Reference units for CO2 concentration in the atmosphere and meaning of a slight downward tendancy during the 1600 I discovered here a set of yearly historical atmospherical CO2-concentrations from year 0 - 2014. Since they haven't mentioned which measure they used, I'm not sure whether it is right to talk about ppm by volume. The name of the file contains the following "mole_fraction_of_carbon_dioxide_in_air_input4MIPs" which leads me to think of ppm by mole.

Do you think  I'm right?

This leading to: is it plausible to have that downward tendency about 1600 and if why?

Thank you in advance for your help.

Edit:

I plotted the data with Excel:

The file you provided do not have metadata nor context, which make it pretty much useless as it is.

But, by reading the title and as you suggested, we can assume that the unit used in the sheet is mole fraction of $CO_2$ in air.

Also the value of the data is fitting the range of the $CO_2$ historic measurements on Earth.

By definition, a mole fraction is the ratio of mole of a given component (solute) over the total mole count in a target solution. In our case, this mean:

$mole\:fraction\:of\:CO_2= \frac{measured\:CO_2}{total\:mole\:in\:the\:sample\:solution}$

This is well expressed and explained here in the section titled: Parts per Million by Volume (or mole) in Air

  In air pollution literature ppm applied to a gas, always means parts per million by volume or by mole. These are identical for an ideal gas, and practically identical for most gases of air pollution interest at 1 atm. Another way of expressing this value is ppmv. One part per million (by volume) is equal to a volume of a given gas mixed in a million volumes of air:
  $1\:ppm = \frac{1\:gas\:volume}{1\:million\:air\:volume}$ at 1 atmosphere pressure.

Thus a simple conversion can be applied and the equation solved, knowing the weight of a mole of $CO_2$ and the typical weight of air. To answer your question, mole and volume are interchangeable in this context.

This would be my honest take, considering the limited available information.

About the downward tendency during the 1600: This was around the time when the Little Ice Age began; There was the Maunder minimum (first low) due to a solar spot low and then a small peak and then the Dalton minimum (second low) before the present peak. Here is an example of how low the sunspot activity was at that time (especially Maunder) from Britannica.com

Consequences of those two events, detectable already during Maunder was a trend of global cooling and a diminution of the atmospheric $CO_2$.


Doesn't increased human activity add to heating the atmosphere directly? My question relates to the fact that 1- the human population is continually increasing, and 2- everybody is constantly 'doing more stuff' (or causing more to be done). So doesn't 'more people doing more stuff' heat the environment correspondingly more and contribute directly to 'global heating'? Yet I have never heard of this argument, only that of increased greenhouse gas emissions blocking the dissipation of solar heat. I leave out the fact that, as people age, at some point they do a lot less stuff. (However, could they still cause overall even more stuff to be done, e.g. when they get sick and need intensive infrastructure -- care, transport, medicines, operations etc.)

There seems to be the general perception, or claim, that everything is 'getting more efficient', so we are thereby using less energy (and heat production, in my above model?). But some comentators say that this just leads us to use a lot more of the new, more efficient technology, so that overall energy consumption and heating increases. Could telephone use today per capita (and over some unit of time) actually consume less energy than it did in, say, 1960? Offhand, it seems unlikely, especially since the definition of 'telephoning' today is much broader than the 1960s' activity.

Could increasing direct heating of the earth by human activity perhaps not explain why, at present, we are seeing consistently higher global warming measurements than were only recently predicted? (Today's Guardian headline: 'Climate crisis: alarm at record-breaking heatwave in Siberia -- Unusually high temperatures in region linked to wildfires, oil spill and moth swarms'.) (Just consider how much 'new heat' is caused indirectly and directly by one more rocket launch. And of course there isn't 'just one more', but many more.) To be sure, a lot of this heat dissipates with time into space by natural processes. But isn't the global warming argument that the sun's heating of the earth is being accumulated in the greenhouse effect, so why shouldn't the 'direct' heat from human activity, released into the environment, also be captured and add to the overall effect? (Apologies to the experts here who may find my proposal much too simplistic, but I would be interested to hear why.)

It does, but globally it's negligible compared to other heat flux densities.

Simply do the math:

World wide primary energy consumption: 162,494 TWh (2018)
Hours/year (2018): 8760 h
Earth surface: 510,100,000,000,000 m²

Assuming all this energy is transformed to atmospheric heating, this is an average heat flux (q=E/t*A) of 0.036 W/m². Locally this varies widely depending on climate (and the necessity to heat or cool buidlings), the degree of industrialisation, the population density etc. One figure I've found in Wikipedia for Germany: 1.2 W/m², Antarctica obviously: more or less 0.0 W/m², Hongkong (2018) 40.2 W/m² (calculated myself). BTW the average geothermal heat flux is 0.087 W/m².

Compare this to the solar contant: 1361 W/m². Considering albedo, day & night etc. the average (solar short wave) flux density on Earth's surface is ~ 175 W/m². The atmospheric back radiation is ~ 300 W/m².

So the average solar short wave flux density on Earth's surface alone is ~ 4,850 larger than the heat flux density directly induced by human energy consumption.

The heat flux density indirectly induced by human energy consumption (CO₂-, CH₄-, N₂O- etc. accumulation in the atmosphere) currently adds up to netto ~ 2.3 W/m² additional back radiation, which is roughly 60 times larger than the directly induced heat flux density.

Conclusion: direct heating of the atmosphere caused by energy consumption is almost insignificant compared to other effects.


Is there a reason most mountain ranges seem to run parallel to coastlines? Eyeballing a map of the world, it seems that most mountain ranges that don't occur along continental fault lines run parallel to coastlines. Is there a reason for this?

Mountain ranges are usually formed as orogeny where tectonic plates collides, known as convergent boundaries.

The continental plates have less density than the oceanic plates and the buoyancy results in that they are mostly above sea level. Continental sea floor is known as continental shelf, but usually, it doesn't reach far from the coastline. Therefor the continental-oceanic boundaries often runs sub-parallel to the coastlines we see today.

At convergent boundaries where oceanic crust and continental crust collides, the mountain ranges can therefor form right at the coastline. Vulcanism is also important in the process as volcanoes forms where oceanic crust is subducted under the continental plates.

Some of the mountain ranges that today are located far from the coast, e.g. the Urals are formed from earlier convergent boundaries between continental plates that today are incorporated in larger plates.

Convergent boundaries explains most of the mountain ranges (e.g the Andes, Himalaya, the Alps, Nihon Arupusu) but there are however some curious exceptions, e.g. the Scandinavian Mountains that are not located near any convergent boundary and might be the result of regional uplift. However, there is an interesting ongoing discussion on how these processes work.

This is a simplified answer that I hope inspire to further studies in tectonic and geology.


How does ice-penetrating radar "see" through kilometers of ice without being absorbed? The BBC News article Isolated lakes found beneath Canadian ice sheet links to the open access Science Advances article Discovery of a hypersaline subglacial lake complex beneath Devon Ice Cap, Canadian Arctic.

The discovery is based on radar "soundings" of the Devon Ice Cap in Nunavut, Canada.

An earlier question What is likely to have happened with these newly discovered antarctic volcanos below the ice? shows sub-surface radar measurements of antarctic ice, in this case to a depth of 1.5 kilometers, and therefore with a total path length of 3 kilometers in ice.

The water molecule is strongly polar and interacts with microwave radiation by absorbing and thermalizing it. This effect is obvious in microwave ovens. Microwave ovens can be used to "defrost" frozen food even a few centimeters thick, using reduced power and longer time. This is necessary because frozen water molecules have a lower absorption than those in unfrozen areas, but they are still quite absorbing.

Radar measurements travel through kilometers in ice round trip, substantially larger than the thickness of a slab of frozen peas.

How is ice-penetrating radar able to work through such long path lengths of ice? Is there a special frequency thats used, or other tricks allowing for extremely weak reflections after bulk attenuation to be detected and measured?

Water molecules do interact with microwaves and in microwave ovens that operate at 900MHZ- 2.5GHz. This Radar instrument operates using Very High Freq Radio Waves at 193MHz [1].

At lower-than-microwave frequencies, the loss factor is much lower, and as a result the wave can penetrate deeper into the ice sheet with minimal absorption. The difference in permittivities between liquid water and solid ice is what allows them to visualise boundaries and identify the subglacial lakes

From Nasa [2]

  Ice, on the other hand reacts differently depending on the radar's frequency. It reflects high-frequency radio waves, but despite being solid, lower frequency radar can pass through ice to some degree. This is why MCoRDS uses a relatively low frequency—between 120 and 240 MHz. This allows the instrument to detect the ice surface, internal layers of the ice and the bedrock below. "To sound the bottom of ice you have to use a lower frequency," said John Paden, CReSIS scientist. "Too high a frequency and signal will be lost in the ice."


Modelling sea levels with gravitational parameters Are there any publicly available programs or source code for modelling global (or local) changes in sea level which include parameters for gravitational tidal effects?

I have a physics background, and recently I started playing with large-scale fluid dynamics as a side project. The oceans and their boundary conditions are incredibly complicated, and I've gotten pretty far out of my depth at this point. I don't have the time or motivation to completely invent the wheel on this, so ideally, I'm looking for a program that would allow me to vary lots of parameters - including the tidal potential of the moon - and output topographical data for sea levels at different locations in the ocean or along the coast. However, I'd be happy with just an open source program that I could modify with additional parameters.

I'm looking into this question predominantly from a hobbyist's "toy model" perspective. In particular, I'm curious about how oceanic tides would change with tidal forces, say, 100x greater than the moon's or with an almost tidally locked moon (e.g. six months between moonrise and moonset). How much land would be flooded with each high-tide and how much reclaimed with each low-tide? If anyone has an answer to that question, I'd be interested in hearing it as well.

Starting from scratch and building a "toy model" is unlikely to be successful here, because while you could certainly model Newtonian tides, much of what happens on the continental shelves is tied very closely into the shapes of coastlines and bathymetry, the interaction between the inertia of the tidal wave and friction on the seabed, and so forth - a lot of non-linear effects, some of which are not fully understood.

My suggestion would be to start with an existing, validated, global ocean model and tweak its input parameters. For example, to simulate a change in the gravitational pull of the moon you could change the amplitudes of the lunar tidal constituents that drive the model (and perhaps also their periods, if you wanted to work out the appropriate orbital mechanics!).

