On the solidity of the Earth's core From what I know from various textbooks, pop-science shows and my classes, the earth's core is solid. But how does the concept of solid and liquid make sense at these high temperatures.

The Earth's core is both solid and liquid. The outer core is molten and produces currents of molten nickel/iron which generate the Earth's magnetic field in a dynamo effect, while the inner core is solid. The reason the inner core is solid is that it is under tremendous pressure, more so than the outer core. Scientists know this from the analysis of seismic waves which pass through the Earth.


Why can't radar's decibel scale be used to determine the intensity of snowfall? According to the FAA's Aviation Weather Services advisory circular,

  Values below 15 dBZ are typically associated with clouds. However, they may also be
  caused by atmospheric particulate matter such as dust, insects, pollen, or other phenomena.
  The scale cannot be used to determine the intensity of snowfall. However, snowfall rates
  generally increase with increasing reflectivity.

Why can't that scale be used to determine the intensity of snowfall?

Snow, unlike rain, has holes as well as different refractive properties. This allows the radar beam to penetrate and reflect the beam differently than an ordinarily oblate rain drop.


Eruptive fissures in Hawaii associated with Kilauea; what are they? What is really happening? I hear news of "eruptive lava fissures" opening up in Hawaii, nine of them at last count. But I don't understand what these are really.

Are these existing, older lava tubes that are suddenly opening to the surface due to recent filling with new lava, or cracks that go through the crust to to deeper chambers of magma, or something else?

update: I've just seen a the video in the CBS News website's Kilauea volcano eruption: Seismic activity increases, earthquakes strike 5 days in a row (scroll down for this particular video). I wonder if there is a better or more technical visualization of the sources for the fissures somewhere?

It can be either an eruption from the top of an existing tube or deep surface cracks opening up existing magmatic systems. I believe, from what I've been hearing in the news, that in this case they are in fact fresh fractures, tectonic in origin, that have relieved local over burden and allowed magma to rise to the surface in areas that had previously been dormant for an extended period.


Is this a fossil we found in a store? We found this rock at a mineral and jewelry store. The gal wrote down what it was and we cannot find what we think she wrote on the internet anywhere. She wrote Mcstrodlite.

You have a nice stromatolite fossil.

A stromatolites are layered bio-chemical accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms (microbial mats) of microorganisms, especially cyanobacteria. stromatolite fossils can be some of the oldest fossils found on earth. Living stromatolites can still be found today.
 (Wikipedia).

This pattern on the underside of a stromatolite fossil is very characteristic.

Cretaceous age stromatolite fossils from Morocco are commonly found for sale online. (Esty)


What are the differences between down-looking and side looking radar? In Radar concept the SAR-Synthetic Aperture radar performs as side-looking to collect information, why it is not downlooking? There are down-looking radar also. So what are the differences between them

A radar measures the time of arrival of the backscattered signal to infer the distance between the target and the platform (satellite, aircraft, whatever). If two targets are at the same distance from the platform, one on the left and one on the right because the platform is looking down, then their signals will arrive at the same time, making them impossible to distinguish. Looking sideways removes this ambiguity. Look at this figure from the Center for Space Research of the University of Texas (there is also a text explanation in the link).


Does the increasing number of significant earthquakes relate to increasing population density in earthquake zones? I've discovered that there's two different sets of data for earthquakes - one for actual number of earthquakes, and ones for only significant numbers of earthquakes. For example, in January 2016 the USGS showed 11 earthquakes of magnitude 6.0 or greater, of which 5 were listed as significant; in February 2016 it showed 9 such earthquakes of which 2 were listed as significant.

I thought that this might explain why some people say that data shows that earthquakes are increasing, while others say the data shows that they are not.

I made a graph of the number of significant earthquakes of magnitude 6.0 and greater using USGS data for 2002 to 20015. There was a steady increase; for example, there were about 45 in 2007, 55 in 2011, 70 in 2014. I couldn't find any explanation for this, but I wondered if this increasing trend correlates to increasing population density in earthquake zones.

I couldn't find a set of historical data for actual (significant and insignificant) over the same period of time.

The only possible linkage between moderate earthquakes and population is that more people create increased groundwater extraction, and hence near-surface fault planes tend to dry out. This effectively increases the friction so that there are less frequent but more violent quakes. However, this would only affect near-surface earthquakes which seldom exceed about magnitude 3 or 4. The really big earthquakes originate at plate tectonic interfaces at depths from about 10 km to hundreds of kilometres. There is nothing that humanity can do to influence processes on this scale.

Another issue is that micro-seismicity occurs all the time - millions of small quakes that go un-noticed every year. Some of these can certainly be caused by humans - but does this really count?


What causes variation of seabed depth relative to fixed chart datum? Please refer to this page of coastal wiki. Quoting:

  ...the reconstructed overall vertical position [of the seabed] with respect to a fixed chart datum may vary by more than 10 cm from survey to survey. The causes of this variation have not been resolved yet.

What could cause this? Could it be a tidal effect? Is there any new information available (specifically on this case)?

Edit: Just to make things clear, I am aware of seabed sonars and their typical error terms, I am aware of coastal morphodynamics - I am looking forward to see if there is any information available attributing a (definite) cause to event described in the wiki page. I also highlighted the relevant part of the question.

Your question is actually a three-part question in disguise, of which I cannot answer all parts, but let me tell you what I do know.

Part 1: What causes variations in vertical position within the context of the refered sentence?

