wave speed is smaller than both horizontal wave speed and vertical wave speed? I am new to GIS and just get the idea of slowness. I can understand why people need the slowness in GIS rather than just the reciprocal of velocity. However, I feel the definition of slowness is weird if we further introduce horizontal and vertical slowness. By intuition, the horizontal/vertical slowness should be the reciprocal of horizontal/vertical speed, and either horizontal or vertical wave speed should be smaller than the wave speed, due as a component. But from MIT 12.510 Introduction to Seismology, it seems that wave speed is smaller than both horizontal wave speed and vertical wave speed.

In summary, only one of the definitions for either wave speed or slowness can enjoy the regular decomposition property, is this true?

I don't know if I fully grasp your question; but I can confirm that slowness and velocity vectors are kind of weird things :-)

Let me describe a simple example (and not worry too much about the mathematical details). If in the figure above, if you point your wave not diagonally but just straight down, what happens? Well, $dx$ becomes infinitely large when the incidence angle becomes $i=0^\circ$, because there is no observable thing happening along the upper horizontal surface, the wave only moves down! At the same time, $dz$ becomes exactly equal to $ds$ when the incidence angle $i=0^\circ$. So, $dx=\infty$ while $dz= ds$, right? I have drawn that in the figure below, for a monochromatic (single-frequency) wave, such that for all the 3 cases, the length of the vector $\vec{p}$ is identical! I have added $c_x$ and $c_z$ as the apparent velocities.

So for a wave moving straight down, the wave moves in 2D for a grand total distance of $ds$, it propagated 0 in the direction of $dx$, and $ds$ in the direction of $dz$. Now your research already suggests that either of the following relations should  hold -- both basically expressions of the Pythagorean rule:
$$
dx^2 + dz^2 = ds^2, \tag{a}
$$
or
$$
\frac{1}{dx^2} + \frac{1}{dz^2} = \frac{1}{ds^2} \tag{b}
$$
If we use our extreme example $dx=\infty$ and $dz=ds$, then only equation b can hold (remember, $1/\infty=0$).

If we multiply every term in equation $b$ with $dt^2$, we get:
$$
\frac{dt^2}{dx^2} + \frac{dt^2}{dz^2} = \frac{dt^2}{ds^2}, \tag{b'}
$$
or realizing that $dx/dt=c_x$ and $dt/dx=1/c_x=p_x$ we get:
$$
p_x^2 + p_z^2 = p^2 = \frac{1}{c^2}, \tag{b"}
$$

With those details out of the way, we have seen the following: $p_x=0$ but $c_x=\infty$, and $p_z=1/c_z$ and $c_z=c$. So we have found that both $\{c_x,c_z\}\geq c$, i.e., both apparent velocities were greater than or equal to the original wave speed! On the other hand, $\{p_x,p_z\}\leq p$, i.e., the apparent slowness components were less than or equal to the original slowness.

And that is the result that holds generally. The apparent velocity components are always equal to or greater than the original velocity; while the apparent slowness components are always equal to or less than the original slowness. This is why equations (b), (b') and (b") give the right decomposition rule, it's the only one where $p_x$ and $p_y$ are less than the full $p$! This is why we can think of such a thing as a slowness vector $\vec{p}=(p_x,p_y)$, because the modulus of that vector $\lvert \vec{p} \rvert^2 = p_x^2+p_y^2$ (which is eq. (b")) behaves exactly like a vector should!

I hope that maybe along the way I answered your question somehow? My apologies for the rather mathematical take on things, but it's the only way I ever understood slowness vectors!


What natural phenomena increase stratospheric ozone? Most of us know that the ozone layer gets depleted due to green house gasses and other factors. Which made me wonder, is there any natural phenomenon that causes an increase in ozone?

Like BarocliniCplusplus said, ozone is generated when you have a single free oxygen atom. This can come from photolysis of O2 in the upper stratosphere, or photolysis of ozone itself, or photolysis of NO2 in the troposphere. The stratosphere gets its NO2 from the breakdown of N2O by other radical species. But NO and NO2 both react with ozone, typically destroying it.

So if you want a natural process that would enhance ozone, I would look for a process that reduces the amount of N2O (or other ozone-depleting species) reaching the stratosphere. N2O is produced by bacteria in soils, so anything that suppresses that production -- especially in the tropics -- would enhance stratospheric ozone. Carbonyl sulfide (OCS) is another species that only photolyzes in the stratosphere and depletes ozone; its concentrations would similarly decrease if there were a decrease in transfer of it from ocean to atmosphere (it's a product of plankton). You could also have a meteorological effect that suppresses deep convection in the tropics, though I can't offhand think of what this would be.

If you're interested in understanding the specifics a bit more (I'm not great at summarizing all of the cycles involved), I recommend checking out http://acmg.seas.harvard.edu/people/faculty/djj/book/bookchap10.html. Daniel Jacob is a pretty influential atmospheric chemist, and he put his whole book online.

NB: NO2 destroys ozone in the stratosphere, but typically enhances ozone in the troposphere. This is because the troposphere has much, much higher concentrations of organic species and the hydroxyl (OH) radical. Instead of depleting O3, the NO produced when NO2 photolyzes can react with HO2 to re-form NO2 and OH, so the ozone-depleting nature of NO is reduced. Since that process re-forms OH, OH can attack organic species and leave the H radical, which then pulls in O2 to form HO2, which will later end up producing an odd oxygen and thus form ozone. (Sorry if this is a bit rambly. I haven't tried to summarize all of this before, so let me know what things are confusing.)


Exhumation of blueschist Blueschist has a mineral assemblage such that it must have formed at high pressures and low temperatures. It must therefore form in subducting slabs (and I believe this correlates with the locations in which it's found). However, that leaves the issue of how to get it to the surface rapidly enough that it doesn't heat up sufficient to reequilibrate and lose the characteristic mineral assemblage.

What are the currently favoured explanations/processes for such rapid exhumation from depth?

Fast exhumation is not necessary to retain blueschist mineral assemblage. This is the classical difference between prograde and retrograde metamorphism, and it's not limited to blueschists. Why do we have eclogite on Earth's surface? What about granulites? Amphibolites? In fact, why do we see any metamorphic rocks on the surface instead of just various clays and quartz?
There are two main reasons for that.

Prograde metamorphism results in dehydration and loss of water(1). Most of the original water content of the rock was in various hydrous minerals, and as you progress in your metamorphic path you lose more and more water to dehydration reactions. While it is true that in blueschist waster can be retained in minerals such as lawsonite, phengite, epidote and glaucophane, most of it is still lost. If you want to reequilibrate the rock to its previous mineral assemblage, you need to reintroduce the water. This can occur occasionally, for instance in this classic example from Norway:

source: http://www.geol.ucsb.edu/faculty/hacker/geo102C/lectures/part11.html
...where a granulite was rehydrated along a joint to form eclogite, but it's usually very localised and uncommon.

Most prograde metamorphic reactions are exothermic, i.e. they release heat. Retrograde reactions are usually endothermic. They require heat in order to proceed, but in the event of exhumation, temperatures are decreasing. There is simply not enough heat around to support the retrograde reactions. Furthermore, you have to remember that lower temperature also lowers the reaction kinetics.

This doesn't mean that fast exhumation cannot occur...
There are pieces of evidence that in some cases exhumation can be even faster than the erosion rate(2). This suggest that orogenic events may also result from simple uplift and not only compression and folding. What causes the uplift? This may actually be the result of crustal thinning and extensional stress regimes, as in the examples of Liaodong(3) and Brittany(4). This phenomenon is also known as a core complex, where extensional tectonics result in low angle normal detachment faults that results in rapid unroofing and exposure deep seated rocks. You may be familiar with oceanic core complexes, so this processes is quite similar.

(1) Forgive me for not including the zeolite facies in my definition of metamorphism.
(2) Rubatto, D., & Hermann, J. (2001). Exhumation as fast as subduction?. Geology, 29(1), 3-6. 10.1130/0091-7613(2001)029<0003:EAFAS>2.0.CO;2
(3) Yang, J. H., Wu, F. Y., Chung, S. L., Lo, C. H., Wilde, S. A., & Davis, G. A. (2007). Rapid exhumation and cooling of the Liaonan metamorphic core complex: Inferences from 40Ar/39Ar thermochronology and implications for Late Mesozoic extension in the eastern North China Craton. Geological Society of America Bulletin, 119(11-12), 1405-1414. 10.1130/B26085.1
(4) Brown, M., & Dallmeyer, R. D. (1996). Rapid Variscan exhumation and the role of magma in core complex formation: southern Brittany metamorphic belt, France. Journal of Metamorphic Geology, 14(3), 361-379. 10.1111/j.1525-1314.1996.00361.x


How much of all current energy on earth arrived as sunlight vs. as kinetic energy during formation? For example, sunlight captured by plants would count in the "arrived as sunlight" category, whilst heat energy in the core of the earth would count in the "kinetic energy during formation" category.

We can try to compare sunlight energy arriving from the Sun and geothermic energy coming from the Earth's interior.
The Earth gets about 340 W/m2 from the Sun(1) while the average geothermic flux is about 0.1 W/m2.(2) Therefore, the current energy of sunlight is way larger than that from kinetic energy during Earth formation.
Additionally, it should be noted that a large part of geothermic energy doesn't come from Earth cooling by getting rid of its formation heat but from radioactive decay, making the comparison with sunlight even more one sided.


What is the reason for differences between these GHCNM and ERSST data? The maps shown below are from here. The first shows data from two sources, while the second only shows data from one source.

What is the difference between the two data sources used? Where does it come from, and what is the accuracy?

What is the reason the first map has data the second one doesn't? The most reasonable conclusion is that it comes from the ERSST data that's not in the second map, but it would be nice to know why there is a difference.