Be aware that running models of this sort tends to be computationally expensive, obviously depending on the resolution - but it should be within the realms of what is feasible on a home computer, if you don't mind things taking a week or two to run (I assume, since this is a hobby project, that you don't have access to HPC resources for it). I'm not sure whether anybody makes a simple but validated model openly available - if anybody knows of one, perhaps they could comment. If not, you might have to build your own using an open source code, which would be substantially more work.


Presence of Diabatic heating term in the continuity equation The tropical circulation paper by Gill (1980) approximates vertical velocity as the sum of pressure and diabatic heating terms (equation 2.5 at page 449).

Since the pressure is already a function of Q, what's the need of writing Q explicitly in this expression? Doesn't it double count p?

In the book - Atmosphere-Ocean Dynamics, Volume 30  the author AE Gill defines the perturbation pressure in the paper that OP references as the following.

Consider a pressure of a reference system (ocean/atmosphere at rest) and let us call it
    $$p_0$$.

It must be noted that a real atmosphere is never at rest and so we consider deviations from the reference system.

Since we are dealing with a vertical pressure gradient for OP's equation(2.5)(the gravitational force matches the vertical pressure gradient for hydrostatic large scale circulations)

$$p_0$$ is a function of $z$ where z is the height coordinate.

Then the perturbation pressure $p'$ is defined in the following way

$$p = p_0(z) + p' $$

So if you add the perturbation pressure to the reference pressure we get the deviation from the reference system.

Similarly a perturbation density can be defined in the following way

$$\rho = \rho_0(z) + \rho' $$

The basis for doing this comes from classical mechanics Perturbation Theory

The question is why is this being done ?

We are looking for solutions that are basically of a oscillatory nature. So in effect this gets rid of the non linear cross terms for which no oscillatory solution exists.

In the specific case of 2.5 from the paper you referenced in addition to the Brunt–Väisälä frequency one needs to consider a "buoyancy forcing" especially in the tropics because of the large contributions from diabatic heating. We are essentially talking of an "open system" where in addition to adiabatic "work" being done you also have to account for heat exchange between a system and the ambient environment. In reality this is assumed as "pseudoadiabatic" process

Then the question is how is the heating rate modeled ? In the AE Gill book this is given by the following equation

$$ Q_H =  -L_V \frac{Dq_w}{Dt}$$

where $L_v$ is the latent heat of vaporization and $q_w$ is the saturation humidity where the word saturation means the saturation water vapor mixing ratios.

Equation (2.5) from OP's paper is derived in Gill's book and is present in the 9th chapter(9.13.7) and will not be derived here but will be stated as is

$$\omega_n = \frac{\partial \widetilde \eta}{\partial t} + \widetilde b_n$$

Here $\widetilde \eta $ is the vertical coordinate(in OP's paper the vertical coordinate is pressure) and $b_n$ is the rate of change of buoyancy  per unit volume. This form is known as the buoyancy forced Shallow water equations

One can get more details about the perturbation theory for the atmosphere by looking at this link - Atmospheric Oscillations: Linear Perturbation Theory

Similarly if you want horizontal pressure perturbations you model the reference pressure as a function of x and y and then consider deviations thereof.

Useful reading
What is the meaning of pressure in the Navier-Stokes equation?


How much fossil fuel came from the Carboniferous? It is said that most of the fossil fuels in existence today (coal, oil, gas) came from the Carboniferous period. A unique set of circumstances lead to the creation of fossil fuels, which depends on anaerobic decomposition:

Plants evolved bark as an effective defense against insect herbivores
Very few organisms at the time could digest or decompose the bark fiber lignin

Suppose that the Carboniferous period never happened, or for whatever reason the period never produced fossil fuels. How much fossil fuel would we have today instead? How much of today's fossil fuel deposits were created during the Carboniferous?

The process you're describing in the question is the one at the origin of coal. Although coal deposits are known from the Devonian to the Quaternary, they have been 3 major periods of depositions (see Thomas 2013): the Carboniferous-Early Permian, the Jurassic-Cretaceous and during the Cenozoic. So, indeed the Carboniferous is one of the main period of coal deposit but I couldn't find any numerical evidence in the literature that this is the "main" period of deposit. The idea that it is is most likely due to the fact that the western Europe and eastern USA coal mines (hence historically the most noteworthy) all happen to be Carboniferous.
But as far as oil (petroleum) is concerned, according to Klemme & Ulmishek 1991 (straight from the abstract):

  Six stratigraphic intervals, representing one-third of Phanerozoic
  time, contain petroleum source rocks that have provided more than 90%
  of the world's discovered original reserves of oil and gas (in barrels
  of oil equivalent). The six intervals are (1) Silurian (generated 9%
  of the world's reserves), (2) Upper Devonian-Tournaisian (8% of
  reserves), (3) Pennsylvanian-Lower Permian (8% of reserves), (4) Upper
  Jurassic (25% of reserves), (5) middle Cretaceous (29% of reserves),
  and (6) Oligocene-Miocene (12.5% of reserves)

See Klemme 1994 for a detailed explanation on the origins of the Jurassic source rocks (i. e. 25% of the world's reserve at the time): most of them are marine, but some are fluvial or from lagoonal inland seas (table 3.2).

References:
Klemme, 1994. Petroleum systems of the world involving Upper Jurassic source rocks. In Maggon & Dow (Eds), The petroleum system - from source to trap, AAPG Memoir, 60: 51-72.
Klemme & Ulmishek, 1991. Effective petroleum source rocks of the world; stratigraphic distribution and controlling depositional factors
AAPG Bulletin, 75: 1809-1851.
Thomas, 2013. Coal Geology, 2nd Edition. Wiley-Blackwell, 444pp.


How have global sedimentation rates changed over the last billion years? Do we have a graph of how sedimentation rates changed over time?

Sedimentation rate presently varies many orders of magnitude depending on the place you observe. The rate of sedimentation is also different. Some places have continual sedimentation, others have episodic sedimentation events.

That is why charts that show changes in sedimentation rate are usually done for individual sedimentary basins, to determine the basin evolution. This is available for many basins, especially if they are of interest to the hydrocarbon industry.


Can a voltage difference precede cloud-to-ground lightning, and can it be measured over a short distance? I recently heard an anecdote about cloud-to-ground lightning striking an area where some kids were playing 20 seconds prior. They experienced their hair rising which would indicate there is a significant voltage preceding such strikes.

I assume that a common multimeter would indicate a very high voltage between the ground and a cloud which is about to produce a ground strike (and it would facilitate the strike).

Would there be some voltage between the ground and, say, 2-3 meters in the air?
How long before the strike would this voltage become noticeable (significant relative to noise)?

There is always a background voltage difference from the ground up, of about 100V per vertical meter resulting in a net voltage difference of about 400,000V between the top of the atmosphere and earth ground. However, being a good insulator, makes for lousy conductivity, therefore the current density is extremely low which would make measuring with a common multimeter pretty hard: there's just not enough surface area on those tiny leads over which to contact air and ground. Add to that the very low current density, and your digital multimeter (DMM) is nowhere near sensitive enough to measure that voltage difference.

Although the moments preceding a lightning strike will generate a potential of tens of millions of volts, using a DMM still leaves you with a few big problems:

1) Lighting is an energy transmission that channels through a "pipe" of ionized air molecules. You'd be hard pressed to predict where that pipe is going to set up, getting there in time, and most importantly, surviving the instant supernova of steam that your body would turn into.

2) You're still left with the problem of the tiny surface area of DMMs leads. Sure, there's a big voltage potential, but the current density is still too small to measure with an unmodified DMM. Like Trond Hansen notes above, you'd need to connect your DMM to a large "collector" to actually see the difference, (then calculate the current density observed based on the surface area of your collector.)


Different atmospheric models available for personal usage? We are two high schoolers who would like to embark on a project to simulate the atmospheres of exoplanets.

More specifically, we would like to change the atmospheric composition of such planets. We have seen various climate models, such as CESM and PlaSim. Unfortunately, CESM appears to be quite complex, while the latter option doesn't have the resources we would need.

Are there any other simulators that may consistently do the same thing, but need lower computer specifications? Otherwise, are there any resources to become familiar with CESM at a high school level?

Furthermore, what would be the required specifications for running CESM on a fairly consistent basis? I have heard that you would need a cluster, but we currently do not have access to one. We may be able to rent one out, but we'd rather be familiar with CESM before we do.

Thank you!

EDIT: (for clarification) I know a bit of FORTRAN, and have access to help from a Physics instructor. Although I understand that it may be out of the reach of two high school students, is there any sort of "crash course", one could recommend on more advanced astronomical physics?

Furthermore, we are interested in a rocky exoplanet, and potentially have access to a cluster/help from a professor.

Thank you once again!

Unfortunately, I don't think such a numerical model exists that would be suitable for high school students' understanding. The simplest climate model around is a zero-dimensional (energy balance) climate model, but a background on mathematics, and programming may be necessary. You can find one here. Wikipedia has one listed. Michael Mann has the source code for such a model, but it is written in MATLAB (you may be able to run it in OCTAVE, since MATLAB is licensed). There are likely many more than just these, considering multiple layers, volcanic eruptions, etc.

The code for the models listed are simplified models that do not consider things like clouds, aerosols, eddy diffusion, etc. This is where Global Climate Models (GCMs) differ. They must consider how fine details, some of which aren't considered by weather models, affect the climate. Therefore, they are usually complicated. Most GCMs I have seen are written in FORTRAN, which is an antiquated language, but computationally efficient. This makes even easy concepts obtuse.

While I have not dealt specifically with CESM, I can infer some things about it. By definition, CESM is an earth systems model, not an exoplanet model. You may be able to adapt some of the parameters to other planets, but it becomes too difficult for just one person to do (because of FORTRAN). There are models for other places, such as GCMs for Mars, but they are difficult to run and not necessarily accurate. Clusters are needed due to memory limitations, and how long they run for.


Were dinosaurs with feathers common? More and more evidence of fossilized dinosaurs with feathers are appearing. Did many dinosaurs have feathers and did this change during the Mesozoic?

Keep in mind that although I am a paleontologist, I am not a vertebrate paleontologist so I might not be aware of every single find ever made of feathered dinosaur.