If you read that section more carefully it is not so much variation of the seabed depth, but variation in the measurement of the seabed depth. Using known fixed structures on the seabed they found out that different runs give a different vertical position of these structures. Let me expand your quote:

  [...] Repeated sampling of stable immobile seabed structures (fishing drag-board traces, ship wrecks) indicates that the reconstructed overall vertical position with respect to a fixed chart datum may vary by more than 10 cm from survey to survey. The causes of this variation have not been resolved yet. Hence, without a vertical reference present within the surveyed area overall variations in the seabed of less than 20 cm cannot be derived unambiguously over periods longer than several months. In contrast, using a fixed seabed structure as vertical reference the precision of multibeam data can be less then half a meter in the horizontal and one centimetre in the vertical [...]

This means that in situations without stable vertical references measurements at different times cannot be compared easily, and simply subtracting the bed heights would not necessarily give the change in bed height over the elapsed time.

However, when there are stable structures, such as a ship's wreck, you can use the difference in the measurements of the vertical position of that structure to correct measurements of the entire seabed, giving a much better vertical precision.

Part 2: What causes variations in the measurements between measurement runs?

The section referenced mentions that the exact causes of the different measurements have not been resolved. Most likely it is a combination of inaccuracies of the used instruments, on which I'm definitely not an expert, and I'm not even sure this is the right Stack Exchange to ask that question.

Part 3: What causes true variations in the absolute seabed height?

This is an entire field of research on its own, called coastal morphodynamics, which is too broad to be answered in a single Stack Exchange answer. Without a specific question you wouldn't get a more sensible answer than it a depends on the seabed composition and water flow.


Where can fluorite be found on Long Island, New York? I'm interested in fluorite (Since Fluorine is my favorite element, and I wanted a sample of it, even if bonded, but I don't want to buy it; that would be no fun), and I'm curious if it can be found on Long Island, New York. Where would the largest geologic formations be that are accessible?

I do not know of fluorite being reported to occur on Long Island. If fluorite is found in NYC, the Natural History museum might have specimens.  You might try contacting a mineralogy / mineral collecting club on Long Island. Someone there would probably know for certain if fluorite can be found.

Fluorite can be found in several limestone formations in New York. See map

Personally, I have collected fluorite from the Penfield Quarry near Webster New York during the mid 1980s.  Some of the waste rock from the quarry was used as breaker wall stone on the lake front in Webster New York.  You could probably still collect fluorite crystals there.

Here is a map of the lower 48 states showing mines where fluorite has been reported to occur.

Other places I have personally collected fluorite

Terlingua, Texas fluorspar mine (massive bedded fluorite)
Spearfish Canyon Black Hills South Dakota (fluorite in geodes in limestone)
Closed rock quarry in Pennsylvania near Breezewood, PA

Locations where fluorite is still able to be collected.

Mines/Mountains near Socorro New Mexico
Mt Antero in Colorado, at high elevation.
Bancroft Ontario - fluorite in calcite (fluorspar)
Burin Peninsula, Newfoundland, Canada (fluorspar)

References:

Wikipedia Fluorite

Maps created using  Digital Rockhounds Companion software.


What type of storm cloud is this? We have had (and are still experiencing) waves of storms passing through this area of the central Queensland 'Capricornia' coast, Australia.  This area is a subtropical coastal environment, close to sea level.

The following picture is one I took from my the balcony outside my lab (facing east):

The storm was moving to the north (left) and that part of the sky was a featureless heavy cloud. The conditions were as follows:

Ambient temperature: 30C (86F)

Wind: strong, to the north

Conditions: Heavy rain periods, heavy thunder and lightning, about 10 minutes later, the sky cleared, temperature rose and the wind dropped to barely a breeze.  Numerous cloud-to-ground and cloud-to-cloud lightning was noticed from this cloud formation.

I am leaning towards this being a 'scud cloud', but a local weather-enthusiast claims it was a weakly formed non-rotating wall cloud.

What type of cloud is this?

I had a rather difficult time telling how the rest of the cloud structure looks; however, I would tend to believe your weather-enthusiast friend might be correct.

A wall cloud - rotating or not - can also be known as a pedestal cloud and is made up of cumulonimbus clouds; generally forming in the strongest part of the storm.
From what I can tell in the picture and judging by the weather that came from it; it sounds like it was a non-rotating wall cloud. Here is an additional reference page that may help you identify it.


where can I download ECHAM climate model data? Is there any website where can I download ECHAM climate model data?

Where to find the data

The German Climate Research Center (DKRZ, Deutsches Klimarechenzentrum) hosts the Word Data Center for Climate (WDCC). You can search the WDCC via the CERA Database (cera-www.dkrz.de).

Looking for ECHAM provides you with several sets of ECHAM model results: here. You get at least the ECHAM data for the second to fourth IPCC assessment reports and some more data sets.

You need to have a login. It can be easily created.

Information on the structure of the data at CERA

You have projects, experiments, and data (sets).

Projects contain overall information on the model setup, on the data producers, and on the validation.

One experiment can summarize several data sets. For a coupled climate model this could mean, that the physical ocean, the biogeochemical ocean, the meteorology, and the atmospheric chemistry are saved as individual data sets, which are than summarized as one experiment.

Experiments can have a doi (digital object identifier). Thus, they are easily citeable in scientific publications and long-term available.

Access data at the WDCC

You can directly download data via the web-interface. As an alternative, you can use jblob, which is a command line utility for downloading data from the WDCC. Jblob also has some options to pre-process data on the DKRZ servers prior to download it -- which might reduce your file size. For both access pathways you need to have a valid login.


Does a hurricane with a smaller eye have a lower pressure? I have heard it said that if there are 2 hurricanes with the same maximum wind speed, and one has a bigger eye while the other a smaller eye, then the one with the smaller eye would have a lower central pressure.  Is this true?