A question was posted on the Skeptics site regarding the claims made in the linked blog post. However, the existing answer currently does not provide much detail and comments were posted suggesting that this site may be able to provide more information about the NOAA data and the science behind it.

The maps shown below are from here.

Actually, except for the deplorable comments (your "here" was a self-titled deplorable blog site), the maps are from NOAA itself. The maps without deplorable annotations:

What is the difference between the two data sources used?

The most obvious difference is that as the name implies, the ERSST includes data from over the oceans. These data are gathered by buoys, ships, and satellites. A not so obvious difference is that NOAA's  merged land–ocean surface temperature analysis incorporates GHCN-M land-based stations that are not used in the GHCN-M land-only map. The locations and ages of the 7280 Global Historical Climatology Network (GHCN) stations are depicted below. Note that the vast majority of the stations in Africa are less than twenty years old.

The land-only analysis uses GHCN-M stations only. It does not use satellite data. Because of this it excludes stations that don't have a solid history of measurements from 1981. This would include the GHCN-M station at the Kigali International Airport in Rwanda, whose data coverage over the last 40+ years is only 48%. The GHCN-M-based land-only map only uses about 2600 of the 7280 GHCN-M stations.
The NOAA Merged Land Ocean Global Surface Temperature Analysis uses satellite data as a sanity check. This enables it to use most of the ~4700 GHCN-M stations excluded from the land-only map.


Cross-line fold of a towed-streamer survey On page 29 of the book 3D Seismic Survey Design by Gijs O. Vermeer, Vermeer says that the equation for a maximum fold in a 3D survey is the following:

$M = M_i \times M_c$

where $M_i$ is the inline fold and $M_c$ is the crossline fold. For a towed streamer, the inline fold is the same as for a 2D geometry which can be expressed as:

$M_{i} = \frac{N_{chan}\Delta r}{2\Delta s}$.

For the crossline fold he states that:

"The midpoint range in the crossline direction of one boat pass equals the number of streamers times the streamer interval divided by two ... normally, the next boat pass is shifted in the crossline direction with this distance, ensuring adjacent midpoint ranges of neighboring boat passes, i.e., no overlap in midpoint coverage between boat passes; hence, crossline fold $M_c = 1$. Therefore, in marine streamer acquisition, usually $M = M_i$ "

I feel that I understand why the inline fold is the same for the case of a 2D acquisition geometry, but I am having difficulty understanding the concept of the crossline fold. Specifically from the previous quote, could someone help me to understand what Vermeer means when he says midpoint range and coverage?

Any help will be greatly appreciated.

By midpoint range he refers to the size (length in the crossline direction) of the area in the subsurface that is illuminated by one pass of the boat. In a simple case of flat and parallel layers, that range is half of the size of the "spread" or receiver patch. BTW, this is true both in inline or crossline directions.

By coverage he means how the subsurface is illuminated by the combination of many passes of the patch over the area of a 3D survey. In common practice, passes are overlapped in the surface by half the crossline size of the patch so that the areas of subsurface illumination are contiguous with no overlap.


How does fertile soil reach newborn volcanic islands? When a volcanic island first surfaces, I assume no vegetation can grow, as it probably only consists of volcanic rock.

How would a volcanic island like Iceland that is far from any continent grow to have soil, and enough of it to grow forests?

Is it formed through hydraulic erosion?
Is it brought from the ocean floor with the currents?
Do aerial currents and birds bring it with them?
If it's something that only reaches the shore, how does it move inland?

This image may serve as a base to illustrate the points from the question:

La Palma, Aridane Valley and Cumbre Vieja volcano:

On the left (north) one sees the incisions of erosion at the flank of Bejenado volcano. It formed between ~500 and ~400 ky ago. Volcanic activity has ceased and it is now slowly weathering down. In the center and right one sees the Aridane Valley and the Cumbre Vieja whith its picturesque cones. The Aridane Valley is an erosional structure formed by a series of landslides slightly earlier than the Bejenado. Cumbre Vieja is an active volcano, last eruption is Teneguia 1971 in the south, just out of the right of the image.

On can distinguish several lava flows from historic and modern times by their darker colour. They are between ~70 and several hundred years old, but the whole island is built of such lavaflows, layer by layer (simplifying here). Wind, weather, insects and birds bring on pollen and seeds. Even on a fresh layer, after just a few months to years, pioneer plants like lichen will start to settle. Once exposed and solidified, the basalt starts to weather and erode. These processes form clay minerals, which release the nutrients to grow more and more plants and biocenoses, and so on. And basalt weathers quickly, releasing a lot of nutrients in relatively short time.

So, yes, your asumptions are in principle on the right track. I'm not sure about the direct role of ocean currents here, and soil is not brought in by the wind (at least not in decisive amounts, more or less dust from a nearby continent will allways be in the air), it forms through weathering of the basalt.

Weathering and erosion are very complex. Obviously, chemical and physical processes play an initial role; once plants have settled, their roots cause physical changes, bacteria from decay amplify chemical processes, and so on.

This is mostly textbook knowledge of the general process. For more specific information about the processes one can read up more on basalt weathering, chemical and physical erosion, pioneer plants, and so on.


How much of the current global warming is due to human influence? Approximately what proportion of the global warming seen over the the last century is attributed to anthropogenic sources?

Firstly it is worth demonstrating that 97% of climate scientists agree that climate-warming trends over the past century are very likely due to human activities.

  W. R. L. Anderegg, “Expert Credibility in Climate Change,” Proceedings
  of the National Academy of Sciences Vol. 107 No. 27, 12107-12109 (21
  June 2010); DOI: 10.1073/pnas.1003187107.

  P. T. Doran & M. K. Zimmerman, "Examining the Scientific Consensus on
  Climate Change," Eos Transactions American Geophysical Union Vol. 90
  Issue 3 (2009), 22; DOI: 10.1029/2009EO030002.

  N. Oreskes, “Beyond the Ivory Tower: The Scientific Consensus on
  Climate Change,” Science Vol. 306 no. 5702, p. 1686 (3 December 2004);
  DOI: 10.1126/science.1103618.

But what percentage of the increase is attributed to humans?  Probably almost of all of it.

The scientist Gavin Schmidt from NASA was asked this question on realclimate.org

His response was as follows:

  Over the last 40 or so years, natural drivers would have caused
  cooling, and so the warming there has been (and some) is caused by a
  combination of human drivers and some degree of internal variability.
  I would judge the maximum amplitude of the internal variability to be
  roughly 0.1 deg C over that time period, and so given the warming of
  ~0.5 deg C, I'd say somewhere between 80 to 120% of the warming.
  Slightly larger range if you want a large range for the internal
  stuff. [emphasis added]

The rapid increase in the human-driven component of the forcing are increasingly dwarfing the small, slow natural forcings, rendering them increasingly irrelevant.


Why does Volcano Lightning occur? There are many pictures I've seen of lightning coming out of the plume of smoke caused by a volcano (Often called 'Volcano Lightning').

Example:

Why does this happen?

To actively take measurements from the mount of an erupting volcano is not practical, so the mechanisms are often modeled in a laboratory, such as what was performed in the article Experimental generation of volcanic lightning (Cimarelli et al. 2014), who determined that volcanic lightning is controlled by the dynamics of the volcanic jet and how much fine particulate matter is present.

A key observation that the researchers found was that the movement of clusters of charged volcanic ash and other particles form to generate an electric potential, critical for the generation of lightning. An idealised diagram of this process is shown below:

Image source

As to why the particles themselves are charged was researched in the article Electrical charging of volcanic ash (Aplin et al. 2014), which suggests the ash becomes charged through fractoemission, triboelectrification, and the “dirty thunderstorm” mechanism, and the authors also suggest that natural radioactivity in the volcanic emissions may play a role.


Is the poleward migration of the maximum intensity of cyclones a result of tropical expansion or are there some other contributing factors? In the recently published article by Kossin et al. (Nature, 2014, dx.doi.org/10.1038/nature13278), they show that there is a trend toward poleward migration of the location of tropical cyclone (hurricanes and typhoons) maximum intensity in most areas of the world.

Their proposed explanation focuses on the tropical expansion (the increasing area of the world where tropical phenomena is observed has expanded in time). Is there some alternative explanation for the poleward migration of the hurricanes?

The shift seems to be occurring in the Pacific and Indian Oceans but not in the Atlantic. How can we explain that difference?

You will find the full text of Jim Kossin's migration paper here.
http://www.ssec.wisc.edu/~kossin/articles/nature13278.pdf
In it he describes his findings only as an empirical observation.  He does state that the migration is consistent with tropical expansion but he does not attribute the migration to the expansion. In fact he does not get into the subject of attribution at all. Perhaps attrbution will be the subject of a future paper. You may wish to check his list of publications from time to time to see if he has written an attribution paper. His (vey impressive) publication list may be found at http://www.ssec.wisc.edu/~kossin/pubs.html


Why are there craters on the moon? The Earth's moon is in synchronous rotation around Earth. The question: Why are there craters on the lit side of the moon and the dark and of which are not parallel with crater schemes on Earth?

There are craters on the Earth, Arizona's Meteor Crater being perhaps the best-known example.  The reason that there aren't a lot more (obvious) ones is that the Earth has lots of dynamic processes, ranging from weather to plate tectonics, that gradually erase them.  The Moon doesn't have these things, so craters last for billions of years.


How much energy does the Moon transfer to the Earth, does this affect the Earth's surface temperature? I'm wondering by how much the gravitation effects, tides etc caused by the moon (and other energy such as moonlight IR) increase the surface temperature of the Earth.

So how much warmer than the blackbody temperature is Earth due to energy imparted by the Moon? Or putting it the otherway, how much colder would Earth be if there was no Moon.

According to a slightly old estimate, the total power input from the tides is approx 3.7 TW [1]. Of this about 3.2 TW is from the moon (the rest is from the sun). Most of it goes into moving the oceans around, and some of it into doing the same with the land - but both ultimately end up as heat.