As far as I can tell, all dinosaurs fossils exhibiting feathers belong to the Theropoda. Here is a (probably dated) phylogeny of dinosaurs from Sereno 1999:

Credit: Paul C. Sereno

Theropoda is the group from Eoraptor to Euornithes.

While Eoraptor  is Triassic, the group diversifies mostly during the Jurassic (still Sereno 1999) and it is also during that time that we start having "common" feathered dinosaur fossil evidence (e.g. Zhang et al. 2008, Sullivan et al. 2014).
Birds (Aves) seem to have appeared in the late Jurassic / early Cretaceous as well, but modern birds (Neornithes), i. e. birds with living representative, appeared only in the late Cretaceous.

I don't know of any proper (sample-standardized, with coherent bias detection and removal) paleodiversity study for the theropods, although there is one for Aves (Brocklehurst et al. 2012), so it's hard to discuss about it at a species level.

In theory, feathers are more likely to fossilize than other soft tissue (Davis & Briggs 1995) but in practice they are mostly found in finely grained sediments such as limestones, thus limiting the amount of outcrops in which they can be found.

Sources:
Brocklehurst, N., Upchurch, P., Mannion, P. D., O'Connor, J., 2012. The Completeness of the Fossil Record of Mesozoic Birds: Implications for Early Avian Evolution. PLoS ONE 7(6): e39056.
Davis, P. G., Briggs, D. E. G., 1995. Fossilization of feathers. Geology, 23(9): 783-786.
Sereno, P., 1999. The evolution of Dinosaurs. Science, 284: 2137-2147.
Sullivan, C. et al. 2014. The vertebrates of the Jurassic Daohugou Biota of northeastern China. Journal of Vertebrate Paleontology, 34: 243-280.
Zhang, F. et al.  2008. A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers. Nature, 455: 1105-1108.


Temporal Resolution of Seismic data Radius of the Fresnel zone is given by
$$Rf=(v/2)(t_0/f_\mathrm{dom})^{1/2}$$
where $v$: velocity of layer

$t_0$: two way travel time

$f_\mathrm{dom}$ :dominant frequency in the spectrum

This shows that high frequencies give better resolution than lower frequencies and resolution deteriorates with depth and increasing velocities.

However I found some text in "Seismic Data Analysis- Yilmaz" which is contradictory.
"Just having low or high frequencies does not improve temporal resolution. Both low and high frequencies are needed to increase temporal resolution. This is demonstrated further in Figure 1.1-30."

Could someone explain what the author is trying to say here or am I making a mistake in interpretation somewhere ?

In seismic data analysis we have to distinguish between vertical (temporal) and horizontal resolution.

The (First) Fresnelzone is linked to the vertical resolution and defines the area in which  the collected energy will still stack constructively.

The temporal resolution however, defines what the wave "sees". The events can still be resolved if their thickness is within $\frac{\lambda}{4}$. However, in some cases it can go down to $\frac{\lambda}{32}$. This is a matter of detectability of events.

Don't forget that we're dealing with superpositions of different frequencies so basically low frequencies will give use the necesseray energy content of general trends, while high frequencies enable us to make a distinction between geologic features.

This file from the university of Oslo gives a nice overview.

(The picture is from a blog post I've written on knowing your wavelength it's CC-BY-SA Source1 Source2


Are there pockets of liquid carbon dioxide in Earth's oceans? The carbon dioxide phase diagram shows that at high pressure and normal temperature CO2 becomes liquid. Since it is heavier than water, I wonder if there are lakes of liquid CO2 at the bottom of the Earth's oceans, and if no, why?

Yes, according to this paper in the Proceedings of the National Academy of Sciences. But they also say that this "lake" of liquid CO2 is covered by CO2 clathrate, so it's not quite your average brine pool.

Note about clathrates:

The following image is from the Wikipedia article on CO2 clathrate. It is a CO2 hydrate P-T phase diagram with experimental data (black squares) from a 1998 paper by Sloan listed in the references of the Wikipedia article.

Note the H2O phase lines drawn in. There is a relatively small habitable area for clathrate somewhere inside about 273-280 K (0-7 ºC) and 10-12 bar (or about 90-110m in ocean depth as calculated here). Above the phase boundary, the clathrate will dissolve to liquid. Below, to gas. What this diagram does not say (according to a knowledgeable colleague) is that clathrate will not readily form or remain in its semi-organized state given very slight amounts of mechanical agitation. Hence why it does not exist en masse under typical seafloor conditions.


Why do meteorologists use DM and equal height surfaces for some maps? In discussions from the National Weather Service, storm systems are often quantified in terms of DM, such as in this forecast discussion from Los Angeles/Oxnard on February 15, 2017:

  A strong and large 487 DM low was located across the Gulf of Alaska.

When the NWS uses "dm" is that short for "dam" as in decameters, or something else? And if so, why do they sometimes give these heights rather than the millibars?

First, yes, DM does appear to be decameters (though Dm would be more proper).  D was actually the abbreviation I was taught for deca in grade school 20 years ago, but it appears da has become the official standard prefix now, perhaps because it was confused with deci (d).  They also list the spelling deka instead of deca as well, perhaps for similar reasons (though that may well still vary by locale?)

Now, actually all typical plots aloft are the varying height values where a given pressure is found (850 mb, 500 mb, 200 mb, etc).

Why do we look at height variations on set pressure levels?

First, for background, it's important to realize that, by and large, pressure and height are proportional, such that either one can determine a strong approximation of the other.  For large-scale weather you can directly invert them using forms of the hydrostatic equation.

$$\dfrac{\partial p}{\partial z} = -\rho g$$

Basically this proves extremely accurate when vertical acceleration is small, which is generally anywhere outside of intense thunderstorms.  Even when it is less perfect, it's a pretty useful approximation for pressure variations important on the scale of synoptic weather.

Actually, the basic weather pressure map we're used to RELIES upon this relationship... typical storm pressures we hear are 900-1000 mb, and maps often look like:

But you'll find that pressure at the ground is lower in most locations than is indicated on such a map.  This is because, despite being called "surface maps", they're actually sea-level pressure maps.  At any station situated above sea-level a weather balloon cannot acquire that sea-level pressure.  So the pressure must be extrapolated downward using these same equations.

But that still doesn't answer why we'd opt for isohypses...

One benefit may be that height maps are similar to topographic maps.

But it well truly stem from early meteorological rules of thumb.  One important forecasting tool before advanced weather models came from the thickness equation (an application of the hydrostatic approximation).  It works out that the thickness between 500 mb and 1000 mb was a helpful indication of what kind of precipitation would fall.  Values lower than 5400 m indicate that the air column is probably cold enough for snow.

It seems quite feasible that this was relationship was noticed even before the equations were understood.  1000 mb is very close to the surface pressure in many of the big cities during the early development of meteorology (such as New York City, Boston, London, and Paris).  So all they'd need to notice is a connection of the 500 mb height and the precipitation type.  This might be easier than spotting a pattern of ratios of 5400 m pressure values to surface pressure values around 0.5.

In the end, it probably goes back to how early upper-air observations were recorded.  It may well have been some guy going up in the balloons until radio, so would they have recorded at equal heights or equal pressures?  Or when radio and the early instrumentation were developed, what would draw them to choose set pressures or set heights?  I don't know the history well enough to give a certain answer to that.

In the modern era, models quite often use pressure coordinates (or similar sigma coordinates).  In addition, if you wished to calculate the quasigeostrophic omega equation or apply the quasigeostrophic height tendency equation, perhaps equal pressure maps might be slightly more useful.  However, I tend to doubt either of these are nearly significant in the overall development of the practice.

Also, why dekameters specifically?

A good contour interval at 500 mb proves to be 60 meters.  With the precision of that final digit being so trivial, and with international communication being precious, they opted to just transmit the first three values.  So 5400 meters just became 540, so dekameters.

Now, on the other hand, at 850 mb the reasonable contour was just 30 meters. (I believe for a long time, they opted to only send the last three digits of the height [as values are typically around 1200-1600 meters, the leading 1 is superfluous].  You can see reporting like this still on the University of Wyoming's website).  At a 30 meter interval, that final digit is twice just a little more helpful to place contours.  So meters were once used for 850 mb or 925 mb versus dekameters for 500 mb.

But, this has additional implications.... The reason these 850 mb heights fluctuate less than the 500 mb heights is because air density decreases with height.  The same mass of air takes up more room at higher heights.  So pressure changes more slowly as you rise:

But not only does this lead to different scales being important on different pressure levels... it could well answer that question of why they chose to record at equally spaced pressures instead of heights in early ballooning.  Otherwise, they'd end up recording a ton of extra upper-level values which proved rather without value.

And why 500 mb values?  The 500 mb map is a very central pressure level (near the level of non-divergence).  Low-level maps like 850 mb will have lows more connected in shape/position to surface lows than lows aloft [850 is often looked at more for thermal and moisture setup].  Upper-level maps like 200 and 300 mb won't have closed lows [and are looked at a lot for wind structure, in addition to short and long-wave trough positions]. So a central level like 500 mb proves to be a very good level to look at upper-level low strength.


What is the importance of oxidation process? I am asking this question, because I don't know the importance of oxidation process at all, and this question pops into my mind because currently I've been researching why apples turn into brown color when is it exposed to air/oxygen.

And I find at that the cause of this is due to the Polyphenol Oxidase (PPO) enzymes being present inside the apple, when the enzyme is exposed to air/oxygen, it triggers a chemical reaction called Oxidation.

Perhaps this is better put on the Chemistry SE page since oxidation is much more important than beyond earth sciences, but I'll give my take on it from an atmospheric sciences perspective.

If oxidation isn't allowed to take place, then the hydroxyl radical ($\ce{^*OH}$), nicknamed the detergent of the atmosphere, cannot remove pollutants from the atmosphere. I think it is evident why removing pollution is a good thing.

This is just one of many uses that oxidation has.


What are the key elements defining the separation between Jurassic and Cretaceous? We have one mass extinction that seperates Trias from Jurassic, roughly huge volcanims over a long period of time, and Pangea starting to divide.
Another mass extinction that marks the end of Cretaceous period, linked to the fall of an asteroid.

However there is no mass extinction between the two:
What are the crucial elements for defining the limit between Jurassic and Cretaceous?

Short answer, there isn't one.