I could only find this old reference(30 years old) Typhoon Structure As Revealed By Aircraft Reconnaissance. Part 2: Structural Variability by Weatherford And Gray 1988.

The conclusion of the authors is that the size of a tropical cyclone's eye does not have much of a observable relationship with the cyclone central pressure(MSLP) and is shown as a weak correlation. Observations reveal that the contracting eye size of a TC on the average is associated with a decreasing MSLP and an expanding eye size is associated with a increasing central pressure.

So let's look at some actual numbers from that above paper -

These are again averages for the period 1980-82 tropical cyclones that have been classified on the basis of size of the eyewall

Eye-class                          MSLP(Central pressure in mb)  MSLP Change(in mb/12 hrs)

No eye                             985                            +/-5

Large eye ( > 28 kms)              987                            +/-8

Medium eye (15-28 kms)             956                            +/-9

Small eye ( < 15 kms)              954                            +/-12

Note from this table how much the MSLP fluctuates over a period of 12 hours  for the smaller eye sizes. Also remember that a vast number of cyclones do not form eyes.

Word of caution if you are trying to view this table from the operational forecaster's point of view it is very likely an individual cyclone may depart from these average values. And while these data sets have been obtained for the Northwest Pacific Ocean it is likely they hold up for other basins as well.


Signatures of acid rain at KT boundary I read in Walter Alvarez' book T. Rex and the Crater of Doom
that the Earth's collision with the large meteor leading to the K-T extinction catalyzed the reaction of atmospheric oxygen and nitrogen molecules to form nitric oxide, which in turn formed highly corrosive nitric acid when combined with water. In addition the impact is thought to have volatilized huge amounts of sulfur contained in anhydrite, which in turn formed sulfuric acid.

This question refers to a thickness of  $\pu{1.8m}$ for the section where iridium could be detected in the K-T boundary, suggesting that the resolution may be too low to note the effects of acid rain following the collision.

Is there evidence in the geological record of the formation of these acid species thought to be associated with the collision, say from deposits and/or effects of the ensuing acid rain?

Estimated sulfur release 325 gigatonnes = 325,000 teragrams. The numbers in this diagram are in teragrams

Sulfur Cycle

so the release is $\approx 1000\times $ today's annual sulfur cycle.

I think most of the sulfur compounds would be washed into the ocean and then deposited into sediments. I can't find how much sulfur is currently in the oceans, this article says gigatons (because you can smell it). I also can't find how fast the increased sulfur would be deposited.

Another issue is that, unlike iridium, there is normally a lot of sulfur in marine deposits, so it is hard to distinguish what comes from Chicxulub.


Saltwater River Freeze and Thaw We live in a house overlooking a salt water river. We overlook a cove. The river feeds into Narragansett Bay in Rhode Island. In the 17 years we have lived here, the river has frozen several times.

In early January of this year there were record breaking low temps which were below zero in our area. The river froze solid for a couple weeks. A couple of days ago we had record breaking WARM temps with steady rainfall. The morning after the rain storm we noticed that the bottom of the river was exposed but no water flow.

This is alarming to me because we've never seen anything like this to this extent where it has stayed without the river flowing into the cove for several days. I searched the web and found this site. Hoping someone can come up with an answer! Thank you.

I suspect that rather than an ice jam as suggested in the comments, that this was a consequence of sustained high winds that happened to be blowing in just the right direction, thereby blowing the waters away from the side of the bay to which the inlet / bayou / saltwater river is connected.

Negative storm surge can drain shallow bays, sometimes dropping sea level by several feet. This happened, for example, along the west coast of Florida prior to Hurricane Irma. (That negative storm surge became a positive storm surge when the winds shifted direction.) This happens with great regularity where I live. The bayous later today and tomorrow will be very, very low due to a cold front that is pushing through right now.


Where does all the salt come from in the Dead Sea? Usually when I think of a lake it should be sweet water as all the water is coming from rivers/mountains and rain and, because it is very low situated, all ground water should also flow into it.
But the Dead Sea is very salty (32%). So how did all that salt came into that lake?

Also, why is it called a sea and not a lake?

The composition of the Dead Sea is quite unlike most other salt lakes, and is not at all like sea-water. Compare the concentrations, in grams per litre:

The potassium, bromine and magnesium are all hugely enriched relative to seawater, so clearly, it is not just a case of evaporation of residual seawater from the time of isolation of the Dead Sea. In fact, the vast majority of the water, and almost all of the magnesium, is derived from rivers draining from the north, from around the sea of Galilee, where magnesium-rich volcanic rocks weather rapidly. Much of the sodium and chlorine is derived from evaporation of rainfall originating from the Mediterranean - rainfall being just massively diluted sea water to start with. The high calcium and potassium comes from evaporite dissolution from the surrounding and adjacent rocks, especially from the Lissan Marl and saline springs emanating therefrom.

The real problem is: Where did all that bromine come from? The Dead Sea has the highest concentration of bromine in the world, and it is far from obvious how it got there. Clearly, there has been a massive concentration process. Maybe it was concentrated in the saline base of a much larger lake during the time of formation of the crustal formation of the Aqaba - Dead Sea - Gollan Heights rift? Any 'armchair theorists' out there with a better hypothesis?


Why is a seismogram interpreted as a convolution? I remember reading in a geology book that a seismogram is a convolution between a source signal and propagation effects.  In layman's terms, what does this really mean?

In simplest terms, it simply means that:

if the source signal is shifted by some amount of time Δt, but otherwise unchanged, then the seismogram will also be shifted by Δt, but otherwise unchanged; and
the seismogram generated by the sum of two (or more) source signals is the sum of the seismograms that would've been generated by each of the individual source signals.