The question of how much this power affects the temperature of the earth is beyond my expertise, but it's a small amount of power at a planetary scale. Some very approximate comparisons:

Tidal power from the moon: 3.2 TW [1]
Total global electricity consumption: 3-4 TW
Geothermal heat flow from the earth's interior: 30 TW [1]
Total sunlight hitting Earth (outside the atmosphere): ~175,000 TW [1,2]

[1] Munk & Wunsch 1998; http://www.sciencedirect.com/science/article/pii/S0967063798000703 - probably paywalled.

[2] https://www.e-education.psu.edu/earth103/node/1004


Are there sufficient quantities of limestone to dump in the ocean to reverse acidification? This question asked: What is the evidence it is feasible to reverse ocean acidification by adding large quantities of a base (bicarb soda)?

The result was:

  Danny Harvey of the University of Toronto has already looked into this. His solution is to deposit 4 Gt/a of limestone into the oceans. To put this in perspective, global coal production in 2013 was nearly double this at 7.823 Gt and it is more than global iron ore production in 2014 of 3.22 Gt.

The respondent then posed the question: Are there sufficient quantities of easily obtainable limestone to do this?

My question is: Are there sufficient quantities of limestone to dump in the ocean to reverse acidification?

Getting figures on the amount of limestone available is difficult.

Apparently "limestone makes up at least 10% of the total volume of all sedimentary rocks".

One way to answer your question is by inference. Cement is manufactured from limestone. Current global production of cement is in excess of 3.27 Gt/a and by 2030 it is forecast to be approximately 4.83 Gt/a. Thus if all limestone currently earmarked for cement production were diverted to neutralizing the acidity of the world's oceans it could be done at short notice. How sustainable it would be over the 200 years required, is another matter. It also raises the question of what happens to all the industries and projects that current rely on a cheap and ready supply of cement?

With much tongue in cheek, the Florida peninsular in the US is predominantly limestone, likewise a significant portion of eastern England, with the "white cliffs of Dover, the karst regions of the eastern Adriatic, southern Europe, southern and eastern Asia and the Nullabor Plain in southern Australia. Would these countries be will to sacrifice their lands to neutralize acidity in the worlds oceans?


What does a mm of rain mean? Lots of people have explained it over many sites but I still can not confidently say that I know what it means when they say Hong Kong experienced 3mm of rainfall last Friday.

Does it mean that 3mm per square meter was experienced in a specific area, or does it mean that the total amount of rain had a volume such that if it was spread over all of Hong Kong the height would be 3mm. Or is it referred to in terms of per square meter?

What is the time period? Is it measured per day, per hour, per minute?

EDIT: The question marked as a duplicate may refer to some aspects of the question but does not effectively ask them. The title of the question refers to something different and the only answer to that question is what I am asking an explanation of.

It's confusing to measure liquid in units of length instead of volume, isn't it? Here's how it works.

"One millimeter of rain" is actually one cubic millimeter per square millimeter. On average, over the area you're talking about, each square millimeter has received one cubic millimeter of rain. If you divide n mm3 by 1 mm2, you get -- n mm!

The field of Dimensional Analysis deals with questions like this.

If there was "1 mm of rain", how much rain did a square meter receive? 1000 mm * 1000 mm * 1 mm = 1 000 000 mm3 = 1 liter. Pour one liter of water into a square container one meter on a side, and it forms a layer one millimeter deep.

To calculate "how much rain fell on Hong Kong" (expressed as total volume), you'd take the area of Hong Kong, and multiply it by 1 mm. That's usually not what people want to know, though -- they want to know how wet things got, and the volume-per-area number is most convenient for that.


How will climate change affect the 3D distribution of lapse rate in the atmosphere? The lapse rate is the rate at which temperature decreases with height. By "3D" distribution, I mean distribution across all latitudes, longitudes, and heights.

Would climate change change the lapse rate more in the poles than the tropics? Would increased humidity be the main reason, or could there be other causes as well?

Stone and Carlson, 1978 suggest that lapse rate is dependent on latitude (i.e. incidence angle and intensity of sunlight) and pressure rather than temperature. It is the sunlight pattern which drives the circulation patterns that are the dominant effect of air temperature with altitude:

  In low latitudes where moist convection dominates, the lapse rate agrees
  closely with the moist adiabatic lapse rate; and in high latitudes where
  baroclinic eddies dominate, the lapse rate agrees closely with the
  critical lapse rate for baroclinic adjustment.

The latitude determines daily changes in temperature due to solar energy. This leads me to believe that changes in average temperature (due to climate change) will not affect lapse rate so much as solar incidence due to latitude (which will not change with global warming). However, there remains the potential effect of increased humidity caused by increased temperatures.

An analysis of lapse rate measurements over broken terrain in Washington state (Minder, Mote, Lundquist, 2010) shows the differences between wetter and dryer conditions on the windward and leeward sides of Mt. Ranier. A calculation of lapse rate up the mountain by season yields this chart:

There are three distinct data sets: the solid black is the same on both a. and b. and is the measurements in 2006-2007 of lapse rate by month. The grey with circles data set from a. and grey with triangles from b. are two historical data sets from different sources. The dashed lines in each data set are on the leeward (dry) side of the mountain, the solid lies on the windward (wet).

As you can see, the seasonal variance is present in all three datasets; as the sun comes more nearly overhead in the summer lapse rate goes up. Also notice that for the leeward data, the lapse rate peaks in Jun, when the sun is highest in the sky, as opposed to July and August, when temperatures are high. That reinforces the thesis that sun angle is dominant over temperature.

However, the other bit of relevant data is that the wet side of the mountains has significantly less annual variability in lapse rate than the dry side. This implies that humidity changes due to global warming will indeed cause changes in lapse rate.

In conclusion, I believe that temperature changes due to climate change will not significantly alter lapse rate; but humidity changes will. However, since humidity changes due to climate change are likely to be much more local and variable than the more globally even increases in temperature, lapse rate changes should be local and variable as well.

So to answer the question directly, the '3D' changes in lapse rate will probably not be significant, in that there will not be a clear global trend across all latitudes, longitudes, and altitudes. However, local changes may be significant depending on local humidity changes.


How to learn the different types of rock I would like to be able to point to a piece of rock and say that is rock type such and such. I have tried learning but it literally seems like an endless list of types and sub types and the pictures don’t really seem to help me. Short of a person taking me out and physically handing me rock specimens, is there any easy way to self learn the different types?

The best way to learn about rock types is to handle rock specimens guided by an experienced geologist.

By handling rock specimens you get to feel the weight of the rock, its roughness or smoothness or if it feels slippery, soapy, glassy, firm or crumbly. Is it weak or strong? You will also be able to better see the colours in the rock, the sizes of the grains of minerals, the way the rock breaks, its cleavage. You can test its hardness. If you have a piece of unglazed white porcelain you can do a streak colour test.

All these sorts of things can help you identify different rock types.

Also, the same rock type can look slightly different in other parts of the world, because of geological and environmental processes that rocks experience in different parts of the world. This is particularly so if the rock is deeply weathered.

Learning the different rock types, alone from books and pictures is a difficult way to learn, befriend a geologist, you'll learn more quickly and it will be more enjoyable.


Structural geology, regarding cross section of two outcrops with similar characteristic but very distinct dip I found an outcrop of sandstone interbedded with claystone which strike/dip is N 195 E/42. Then, around 4 km at the south of previous outcrop, i found another outcrop with similar characteristic, but the strike/dip is N 132 E/79. The question is what should I do to make a cross section? should I connect the bed layer, considering their similar characteristic, or make a new layer, considering the distinct strike/dip? (could it be angular discontinuity?)

Is this a homework question?

These are quite steep dips, strongly implying that substantial deformation (folding) has taken place. The interlayering of steep mudstone pretty much rules out your outcrops as being original bedding structure. Draw your examples in plan, using the normal dip and strike notation. Sketch in some possible continuation of the strike (as curved lines). Then consider what style of folding could have created this pattern. Consider also the possibility that the fold could be steeply plunging.

When you have an idea of the structure from the plan view, this should guide you in deciding the orientation of the cross section.


How are the ZNE, ZRT and LQT coordinate systems defined? I'm confused about the direction of Z (upward or downward?), R (outward or toward the source?) and T.

Z depends upon convention, but in geophysics we typically use Z=positive downward. R is radial and the positive direction is defined in the direction FROM the source TOWARD the receiver. T polarity can be determined from the right-hand rule once you have Z and R.

For reference, this is the based on the convention for polarity as described by Aki and Richards (1980).


How can the following equations for meandering rivers be theoretically obtained? It has been observed that the shape of a meandering river is roughly circular, not sinusoidal (Leopold and Wolman 1960).  It has also been observed that the following mathematical relationships tends to hold:.

$$\lambda \sim 11 w$$

and

$$r \sim 2.3w$$

Where $r$ is the radius of the circular bend, $w$ is the width of the river, and $\lambda$ is the length of the meander (wavelength), as labelled in the diagram below.

Since this pattern was first observed in 1960, has a theoretical model of meandering rivers been obtained that explains the above observed relationships and if so, what is the theoretical explanation of this relationship?

Note:  Given $r \sim 2.3 w$, it can be shown that $\lambda \sim 11 w$ from geometrical principles, or vice versa.  For example $\lambda$ should be equal to

$$0.5w + 2r + w + 2r + 0.5w = 2w + 4r = 2w + 4(2.3w) = 11.2 w$$

So since the two equations are not completely independent, the question is how could either of these relations be determined from a theoretical basis.

References

Leopold, Luna B. and M. Gordon Wolman, 1960, River Meanders, Geological Society of America Bulletin, no. 6;769-793, https://www.usu.edu/jackschmidt/files/uploads/Fluvial_2013_Labs/Leopold_Wolman_1960.pdf

I'm gonna hazard a guess here: They can't. While I don't have any evidence for this claim, it seems likely that there are too many small-scale non-linear processes feeding in to the overall generation process to ever be able to sensibly derive any kind of analytical solution based on physical first-principles. I think that's what you're asking.