The J-K boundary does not have a well defined fingerprint or marker, because of this it is in flux with different studies constantly offering to tweek or redefine its date based on their own criteria.

https://www.sciencedirect.com/science/article/pii/019566719190001S

https://ui.adsabs.harvard.edu/abs/2017EGUGA..1912252L/abstract

https://www.researchgate.net/publication/236003223_Fixing_a_basal_Berriasian_and_Jurassic-Cretaceous_J-K_boundary-_perhaps_there_is_some_light_at_the_end_of_the_tunnel


Unable to prepare input file for HSPF software for watershed modeling! I am trying to use BASINS 4.1 software to prepare input file for HSPF (.uci). When I launch HSPF from BASINS software, I have to direct the sofware to read a time series file (.wdm). In my case I am unable to tell the sofware to do this because the 'met stations' tab is not providing me the option to do this. I am having complete blank 'met stations' tab. Anyone has any ideo how to fix this problem? Or is there any other way to prepare input file for HSPF (.uci file) without using BASINS?

I have found the solution and it seems that in BASINS 4.1, user has to import wdm file before launching HSPF by going to 'File' and then to either 'import data' or 'manage data'.  Once this step is done, BASINS 'understands' that there is a wdm file and then the user can add the wdm file from 'met stations' tab.
The tutorials on epa site correspond to BASINS 4.0 and in BASINS 4.0, one doesn't have to go through the so call 'import data' step before launching HSPF.


Can the crust be compared to an arch? Since tectonic plates are held together by lateral stress, friction, and gravity, and the Earth is a sphere, they work just like a full-circle arch or full-sphere dome. So can the crust be compared to an arch?

An arch is a poor analogy for tectonic plates.  The lithosphere is  supported beneath by the mantle, unlike an arch which is unsupported beneath.  If the lithospheric plates were only held together only by lateral stress, friction with surrounding plates and gravity, how would they move relative to each other?  How would forces at the plate interfaces vary?  How would subduction work without the whole thing falling apart?  I am not a geologist but I cannot see how this arrangement would work.

The mantle "fluid" that sits underneath the lithosphere convects and drives plate motion.  It accepts subducting plates and emits new oceanic crust along the mid-oceanic ridges.  The support everywhere underneath the lithosphere by the asthenosphere makes an arch a poor representation for the physics at work.

Yes, you are correct that at the tectonic plate edges there is lateral stress and friction and that the whole plate is subject to gravity.  What you are missing is  that the crust is everywhere supported underneath.  An arch relies on the lateral stress to stay standing while tectonic plates do not.


What is this rock found in the Illinois Valley of Southern Oregon? I found this odd shaped rock along a rocky river bed (dry) near the Illinois river in Cave Junction,  Oregon.  It is shaped like a Club and is super heavy.  It has a distinguishable ring around the base uniform in size,  and makes a dense ringing sound when rubbed?  I see some reflective flakes when turned and grainy but solid material on surface, 18 inches length. any ideas?

This is a sandspike concretion

Pictures can be seen here

Sometimes, only a spike is found and sometimes the spike has some 'balls' or round concretions attached to it.


Employment of Volcanologists and Petrologists What industries or government departments hire volcanologists and igneous petrologists/geochemists in the United States?

The first department that comes to mind is obviously academia, i.e. faculty or research positions at universities. However, there are many other career paths available (hopefully: there are not enough academic positions for every student completing a Ph.D...). For volcanologists, there is actually a nice site called volcanologists outside academia. As the name suggests, it compiles various testimonies about people who got a Ph.D. in volcanology but now work outside academia. They have also conducted a survey to gather more data. The results show that there are very diverse employment possibilities, including (but not restricted to):

Outreach/science communication
Museums
Academic publishing
Data analysis
Material science
Instrument companies
Tourism...

I'm not sure for igneous petrologists/geochemists, but I think the possibilities are pretty close.
Edit: I just realized I completely forgot to mention volcano observatories, which represent a "large" source of employment for the community (relative to its size). IAVCEI's Early Career Network has put up a series of videos where observatory workers describe their job. Another series about careers in academia is planned, so stay tuned!


How to know to which PC (Principal Component) a sample belongs in EOF/PCA I applied EOF (Empirical Orthogonal Function, a type of Principal Component Analysis, PCA) analysis to a dataset(geopotential height at 925hpa from ECMWF-interim reanalysis data) that contains 3 coordinates (time, longitude, latitude). Moreover, spatial field data at each time level was defined as sample or origin pattern. The results of the EOF showed that the first 4 PCs can explain 95% of the variance. How can I classify the sample or origin patterns into different PCs? In other words, which PC is similar to the origin patterns mostly?

I recommend you read Monahan et al. (1990) for a thorough explanation of Empirical Orthogonal Functions. I suggest you pay attention to the way the principal components are extracted. Ultimately, there is no guarantee that a sample belongs to a specific component. What you are working with is eigenvalues/eigenvectors and thus a specific data point can have influences from multiple components. The EOF provides a time series of eigenvalues for each component. The larger the eigenvalue for that component at a specific time, the more that component explains the data point.

If what you need is to assign a data point to a component, I would recommend a cluster analysis instead. For instance Smith & Aretxabaleta (2007) present an improved methodology to separate regimes that outperforms the EOF analysis in an ENSO-influenced dataset.


Seismic data processing software For processing seismic data, why is Seismic Unix so important? What distinguishes it from other seismic processing software like GLOBE Claritas or Omega?

Is it argued that processing capabilities are superior to other seismic processing software or that it is easier to use? Does it get recommended for use because of cost or its wide use?

Packages as Seismic Unix and Madagascar represent a different philosophy than commercial products.

The packages are open source, so any user can look at the code, understand how it works (or why it doesn't) and even produce reproducible research so other geophysicists can test the results and use the methods. A great way to learn about seismic processing is indeed by reproduce earlier studies.

A lot of new processing methods are developed within the Seismic Unix and Madagascar groups, and they are great sources if one needs a special tool for a special problem.

The packages are free and are widely used by universities, but they can also be useful for processing companies. It is easy to share or sell projects if they are built in code that everyone have access too.

If the processing capabilities are superior or not is generally about opinion, but at least the results can compare well with commercial packages. Sometimes they can be used in the same workflow, e.g. the geometry might be easier to do with a GUI but processing might be just as easy in a script.

My own experience is that the learning curve is rather steep in the beginning, but once you understand the basic tools, Seismic Unix and Madagascar are just as easy, or even easier to work with. Especially if there is a problem or you need to do something unconventional with the data.


Data of terrestrial evapotranspiration over large areas? I have been looking for information regarding the total amount of water that evaporates from terrestrial systems and found some global estimates like this one

http://www.waterandclimatechange.eu/evaporation/average-monthly-1985-1999

However, the units are mm/year but that doesn't mean much without the area. Are there any estimates of evapotranspiration that are available? Or how could I calculate evapotranspiration by area using maps such as the ones I have linked to?

Millimeters per year measurements have an area component built into them, they're actually in cubic millimeters per square millimeter. So one millimeter of rainfall is enough to cover the given area that rainfall is for to an average depth of one millimeter. For example if the area is a 100 square kilometer catchment then 1mm of rainfall is 100,000,000 cubic millimeters (also millilitres), or 100,000 litres of water. Evapotranspiration is measured using exactly the same unit conventions. Hope that helps.


What are the tectonic implications of the Quaternary Igwisi Hills, Tanzania, kimberlite volcanics? The Igwisi Hills Kimberlite volcanic features in Tanzania are described in the article Mapping the Igwisi Hills kimberlite volcanoes, Tanzania: understanding
how deep-sourced mantle magmas behave at the Earth`s surface (Brown and Sparks), as being Quaternary or younger in age and consistent with my earlier question and answer, What is it about ancient craton geology that results in associated kimberlite pipes containing economic diamond deposits?, it had erupted through the Tanzania Craton.

The article Tectonic setting of kimberlites (Jelsma et al. 2009) has made correlations between older kimberlite volcanics and aspects of the supercontinent cycle, specifically:

  Kimberlites can be viewed as time capsules in a global plate tectonic framework. Their distribution illustrates
  clustering in time and space. Kimberlite ages span the assembly and break-up of a number of
  supercontinents, such as Rodinia and Gondwana. These supercontinents show time lines with (i) broad
  periods devoid of kimberlite magmatism corresponding to times of continent stability, and (ii) narrow
  kimberlite emplacement windows corresponding to times of fundamental plate reorganizations.

Implying a link between parts of the supercontinent cycle and kimberlite magmatism.

However, this implied tectonic setting does not seem to match with Quaternary Tanzania, when the Igwisi Hills kimberlite volcanoes erupted.  Therefore, what are the tectonic implications of the Quaternary Igwisi Hills, Tanzania, kimberlite volcanics?

The only thing that comes to mind is the East African Rift tectonics, but are not sure about this link.

The Igwisi Hills kimberlites erupted through the Archaean aged Tanzanian Craton, which resides in between the eastern and western branches of the East Africa Rift (1), in the vicinity of the Gregory Rift (2). It is a series of 3 volcanoes, evidence has shown that these eruptions were the result small volume monogenetic eruptions (3).

Seismic studies and observations detected that the cratonic lithosphere base is approximately 170km, after which, there is anomalously low velocities to a depth of about 350km (1), which according to models described by Weeraratne et al. (1) indicate that beneath the cratonic crust, there is the presence of high temperature and the presence of melt:

a transition to a younger 'more fertile' asthenosphere.
crucially in terms of the local tectonics, indicate the presence of a mantle plume head causing the craton to experience uplift.

The mineralogy of xenoliths in the pyroclasts and lava further indicate that there has been small degrees of carbonate-apatite bearing peridotite source melts from depths greater than 110km. (2)

Brown et al. (3) conclude that the fact that these kimberlitic volcanics are so comparatively young, they may indicate that a new phase of kimberlite activity may be starting in the Tanzanaian craton, especially when considering the mantle plume and active rifting in the adjacent East Africa Rift branches.  This suggests that a link between kimberlite volcanism and the supercontinent cycle maybe too much of a simplistic view, when the reality is probably closer to individual plate reorganisation (in this case, the eventual splitting of the African continent).

References

(1) Weeraratne et al. 2003, Evidence for an upper mantle plume beneath the Tanzanian craton from Rayleigh wave tomography, Journal and Geophysical Research.