Basically, it works exactly like an ordinary echo: what you hear is the original sound, or rather several overlapping echoes of it, each reaching you by a different path, delayed and attenuated by varying amounts during its propagation.

Mathematically, this process can be represented by convolving the source signal waveform with a function, called the convolution kernel, that describes how the signal is spread out and split into multiple echoes.  Specifically, the convolution kernel is northing more or less than the waveform of the echo that would, in principle, be produced by an "ideal unit impulse" source signal — that is to say, a source signal consisting of a single, infinitesimally short pulse of sound pressure carrying one unit of energy.  For this reason, the convolution kernel is also known as the impulse response of the system.

The convolution process itself, in the simplest case, merely amounts to summing together several shifted and scaled copies of the impulse response.  Specifically, this is the case when the input signal can be represented (or at least approximated) as a sum of several pure impulses.  More generally, any input signal can be mathematically represented as a sum — or, more properly, an integral — of infinitely many tiny impulses spaced infinitely closely*, in which case the resulting seismogram is simply the integral of infinitely many infinitely small shifted copies of the impulse response.  This is precisely what a convolution does.

*) Mathematicians, and perhaps some physicists, reading this will cringe at this point; while a sum of impulses can indeed approximate any function as a measure in the weak sense, it's not a good approximation is most other senses.  Nonetheless, it is a rather useful and concrete way to think about convolutions.

One reason why thinking about seismograms as convolutions is useful is that, if we know the physics of seismic propagation and the geological structure of the area through which the signal propagates, we can calculate the theoretical impulse response function of the system and convolve it with a simulated source signal to obtain a synthetic seismogram.  Conversely, given a real seismogram and the source signal that produced it, we can deconvolve them to obtain an approximation of the impulse response, which can then yield tomographical information about the geology.


Geometrical differences of subduction zones I am looking for geometrical differences in subduction zones. What are the differences, in dip, curvature of the interface, thickness of the plates etc.?

There are differences between the Chile and the Mariana type (as sketched here), but what about the other subduction zones like Alaska, Japan, Sumatra?

Differences in subduction geometry depend mostly on what type crust takes part in the collision (oceanic to oceanic, continent to continent, oceanic to continent), the speed of the two (or three) colliding parts and the relative movement of the two plates.
Many subduction zones share similar characteristics (like back arc compression and volcanic arc) but there are many differences too. The general geometry of a subduction zone is, in general, well understood, but there are still many questions about how, why and when, mostly because most of our measurements are indirect and the interpretation is still problematic. You can read http://www.platetectonics.com/book/index.asp for a very good and simplified explanation of tectonic plate movement.


Role of radiation parametrization update frequency in Tropical Cyclone simulation I am using a mesoscale model to simulate a tropical cyclone. The model input file has an option of 'Frequency of Radiation Tendencies update time' for Longwave and Shortwave radiation. According to me, all the parametrization schemes are updated at every time step,then why is it mentioned separately and how will it work? My question might be vary basic but instead of having the codes, I am unable to visualize what is happening with the radiation parametrization in my model.
Is there any tutorial where I can get its clear description?

I am also searching for a tutorial for TC simulation where the basic steps to simulate a TC are given for beginners. It will be of great help if I can get it here.

Parameterizations are not usually updated at every time step, generally speaking. Radiation parameterization, in particular, is the most computationally expensive parameterization, since it calculates the integral of an exponential of an integral.

So what happens is you set a frequency to update the radiation parameterization, say every 30 minutes. So your model wiil find the diabatic heating tendencies from the initial state and use that for the first 30 minutes of model-time. After the first 30 minutes of model time, the parameterizations recalculate the diabatic tendencies based on the model values (such as clouds, etc). The shorter the timestep, the more you will account for changing model conditions. In short, it is how frequently the radiation parameterization is invoked.

So for example, if you are modeling your tropical cyclone, and you have the update frequency for too long of a time, you could be heating a place like the eye is passing over it, but the eye has already moved.

The shorter the frequency, the more the radiation will adapt to the model state, but at the cost of computational time.


What caused the earth's climate to stabilise ~10 thousand years ago? We can see that the last glacial period ended 12-10K years ago. Interestingly enough, this also appears to coincide with the rise of large human civilisations.

My question is: What caused the earth's climate to stabilise ~10 thousand years ago?

You need to examine the assumption that it "stabilized". Rather (and simplistically, of course), the Milankovitch cycle en.wikipedia.org/wiki/Milankovitch_cycles moved from a stable Ice Age regime to an interglacial one.  Absent the current human interference, it would (IIRC, anyway) continue the interglacial for some tens of thousands of years, before entering another ice age.

Nor does the end of the last Ice Age really correlate with the rise of large civilizations, since there was about a 5-6K year gap.  IOW, roughly as long from the end of the Ice Age to the first civilizations, as from them to the present.


Did the Haber-Bosch process enable the population explosion? Im a bit confused on how crucial Nitrogen fixation with the Haber-Bosch process really was. On the Wikipedia page of the Haber-Bosch process it says:

In combination with pesticides, these fertilizers have quadrupled the
productivity of agricultural land.
With average crop yields remaining at the 1900 level the crop harvest
in the year 2000 would have required nearly four times more land and
the cultivated area would have claimed nearly half of all ice-free
continents, rather than under 15% of the total land area that is
required today.
Due to its dramatic impact on the human ability to grow food, the
Haber process served as the "detonator of the population explosion",
enabling the global population to increase from 1.6 billion in 1900 to
today's 7 billion.

