trilling (2016) discusses cryovolcanism and two other processes as ways to resurface Pluto and remove craters:

Viscous relaxation. Ices on the surface “flow”, removing certain surface formations.
Convective overturn. Temperature differences in convective cells cause flows similar to those in viscous relaxation.
Cryovolcanism. In addition to releasing methane (and potentially nitrogen), cryovolcanism can heat up parts of the surface, melting ices, which then erode features.

So far, two cryovolcano candidates have been tentatively identified, Piccard Mons and Wright Mons:

Image from Nature; image credit NASA/SWRI/JHUAPL.

The cryovolcanic situation on Pluto may be closer to that of Enceladus than that of Europa. Plumes were observed on Enceladus’s south pole by Cassini, which appear to be cryovolcanic in nature:

False color photograph of Enceladus’s south pole jets. Image in the public domain.

Tidal heating is thought to be a large contributor to the heat necessary to trigger the plumes. However, this is likely not enough. One explanation is the hot start model, popular for many years, in which Enceladus initially generated enormous internal heat through the decay of radioactive isotopes of aluminum and iron. Other elements that are slower to decay could then have provided more heat as the aluminum and iron stopped producing heat. The subsurface ocean that may have resulted on Enceladus could also exist on Pluto, according to Hussmann et al. (2006).

This is only one possible explanation for a heat source to power cryovolcanism, but there does need to be some sub-surface process on both Enceladus and Pluto that can cause these effects. The hot start model is a good option.


Correct phrase for a 'forgetful' natural system? This is a rather general question: assume I have a system that has a certain 'forgetful' property, which means that while I can offset its current state for a moment, it will eventually return to its undisturbed state. An example would be a length of river (say, 100 m) from which I extract a certain amount of water: two days later it would not matter if I had removed the water or not. The system would not show any traces of my previous actions.
The opposite case would be a rock, a chunk of which I chisel away. Two days later the gap would still remain; the 'system' would never return to its original state.

What would you call a system that displays such 'forgetfulness'?

How would you call a system that displays such 'forgetfulness'?

In one word, dissipative. In multiple words, a system whose autocorrelation function tends to zero as time tends to infinity.

Note that the autocorrelation function may not exist; this concept implicitly assumes a linear (or approximately linear) system. Consider a river. Adding a small impulse of water upstream (e.g., a not-too-large downburst) results in the river flow increasing briefly but eventually stabilizing to some nominal value. Adding a slightly larger impulse results in a similar but slightly larger response. But adding a huge impulse of water upstream (e.g., a very large and rapid snowmelt) may cause the river to carve itself a new channel. With this huge impulse, the flow at some downstream point will increase initially but then drop to zero and stay that way because the river no longer flows past that point.


Do current general circulation models model climate oscillations? Ten years ago I studied the third report of the Intergovernmental Panel on Climate Change with some friends. I remember a bit of a hedge in the report, to the effect that general circulation models were not currently modeling climate oscillations (El Niño, the Pacific Decadal Oscillation, etc.), but were beginning to do so. It made me suspicious at the time, that the GCMs were not really capturing the variance we see in the climate. I am curious whether current general circulation models produce these oscillations.

How the models do at this sort of interannual variability for the current climate is described in Section 9.5 of the Fifth Assessment Report (AR5). For example, the section about ENSO says,

  The representation of ENSO in climate models has steadily improved and
  now bears considerable similarity to observed ENSO properties.
  However, as was the case in the AR4, simulations of both background climate (time mean and seasonal cycle, see Section 9.4.2.5.1) and internal variability exhibit serious systematic errors, many of which can be traced to the representation of deep convection, trade wind strength and cloud feedbacks, with little improvement from CMIP3 to CMIP5.

  While a number of CMIP3 models do not exhibit an ENSO variability maximum at the observed 2- to 7- year time scale, most CMIP5 models do have a maximum near the observed range and fewer models have the tendency for biennial oscillations. In CMIP3 the amplitude of El Niño ranged from less than half to more than double the observed amplitude. By contrast, the CMIP5 models show less inter-model spread (Figure 9.36). The CMIP5 models still exhibit errors in ENSO amplitude, period, irregularity, skewness, spatial patterns or teleconnections.

  ...

  Detailed quantitative evaluation of ENSO performance is hampered by the short observational record of key processes and the complexity and diversity of the processes involved. While shortcomings remain, the CMIP5 model ensemble shows some improvement compared to CMIP3, but there has been no major breakthrough and the multi-model improvement is mostly due to a reduced number of poor-performing models.

In short, it's a bit of a mixed bag and it will depend on which metrics you use to assess the variability.  Something like the NINO3.4 index is simple to calculate, but getting a good (or bad) score doesn't necessarily indicate how well your model simulates the relevant processes (e.g., ocean mixed layer dynamics, air-sea interactions, convection).