So, basically, these equations are an empirical model. The parameters don't have any relation to the physical processes that generated the meanders - they are just descriptions of the resultant shape. The generation process for a model like this is something along the lines of:

Inspect the data qualitatively
Come up with some potential models that could approximate what you're seeing. In this instance, sinusoidal and sequentially linked circles look like they might work.
For each model, apply and verify:

Attempt to fit the model to some of the data.
Apply the model to some of the rest of the data, and check it's performance (also, pay attention to parsimony).

Choose the model with the best performance as your model.
With your model, perform some analysis of the model fit (residual analysis, etc). If it looks like there are patterns in the residuals that could be reasonably modelled, go back to 2. and come up with some model variants.

As far as I can tell from the referenced paper, this is roughly the process that the authors used. The values of each of the parameters are basically empirically obtained, to allow the model to best fit the majority of the data.


How will climate change affect planetary waves? You can see planetary/rossby waves in the meanders of the jet stream. In short: If an air parcel moves from warm subtropics towards the pole, it will deviate toward the east due to conservation of angular momentum (movement towards the equator will lead to deviation toward the west). That results in a meandering motion.

How will climate change affect planetary wave activity and zonal wavenumber?
Does polar amplification reduce planetary activity because of a smaller temperature gradient between subtropics and polar region? Will cooling of the stratosphere influence planetary waves as well?

As a non-climate specialist, this topic is on the edge of my understanding of meteorology, but here are some papers that I found potentially relevant to your topic.

Here is a quote from the summary of Limpasuvan and Hartmann, 1999:

  The planetary wave propagation characteristics can be used to link
  changes in the tropospheric annular mode to changes in the strength of
  the stratospheric polar vortex during winter. Planetary waves are
  strongly attracted to polar regions during the low phase of the
  annular mode when the tropospheric westerlies are displaced
  equatorward. We should expect a weaker stratospheric polar vortex
  then, since planetary waves weaken the polar vortex by generating
  irreversible mixing.

And here is a quote from Shepherd and McLandress, 2011

  In particular, the tropospheric warming that is robustly expected from
  climate change leads to a strengthening of the upper flanks of the
  subtropical jets, which causes the critical layers on the equatorward
  side of the jets to move upward, and with them the Rossby wave drag,
  allowing more Rossby wave activity to penetrate into the subtropical
  lower stratosphere (Figs. 4, 5). Because the subtropics represent the
  critical region for wave driving of the Brewer–Dobson circulation, the
  circulation is thereby strengthened.

So my conclusion from these two papers (there is obviously a lot more detail in the full text) is that polar vortex will weaken, subtropical jets and Brewer-Dobson circulation will strengthen, and Rossby waves will penetrate farther south. Of note, neither paper seemed (to me) to indicate that a cooler stratosphere was predicted.


Help understanding this image of an unusual double reflected rainbow The BBC News item Double reflected rainbow photographed in Orkney shows an unusual kind of double rainbow.
According to the article:

The image was captured by Martin Gray at Gyran on Tuesday morning, who described the sight as "amazing".
He said: "I'm used to seeing double rainbows, but this was a really weird-looking thing."
[...]
"I quickly snapped a few photos. It was extremely bright, and odd looking - all odd angles. "But I didn't even notice the faint fourth arc until I carefully looked at my photographs."
BBC weatherman Simon King said it was an "impressive" photograph. "It's a really impressive double reflected rainbow," he said. He said the photographer had a loch behind him at the time.
As a result, sunlight had bounced off the loch before reaching the water droplets from a rain shower in front of him. The sunlight was then bent and reflected inside the droplet back to the photographer.

Question: I've annotated the image and numbered each of the arcs. Is it possible to sort out what's going on and which phenomenon are responsible for each of them?

Credit: Martin Gray & BBC; Gyran, Orkney Islands, Scotland

What you are seeing are a primary rainbow (rainbow #2 in the linked image), its secondary rainbow (#4), a reflection rainbow (#1), and its secondary (#3).

Note well: The linked article called these reflected rainbows, but that is incorrect. A reflected rainbow is yet another atmospheric optical phenomenon that occurs when one sees what appears to be the reflection of a rainbow on water in front of the viewer. The water was behind the photographer in the linked image, and the extra two rainbows were in the sky rather than in the water. (There is no water in the linked image.)

The reflection of the Sun off of the water behind the viewer result in a reflection rainbow in front of the viewer. The center of a primary rainbow is the antisolar point from the perspective of the viewer of the rainbow, which is below the ground. The center of a reflection rainbow is the anthelic point of the reflection of the Sun, which is above the ground. Thus rainbow #1, the primary rainbow from the Sun itself, is lower than rainbow #2, the primary rainbow from the Sun's reflection off the loch behind the photographer. The two rainbows intersect at the ground.

Rainbows can have secondaries, and so can reflection rainbows. These are bows number 4 and 3. Note that the sky and land are darker between the primary and secondary, brighter outside the secondary, and much brighter inside the primary. The lighting outside the secondary is the natural lighting level.

One way of looking at rainbows is that they transfer some of the light that would normally fall between the primary and secondary to inside the primary, and that this transference changes a bit with frequency.


To what year do we need to return to prevent climate change? I regularly see articles like this where a country has or has committed to reduce their carbon emissions by a certain percentage in relation to a certain year. That article mentions that Scotland has dropped their emissions to 49% below 1990 levels.

Other discussions talk about cutting carbon to come under a 2 degree, or 3 degree warming level.

How do these two relate?

If everyone goes back to 1990 how many degrees does the planet warm?
What do different 'years' look like 2000? 1960?

edit: The answers given pretty much cover it but what I was really after was a bar graph or similar that says 1960: 0.3 degrees, 1990: 1.1 degrees, 2000: 2.0 degrees. ie how do year levels correspond to warming predictions.

As Gemechu Fanta Garuma commented, the IPCC Assessment Reports (at time of writing, AR5 is the latest) and its special reports are the best place to go for a comprehensive summary of the science as it was a small number of years ago.

In terms of greenhouse-gas concentrations that are stable and civilisation-friendly, the range 300-350ppm CO2 is as useful a range as we're likely to get for now - 350 is when coral bleaching starts to become a serious problem, and trashing the ocean ecosystem is a shortcut to threatening human civilisation, so we should probably avoid that. And for methane, say around 1000-1300ppb.

It's not a question of "returning to a year". We don't need a time machine, and we don't need to wind back everything that's happened. I've no wish to return to 1980, for example, and I'm not sure why anyone else would (I was there and it was largely rubbish). This is not about undoing decades of human progress. What we do need to do is to keep the concentration of greenhouse gases in the atmosphere at levels that keep the climate fairly stable at the timescales of human lifetimes, so that we avoid massive disruptions and a potential threat to human civilisation. Had we started doing that when this was first flagged up as a major issue by scientists in the 1970s, we would have done it much cheaper, much sooner, and with less collateral damage. (like in the old proverbs: an ounce of prevention is worth a pound of cure; and a stitch in time saves nine)

We have already caused some climate change. It will take 30 years for the full effects of what we've done to date, to show up. We may already have caused trillions of pounds of damage to our natural capital - but we'll only know the full scale of the damage when it's far too late. Theoretically, we could avoid some of that damage in the next 30 years by putting the global economy to work to tackle the problem seriously. However, the political will just isn't there. Most of the people who'll suffer the worst of the damage are too young to vote, or haven't been born yet. Most of the people with the ability to do something about it (voters, politicians, business leaders) will be dead before the worst of the damage hits.

The Keeling Curve shows how atmospheric CO2 concentrations have changed over time:

(chart Scrippsnews - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=69539214)

As for the relationship between atmospheric concentrations of greenhouse gases, the change in average global temperatures, and actual changes in climate, that's a set of very complex relationships wrapped in uncertainties and unknowns. And these things are generally nowhere near as simple as a neat, reversible one-to-one function: even if we were to restore greenhouse gas concentrations to where they were in 1980, does not mean that the climate will return to just as it was then.  And that's why mitigation action is so very urgent: we are driving in thick fog very close to the edge of a cliff. The smart thing to do is to stop driving and work out what's going on. Which means getting to zero net emissions as fast as we can without destroying everything else in the process.


Typical values of Glen flow law for glaciers? The Glen flow law for glaciers is a common relationship linking stress to strain. At its simplest,

$\Sigma = k\tau^n$

where $\tau$ is stress, $\Sigma$ is strain, and $n$ is roughly 3.

I understand that $k$ depends on temperature and material properties of the ice, and that it can vary over two or three orders of magnitude.

I have been searching the literature to find some example values of $k$ (also called $B$ and $A$) but so far I've had a surprisingly hard time. Is there somewhere that has a compilation of $k$ values from various studies?

For glaciology related doubts, the first place to look is The Physics of Glaciers by Kurt M. Cuffey, W. S. B. Paterson. Going through the section 3.4.5 Controls on Creep Parameter A, should give you a good insight on the topic. It also includes example values.

As well as recommendations for values of A as a function of temperature.

This section is included in the preview of the book on Google books.


Migration Routes for Animals from Asia to America The jaguar is a close relative of the Asiatic leopard and must have had a common ancestor within the last 5 million years. The South American tapir is obviously closely related to the Malayan tapir and must also have had a common ancestor within he last 5 million years. How did the leopard and tapir, typically tropical species, get from Asia to South America?

An obvious route would be the land route via the Bering Straits and the southern shore of Alaska which was used by humans about 15,000 years ago when the Ice Age had lowered sea level, but both animals are tropical and it is hard to believe they would have chosen such an icy route. The jaguar and tapir have in any case been separated from their Asiatic relatives for a lot longer than 15,000 years. I am wondering whether they could have arrived via a different route from the one chosen by the earliest human inhabitants of the Americas. Can anyone throw any light on this?