(2) Dawson, 1994, Quaternary kimberlitic volcanism on the Tanzania Craton, Contributions to Mineralogy and Petrology (abstract only - paywalled)

(3) Brown et al. 2012, Eruption of kimberlite magmas: physical volcanology, geomorphology and age of the youngest kimberlitic volcanoes known on earth (the Upper Pleistocene/Holocene Igwisi Hills volcanoes, Tanzania), Explore Bristol Research (abstract only - paywalled)


Where are the magnetopheres weak points on Earth? The picture below shows how a magnetosphere has defined points on the solid magnet and on the moon where cosmic radiation has a window, gap, or focal point. I'm not sure what to call these areas?

Where on Earth are these areas? Is there a map where the magnetosphere or local natural magnetic fields has this same effect?

The region where the Earth's internal magnetic field is weakest is known as the South Atlantic Anomaly (SAA). In this region at Earth's surface, the field is approximately one third the strength of the region of maximum strength (near the North and South magnetic dip poles), so roughly 20,000nanoTesla versus 60,000nanoTesla.

The weaker field seen at Earth's surface is caused by opposite polarity field at the surface of Earth's outer core (inwards instead of outwards like in the rest of the Southern hemisphere). It allows the radiation belts closer to Earth's surface, and allows charged particles to penetrate lower into Earth's atmosphere, increasing the risk to satellites flying through the region.

  Source: NASA, via wikimedia

  Source: USRA The weaker region of field over the SAA allows the radiation belts closer to the surface, so increases the occurrence of electrical upsets (yellow dots in the image) on satellites flying through the region, here the TOPEX/Poseidon satellite. The contours are magnetic field intensity in nanoTesla.


High vertical resolution atmospheric sounding data I'm currently doing some analysis using atmospheric sounding data available at University of Wyoming (I assume these are from the GTS network).
But, the vertical resolution of the sounding data available at University of Wyoming is very low for my use case. Except for the low vertical resolution, this data is perfect for my analysis.
Is there an atmospheric sounding dateset that has higher vertical resolution that I could use?

Looking for similar for another recent question, I stumbled across https://www.sparc-climate.org/data-centre/data-access/fisaps/ which lists quite a few options on HVRRD (high vertical resolution radiosonde data)
Looks like a lot to sift through, but if your project can work for past data over the US, I found that from ftp://ftp.ncdc.noaa.gov/pub/data/ua/rrs-data/ I was able to download the files and extract them using their software, resulting in data every second, typically about 5-10 meters apart... here's a clipped view with a rough idea of the type of data it has (also has v-wnd):

Perhaps that fits your needs?
If not, and you can't find any useful data from the first link, maybe also try looking around https://madis-data.ncep.noaa.gov/madisPublic1/data/point/ ... there's things like ACARS (commercial aircraft sounding data), MADIS data (satellite), radio profilers, etc.  Though less confident you'll find a resolution you want, never hurts to try.
But hopeful you'll find what you need with the HVRRD stuff!


Is there any covalent crystals that can be easily synthesized? I am looking for a kind of crystal that can be artificially made at relatively low temperatures (below 1500 degree Celsius) and relatively quickly (not geological time). The product is ideally monocrystalline, not reactive to oxygen or moisture and not metallic. Ice is excepted.

If such a material exist, I would like to know its name, composition and any other noteworthy properties. If there is anything wrong with the premises of the question, please point it out.

Silicon carbide is covalent and can be synthesized at atmospheric pressure by the Acheson process. Temperatures may actually be somewhat higher than your range but are easily achieved by the process.

1,4 dichlorobenzene (used in moth balls) is a compound that forms crystals at low temperatures. I think the molecules in the crystal are joined only by weak bonds so I don't know if that is what you are after.


Tornadoes meeting with an Immovable, Unbreakable, Large Cube What would happen to a tornado if a Large, Immovable, Unbreakable and Obsidian Cube was in its path?

The tornado is on a flat plain... but is heading towards the cube.

By large, I mean the length of the cube's edges is as long as half the width/height of the tornado, whichever is larger.

Or is this more Physics, instead, of Earth Science?

It depends.

Take a look at this recorded presentation from the 27th Conference on Severe Local Storms by David C. Lewellen and the accompanying pre-print.  This talk focuses on the effect of buildings on tornadoes though the buildings are examined as fixed blocks they are not modified or damaged, but remain a fixed obstacle to the tornado (he toward the end does show that he models forces of the tornado on the building but does not allow that to change the building).

The effect of the block depends on whether the tornado is high or low swirl, the relative position of the block to the tornado and the size of the tornado.  The block weakened some tornadoes and strengthened others.


Why are there different vertical gradients of temperature in different layers of the atmosphere? The temperature of the troposphere decreases with altitude whereas it is opposite in the stratosphere and again fluctuates. Why is this so?

The strong heat flux through the Earth's atmosphere, the presence of greenhouse gases, convection, and mixing conspire to push the troposphere away from thermodynamic equilibrium (isothermal atmosphere) and toward an adiabatic atmosphere. The natural drop in density with altitude means an adiabatic atmosphere is subject to a lapse rate, a nearly linear drop in temperature with increasing altitude.

Temperature rises with altitude in the stratosphere because this is where the ozone layer exists. The troposphere is primarily heated from below. In contrast, the stratosphere is primarily heated from within via absorption of ultraviolet sunlight by oxygen and ozone. A similar situation exists in the thermosphere, which is where the extreme ultraviolet and higher frequencies of sunlight are absorbed.

The thermosphere is where atmospheric temperatures attain their highest values. (BTW, you wouldn't feel those extreme temperatures if you put on a spacesuit and took a spacewalk in the thermosphere. There's hardly anything there that high up.) In between the thermosphere and stratosphere is where atmospheric temperatures attain their lowest values. This is the mesosphere. Most of the extreme wavelength radiation has already been absorbed in higher layers. The mesosphere is too thin to support an oxygen-ozone cycle. All that's left is radiational cooling supported by a strong greenhouse effect, making the top of the mesosphere (the mesopause) extremely cold.


Modelling extreme rainfall events: 'blanket approches' when considering soil infiltration For my thesis on modelling an extreme rainfall event with a 2D surface runoff model I'm supposed to consider the effect of soil infiltration on the runoff: In my work description it says I'm supposed to "choose an appropriate approach to model soil infiltration because 'blanket approaches' (if its the correct english translation) have uncertainties". As an 'appropriate approach' I got recommended to use a software which computes a runoff-coefficient. But what are the 'blanket approaches'? I probably need to use one or more of those 'blanket approaches' and compare them with the results from the software. Any ideas what is meant?

I would be surprised if the rainfall-runoff relationship would show a linear relationship for extreme events. I would consider that to be a blanket approach, if you mean using a constant coefficient. So consider using a higher order relationship.

Another thing to consider is whether the rainfall runoff relationship depends on the soil moisture. Maybe check out how other models like SWAT deal with this.

To be honest, I think that the amount of soil infiltration will be insignificant for extreme rain events because it occurs too slowly compared to the rainfall rate and other uncertainties.


Zoeppritz equations derivation I have been long looking for the derivations and step by step explanation of Zoeppritz matrix but either internet is full of final versions or I can’t find it...I would be very thankful if anyone can direct me or provide me with derivations.

The Wikipedia entry for Zoeppritz equations says:

  A full derivation of these equations can be found in most exploration
  geophysics text books, such as:

  Sheriff, R. E., Geldart, L. P., (1995), 2nd Edition. Exploration
  Seismology. Cambridge University Press.


How do I read IASI GDS L1C in Python? I'm trying to read IASI GDS Level 1C data (all spectral samples) in the EUMETSAT EPS Native Format, as documented in the Generic Product Format Specification (PDF, 738 KB, 72 pages) and the IASI Level 1 Product Format Specification (PDF, 2.5 MB, 60 pages).  EUMETSAT supports a reading routine in IDL.

The IASI Level 1 Product Guide (PDF, 5.8 MB, 110 pages), section 5.1, notes that

  The products can be read using standard HDF libraries

but trying to open a test file with

h5py.File('IASI_xxx_1C_M02_20110528114454Z_20110528132653Z_N_O_20110528132912Z.nat', 'r')

results in

OSError: Unable to open file (Unable to find a valid file signature),

and neither the Generic Product Format Specification nor the IASI Product Format Specification mention HDF, which would be odd if the format was HDF-compatible.

The Basic ENVISAT Atmospheric Toolbox (BEAT) contains a component called the Common Data Access toolbox (CODA; also available on github).  BEAT and CODA are written in C and have bindings for Python (as well as Matlab, IDL, and a few other languages).  Among the long list of supported products is IASI L1C.  Apparently, BEAT is going to be replaced by HARP (github page), but HARP reportedly does not yet support IASI L1C.  BEAT, CODA, and HARP are all available under the GPL.

Although the BEAT website reports Python bindings are only available for Python 2.7, I have successfully used CODA with Python 3.5 (I did not try BEAT as I do not currently need the higher-level functionality it offers).


Are Fluvial and River Terraces the same? I study about fluvial terraces. However, resources related to this topic are limited. When I searched fluvial terraces in geomorphology books, I cannot find anything, but I find river terraces. My English is not good, so I am not sure fluvial terraces and river terraces are same. Do these two terms represent the same topic, please help me?

In English, the word fluvial comes from the Latin word for river.
Fluvial processes are processes associated with rivers or streams and the deposits and forms created by them.
River terraces and fluvial terraces are the same thing.


How long will it take for the ocean to erode Rockall? Loosely related to the question Will the ocean eventually erode all land?:

How long will it take for the ocean to erode Rockall (an uninhabited granite islet within the exclusive economic zone of the United Kingdom)?

On the assumption that plate tectonics is paused. (If you know that plate tectonics will carry rockal below the waves before it erodes please do mention this in your answer!)

I understand that the rate and size of storms will have an effect, both of which are unpredictable, therefore I am more than happy with an order of magnitude indication.

If you have any sources to back up numbers you've used in calculations, such as the rate of erosion of the basalt, that would be great, as I would love to do some further research.