However I have read that the products labelled "Bio" in the stores in Switzerland that don't use nitrogen fertilizers have only about 20% lower yields, which is a dramatically different number than what the Wikipedia page on the Haber-Bosch process claims (quadrupling of productivity).
What am I missing? Did the nitrogen cycle change so much so that we don't need nitrogen fertilizer nowadays? Did new technology enable us to get similar yields without nitrogen fertilization? What explains these numbers? Was crop rotation an unknown concept in the 1900’s?

There are a number of factors that went/are going into the population explosion, food is only one vaccination and antibiotics are a big factor as well.  within food fertilizer is again only one of many factors. Better crop strains, mechanized and better farming techniques, soil science, pesticides, refrigeration, and a dozen other factors contributed.  Keep in mind artificial fertilizers get less important as you go back in time as well so calling it the detonator is incorrect and misleading.

Now when considering crop rotation, crop rotation has pros and cons, there are several nutrients plants need and rotation only helps with some of them, and it relies on having compatible crops to rotate which not every crop or environment has.

Keep in mind the piece wikipedia is quoting is not a peer reviewed paper but an essay in nature, which explains it is referring to several modern countries that fertilize almost exclusively with artificial fertilizers. It is not claiming they cannot use other fertilizers.


Does Contwoyto Lake empty into both Bathurst Inlet and Chantrey Inlet? Contwoyto Lake is a large lake in northwestern Nunavut.  Descriptions of it say that its primary outlet leads to Bathurst Inlet.

Does the lake also have an outlet that leads to Chantrey Inlet, reaching the sea 300 miles to the east?

According to "Evaporation from a Small Lake in the
Continental Arctic using Multiple Methods" Nordic Hydrology, 27, 1996, 1-24:

  Drainage from Contwoyto Lake occurs through the Burnside River and Back River

So, yes, to Bathurst Inlet via the Burnside River and to Chantrey Inlet via the Back River.

You can trace out the two paths on the following topo map: http://en-ca.topographic-map.com/places/Contwoyto-Lake-947046/

The Back River outlet is at the south end of the lake and flows through a series of smaller lakes.


How big a risk is Mount Vesuvius for the local population? How much of a risk does Mount Vesuvius pose for the population of the surrounding area?

There are lot of studies on the past activity of Mount Vesuvius. Eruptive deposits have been studied and dated in order to reconstruct the type and timing of past eruptions. This can give some indication of what to expect even if, and I cannot stress this enough, past activity patterns of a given volcano does not predict its future activity. It can give a tendency, but volcanoes remains unpredictable, as shown by recent examples in well-monitored countries like Japan (Mount Ontake 2014 eruption) or Italy (paroxysmal eruptions at Stromboli last summer).

That being said, a study by Cioni et al. (2008) came up with some interesting results. They found that there is a positive correlation between the magnitude of an eruption and the repose time before this eruption. Meaning: the longer we wait before an eruption of Vesuvius, the larger the eruption will be. It's their figure 6:

You can see that Strombolian (= small) eruptions happen after a few years of repose while sub-Plinian and Plinian (= large, like the one that destroyed Pompei) eruptions are preceded by long repose periods. However there is some scattering, especially in the zone shown by a red box:

  In particular, a large variability in the magnitude and eruption style of the past eruptions is apparent for a window of repose time from dozens to hundreds of years.

And now we are exactly in this box: the last eruption of Vesuvius was in 1944, 76 years ago... So according to this study, and assuming the volcano will keep following this pattern (which is not sure), if Vesuvius does erupt tomorrow, it could be up to a violent Strombolian eruption. This type of eruption would not be a major threat to the local population; the main threat is pyroclastic density currents (PDC), which happen mostly with sub-Plinian and Plinian eruptions (their Table 2). The last eruption (1944) falls in the "violent Strombolian" category; lava flows destroyed several villages, but no one was killed.


How to distinguish P, S, Love, and Rayleigh waves in a seismogram? What features should I look for to determine each of these kinds of waves in a seismogram?  What signal processing methods (filters, transforms, etc...) should I use to determine them?

There are two important ways to recognize different types of waves in seismic records:

Their velocity. These waves travel at different speeds: P-waves are fastest, then S-waves, then Love waves, then Rayleigh. Since seismic recordings are measures of earth displacement, particle velocity, or water pressure over elapsed time, this means the waves show up at different times in the record. If we know or guess their velocities, then we can model the arrival times at various stations and try to recognize the different wavefronts. Here's one example of a shot record (distance x on the horizontal axis, time t on the vertical) where you can see reflected P-waves and Rayleigh waves: the slope of the arrivals is a function of wave speed. Once we can discriminate them in some domain (commonly t–x, f–x, or tau–p), we can design filters that exploit this fact.
Their mode of oscillation. The waves are distinguished by different types of particple motion. For example, P-waves are longitudinal, S-waves are transverse, Rayleigh waves are circular. So if we have a sensor that can detect particle motion in three dimensions, we can recognize waveforms that way. In the oil & gas industry, where seismic reflection data is an important tool, so-called multi-component (or three-component, or 3C) sensors are now widespread; here's one example. I'm afraid it's beyond me, but I know one of the methods they use to unpack the different waveform polarizations is singular value decomposition.

Reconciling P- and S-wave reflections is one of the great problems in reflection seismology today. Everything is made more complicated by the fact that these waves can convert from one to the other. For example, when P-waves reflect from an elastic interface, like rock broundaries, some energy is converted into S-waves. Furthermore, some recording equipment is more sensitive to vertical ground motion than to horizontal (e.g. single component geophones), so our records are often strongly filtered. The result is that unpeeling multiple wave types is not easy.