Continental drift played a part in isolating Old World monkeys from South American monkeys and setting Australia adrift carrying only marsupials, so is there a possibility that when Africa and Amazonia were closer together, immigration from Africa could have taken place, bearing in mind that there were times when sea levels were much lower?

The jaguar is a close relative of the Asiatic leopard and must have had a common ancestor within the last 5 million years. The South American tapir is obviously closely related to the Malayan tapir and must also have had a common ancestor within he last 5 million years.

While the first statement is more or less correct, the latter is not. The Asian and American branches of the tapirs split about 25 million years ago.

Regarding migration routes, felines have migrated back and forth between Asia and North America many times in the last eight million years or so. The ancestors of Tapirs apparently migrated back and forth between North America and Europe before 25 million years ago, when the climate was much warmer and the continents had slightly different shapes.

  ... is there a possibility that when Africa and Amazonia were closer together, immigration from Africa could have taken place?

Regarding South America, there were very few placental mammals in South America until about 3 million years ago, when the Isthmus of Panama formed. The age of the Isthmus is debated. The sudden appearance of placental mammal fossils about 2.7 million years ago in South America, including jaguars and tapirs, is not. South America's jaguars and tapirs migrated to South America via North America rather than Africa.


Would ultrasound be a valid method of mapping ocean floors given the perceived "gel" is ocean water? I am a scuba diver, with a big idea that would require me to map various dive sites as I went to them and dove in them. The typical size and other implications of sonar technology would essentially render this impossible.
So I thought, would it be possible to use ultrasound instead? This would theoretically require a device that could, instead of seeing through the warm gel that hospitals use, see through cold ocean water. I've done some research but have not gotten a definitive answer, which is understandable since no one has asked the question.
And, secondly, if ultrasound is not possible, what else is typically (or not typically) used in oceanography besides sonar?
Thanks!

It seems that attenuation is much greater at ultrasound frequencies:
50 khz   12-15 dB/km
0.5khz   0.024 dB/km

It depends on what distance and resolution you need.


Are cattle really contributing to global warming? Let me be straight up. I'm a physicist, I've no doubt about climate change and the part we play in it.  I had been reading about cattle being one of the alleged main causes of climate change.

I get that they make methane, and we have a LOT of them, So I ran some numbers:

Roughly 93 million cattle in the United states in 2017 (some sources claim lower, but I'm going with the higher one).

Prior to humans killing the Buffalo off, there were approximately 50-100 million of them across the united states.

A quick Wiki search, estimates that buffalo (bison) produce significantly more methane than domestic cattle (though I don't know for sure that this is true).

These numbers seem to match up pretty well insofar as they're greenhouse gas contributions, so now I'm wondering if the argument is viable?  I know there were other herds around the world too, so I just found myself rather curious. Has anyone run the numbers thoroughly?

On the flip side, I could see the sheer number of humans being an issue, I'll try and run that later.

Let's just talk about cattle here and ignore other factors related to cattle production for now.
The current cattle number (93 million) you found is probably the total number of dairy cow and beef cattle. In your argument, it is possible that bison has much more emission than cattle on pasture. But the emission from cattle in feedlot and dairy farm is much larger than the cattle on pasture because of their diet chosen by us (human).
Typical beef cattle (steers and heifers) in the U.S. spend one year on pasture, and 5-6 month in feedlot before slaughter (unlike Argentina beef cattle which are fully raised on pasture). In feedlot, these young cattle (yearlings) are intensively fed with high protein feed in order to get them fatten up in a very short time. The U.S. dairy cows spent most of their time on dairy farm (unlike the Swiss cows who are raised on pasture). They live for about 5 years and are continuously fed with high protein forage to ensure their milk production. Both beef cattle and dairy cows have a high protein diet that result in high emission of methane (the impact of methane is 25 times worse than CO2 in terms of warming).
The closest comparable cattle to bison is beef cow which spend most of its life time (about 10 years) on pasture and are only occasionally fed with low quality hay when there is a shortage on pasture. But again, the life span of a beef cow may be different from the buffalo and beef cows may eat more because they are basically pregnant very year(!).
California has this new policy that tries to cope with dairy cow methane emission from their manure. If you are interested, there is a recent study done by University of California Agricultural Issue Center here (https://aic.ucdavis.edu/wp-content/uploads/2019/01/DairyManure-1.pdf).


How can parameters of the ionosphere be calculated? How can parameters of the ionosphere be calculated? Specifically, how do we calculate total ion density, total ion temperature and individual major ion densities from I-V Characteristics curve of ionospheric plasma. The I-V characteristics curve is obtained using ion Retarding Potential Analyzer (RPA) onboard a spacecraft.

Answer to that one: What you describe is a measurment, not a calculation.
The measurment you describe varies the potential difference at a satellites Langmuir probe. The potential difference then attracts or deflects ions, and deflects or attracts electrons. Those electrons and ions are the current being picked up by the Langmuir probe.
Then follows a translation of current into local ion or electron densities. Different ion species can be distinguished w.r.t each other because they have different inertia, and thus different arrival times. I'm not sure how many ion species one can distinguish however in this way.


Why is streak different from color? Many minerals have a streak that's surprisingly different from it's outward color. Why is this? What causes the optical properties to change if the mineral is powdered?

Thanks!

It mostly has to do with the fact many minerals are partially translucent.

Trace impurities or even crystal structure can dominate the color of a translucent material but when ground in to a fine powder (streak) they can no longe do so and you can see the true color.

In other minerals surface oxidation can mask the true color.


Why limestone formation was not a concern in atmosphere oxidation event? I have just got to know why Fe was a problem. After clay (alumnum) and Silicon got oxidized, there has left a lot of unoxidized Fe in the crust, whose oxidization has finished during GOE. But, ferrum was not the only consumer of the oxygen.

If I look at the upper layer of the soil

you will see a lot of CaCO3 (aka limestone or calcite) and oxidized aluminum Al2O3 (aka the clay) with sand below it. Nowhere you will see the (oxidized) Ferrum in noticeable amounts. How could Fe be the major consumer of the oxygen despite calcite is present in much larger amounts?

First, let me clarify this again:
Al2O3 is not clay.
Now, back to topic. You are mixing apples and oranges here. The geological section you are referring it was deposited 2 billion years after the GOE. This was long after all surface iron was oxidised, and abundant oxygen was present in Earth's atmosphere.

Nowhere you will see the (oxidized) Ferrum in noticeable amounts

Iron is not present in this geological section, but it is present elsewhere. You are looking at one specific section in one specific locality on Earth's surface. It is flawed logic to infer what you are based on this.

How could Fe be the major consumer of the oxygen despite calcite is present in much larger amounts?

Because at this stage, neither calcium nor iron were "consumers" of oxygen. Oxygen has been consumed before, and then this consumption stopped once all of the iron was oxidised. This is why oxygen today exists in the Earth's atmosphere.
From the comments:

@Pont The layer is younger, it is basically made of oxides. A terrible amount of oxides appeared after the GOE but their formation did not delay the atmosphere oxidisation the way free Fe did.
I have checked the chemistry. Calcium + water gives me hydroxide. It will exchange CO2 for H2O to from the limestone. This suggests that we still consume Oxygen from the atmosphere. Which pre-oxidization are you talking about?

Metallic calcium probably never existed in the Earth at all. The GOE was a process in which only iron was oxidised (out of the major components of the Earth's crust). The oxidation of calcium, aluminium, silicon, etc, occurred much before that. It occurred when the Earth was forming, and possibly even in the solar nebula that existed before Earth even formed. This was 2 billion years before the GOE.
Let's put this on a time line:

~4.5 billion years ago, Earth formed. Calcium, aluminium, silicon were all oxidised. Only some of the iron was oxidised.
~2.5 billion years ago. Photosynthesis causes oxygen to rise, but the rise is limited because of the presence of iron in the crust. Any oxygen that is produced, is consumed by the oxidation of iron. Eventually all iron is oxidised and oxygen contents can freely rise.
~0.5 billion years ago. The section you refer to is deposited.


How to convert soil moisture units from meteorological model? I am using the outputs of the ALADIN meteorological model, in particular I need volumetric soil moisture. However, the output from ALADIN is in "funny" units - $\mathrm{kg/m}^2$ per top 1 cm. Is it acceptable to assume water density $\rho_w = 1000~\mathrm{kg/m}^3$ and calculate as follows:
$\frac{\mathrm{kg}}{\mathrm{m}^2.\mathrm{cm}}*\frac{100}{1000} = \frac{\mathrm{m}^3}{\mathrm{m}^3}$? So basically just take the values and divide them by 10? I don't need to be extra scientific, but I don't want to miss anything crucial.

Your method looks OK, however, water density varies with temperature.

Not knowing exactly what your aim is or how accurate/fussy you want to be, you may want to consider using the density of water for its temperature rather than accepted average of $1000 kg/m^3$.


What is a Geophysical Model Function (GMF)? I have heard the term mentioned many times in seminars, and in papers on remote sensing. What does it mean? References would be helpful if available.

In remote sensing you often do not directly measure the variable of interest, i.e., you measure it via some other variable that you can measure (depending on the type of instrumentation). The model function is simply the function which relates the observed variable to the variable of interest, just like y=f(x).

E.g., y could be wind speed, and x the energy measured by the scatterometer.


How is dense magma able to rise and punch through continental crust? I am trying to understand how a dense basaltic lava is able to rise and punch through the continental crust, such as in mantle plumes or the Great East African Rift.

My understanding of plate tectonics is that continental crust is made from less dense silicates, where as oceanic crust is made from denser silicates.

The origin of continental crust is from the differentiation of Earth, where silicates rose to form the mantle and even lighter silicates rose, then cooled, to form the crust of early cratons.