Impossible to give an accurate answer because nobody has ever studied rates of erosion of this kind of rock in such a setting. Typical long-term rates of cliff cut-back in an exposed position are 5 to 20 cm per year, but that is for average rock, which is much softer than Rockall. This is a complex rock, mainly comprising Aegirine Granite, and containing some unique minerals. I'm guessing that the combination of sea salt corrosion, frequent wetting and drying, and chemically aggressive leachate from all that guano will result in a rate of chemical erosion of 0.5 to 5.0 mm per year. Let us say 2 mm per year - a high value but under the extreme circumstances, certainly plausible.  Given that the rock is only about 25 metres along the lesser axis, and that chemical and weathering attack will occur on all sides, that should give a 'demolition rate' of about 6000 to 7000 years. But that's only chemical erosion. There is also the physical erosion to consider. None of the photographs I have seen give a good impression of the potential for basal abrasion. What your photograph does indicate however is that there are eroding oblique fractures. These will facilitate sea water and wave ingress which will eventually fragment the rock and accelerate its demise. Overall I would be very surprised if there is anything left above the waves in 4000 to 5000 years from now. Even without erosion, climate change is likely to raise sea level at least 7 metres by that time, in which case it may completely disappear in as little as 2000 to 3000 years.


Using Enhanced Rock Weathering in the Sahel Region of Africa A recent Guardian article "Spreading rock dust on fields could remove vast amounts of CO2 from air" has gotten some attention in the nongovernmental and UN organizations working in the Sahel who are desperate to combat the adverse effects of climate change in the region. This article is based on a Nature publication on enhanced rock weathering (ERW).
Let's pretend a large international organization has tasked a newly employed software developer to look into the feasibility of performing ERW in the Sahel. Now this let's say this software developer, who has no geological background whatsoever, is trying to figure out what it would take to run a ERW pilot in the Sahel and decided to investigate Bol, Chad to have a specific place to focus on.
Ideally, this pilot would seek to test two things (i) is ERW feasible to perform in the region of conflict, (ii) does the crushed basalt or silicate, which is added to the soil, increase crop yield?
In order to determine if this pilot is feasible to even consider I think the following should be investigated:

Current farming methods in the region
Feasibility of acquiring and transporting crushed basalt or silicate
Method for applying the basalt or silicate to the soil

What else should I look at?
If you were given this (completely hypothetical) task where would you start?
Is there any giant red flag I am missing which would be enough of a reason not to move forward with a pilot?

OK I did a paper on mitigating climate change by enhanced weathering of rock on agricultural land for my masters (2014) it's not brilliant, but it does include some useful references if you want to research this further.
I would imagine the main limiting factor in the Sahel region would be that the process needs to be wet. So you're possibly only talking about being able to add material to irrigated areas. There are also the limitations you've already discussed of getting the material on site. In terms of crop yield, I would suggest that it will only increase plant growth in areas which do not already have alkaline geology (and I have no idea what the geology looks like in the Sahel, I'm afraid) and adding too much to soils may well actually decrease site fertility without the addition of something else (manure is the traditional amendment)
As far as I'm aware, enhanced weathering is perfectly technologically feasible, but it does have a limited application - due to the sheer quantity of it we'd need.
Hope this helps.


Is it meaningful to assume static pressure to be constant along a streamline? I am looking at Bernoulli's equation formulated in two dimensions, which reads
$$\frac{v^2}{2}+c_p\theta_0\pi+gz \equiv \mathrm{const.}$$
along a given streamline $\gamma$, where $v=|\mathrm{v}|$ for the flow field $\mathrm{v}(x,z)$ which is in steady state (i.e. $\frac{\partial\mathrm{v}}{\partial t}\equiv 0$) and $\pi=\left(\frac{p}{p_0}\right)^\frac{R}{c_p}$ is the Exner function. The potential temperature $\theta$ is assumed to be constant equal to $\theta_0$ along $\gamma$. Now if we assume $\pi$ to be constant along $\gamma$ as well, we end up with an upper bound to the maximum upward displacement an air parcel with initial velocity $v_0$ and initial height $z_0$ can attain, namely
$$z_{crit}= z_0+\frac{v_0^2}{2g},$$
since
$$v^2=0 \text{ if and only if } z-z_0=\frac{v_0^2}{2g}.$$
But is the assumption that $\pi$ is constant along $\gamma$ a physically useful one? I cannot find a discussion concerning this in any textbook on meteorology I currently posses, neither in internet resources. Any advice/resource would be appreciated.

If you assume both hydrostatic and pure geostrophic balance, that is a valid assumption.

In Einstein notation, $$u_i=-\frac{1}{f \rho}\frac{\partial P}{\partial x_j}\epsilon_{ij3}$$

If we look at the equation for the streamline:$$u_i=-\frac{\partial \psi}{\partial x_j}\epsilon_{ij3}$$, then we can see that

$$-\frac{\partial \psi}{\partial x_j}\epsilon_{ij3}=-\frac{1}{f \rho}\frac{\partial P}{\partial x_j}\epsilon_{ij3}$$

which simplifies down to $$\frac{\partial \psi}{\partial x_j}=\frac{1}{f \rho}\frac{\partial P}{\partial x_j}$$. Thus, for isochoric (incompressible) geostrophic flow on an f-plane, the streamfunction only depends solely on pressure.


Recommendations for books on boundary layer Meteorology? Does anybody have any recommendations on books tackling Boundary layer Meteorology? I've seen the book by Roland Stull and Arya, but are there any other more updated ones that are as good as these two?
Also, would anyone have a resource for the full solutions to Stull's book for BL Meteorology?
Any help would be highly appreciated. Thanks!

Is there any particular aspect of boundary layer meteorology? Or just something general?
NOTE: I have not read all of these nor do I know anyone who has read these, but judging by the year published or level of detail, these may serve whatever purpose you want. I found these mostly by Googling. I recommend looking at the preview offered in each website.

Turbulence by John Wyngaard- published in 2010
Fundamentals of Boundary-Layer Meteorology by Xuhui Lee was published in 2017, but from the brief look inside, I don't see a large difference from Stull or Arya.
Atmospheric Boundary Layer Integrating Air Chemistry and Land Interactions (2015)
Turbulence and Dispersion in the Planetary Boundary Layer By Francesco Tampieri · 2016


Standardized scale for coastline length or mapping in general? Measuring the length of a coastline depends on the scale of the measuring tool. The smaller the scale of your tool, the longer will your measured coastline be. The reason for this is the fractal property of coastlines. This is well known since a paper by Benoît Mandelbrot "How Long Is the Coast of Britain? Statistical Self-Similarity and Fractional Dimension".

Now I was wondering if there is a standardized mapping scale to come up with global or country wise numbers of coastline length?

And furthermore, if there even is a general rule for all mapping purposes, which scale is to be used in mapping?

Is there maybe even something like an ISO standard for this?

One standard that has be used by the USA is to measure the distant between points on the coast at intervals of 30 latitude minutes, as measured on a 1:1,200,000 scale map.

See chapter 5 of Measurements from Maps: Principles and Methods of Cartometry by D. H. Maling for further information and other standards that have been used.


Why is there no desert in Southeast China? Arabia, Sahara and Southeast China and India all are on the tropic of Cancer yet Southeast China and India are not deserts. I know that India is not a desert because of monsoon wind which causes heavy rain. But China doesn't have that kind of wind. Also Tibet which is in Southwest China is very dry because the moist air doesn't get over the Himalayas. But east of that you would normally expect there to be another big desert, but there isn't. Why is this?

This is a very active region for tropical storms.

NASA


If US emissions went to zero how long until global emissions reach current levels Given the current global CO2 emission trends, if the US overnight magically went to zero emissions (without affecting worldwide emissions), how many years until global CO2 emissions return to exactly where they are now.

That will depend on the emission scenario you pick for the future, the more recent scenarios are the RCP's (Representative Concentration Pathway).

RCP scenarios

The scenarios involve future pathways in the emissions of a large range of different chemicals (Greenhouse gases and aerosols). Each RCP have a temperature tag, for example RCP6.0, is a scenario that consider many geopolitical, social and economical predictions and that would result in an emission pathway that would the radiative forcing (input energy to Earth) by 6.0 W/m$^2$ by year 2100.

The data associated with the RCPs can be accessed in the RCP Database, this is a plot generated there with Global $\text{CO}_2$ emissions for all four RCP scenarios.

According to this data, the U.S. was responsible for 14.34% of the global emissions of $\text{CO}_2$ on 2015.

If we consider that overnight all scenarios switch to a  version of themselves with a 14.34% emissions reductions (i.e. like if the US stopped all its emissions suddenly), the plot would look like this:

Where the dashed line is the new emission pathway and the thin dotted line marks the global emission level before the US $\text{CO}_2$ shutdown.

We can see that for RCP2.6 and RCP4.5, the world would never get back to emission rates as high as those of today. And for the more pessimistic scenarios it would take at least 10 years to go back to those levels: For RCP6.0 it would go back to current levels by 2041 and for RCP8.5 by 2029.

There are many simplifications on this calculation, but gives you a first approach. If you are interested in another emission scenario you can apply the same methodology or a better one, but maybe this can serve as a starting pint.


As the number of ocean dead zones increases, is the world's primary source of atmospheric oxygen (phytoplankton) at risk? Disclaimer: I am not a scientist.
I was wondering if there is a concern that the world will run out of breathable atmospheric oxygen as the number of dead zones in the ocean increases with global warming. This concern is based on the understanding that 60% (give or take) of our breathable oxygen is produced by phytoplankton. I have read a few peer reviewed articles to that effect, all by the same author, but haven't seen any articles that counter that concern.

Yes, it is, though probably not immediately. Ocean and atmosphere deoxygenation is a thing, and many publications are out.
In a larger context, deoxygenation is indeed inevitable even if we ignore anthropogenic warming. Increasing solar flux alone (the sun get's hotter over its lifespan) could reduce the atmospheric oxygen to 1% of present day level within around a billion years, says this publication.
This publication estimates that almost 80% of ocean deoxygenation under current day CO2 levels have not been realized yet, but they say that oceanic surface deoxygenation will stop once CO2 emissions stop, while the deep ocean oxygen levels will continue to decrease.
A global warming by 6°C (which is at the upper end of current projections until the end of this century) could tip the oxygen production by phytoplankton, cancelling the ocean's role as a main oxygen producer.
Citing from the abstract:

[...] If, in the course of time, the oxygen production rate becomes too low or too high, the system’s dynamics changes abruptly, resulting in the oxygen depletion and plankton extinction. Our results indicate that the depletion of atmospheric oxygen on global scale (which, if happens, obviously can kill most of life on Earth) is another possible catastrophic consequence of the global warming [...]