Section 9.5 also has information on other modes of variability, including the Pacific Decadal Oscillation, the Madden-Julian Oscillation, Atlantic Meridional Overturning Circulation, etc.  It's worth a read.


Is there a mountain-shaped iceberg? From Iceberg - Wikipedia, the closest mountain-shaped iceberg seem to be dome iceberg:

Different shapes of icebergs. 1: Tabular; 2: Wedge; 3: Dome; 4: Drydock; 5: Pinnacled; 6: Blocky.

However, dome icebergs seem to be like two mountains attached to their bases, not a single mountain one:

Is there an iceberg that is simply gradually larger to the bottom, even when passing the water surface?

Ice being less dense than water, icebergs float to the degree they displace water, with about 1/8 of their mass above the surface. Icebergs are also dynamic, melting from exposure to sunlight, warm air and water, eroding, and fracturing, and pushed by both wind and waves. (Notably the descriptions used in the Wikipedia article generally apply to the shape of that small portion of an iceberg visible above the surface, not the gross geometry of the whole berg.)
Geophysicist Henry Pollack explored the potential stable positions of icebergs in a Physics Today article titled "Tip of the Iceberg":

When a totally submerged lower-density body is released, the buoyancy
force causes it to rise until it reaches a floating equilibrium. The
tip then rests above the surface and the root below it, with the mass
of each determined by the density contrast between the floating solid
and the surrounding fluid.

A floating object is only stable to the extent that its center of gravity is aligned above its center of buoyancy, Pollack writes, "...ice cylinders floating in water will stabilize in only two orientations—with the cylindrical axis either perpendicular or parallel to the water surface;" With an idealized ice-like cylinder 9/10 the density of water, the mass can't be stable if it's taller than it is wide.
The geometry won't be much different using an idealized cone shape -- a cylinder widening along its length -- for your mountain. It can only be short and squat,  and if it's at all unbalanced at any point in its life, it'll flip to a new stable equilibrium, on its side or upside-down.


Why does wind direction change in a front? Plenty of answers answer the question that it happens but I can't find a good answer as to why the wind shifts during the passing of a front.
For an extreme example see:

(in Dutch, x is hours and y is wind direction in degrees)
Where a passing cold front moved the wind directon from south to northwest.
The other question provides a very broad answer as to why wind changes in general and the answers there are applicable in general. My question is about the specific circumstances of a thermal front and what causes the change in the balance of forces to suddenly allow or force the direction of the wind to change direction.

An answer I got on Reddit which seems to make sense is that fronts are usually accompanied by a pressure change which locally reinforces the "normal" geostrophic wind which changes the wind direction.
If anyone has a more in depth answer I'd love to hear it.


Wind profile below the aerodynamic roughness length The vertical profile of horizontal windspeed is often given by the so-called "log-law":

$$u(z)=(u^*/k)\ln(z/z_0),\ \mathrm{for}\  z>z_0,$$

which can be found here.

As can be seen from the equation, when $z=z_0$, $u(z)=0$. But what happens below $z_0$? If we continue to use the same equation, for $z<z_0$, $u(z)$ becomes negative and changes direction, which seems absurd.

The key text here is "for $z>z_0$".  It's telling you that, while you can evaluate the equation for other values of $z$, outside of that range the equation is not a valid description of the physical system.  The equation could be written piece-wise to be complete:

$u(z) = \begin{cases} (u_*/k) \ln(z/z_0)& z>z_0 \\ 0 & z\le z_0\end{cases}$

But this doesn't really add anything useful.  In practice, the "log-law" is used to describe the wind profile over 10s of metres and values of $z_0$ range from 1 mm to 2 m, so values of $z$ are likely to be in the valid region.  If you do need to make calculations that close to the surface (in the interfacial sublayer) then you'll need a different equation anyway.


How deep was the Vredefort Crater when it happened? The Vredefort Crater is one of the biggest known impact craters on earth. How deep would it have been, relative to the original ground height, immediately after the dust settled, and before any erosion kicked in?

Is there a general relationship between the diameter of a meteorite crater and it's initial depth?

Therriault et al. (1993) suggest an initial diameter of 192-300km. Turtle & Piarazzo (1998) suggest a smaller initial diameter but make no estimates of the depth; they do, however, suggest an impactor of 10-14km diameter. Dietz (1961) describes the impact crater as "40km across and 16km deep" - i.e. does not take into account the extensive erosion that has occurred in this location. Grieve et al. (2008) also give no estimate of transient depth.