Is CO2 in the Pacific Ocean depleted or enriched in Carbon-13 compared to the Atlantic, and why? Due to thermohaline circulation, the Pacific water is more 'aged' so there is a higher amount of total dissolved inorganic carbon (e.g. CO2) in the deep Pacific when compared to the Atlantic. However, I don't know how this affects the relative 13C/12C enrichment of the Pacific.
Factors I've thought about:

Oxic respiration of buried organic matter is the source of CO2 in the deep ocean.
Deep Pacific water has accumulated more respired CO2 since the Pacific is at the end of the deep circulation.
Algae and microbes fractionate against 13C in favour of 12C.

"The decrease in δ13C as water flows from the Atlantic to the North Pacific is due mainly to the addition of organically produced material and its subsequent oxidation as it falls through the water column. Marine organic carbon has a δ13C of near -250/00, hence the addition of this material decreases the δ13C of the ΣCO2." (from conclusion)

P. M. Kroopnick, Deep-Sea Research Part a-Oceanographic Research Papers, 1985, 32, 57-84.
https://www.sciencedirect.com/science/article/pii/0198014985900172


What's the difference between Waste Water Reclamation and Waste Water Reuse? I received a project which there's the follow topic:
Waste Water Reclamation and Reuse
Are they not the same meaning, reuse and reclamation in this case?

Water reclamation is the process of capturing, transporting and treating water so it can be be reused, particularly if the water is contaminated. Depending on the type of contamination treatment facilities can be a processing plant or a specially constructed/adapted system of biological wetlands with a slow flow of water through them.

Re-using water is using water more than once regardless of whether it has been treated or not. For waste water to be reused it must first be reclaimed and treated.


Is plate tectonics a hoax theory? How can tightly packed plates move? Here are two questions I had ever since I first heard about plate-tectonics.

How can the plates move? Before you suggest me some page to read about plate movement mechanics, let me clarify that I am not asking about the mechanics behind plate movement here. But I am talking about the physical possibility of plate movement.

When we look at the map of plates, all of them are tightly packed, with not an inch of space or gap to move. The complex shape of surrounding plates, blocks all freedom of movement. Then how can the theory say that plates can move?

If you can't follow my explanation, consider a jigsaw puzzle in which the blocks are correctly set up. Can we move a block from the middle now? We can not because the blocks are tightly interlocked, and because of their complex shape. The same is the situation here too, in fact much more complex! Each plates is tightly surrounded by complex shaped other plates, making any movement in any direction impossible!

See the below given a map of tectonic plates for example. It is evident the plates are actually interlocked so tightly that, it is impossible to move in any direction, because of the presence of another plate in opposite direction. There is no freedom of movement available, in any direction! The complex shape of plates make movements impossible!

My second question is this: It is said that, all continents were a single large continent millions of years ago. And then much later, continents 'drifted away', reaching current shape and locations.

If tectonic plates does not even have hundreds of miles of gaps between them to move, how can continents drift away so far, even thousands of miles away?  Certainly plates can't move this far, because the whole earth surface is divided into plates, with no space left for plates to move thousands of miles.

So how did the continents drift away this far? Or do we have to assume that continents are simply floating over the tectonic plates?

Is the plate tectonics theory a complete hoax?

tectonic plates are not completely rigid they can bend, flex, and in the case of oceanic plate, get pushed under each other and melted back down.The plates move by sliding under each other, melting, or bending

Take a toffee-bar candy, hang most of it off the side of a table and put something heavy on the other end to hold it in place, wait a few hours, just under its own weight it will bend 90 degrees. However bend it fast by only a few degrees and it will snap. Rock behaves in a similar fashion, do it slowly enough and with enough force and you can bend it. Basically all solids behave like this to a certain extent. tectonic plates are not rigid on the large scale.

bending rock leaves behind traces like this and this

bend it to fast and the rock breaks creating a fault lines like this and this

plates pushed down get remelted, it helps if you think of oceanic crust as exposed mantle that has been cooled into a solid, while continental crust is much less dense and sort of floats on top of the more liquid mantle. that's why continental crust does not subduct but oceanic does. In essence there are huge gaps between the the permanent plate material, it just cools when exposed forming a hard surface skin called an oceanic plate.

we can even see that in how earth quakes behave around subduction zones getting deeper and deeper in the direction of movement until the stop indicating where there are no solids left to break.

here is an earthquake depth map for japan. notice how they get deeper in the direction of the movement of the pacific plate (west by NW) as it dives under japan.

If you look at a global map of plate movement you will notice that at then end of a moving plate (in the direction of movement) is either a mountain range or a subduction zone, or often both.


Are there situations where the groundwater table doesn't follow the morphology of the surface? In most or all geological site reports I read, the groundwater table (of the uppermost groundwater layer) always followed the morphology of the surface. Is this always the case? Are there signs for situation where this might not be the case, something I can see on the surface?

The groundwater table depends on a lot of properties. These include precipitation rates, permeability/transmissivity of the subsurface and regional groundwater flow. There are two different regimes that are distinguished: one with a topography-controlled watertable and the other with a recharge-controlled watertable.