If the mantle that forms oceanic crust is composed of dense silicates, how is it able to rise up and punch through the continental crust, pushing it apart to form ocean basins, as in areas of rifting or mantle plumes?

My intuition tells me a dense material should not be able to rise from depth and displace a lighter one.

Your intuition is quite correct: Other factors being equall, a dense magma will not rise through lighter rocks. The exception is if it is under pressure, in which case a fluid magma will escape through 'pressure release' pathways, either laterally or vertically (or in complex geologic structures, in a variety of irregular pathways). Magmas may begin to crystallize at depth. As they do so, the volatile components, such as water, carbon dioxide, halogen acids, and sulphur dioxide, become relatively enriched in the residual magma, where they can build up enormous gas pressures. The most spectacular results are in Plinian-type volcanoes, and in many less dramatic eruptions. Consider, for example, pumaceous lava, which is essentially gas bubbles frozen-in during the process of escape. At depth there are no such bubbles. but the gasses are still there, and still exerting a huge pressure.

Otherwise, a magma may simply rise because of thermal expansion reducing the density to less than that of the host rock. Most likely the magma will rise as a combination of both mechanisms.

Also, you mention the Great East Africa Rift, which is notable for some extraordinary carbonatite lavas and related carbonatite-silicate hybrids, which are less dense than almost all of the other African crustal rocks.


Does anyone know a book/article/research that talks about forest fire prevention? In my college we have to start our thesis in the third semester, so I'm going  to do a research about forest fire and its prevention. However, I'm struggling to find a article that talks about that specifically. All that I can find is people talking about how important is to have good soil and vegetation, which is really vague.

This book is based on Australian experience, some of it may be relevant of North American wildfires. I read it ten years ago.

Paul Collins, Burn - The Epic Story of Bushfire in Australia, Allen & Unwin, 2006, ISBN 9781741750539, ISBN 1 74175 053 9.

Part 4, titled: The Great Fire Debates, has three chapters (9 to 11);

 09 To burn or not to burn
 10 Fire thugs
 11 Fireproofing Australia.

Contact for Allen & Unwin:

83 Alexander Street
CROWS NEST NSW 2065
Australia

Telephone: + 61 2 8425 0100
Fax: +  61 2 9906 2218
Email: info@allenandunwin.com
Web: [www.allenandunwin.com][1]

Another book you may want to try is:

Stephen J. Pyne, Burning Bush - A Fire History of Australia, University of Washington Press, Seattle & London, 1998.

Also published by Henry Holt & Company, New York, 1991

As part of his "Cycle of Fire" suite of books, the same author has written books, titled:

Vestal Fire: An Environmental History, Told through Fire, of Europe and Europe's Encounter with the World
Fire in America: A Cultural History of Wildland and Rural Fire
World Fire: The Culture of Fire on Earth

The CSIRO (Commonwealth Scientific & Industry Research Organisation) in Australia, used to have two departments that researched bushfires/wildfires:

CSIRO Division of Forest Research Library
CSIRO National Bushfire Research Unit

Stephen J. Pyne mentions them in his book. You might be able to get access to the results of research carried out by the CSIRO.

Just be mindful of the different terminologies used in different countries to describe the same thing: bushfires in Australia and wildfires in North America.


Saharian calima dust, apart of Fe2O3 does contain FeO? It is repeated often that Saharan calimas are fertilizing often Atlantic ocean. But I suppose that most of Saharan dust contains Fe2O3 and not FeO. Am I right?

I think you are correct. Typical sand is silica (white) with a little Fe2O3 (red) to give a "sand" color. FeO is black and over geological time in air, oxidizes further to Fe3O4 with hydroxides and hydrates (black and dark brown) and eventually Fe2O3.


What is the Calcite Compensation Depth and what is its significance for carbonate deposits? What is the Calcite Compensation Depth (CCD) and what is its significance for carbonate deposits?

The Calcite Compensation Depth is the depth below which all calcite minerals are dissolved. The solubility of calcite (and the amorphous variant aragonite) depends on both pressure and temperature. Under high pressure, low temperature conditions calcite is most soluble, and in deep parts of the ocean only siliceous deposits are found.

Typical values for the CCD are between 3000 and 4000 m, but since the CCD also depends on the amount of calcite in the water it can occur as shallow as 2500 m (in parts of the Pacific Ocean). These shallow zones are often caused by high biological activity of carbonate shell forming organisms.

Taking all this together it becomes clear carbonate deposits can form and/or be preserved only above the CCD.


What is the steepest surface that can hold snow? I know it depends on the type of snow (dry or wet) and the rougness of the surface. I'm looking for an approximate rule of thumb answer. Assuming a reasonably smooth surface, at what angle it's likely to be free from snow?

Google results only discuss snow and slopes in context of skiing and roofs not caving in. Obviously, a snow safe roof (60+ degrees) will still accumulate a few inches of snow.

For example, imagine a sandwitch board sign. What's the minimum "uprightness" for it to not get obscured by snow and stay readable throughout the year?

What's the minimum "uprightness" for it to not get obscured by snow and stay readable throughout the year?

The answer to this problem is not in the angle at all. No amount of math will give you an angle at which you can reasonably presume your surface will remain clear. Snow can (and does) accumulate on vertical and even negatively sloped surfaces. Instead of thinking about the angle, you should be thinking about the materials and conditions involved.

There are lots of factors that determine whether snow will stick, but a few that stand out most are:

Temperature differentials between a surface and the atmosphere:

This is particularly noticeable on surfaces of enclosures such as vehicles or buildings where the internal temperature causes the surface to be out of sync with the environment. You might notice snot collecting on the vertical glass surface of car side windows. This will be more pronounced in cars that were parked full of warm air when it started snowing. The warm glass would have melted the initial snow flakes. The wet surface will eventually freeze giving  a textured surface for new snow flakes to sit on instead of sliding off.

The same is true for objects with thermal mass that retain heat or cold after a sudden change in air temperature.
Surface properties such as roughness.

If even a few snow flakes find purchase on a surface, more will  find a way to build on that and obscure your surface. This is far more important than angle.
Atmospheric conditions such as humidity and the nature of the snow fakes formed.

To effectively keep a surface clear it should be ① smooth, ② quickly transfer heat to adapt to the current air temperature, and ③ be sheltered from being in contact with falling snow in the first place. Even highway signs with are smooth, vertical and thin metal are only so effective  at staying clear and in some regions will have eaves protecting them from some snowfall.


How do they get "deep lunar mantle" samples? Phys.org's Study suggests Earth and Moon not identical oxygen twins says

They found that the oxygen isotopic composition varied depending on the type of rock tested. This may be due to the degree of mixing between the molten Moon and vapor atmosphere following the impact. Oxygen isotopes from samples taken from the deep lunar mantle were the most different to oxygen isotopes from Earth
"This data suggests that the deep lunar mantle may have experienced the least mixing and is most representative of the impactor Theia," said Sharp. "Based on the results from our isotopic analysis, Theia would have an origin farther out from the Sun relative to Earth and shows that Theia's distinct oxygen isotope composition was not completely lost through homogenization during the giant impact."

and links to Erick J. Cano et al, Distinct oxygen isotope compositions of the Earth and Moon, Nature Geoscience (2020) which is paywalled. The abstract says:

Here we present high-precision oxygen isotope analyses of a range of lunar lithologies and show that the Earth and Moon in fact have distinctly different oxygen isotope compositions.

but "lithologies" sounds like it refers to lithosphere which doesn't sound like it includes the "deep mantle".
Question: How exactly do they take deep mantle samples from the Moon and get them to Earth? How deep does one have to go to reach the deep mantle? From what I remember the Apollo astronauts either simply walked around and picked rocks up, or hammered off some bits, or occasionally did some hand-drilling. They loaded about 100 kg up each time and flew them back to Earth made possible by throwing life-support equipment out the door as well as other less necessary items before takeoff. The deep mantle sounds pretty-much out of reach

There are three ways samples of the mantle could arrive on the surface of the Moon.

Drilling deep holes into the mantle, take a sample and send to the
surface.
As ejecta from a large deep impact crater, particularly where the
crust is thin.
During volcanic eruptions, the upward moving magma tears of chunks
of mantle from the walls of the volcanic "vent" and ejects pieces of
mantle embedded in the resulting lava as xenoliths.

We know the Apollo astronauts only drilled down about 20 cm into the regolith, so there are no drilled samples of the Moon's mantle. This means that the only way we might have a sample of the mantle is by serendipitously picking up a sample from the surface after it was ejected by the other two methods.
The Chinese rover Yutu, on the far side of the Moon, in the South Pole Aitken Basin

... which was formed by a celestial collision over four billion years ago. With a diameter of 2,500 km and a depth of about 13 km, the basin is the moon’s oldest and largest impact crater. Very large impact craters can potentially penetrate through the crust and enable probes to sample the lunar mantle.
... the lunar soil at the landing area contained a large amount of olivine, low-calcium pyroxene and a small trace of high-calcium pyroxene, which are very likely from the lunar mantle.

Notice the term "very likely" near the end of that quote.
If no one has ever seen it, how do we know what the lunar mantle looks like?

The properties and composition of planetary interiors are inferred by indirect evidence.  Seismometers left on the surface by Apollo crews measured the velocity of seismic waves inside the Moon, an indirect measure of the density of the deep interior.  The density of the mantle is high enough so that common surface rocks cannot make up a significant portion of it; the rocks must contain large amounts of the minerals olivine and pyroxene.  In addition, the mantle rocks were partially melted to make the mare basalts that cover the surface in places.  The chemical composition of these lavas show they were made by melting a rock rich in magnesium and iron.  Finally, xenoliths of the Earth’s mantle are sometimes found entrained in lavas – these pieces are made up of the olivine-pyroxene rock peridotite (after the mineral olivine (the gem form is peridot) that makes up most of it.)  So the idea that the rocks of the mantle are olivine-rich is a well-grounded concept for which we have abundant independent evidence.