Numerical modelling of the impact diameter-crater depth relationship has been carried out: see e.g. Wünneman & Ivanov (2003), which also discusses crater morphology; meanwhile Turtle et al. (2003) suggest that for an impactor of 10km diameter the maximum transient crater depth will be 24km.

It seems likely that difficulty in estimating transient depth arises due to the 2Ga history of erosion in the area; as such the best option is probably to appeal to uniformitarianism, and assume that the Vredefort-forming impact obeyed the same diameter-depth relationship as has been modelled for the population of recent craters in works cited above.


What type of minerals exist in this rock? ![enter image description here]Arizona desert wash
A very heavy rocking have a few and when busted open beautiful veins of dark silver sometimes yellow gold.light pink and teal looking(https://i.stack.imgur.com/HRJgq.jpg)white semi round .very heavy

It is massive white quartz also referred to as milky quartz, the streaks are  trace impurities and can occasionally include valuable metals like gold but just as often included fools gold (pyrite).

This chat can help with more detailed identification of trace metals https://www.mindat.org/mesg-11-219962.html


Are greenhouse effect and ozone depletion correlated? I have read that these phenomena do not have an interaction.

However, I would think if CFCs cause the ozone layer to thin, and more UV radiation enters the Earth system, the Greenhouse Effect would cause global warming would increase.

So:

Will the infrared energy emitted by the Earth increase with a higher input of ultraviolet radiation?

Ozone protects us by absorbing ultraviolet radiation
As shown in this Chemistry.SE answer, ozone breaks upon incidence of various energies of UV radiation to form oxygen, which itself is somewhat effective at blocking UV radiation at other energies. THe key is that the incident UV radiation transfers its energy to the reaction products in order to break the bonds holding ozone (or oxygen) together.
As opposed to protecting us from UV, the only way for ozone to protect us from global warming is for it to reflect the incident UV radiation back into space. That is not what it does. UV that enters the Earth's atmosphere and interacts with the ozone stays in the Earth's atmosphere.
Therefore, your question premise is flawed when you say "if ozone layers gets smaller, more UV radiation enters on Earth." That is not true, because UV radiation that that enters the Earth will be absorbed by something, whether it is ozone or the rest of the atmosphere or the ground.
Global warming deals with infrared radiation
Furthermore, 'global warming' is primarily concerned with radiation heading outwards in the infrared band. IR radiation emitted from the ground is blocked by CO$_2$ in the atmosphere and prevented from escaping into space. So the effect of ozone on UV radiation will have little to no effect on 'global warming'.


What type of yellow-green stone is this? It's greenish yellow with white. Got it in a mixed stone package from Amazon.

No luster, I'd say a 7 in hardness, it doesn't look homogeneous.

I think your mineral specimen is smithsonite based on texture and the dark metallic specks that appear to be galena.


Flight time differences between flying east and flying west Why is it that flying west takes longer than flying east despite the fact that the Earth is rotating eastward around its own axis?  I had always thought flying west would take shorter than flying east but after a few round trips from New York to San Francisco I've found that it's just the opposite.  The same when flying from London to Moscow: flying east is always quicker.

The Jet Stream is the cause for slower flight times to the West. It flows from West to East at high altitudes and therefore helps planes flying East but causes extra resistance for planes flying West.


What is the difference between Precipitable Water (PW or PWAT) and Quantitive Precipitation Forecast (QPF) in terms of computer weather model data? When I take a look at weather models, there is an option to take a look at PWAT or QPF. What's the difference?

Precipitable water is the total amount of moisture throughout the air (the total in the entire tropospheric air "column"; most moisture is found in the lowest few km, due to decreases in temperature and density and where humidity sources being at the ground).

Whereas QPF is the amount of precipitation that has fallen or is predicted to fall in a certain period of time (often 6 or 24 hours).

Generally more moisture (higher PWATs) do indicate the potential for more precipitation.  But you could definitely have a large PWAT and get no rain/snow/etc to fall from the sky.

I believe the greatest PWAT values are typically found in the warm saturated columns near tropical cyclones (hurricanes/typhoons).  From experience, in the US South, PWATs near/above 2 inches are generally considered quite large in the summer, and tend to indicate a greater chance of rain from air mass/sea breeze/frontal storms.

Whereas hourly rainfall rates can often be nearer 3-5 inches per hour, and locations can report over 20 inches of rain in a day [rainfall records].


Potential explanations of Red Sea crossing I am looking for a believable explanation of the Red Sea Crossing in the Bible. This would involve either strong winds(which is mentioned in the Bible) or plate tectonics which could cause land to rise up and fall again.

My problem with wind is that I know of no incident where strong winds parted a sea --- even one as shallow as the Red Sea which is, as far as I know as low as 50m in some areas. Winds always move inland not parallel to the coast. Tidal waves and tsunamis always crash into the land not part the sea. Unless I am mistaken.....