A topography-controlled watertable closely follows local topography, while a recharge-controlled watertable only follows the regional topography, and so 'following the morphology' is partly scale dependent. To give an estimate of which regime is more likely at a location, Haitjema and Mitchell-Bruker (2005) studied a number of models and came to the following equation:

$$
\frac{\overline{R}_r}{K} \cdot
\frac{\overline{L}}{\overline{D}} \cdot
\frac{\overline{L}}{z_{\text{max}}}
\left\{
 \begin{array}{ll}
 > m & \text{topography controlled} \\
 < m & \text{recharge controlled}
 \end{array}
\right.
$$

Where the terms have the following meaning:

$R_r$ is the average anual recharge rate
$K$ is the aquifer's hydraulic conductivity
$L$ is the average distance between surface waters
$D$ is the average aquifer thickness
$z_{\text{max}}$ is the maximum distance between the surface water levels and terrain elevation
$m$ is either 8 for one dimensional groundwater flow, or 16 for radial-symmetric groundwater flow (in a circular aquifer).

In cases of a relatively low permeability combined with enough recharge by precipitation the groundwater is likely to follow the surface. However, for example in karst areas, where extensive networks of caves and tunnels in soluble rock cause a very effective drainage over long distances, the groundwater will follow the surface on a much more regional scale. Also, areas with high relief groundwater at least isn't parallel to the surface, and for example in sand dunes, the groundwater level is usually relatively flat compared to the dune.


What is the difference between a high-resolution model and a regular model run? So we have high-resolution models like the HRRR (High Resolution Rapid Refresh). But what exactly is the difference between a high-resolution model and a regular model? I realize that the higher resolution models are more accurate, but why is this? Is there more data fed into the computer?

Also, are there criteria that a model must meet to be called high resolution, or is it just an arbitrary name?

High resolution means that the grid mesh the model uses is fine, or put another way, $dx$, $dy$, $dz$, and $dt$ are small numbers.  A model like the HRRR uses a horizontal resolution of 3 km, whereas some of the older regional models used horizontal resolutions of 30 km (though even the NAM is using 5 km these days).  Comparing resolutions to GFS and ECMWF models is a bit less straightforward because those models solve in a spherical coordinate system using spectral methods, and resolution will vary with latitude).

Higher horizontal grid resolution also implies higher vertical resolution and a smaller timestep.  The vertical resolution will be a consequence of wanting to avoid large aspect ratios in your grid box and the smaller timestep follows from the need for numerical stability (see CFL criterion).  The biggest direct result of the increased resolution and decreased timestep are increased memory and drastically increased computational requirements.  Because of this, operational forecast model resolutions will be limited by how long is acceptable for the model to run before output is available, which is a function of the supercomputer crunching the numbers.  You will generally find much higher resolutions in non-forecast research settings than operationally.  For example, I simulate supercell thunderstorms with 250 m horizontal resolution, but I can also spare an entire day to simulate a few hours whereas an operational model only has a few hours to simulate many days in a much larger domain than I use.

I don't believe there is a specific requirement to call a model "high resolution" and I think you'll find that the implied resolutions will be quite different between a climate modeler and a mesoscale modeler.

Differences in accuracy in higher resolution models generally boils down to resolving more of the physics explicitly.  A model running with 30 km resolution cannot resolve convection (thunderstorms), and must parameterize this as a sub-gridscale effect.  You might see terms like "cloud resolving" applied to high resolution models because of this.  A model running at 3 km resolution will be able to explicitly resolve convection.  A large eddy simulation (using filtered Navier-Stokes equations) will be limited to resolving eddies on a scale based on the grid resolution, and will parameterize the smaller scales.  Please see this paper1 for further discussion on the impact of resolution on resolving deep moist convection.

Finally, the data going into the model will make a difference (weather is chaotic and extremely sensitive to the initial conditions).  The HRRR is initialized from the RAP with a data assimilation period for observed radar.  RAP is currently a 13 km model but is moving to 3 km this summer. RAP gets its background fields from GFS and assimilates quite a bit of data on top of that.  While the smaller grid boxes help capture more of the physics, the quality of the data fed into the model is also helping quite a bit with accuracy because it improves the initial conditions.

Bryan, George H., John C. Wyngaard, J. Michael Fritsch, 2003: Resolution Requirements for the Simulation of Deep Moist Convection. Mon. Wea. Rev., 131, 2394–2416.
doi: http://dx.doi.org/10.1175/1520-0493(2003)131<2394:RRFTSO>2.0.CO;2


The difference of vertical advection and convection process for chemistry species In atmospheric, the change of mixing ration $C_i$ of a chemical species $i$ is determined by:

$\frac{\partial C_i }{\partial t} = -\bigtriangledown (VC_i)+\frac{\partial  }{\partial z}(k_z\frac{\partial C_i }{\partial z}) + (\frac{\partial C_i }{\partial z})_{dry}++ (\frac{\partial C_i }{\partial z})_{wet}+(\frac{\partial C_i }{\partial z})_{conv}+P_i-L_i+E_i$

The first term represent the $Ci$ change due to horizontal and vertical advection.
The fifith term on the right hand represent the $Ci$ due to the vertical convection.

I have read about this question "What exactly is the difference between advection and convection?".

The answer told, which I quoted:

  Advection is the movement of some material dissolved or suspended in the  fluid.
  Convection is the movement of a fluid, typically in response to heat.

But when we are just talking about the chemical species. They are not in fluid form. So,how dos the convection process mean?

Update:  The equation was from a phD dissertatio Climate and Air Pollution Modeling in South America focus on Megacities. Links here

The difference between advection and convection in Chemistry Transport models (CTMs) is a question of scale:

Advection is driven by winds that are provided by the meteorological input dataset. Thus, the wind is resolved in the meteorological data.
Convection is driven by sub grid processes (e.g. temperature gradients) and is paramterized in CTMs.