What factors affect the size of rain shadows? Rain shadows are dry areas on the lee side of mountains. Due to humid air condensing and precipitating as they are lifted up and over the mountains, they lose moisture by the time they reach the lee side, forming a relatively dry area.

What factors affect the size of this dry area, and how?

Of course, first you will need a collision zone where moist air collides with dry air - and therefore you will need to consider a considerable air flow in the opposite direction to the flow responsible for the rain shadow.

For example, in Eurasia, the Himalayan rain shadow extends up to the Kazhak steppes, until regional climatic effects of the Black Sea and Caspian Sea moderate the dryness. The Russian heartlands are blessed with the Dvina-Sukhona river; which starts at the lake Kubenskoye; which is blessed from Baltic Airs, still under the effects of the westerlies: thus you do not directly have a moist airstream colliding with the dry air from the opposite direction, but from the side.

In contrast, the German northeast, Mecklenburg-Vorpommern is within the rain shadow of the central German Harz mountains - but the river Oder is also inside the rain shadow. This brings us to the second point: topological relief. Is it sloping towards the rain shadow, such that the rain water from the other side drains into the rain shadow?

In this case, sooner or later you will form rivers - and lakes, unless the river meets the sea very quickly (as in the case of Germany and the Baltics). As soon as you have lakes, the rain shadow will be moderated.

Taking yet another example, the Kalaharis: east of Namibian Great Escarpment, and west of Highveld/Drakensberg. Thus Kalahari lies within a rain shadow from both east and west - and despite the river Okawango flowing in it, the climate is not moderated.

So there are uncountably many factors that contribute to your question.


Do any rivers deposit sediment in their deltas fast enough to counteract sea level rise? Assume a 1m per century sea level rise. Looking at a topographic map it quicly becomes clear that Bengal, the Netherlands, the lower Mississippi, South American Mesopotamia, etc will all soon be underwater.

Which rivers, if any, deposit sediment in their deltas or mouths fast enough to counteract a 1m per century rise in sea level?

This is a hugely complex subject for which a categorical answer requires detailed river basin modelling and process calibration. The short answer is that in the short term many rivers deposit sediment much more rapidly than the hypothetical 1m per century, because sediment transport is roughly proportional to the fourth power of the stream velocity. So enormously high deposition occurs in the few hours per year of peak discharge. Mean annual deposition, however, is a different issue, and inordinately difficult to measure. A typical mean rate of sedimentary deposition is roughly 2 to 3 mm per year +/- at least an order of magnitude. This is slightly less than the current mean rate of sea-level rise, but remembering that the rate of sea-level rise is accelerating, and is likely to continue accelerating well into the next century. Projected rates of sea level rise by 2100 are tricky to estimate (too many unknowns) but >10 mm/year seems likely, in which case probably no significant rivers will be able to compensate by high sediment deposition. There will be occasional anomalies, such as the rivers around Mount Pinatubo in the Philippines, which had jaw-dropping sediment loads for the few years after the volcano erupted, caused by huge quantities of un-cemented volcanic ash over entire catchments, coupled with typhoon rainfall.

In the case of really big rivers with perennially high sediment loads, one thinks of the Mekong and the Ganges-Meghna-Brahmaputra, both of which have huge monsoonal sediment fluxes. Both river systems have pro-graded their deltas surprisingly recently. Check out their delta areas on Google Earth. All of that sediment was deposited during the last 6000 years. During most of that time, sea level rise seems to have been very modest, averaging about 1.5 to 2.5 mm/year.
Since you pose a climate-change related rate of sea level rise, one must also consider how climate change will affect the hydrologic response of these catchments, and hence how the rate of sedimentation will change? Even with a three-year research grant I would be hard-pressed to answer that question, but my suspicion is that sea-level rise will win, and most of the major deltas will succumb to the waves.


How do I represent wind direction on a UTM (Universal Transverse Mercator) map projection? What does it mean when I say "the wind direction is 50o" on a UTM map? Which direction is the 0o reference?

For example, if I draw a wind vector V as seen in the image below, what degrees does it correspond to for the UTM map?

Meteorological winds are referenced from North being 0$^{\circ}$ increasing in a clockwise direction.  Additionally, they are named for the direction the wind is coming from.  Your vector on the map, which is mathematically 45$^{\circ}$ is meteorologically 225$^{\circ}$ aka a southwesterly wind.

A 0$^{\circ}$ wind is a wind from the north (math vector 270$^{\circ}$).
A 180$^{\circ}$ wind is wind from the south (math vector 90$^{\circ}$).
A 50$^{\circ}$ wind is from the northeast (math vector 220$^{\circ}$).

In general if $\alpha$ is the mathematical angle and $\beta$ is the meteorological angle, then the relation between the two conventions is given by $$\alpha = 270^{\circ} - \beta$$ where angles are specified in degrees.

Image from https://www.e-education.psu.edu/meteo300/node/719 from Penn State available under CC-by-nc-sa-3.0


Is there an earth science discipline, or subdiscipline, that only studies magma or lava? I know volcanologists study volcanoes. Is there a subdiscipline that only studies maga or lava? A magmatologist?

Perhaps they are called Igneous Petrologists ?

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


Does Earth's air leak into space over time? From my current understanding, Earth's atmosphere and air are held by the balance of two forces: 1. Earth's gravity and 2. Air pressure from air out to space.

Is my understanding correct?

So, do these two forces always stay the same? If they are not the same, have the earth lost its air into space? And if so by how much each year?

Earth's atmosphere does escape over time, albeit very slowly.

The distribution of kinetic energies of molecules in a gas obeys (more or less) a Maxwell-Boltzmann distribution. Notice that the graph is asymptotic, so in a suitably large population of gas molecules, there is a non-zero probability that some of those molecules will have a an arbitrarily large kinetic energy. This implies that in the population of gas molecules constituting Earth's atmosphere, some of them will have kinetic energy such that their velocity exceeds the Earth's escape velocity and provided that their paths are oriented away from any obstacles (including the Earth's surface itself) and they don't collide with anything, those molecules can escape. On average, only a small number of molecules will actually achieve all these conditions. The end result is that atmosphere does indeed escape, but the effect is tiny - only on the order of grams per second due to the process described above according to this article I found.

This is not the only process responsible however, phenomena like the solar wind also have a role in liberating gas molecules from the Earth's atmosphere.

The effect is much more pronounced on other rocky planets in the Solar system, for example Mercury has very little atmosphere due to it i) being extremely hot and ii) being bombarded by highly energetic particles from the sun much more than we are. Similarly, Mars has a predominantly carbon dioxide atmosphere that is thought to have been much thicker in the past than it is now, and therefore must have escaped somehow (assuming you don't believe stories like Total Recall where the atmosphere is intentionally held captive ;) - although in fact the Martian atmosphere does condense at the poles leading to a significant amount of atmospheric agitation with the changing of the seasons)


What is the highest balloons possible in a chain? The BU60-1 balloon attained an altitude of 53.0 km (32.9 mi; 173,900 ft).

Weather permitting, would a series of climbable balloons in a chain be able to be linked from the ground to that height of 53 km?

To gain altitude each balloon must be gradually bigger.
At the bottom balloons would be made of more durable material.

I have found no record of this being done with higher tech weather balloons.

It would certainly be possible to construct a series of balloons that reached neutral buoyancy at different altitudes, so in that sense the answer is "yes".

I'm not sure whether there's necessarily any correlation between balloon size and altitude, except in that a given balloon will expand as it rises.


Do Hydro-Carbon extraction units pollute ground water? I am from India, Tamilnadu state. Our nation has planned to have hydrocarbon extraction units in our Thanjavur villages. We, a 70 million people Tamilnadu state get most of our rice from that region.

Our government says, An extraction unit requires only 5 acres and it won't affect the nearby farmers or the ground water at all.

Some people say Hydrocarbon needs to be extracted from the ground level deeper than that of water. So it requires polluting/draining all the ground water and the process will exterminate agriculture in that area.

We do not have reliable rain for decades to farm. We rely mostly on the ground water for food production.

Thank you.

The types of hydrocarbon extracted from the ground ranges from gas to crude oil and bitumen. Each deposit of hydrocarbon is different; some are all gas whereas others are various types of crude oil or mixtures of oil and gas.

Extraction methods also vary depending on the style of geology containing the hydrocarbon.

Geology with relatively large spaces between the grains of the rock, such as sandstone, may have hydrocarbons that can flow easily. This type of deposit represents the classical oil deposits, such as in Saudi Arabia. Generally, with such deposits, holes are drilled into the deposit and oil is pumped out.

Geology with very tight spaces, such as shale, do not have the conditions for hydrocarbons to flow easily. In this type of geology the rock needs to be fractured to allow the hydrocarbon fluids to flow more easily. To achieve this a relatively new technique called fracking is used to fracture the rock containing the deposit.

Both classical hydrocarbon extraction and fracking require the use of drill holes to access the deposit. If the deposit of hydrocarbon occurs below a water aquifer, or other form of ground water storage, the drill holes that access the hydrocarbon deposit will pass through the underground water store.

To prevent the hydrocarbon wells (drill holes) from contaminating the water lying above them, the wells need to be cased (lined). The casing of hydrocarbon wells needs to be done by people who are committed to doing so and who are extremely competent in doing such tasks.

Nothing is ever perfect and there will always be risks of well casing failing which would result in ground water contamination. It then becomes a question how large is the risk, what will be the effect of such a risk and who is prepared to take such risks.


Is there a measure for the "dominance" of a city's population? since there are topological isolation as well as prominence as measures to describe how "dominant" a summit is in comparison to the ones surrounding it, I was thinking about a similar measure to describe the dominance of a city in terms of population.

This would be a nice asset for an automatic map labeling system which labels cities on a map, omitting suburbs of a bigger city right next to them and featuring smaller towns which are the biggest cities in a certain radius, though.

I can think of it as a function which takes the population of a city and the distance to the next more populous city and generates some kind of "dominance score". The higher it is, the more likely it is to be featured on a map.

So are there already any algorithms covering this? Or maybe just "best practices" I can use?

Exciting question... it's something I've wondered as well, both for interest purposes and for utility in programs like you mention (I posed a fairly related question in the cartography SE site proposal).  I've searched a long time but could not find any term/calculation for this... perhaps I too just did not know the correct term to use?