Concerning the Apollo samples,

Despite an exhaustive search of the Apollo samples, no samples of the mantle have been found, either as a fragment of basin ejecta or as a xenolith in the mare basalts.
... Data from the orbiting Japanese Kaguya mission shows that olivine is present in the surface deposits of some lunar craters.
... they mapped out the occurrences of these olivine deposits and found that many of them occur within the rims of large impact basins.  Based on models produced from gravity mapping, the crust of the Moon is thought to be thin here and the mantle is close to the surface.  Thus, these large impact basins could have excavated chunks of the mantle, throwing them out onto the surface of the Moon.
... Why is the mineral olivine important?  Olivine is a silicate mineral rich in magnesium and iron; it forms one of the basic, silicate building blocks of the rocky planets.  In magma (liquid rock), olivine crystallizes first and its composition is a key indicator of the composition of the magma.
... Being dense, crystallizing olivine would sink in the liquid magma, slowly accumulating deep in the Moon.  As the entire Moon solidified, these “cumulate” layers of olivine and other iron-rich minerals would make up the mantle.
... Olivine is a very common mineral and abundant in the lunar crust.  A curious fact is that olivine grains in lunar highland rocks tend to have high amounts of calcium, a minor element but a key diagnostic of the crystallization environment.  In Earth rocks, olivine formed at depth has very low concentrations of calcium.
the olivine crystals in dunite (a rock made up almost completely of olivine) from the Apollo 17 site – a sample proposed as a piece of the lunar mantle – likely came from the accumulation of crystals at a depth of only a few kilometers, far shallower than the tens of kilometers depth to the mantle.
... Because the Kaguya spectral mapper is detecting only the presence of olivine, we cannot distinguish between pure olivine and olivine crystallized with plagioclase, what lunar scientists call troctolite.  Troctolite is common in the Apollo highland samples, but is a relatively rare rock on Earth.  It consists of (more or less) equal parts olivine and plagioclase, a calcium- and sodium-rich silicate mineral.  Troctolites make up some of the most deeply derived rocks found in the Apollo collections, but all studied to date seem to be of crustal, not mantle, provenance.  There is no objective evidence that the olivine seen by Kaguya is not derived from troctolites and/or dunites of crustal (not mantle) origin.

In short, the sample tested most likely wasn't from the mantle but because of mineralogical similarities it is being used as an analogue for a mantle sample.


How long does it take to refresh the entire water supply in the Earth's atmosphere? Water in the atmosphere is present as vapour, liquid and ice. It is just a small amount of the Earth's total water supply. I'm wondering how long it will take to rain down all the water from the atmosphere and "replace" it with new water by evapotranspiration.

This will give an indication for the maximum accuracy of weather forecasting while atmospheric water plays an essential role in climatological conditions.

The term you are looking for is called residence time or residency time.  This UCAR Science article suggests it is about 9 days on average.  This should be verifiable by dividing the average global precipitable water by the average global daily precipitation.

I don't see any reason why the residency time of water would offer any hint of weather predictability limits. If the equations to predict evapotranspiration used in forecast models have skill, shouldn't the 9 days not be the limit (and how limiting a factor it is would depend upon how skillful those equations are)? The residence times of vehicles on roadways is probably near/less than an hour, yet we can forecast traffic quite reasonably well in advanced in at least many circumstances (and that's prone to the much more volatile nature of human choice/error)!

Indeed I think the "residence time" of energy in the lower troposphere, if such an idea even has sense, may well be shorter than a day for the Earth given the continual heavy IR absorption and reemission rates in the atmosphere, and the dominant input being solar energy. But we can forecast much longer periods than that well.  We have great understanding of insolation into the Earth-air system, and then quite solid skill at predicting its transfer, even with the complexity of clouds and other feedbacks.  So we can outdo such a timescale even if energy passes through the system indeed quite quickly.  Likewise, there seems to be no reason for the 9 days to be a particularly meaningful limit on the atmosphere.


Is there a minimum snow depth to be considered as presence of snow? I want to create a variable "snow cover" with values presence/absence of snow for different weather stations (to work later with NDSI from Landsat images with a pixel size = 100 m). I got snow depth values (cm) from weather stations, but I'm wondering if there is a formula or a minimum depth I should consider as presence of snow. Reading the methods used to estimate snow depth, values are based on different measurements around the station, but it does not specify how big the area is.

can you please advice on this matter?

A measureable amount of precipitation is considered to be at least 0.01 inch of water. Since on the average 10 inches of snow melt to 1 inch of water, this corresponds on the average to 0.1 inch of snow. Anything less is considered a trace (too little to measure).


Database of color wavelengths of minerals I was wondering about the physics of color, and now am interested in finding out if there are any resources (databases, text files, html tables, or pdf listings) of minerals and their associated colors or (ideally) color wavelength spectrum.

For example, amethyst might have a white, silver, and purple color spectrum. Onyx might have a grey, blue, or black color spectrum. Granite another spectrum. Wondering (a) if any of this information is captured in any form on the web (such as 1 journal article per mineral/rock type), and (b) if it is aggregated into a database, text file, table, or other sort of list which includes lots of types, so it would say the wavelength of visible light that it emits, or some ranges of it, or even a hex color range.

This type of information is made available through the USGS Spectroscopy Lab.

There is a researchable database of their current spectral library with the appropriate information for each mineral signature (formula, sample_id, type and more). Here is an example of the signature for Hematite:

Further, there is an up to date publication accompanying the database titled USGS Spectral Library Version 7, available here.


Slope of Saturation vapor pressure versus temperature-A parameter in Penman's equation How is mm of Hg per degree Celsius converted to kPa per degree Celsius? I also need  the equation for computing the value of A (slope) in mm of Hg per degree Celsius.

You can convert mm Hg to kPa with the conversion factor $0.133322368\ \mathrm{kPa\ mmHg^{-1}}$.

Saturation vapor pressure as a function of temperature is

$$ e_s(T) = e_{s0}\exp\left[\left(\dfrac{L_v(T)}{R_v}\right)\left(\dfrac{1}{T_0} -\dfrac{1}{T} \right)\right], $$

where $L_v(T)$ is the specific enthalpy of vaporization, $R_v$ is the specific gas constant for water vapor, $T_0$ is reference temperature (273.15 K) and $e_{s0}$ is the saturation vapor pressure at $T_0$ (611 Pa).

You can find the slope of this curve by taking the derivative $\dfrac{d e_s}{dT}$.

Note that the units of $e_s$ and $T$ are Pa and K respectively in the equation above.


Why does the El Niño Stop? The reason for the initiation of the El Niño is unknown, but what is well known is how it progresses once initiated.  The West Pacific warm pool begins to drift East, and the strength of the trade winds begins to decrease.  In turn, the decreased trade wind strength further enhances the drift of the warm pool to the East, and this in turn further decreases the strength of the trade winds.  It appears as though this forms a positive feedback cycle, so what is responsible for the cessation of the El Niño event?

I think it is important to think of the El Niño as just one of the components of a large scale global atmospheric-oceanic phenomenon known as the El Niño and the Southern Oscillation (ENSO). ENSO takes shape as fluctuations of the rainfall, wind, ocean currents and waves. They are by nature very irregular.

The Southern Oscillation (SO) was first discovered by Sir Gilbert Walker who conducted seasonal averages for pressure and rainfall at a number of stations around the world. He found that a single spatial pattern was dominant where regions of high pressure in the central South Pacific Ocean and low pressure near Australia and India reverse and the highs turn into lows and the lows into highs. The SO is an atmospheric phenomenon, on the other hand, the El Niño is an oceanic process. Nonetheless, the interconnectedness between both phenomena is significant such that they cannot be considered alone, as pointed out by Bjerknes (1966). The combined action of ENSO is known to cause drought in Australia and the reduction of upwelling in the western coast of South America (which has disastrous consequences for nutrient delivery).

There is general agreement that one of the necessary ingredients for the initiation of the ENSO event is the reversal of the general equatorial Trade Wind pattern, an easterly steady wind due to a Walker cell. Westerly wind bursts spanning thousands of kilometers and acting over days or perhaps weeks at a time set off internal waves that transport energy westward and eventually poleward along the western coast of South America, some of that energy bounces off and radiates back east. See sketch below:

The equatorial isopycnal depression moves eastward along the equator as a Kelvin wave until reaching the western coast of South America relatively unchanged. These are shallow water waves so the speed is just $c = \sqrt{g'D}$ where $D$ is the depth and $g'$ is the reduced gravity, so they travel at about $c = 2.5$m/s plus 10-20% because they are literally advected by the Cromwell Undercurrent. They transport large amounts of energy over vast distances, depositing it far away from the generation zone in the western Pacific Ocean. Namely, after arrival on the east Pacific coast the equatorial Kelvin wave energy degenerates into two coastal Kelvin waves propagating poleward, and into new diffuse equatorial Rossby waves radiating towards the west Pacific. It is this removal of energy from the Western pacific through the development of these complicated wave motions and other more subtle processes that eventually brings an ENSO event to an end (chicken and egg?). Because the energy is removed, the SST drops, the trade winds resume thus ending ENSO.

I like the quote from the link in @DavePhD's answer:

"An El Niño event contains the seeds of its own demise."

Source:

Regional Oceanography: An Introduction By Matthias Tomczak


Relationship between pressure, temperature and density in meterology I have been learning meteorology a bit on my own, and one thing that never gets answered clearly is the relationship of pressure, temperature, and density.

When I looked it up, the density of air at various temperatures varies quite a bit - if I recall, from something like 1.1 to 1.5 kg/m3.