Plate movement that both raised and lowered the seabed seems more likely and the Red Sea sees a lot of earthquakes. I've heard the surface area can be crossed in as little as 4 hours. Does anyone know of an example where the land was both raised and lowered in an earthquake, high and low enough to create both a crossing and drowning ?

To my knowledge, the best study looking at potential explanations for the Red Sea crossing is the one by Nof and Paldor (1992). They present a couple of plausible scenarios for the crossing. The main one is the effect of strong winds blowing along the Gulf of Suez and they find that the sea level drop could be sufficient:

  It is found that, even for moderate storms with wind speed of about 20 s−1 receding distance of more than 1 km and a sea level drop of more than 2.5 m are obtained. These relatively high values are a result of the unique geometry of the gulf (i.e., its rather small width-to-length and depth-to-length ratios) and the nonlinearity of the governing equation. Upon an abrupt relaxation of the wind, the water returns to its prewind position as a fast (nonlinear) gravity wave that floods the entire receding zone within minutes.

The second mechanism involves a tsunami propagating along the Gulf of Suez from the Red Sea, but it seems like way more of a stretch.

Nof D. and N. Paldor, 1992: Are There Oceanographic Explanations for the Israelites'Crossing of the Red Sea?. Bull. Amer. Meteor. Soc., 73, 305–314.
doi: http://dx.doi.org/10.1175/1520-0477(1992)073%3C0305:ATOEFT%3E2.0.CO;2


Why does the wind periodically change direction? Image Subtitle: Wind going across the page - and changing direction

To clarify, imagine you were sat in a boat in the middle of a lake recording the wind direction every minute. You notice that the wind changes direction roughly every five minutes from 340° to 360° and back and forth...

On other days the time between and the amount (°) of wind shift can be bigger or smaller.

I presume it is something to do with the wind going over land:

It is known that the wind is directionally deflected over land (frictional effects)
Wind higher up in the atmosphere is less hindered and so less deflected

My guess is that the wind experienced on the lake is an alternation between these though the exact mechanics of it is beyond me. I would greatly appreciate a true explanation.

For the answer to why there is wind, see: Where does wind come from?

That establishes the forces at work driving the wind, namely:

non-linear advection of momentum
the pressure gradient force (PGF)
the Coriolis force
friction

Friction is less over water than over land, and so the wind will tend to flow more parallel to the isobars than they will over land at the earths surface.  The force balance between the PGF, Coriolis and friction is easy to conceptualize:

Image taken from University of Illinois at Urbana-Champaign, credits at http://ww2010.atmos.uiuc.edu/(Gh)/abt/aknw/dvlp.rxml

In this we can see that see that wind will flow with low pressure to its left, and cross the isobars slightly toward the low pressure.  The angle of the wind crossing the isobars is related to friction.  The direction of the wind is related to the orientation of the isobars and friction.  The speed of the wind is related to the spacing between isobars (close = fast, far = slow).

However, this only explains a steady-state wind in equilibrium, which is great for theoretical explanations but is too idealized for the real atmosphere.  In your observations on the lake, the flow is not steady-state and that pesky non-linear term is at work.

The lowest level of the atmosphere is called the boundary layer, and this extends from the surface to roughly 1 - 2 km.  During the daytime this boundary layer is "well mixed", which just means it has a uniform potential temperature and moisture profile and it is turbulent.  To really over-simply turbulence, consider swirling motions of different sizes.  At the largest sizes these swirls are the size of the depth of the boundary layer.  At the smallest sizes the swirls are on the scale of millimeters, and there are swirls at all of the intermediate sizes.

Let us just consider the biggest of the swirls.  The top of these swirls are at the top of the boundary layer where the wind is typically faster (it can be slightly faster, or much faster).  This swirl will mix some of this momentum down to the surface, at the bottom of the swirl.  These swirls are moving around as well, not sitting in one place.  Where the swirls are, there will be a different wind velocity than where they arent, and it will depend on the orientation of the wind, the swirl and the momentum being mixed downward to the surface.  If you were standing at one place, this would give you the effect you observe, winds that change direction and/or speed.

Now consider all of the different sizes of eddies doing this, and things become a mess (turbulence!).  On some days the this effect is small and you might just notice subtle changes in the wind, and on other days you might have strong gusts and "bumpy" air.

Finally, lets get back to the lake. The lake has a temperature flux and a momentum flux with the air above it, which produce changes in the wind.  All of this wind is moving mass around and the net result of this is that the wind is causing the pressure field to evolve, and these changes feedback into the wind.

The above effects can be rolled into the non-linear and friction terms in the momentum equation, which are the reasons that your observations of the wind periodically change directions.