As a result, for a very basic calculation, I created an Excel spreadsheet and worked with US locations to formulate a simplistic prominence... calculating just the distance each city is from the nearest larger city.  The outcome was this Sporcle quiz.

My results are likely not of great use for within a mapping program, as it takes no account of the degree of relative population size... but certainly would be interested in knowing more about that as well, as I've looked for a way to better prioritize the cities shown in a weather mapping solution I use.  Not sure you'd be able to use contouring methods given the discretized nature of population.  Instead I'd imagine perhaps iterating until you find the radius from the city border centroid where the surrounding population matches the population of the city.   That sound like a more complex GIS problem, one I've considered asking before but haven't even been sure how to narrow down into a basic enough question for SE!  Still, if there's no luck here of existing formulas, and you work out what way you want to calculate such a prominence (and can then boil it down to a basic question) GIS StackExchange may be the place to try.  Hopefully you'll give us the link to any questions you propose there so users here can follow any resolution!

If the basic prominence I calculated is somehow useful, I could dig up the full spreadsheet.  I believe I also might have found a potential global dataset as well, but never followed it up.

I cannot exaggerate how exciting it is to see someone else thinking about this topic, and hope your question brings some further better answers from those in the know!


Seismogram deconvolution in SAC Good day! I have a problem replicating a result. Let us consider the top plot here:

On the plot, velocity is in mm/s. I think the problem is to remove instrument response correctly. I downloaded seismogram and pole-zero instrument response. I want to obtain velocity data. The instrument response is already given in velocity. I was able to get synthetic seismograms as shown in the figure, but I have a problem working with real data.

I need a signal to be filtered in 0.001–0.004 Hz

Using IRIS SAC software, I do:

SAC> r KYK_BHZ
SAC> rmean
SAC> rtrend
SAC> taper
SAC> trans from polezero subtype KYK_LHZ.zp
SAC> bp p 2 n 4 c 0.001 0.004

I do not set FREQlimits for transfer function at all here, but I tried to do it like 0.0009 0.001 0.004 0.005 or 0.0009 0.001 1 2, but it also doesn't work.
My synthetic seismogram is 1 Hz data, so I don't do any  resampling.
I tried to do trans from polezero subtype KYK_LHZ.zp to vel, but it also doesn't work.

Both the data and zero-pole files are here.

Thanks!

I typed in the commands as shown using your data in SAC. I've uploaded my result.  The plot window shows the result of the commands run in the highlighted red area. Is this what you are trying to do? The plot xlim is set from 1750 s to 2700 s.


How to read a NetCDF4 file in Matlab? I have downloaded the sea surface temperature data from the Ocean Color website, the file is in NetCDF format and contains no of geophysical_data variables like sst, qual_sst, flag_sst, bias_sst, etc.
I used the following MATLAB code for file read and it is giving me an error:

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

Error:

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

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

Error in ncread (line 58)
vardata = ncObj.read(varName, varargin{:});

Can someone tell me what is the cause of the error?

These days I use: ncgeodataset. The routine allows for the extraction of a subset of data without having to load the entire file or even an array into Matlab. It is great for large datasets.


Why does wind blowing against a strong current create way bigger waves? It's a well known fact that wind will cause very big waves if blowing against a strong current, for example in the gulf stream off the US coast, or in the bay of San Francisco with a very strong (5 knots+) tidal current.

Notably, a 30 knots wind against a 3 knots current will create way bigger waves than a 33 knots wind against no current at all, even-though the relative speeds are obviously the same.

What is the explanation of this phenomenon?

There are two physical processes at play here:

Wind speed relative to the ocean surface
Wave focusing and blocking in opposing current

Wind speed relative to the ocean surface

As you describe in your question, wind speed relative to the ocean surface varies depending on the current orientation and magnitude. The rate of wave growth is proportional to the wind speed $U$ in direction of the wave relative to the phase speed of the wave $c_p$, squared:

$$
S_{in} \sim \left( U - c_p \right)^2
$$

However, the wave phase speed is modulated by the current:

$$
c_p = c_{p0} + u
$$
where $c_{p0}$ is the intrinsic phase speed (phase speed in absence of currents) and $u$ is in the direction of the wave. Negative value of $u$ is then an opposing current. Wave growth is then:

$$
S_{in} \sim \left( U - c_{p0} - u \right)^2
$$

Let's plug in some numbers here. Let's say $U = 10\ m/s$, $c_{p0} = 3\ m/s$, and $u = \pm 1\ m/s$:

In the case of following current, $u = 1\ m/s$, $S_{in} \sim 36\ m^2/s^2$ ;
In the case of opposing current, $u = -1\ m/s$, $S_{in} \sim 64\ m^2/s^2$ ;

Thus, by changing the orientation of a moderate current in characteristic wind and wave conditions, we increased the rate of wave growth by a factor of 1.78! This effect will be more powerful the smaller the relative wind speed $U - c_{p0}$ is.

Wave focusing and blocking in opposing currents

Wave energy is advected (transported) by the waves' own group speed $c_{g0}$ and also by currents. If for simplocity we drop all the other terms in the wave energy balance equation, we get:

$$
\dfrac{\partial E}{\partial t} = -\dfrac{\partial \left[\left(c_{g0} + u \right)E\right]}{\partial x}
$$

The crux here is in the modulated group speed $c_{g0} + u$. If the waves propagate into an area of increasingly stronger opposing current, there will be a convergence of wave energy in that space, which will manifest itself in increase of high and steep waves. At the point where $c_{g0} = -u$, that is, the current is exactly countering the group speed of the waves, they can no longer propagate in that direction! Wave energy accumulates locally and vigorous wave breaking ensues.

Summary

Wave blocking is a different process from the wave growth dependence on relative wind speed described above, but, they often correlate because young windsea (short waves locally generated by wind) are almost always aligned with wind direction, so all you need is the currents to oppose wind for both of these effects to come into play at the same time.

Both are likely to occur in strong and steady western boundary currents such as the Gulf Stream, Kuroshio, Aghulas, and Brazil current, and also in any region with strong tidal currents.

More on this topic in the answer to this question.


XRF analysis - recalculating results For TAS diagram plot, one need to recalculate Major oxide data (NaO, K2O, SiO2).

Do one need to recalculate the ppms of Zr,Nb and Y and % of TiO2 for Zr/TiO2 vs Nb/Y diagram plotting for rock classification?

It is best to recalculate all major oxide (including TiO2), trace elements are not important. No need to recalculate them.


Why is ocean salinity not a good chronometer? In 1910, George Becker published The Age of the Earth, in which he used the sodium accumulation rate in the ocean to estimate the earth's age as 50 to 70 million years. We now know through various methods that the earth is much older, and as far as I can tell there hasn't been much interest from scientists in using ocean salinity as an age indicator since Becker.

One more recent paper, "The Sea's Missing Salt" (PDF), claims a maximum age of 62 million years after totaling sodium inputs and outputs. I've found a couple claims of measurement error floating around the Internet, but can't find any solid citations. I did find a reference to "The sodium cycle and the age of the ocean", but it's behind a paywall and I cannot read it.

Why does this salt chronometer not agree with the other dating methods? That is, what went wrong in computing the age of the earth from ocean salinity?

A good chronometer is one that satisfies the following conditions:

We know exactly how much it had of something when it began
We know exactly the rate of the accumulation of the thing, and the rate is constant.

For example, U-Pb dating in zircon is an excellent chronometer. We know exactly how much Pb is in zircon when it crystallises (= none) and we know exactly the rate of Pb accumulation by radioactive decay of U (with two separate isotopes, not one! Rejoice!).

On the other hand, sodium in the ocean is a terrible chronometer. First of all, we don't have full understanding of how and when the ocean formed, let alone how much sodium they contained in the beginning. In contrast to Pb in zircon that starts with zero and goes up, the amount of sodium in the ocean is a function of many variables. These variables change with time. How much sodium do rivers input into the ocean? Depends. During orogenic periods quite a lot. During other periods less than a lot. Volcanic eruptions? Periods such as the Siberian or Deccan traps surely input a lot, but what about other periods? Removal of sodium is also non a constant process. As bon said in the comments, you have mass removal events such as the Messinian crisis. Sodium lost in ocean floor alteration is a function of how much seafloor spreading you have at that time, and the rest of the ocean chemistry. All this changes throughout geological time. The rate is not constant!

The paper that you linked to from the Institute for Creation Research has a long list of inputs and outputs of sodium and attempts to quantify it. First of all, I would be skeptical of anything coming out of there, because religiously motivated people tend to cherry-pick the data that fits their belief. But ignore that, even if their data is 100% correct, it is still correct for today. For now. As mentioned before, the input and output fluxes change drastically over time. It is impossible to assume a constant rate for that!

Quoting from that paper:

  It is God’s world that we are studying by scientific
  methods. It is God’s handiwork that we are learning
  about through those studies. God deserves to be
  praised  and  honoured—and  believed—for  what
  we  have  been  able  to  learn  about  his  world.  If
  our careful study of God’s world brings us false
  or unreliable information, then what can it mean
  for the Psalmist to sing, “The heavens are telling
  the glory of God; the skies proclaim the work of his
  hands.”?

Other than the fact that this passage does not belong in a scientific paper, it mentions the scientific method. Well, they fail at the scientific method because they make assumptions that make their entire study invalid.

2019 EDIT

A new open access paper shows that quite a lot of chlorine ends up in subduction zones, and removed from the oceans. As there are different subduction fluxes throughout geological time, this is another reason for salinity being a bad chronometer.


How can methylmercury in the ocean be reabsorbed into the atmosphere? The Sacramento Bee news article Toxic fog may be poisoning some of California’s mountain lions, study says says

  Algae in the ocean convert mercury to methylmercury, its most toxic form, which can be reabsorbed into the atmosphere and come ashore as marine fog, the release says.

Methylmercury [CH3Hg]+ is an ion with an atomic mass well over 200. I don't think that it would readily evaporate, so how can it be reabsorbed into the atmosphere?

Much of the methyl mercury that enters the atmosphere may be dimethyl mercury, $\text{(CH}_3\text{)}_2\text{Hg}$.  This is a very volatile compound which, if it were pure, would have 50 mm mercury or more vapor pressure at 20°C.  Complexes involving more electronegative ligands, such as the chloride $\text{CH}_3\text{HgCl}$, are significantly less volatile, but still have more vapor pressure than purely inorganic mercury compounds.