My confusion comes from trying to understand weather formation.  A typical text says that, for instance, heating of the earth leads to thermals that rise due to their higher temperature and lower density, leading altitude increasing and to temperature dropping at the dry adiabatic lapse rate, then the moist adiabatic lapse rate, etc.  But it is always done using "parcel" arguments.

From basic thermodynamics, heating could lead to a combination of temperature increase, pressure increase, and physical expansion (if there is no fixed container).

Specifically, the ideal gas law gives:

$$PV=nRT $$
or
$$P=\frac{n}{V}T$$ (ignoring the constant of R)
or
$$P=\rho T$$where $\rho$ equals density.

Am I wrong to assume that the simplifying assumption is that, to a first order approximation, the density can't really change much about an area since a parcel of air could expand, but the whole atmosphere locally can't (since the 'parcels' all abut)?  In other words, ground heating causes temperature to rise, and thus presumably pressure, but to a negligible degree decreases density?

This would seem to imply higher pressure from heating actually leads to a net kinematic effect of driving the column of air upwards (as molecular pressure against the ground increases), where it can expand against lower pressure air above due to the fact pressure falls quickly with altitude - but there really isn't expansion or a decrease in density near the surface itself.

The typical "parcel lifted by a helicopter" argument fails to explain how it really all holds together and actually happens, since there is no 'container' for the gas in reality.

Another way to see this is in this example.  Suppose I have a hot tub in Antarctica in winter (I have one in Idaho in winter which is close enough).  The ambient temperature may be -30C or about 240K, and when I open the cover there is water at about 30C or 300K.  I can see thermals climb; the air, perhaps, is heated to 270K (being generous).  But the new air that gets sucked in and heated over the surface to 270K and then rises would immediately seem to be at higher pressure than ambient air since $$P=\rho T$$ I could even believe the kinematically more energetic air could cause an expanding 'plume' radially a bit as it rises, since the higher P and T slightly pushes out on less energetic ambient air.  But that just means $\Delta P$ is slighlty reduced to take into account the expanded volume of the plume; $\rho$ has dropped slightly, but nowhere near how fast it will drop if it gains altitude and has truly lower pressure about it.

In reality, it seems:

locally the (synoptic) pressure is close to fixed - and varies only a few percent globally at sea level;
the gradient of pressure change is in the $z$ direction;
local heating increases T and thus P, except to the degree that increased P allows it to form an expanding plume (which is a few percent, so second order);
Really, the more energetic (kinetic) molecules have no where to go but up, what is really causing any updraft.

'Locally' and 'synoptically' are conflicting adjectives. Synoptic means overall, or large horizontal scale- think thousands of kilometers.

You are right on some accounts. Synoptically, pressure doesn't change much, depending on your qualitative definition of 'much.' On a percent scale or day-to-day experience, absolute temperature fluctuates more than pressure. But the gap of those fluctuations result in changes of density, leading to changes in buoyancy.

The vertical momentum equation :$$\frac{\partial w}{\partial t}+(\vec{v}\cdot\nabla_H)w+w\frac{\partial w}{\partial z}=-\frac{1}{\rho}\frac{\partial P}{\partial z}- g + \nabla^2w$$ when applied to synoptic scales can be treated as approximately hydrostatic: $$\frac{\partial P}{\partial z}=-\rho g$$.
From this equation, as well as the ideal gas law, the hypsometric equation may be derived.

Although the vertical gradient of pressure is large, gravity is also large, which explains why the atmosphere is not lost to space and vertical motions aren't usually large in horizontal scale.

Using said hypsometric equation, it can be shown that changes in vertically-averaged temperature lead to synoptic scale changes in surface pressure.


Can a person's individual carbon emissions become negative over their lifetime? Imagine that a person's individual carbon emissions were logged and accounted for in a ledger over an entire lifetime.  If that person could perform certain actions to subtract from their carbon emissions in this ledger, what might these actions be?  Via such actions, would it be possible to end up with a carbon negative final total at death, assuming that person continues to indulge in all the activities that currently contribute to global climate change (e.g. eating red meat, using fossil fuels)?

For example, is there a rough number of trees that would need to be planted to 'pay' for these emissions in the ledger over an entire lifetime, and then some (assuming average life expectancy of person living in 1st world country)?

Edit: I understand such a question is necessarily vague due to the sheer number of variables at play.  As such, I wouldn't be looking at exact numbers, rather some kind of scale.  That is, I would be interested to hear whether something needs to be done hundred's, thousands, or tens of thousands of times, etc.  In regards to the individual, let's assume a 'typical' person who lives in Australia (from the Census) and is "married and lives in a couple family with two children" and "lives in a house with three bedrooms and two motor vehicles".  Feel free to make any other assumptions, and if possible, skew to the worst-case/heavy use scenario - for example, motor car and/or heating/cooling is used every day, eats red meat every meal, etc.

Aussies emit ~15 tonnes CO2 per capita per year. Current carbon capture and storage technology can bury CO2 for \$40-\$57 per tonne (estimate for early 2020s). So, yes, you could do this for ~$50,000 .
Underground storage is relatively permanent. As for trees, you could plant one of these,

1,700 tonnes  CO2 and lives 3,000 years. With any kind of trees you will need to assure your patch of forest remains treed for millenia. As for the number of trees, I think forested area is a better measure:

Approximative values of the carbon content (tonnes per hectare) for various vegetation types.
Source : IPCC, 2001

You would need tens of hectares.


Defining dry/wet season in Europe I am developing a remote sensing model and I also want to consider the climate data.

My question is, how can I define a dry/wet season for a country like e.g. Austria?
I have the weather data for three years and I would like to separate the dates into dry and wet.

Two approaches:

Search tourist websites for the countries you are interested in. They very often have average data on temperature and rainfall by month.
Just Google countryname monthly rainfall. You may get general descriptions instead of hard (tabular) data, but since you only have to collect the data once, that's doable.

But as you get from the comments below your post, how useful that data is remains doubtful.

As an example: The first hit for the austria monthly rainfall search says:

  ... altitude determines the precipitation pattern; while high-level areas in the Alps may have a high average rainfall in excess of 2000 mm per year, while some regions in the flatlands of Austria have only 600 mm annually.

(emphasis mine)

Note that this page mentions the WeatherOnline (UK) Climate of the world page as its source. There you have descriptions for many countries.


Does anyone have a geological map 1 / 1 000 000 or 1 / 50k of Morocco in HD? I am having a problem reading in my low version map.
Besides, any tips on where I can find "free" maps?
Thank you!

It is not so evident if you look for the big picture (grammar school's project?), or detail and specific region.  Because even today, the geological mapping of Morocco is not complete (gouvernmental reference), the 19 already digitized geological maps about Morocco  on gallica.fr may be an interesting entry for you.  The GUI interface is more helpful for books, than for maps (selection of the page, export as .pdf / .jpeg), but there is a zoom and pan option to see some details on the maps pretty well.
E.g., a more general one by Brumnich (1936, 1:500'000) here, or one with stratigraphic / petrographic details about central Morocco by Termier (1932, 1:200'000) here.


ocean current frequency In this paper by Muller and Garrett it is stated:

  It is a standard expectation that
  currents in the ocean interior with frequencies
  much less than the Coriolis
  frequency will lead to an Ekman flux in
  the frictionally influenced boundary
  layer near a solid boundary, and that convergence or
  divergence of this flux will have a back effect on the
  interior currents.

I do not quite understand what is the frequency of a current.
How does it dynamically relate to the Coriolis frequency?

Ocean currents can be described as flow oscillations that are forced at different frequencies. In the absence of any external forces (wind, friction), the resulting flow is the inertial motion, which is the response to the balance between Coriolis and inertia. The Coriolis parameter, $f$, can be described as a frequency: the effective planetary rotation frequency of a parcel of water. So, $f$ is called Coriolis frequency or inertial frequency.

There are many examples of currents that do not oscillate at the inertial frequency. The simplest examples are the tides. For instance, at 43.5N, the Coriolis frequency is $10^{-4}$ $s^{-1}$, which is equivalent to an inertial period of $17.4 h$. The main semi-diurnal tidal constituent, $M_2$, has a period of $12.42 h$, which results in a frequency larger than the inertial frequency (at mid-latitudes). The oscillations that happen at frequencies larger than Coriolis are called super-inertial flows. On the other hand, the diurnal tides (e.g., $K_1$, $O_1$) have periods of around $24h$ and thus have frequencies smaller than the inertial frequency (at mid-latitudes). The oscillations that happen at frequencies smaller than Coriolis are called sub-inertial flows.

Flow spectrum showing energy peaks at certain frequencies: diurnal tides ($O_1, K_1$), semidiurnal tide ($M_2$), and Coriolis (inertial) frequency ($f$).

In the real ocean, the balance between planetary vorticity (Coriolis) and inertia is only part of the story. There are usually other forces acting on the flow. For instance, when the balance is between Coriolis and the pressure gradient, we end up with the geostrophic balance. The resulting geostrophic currents can be described as a zero-frequency motion as there is no acceleration (steady-state).

Another important force is the effect of the wind. When we consider the balance between Coriolis (planetary rotation) and the frictional force (stress) caused by the wind, the balance results in Ekman flow. In the Ekman case, the mixing in the layer near the surface (boundary layer) needs to be considered. The same type of balance is present in the ocean in the vicinity of the bottom, as another boundary layer is established there for the flow to go to zero at the bottom. The resulting effect of these frictional forces is that the flow does no longer oscillate at inertial frequencies.

In the paper you mention, they describe how the frictional effects near the boundary (Ekman balance) influence the interior flow. The interior of the ocean tends to be in geostrophic balance (frequencies smaller than inertial). The boundary flow effects tend to propagate into the interior modifying the geostrophic balance. A good example of this effect is Ekman pumping: cyclonic winds cause Ekman transport, that in turn causes a surface divergence, and in order to balance the flow, result in vertical flow (upwelling). This effect is called Ekman pumping and modifies the interior flow to compensate boundary flows.