See for example:

Pleim, 2007a. doi: 10.1175/JAM2539.1
Pleim, 2007b. doi: 10.1175/JAM2534.1
Rasch et al., 1997. doi: 10.1029/97JD02087


Why is the level of UVA radiations on the earth surface the same throughout the day, while the level of UVB significantly varies? I read on https://www.uexpress.com/ask-the-doctors/2018/1/17/no-matter-the-time-of-day

  UVA maintains the same intensity all day, which makes dawn-to-dusk sunscreen use important

Whereas on weather.com I can see that the UV index, which mostly tracks the level of UVB, significantly varies throughout the day.

I read that the UV index mostly tracks the level of UVB radiations on https://en.wikipedia.org/wiki/Ultraviolet_index:

  Because of the way the UV index is calculated, it technically expresses the risk of developing sunburn, which is caused mostly by UVB radiation.

Why is the level of UVA radiations on the earth surface the same throughout the daylight hours, while the level of UVB significantly varies?

UVA rays are very penetrating and are not weakened by the ozone layer, so are much the same throughout the day. UVB rays are of shorter wavelength, much less penetrating, and are weakened by passing through the atmosphere. At different times of day there are thicker or thinner layers of atmosphere to pass through. Near sunset, the UVB rays will be oblique, and therefore have a greater thickness of atmosphere to pass through, so will be consequently weakened. UVC rays are of even shorter wavelength and are mostly blocked by the ozone layer.


What conditions could produce 50 km long lava tubes? Detection of a new 50 km long lava tube in the Moon has just been reported. See JAXA probe finds 50-km cavern under surface of the moon, this JAXA news page (the English page has not yet been updated, stay tuned) and Detection of intact lava tubes at Marius Hills on the Moon by SELENE (Kaguya) Lunar Radar Sounder Kaku, T. et al, accepted for publication in Geophysical Research Letters, DOI: 10.1002/2017GL074998.

The discovery of the sub-surface tube is a result of careful analysis of low frequency radar soundings from about eight years ago, as described in this answer.

There is also a previously reported, partially collapsed lava tube, visible from surface imagery, shown below, which also seems to be about 50 km long.

Question: This seems extremely long to me. I'm not very familliar with this field, but isn't it unusual for a well defined, narrow flow to continue for such a long distance? Is there anything of similar length on Earth?

below: Previously identified collapsed cave from Lunar Reconnaissance Orbiter imagery, captioned:

  This section of WAC frame M117773324 shows the area where the feature transitions from a chain of collapse pits to a continuous uncollapsed segment. A large depression at the northern tip of the chain maybe a possible source region for the flow of lava across this region. The chain is approximately 50 km long. Image resolution 58.9 m/pixel [NASA/GSFC/Arizona State University].

In Hawaii, the Mauna Loa lava tube from the 1859 lava flow

  enters the ocean about 50 kilometers (31 mi) from its eruption point

And in the Undara Volcanic National Park in Queensland, Australia

  Bayliss Cave is the remains of a lava tube that was once over 100 kilometres (62 mi) in length.

So a lava tube, 50 km long on the Moon, may not be that remarkable.

Additionally, The Undara field has feature call the Wall, which is a continuous ridge 40 km long and 20 m high.

  The Wall is believed to be the closest terrestrial analogue to the basaltic ridges seen on the moon. The longest lava flows in the Solar System are on Venus.


What is the earliest sedimentation we know of? Did large-scale sedimentation occur in any great amount during or soon after the Hadean/Archean period? Or did it only start later, because of the intense geological activity?

The oldest known metasedimentary rocks are about 3.8 billion years old, formed in the Eoarchaean era.

'Metasedimentary' just means they have been metamorphosed, so they started out as sediments. They are found in the Isua Greenstone Belt of southwestern Greenland. You can read about their discovery in Moorbath (2009). Quoting from there:

  Published zircon dates strongly suggest that the depositional age of at least part of the [Isua supracrustal belt] could be closer to 3.8 Gyr than to 3.7 Gyr.

According to the International Commission on Stratigraphy (Cohen et al. 2013), this puts them firmly in the Eoarchaean era.

References

Cohen, K, et al. (2013). The ICS International Chronostratigraphic Chart. Episodes Journal of International Geoscience 36 (3). Link to PDF.

Moorbath, S (2009). The discovery of the Earth's oldest rocks. Notes and Records 63 (4). DOI: 10.1098/rsnr.2009.0004


Alternative WMS servers for GOES-East satellite imagery I'm having some difficulty finding a WMS (web mapping server) for North America GOES-East satellite imagery that matches my needs (visible and IR4, timely, with no alteration of grey-scale pixel values).

I have tried the Iowa State and Nowcoast servers, but, for various reasons, the data isn't exactly what I need. I would like to experiment with other WMS servers, but I can't find any.

Do you know of any alternative WMS servers for GOES-East satellite imagery, other than Iowa State and Nowcoast?

The Real Earth server from SSEC seems to be a good choice.

https://realearth.ssec.wisc.edu/doc/dataaccess.php


How long does earth take to recover from mass extinctions? What is "normal"? Wikipedia states the following about the P-Tr extinction event:
"Because so much biodiversity was lost, the recovery of life on Earth took significantly longer than after any other extinction event,[5] possibly up to 10 million years.[10]"

The source for the claim about 10 million years is this article: https://www.sciencedaily.com/releases/2012/05/120527153810.htm

Another wiki article states:
"Life on land took at least 30 million years to fully recover from the environmental disruptions which may have been caused by the eruption of the Siberian Traps.[10]"
Source: https://en.wikipedia.org/wiki/Siberian_Traps#cite_note-SahneyBenton2008RecoveryFromProfoundExtinction-10

I have a lot of questions about this.

Frankly 10 million years sounds like a very short time to me in this context. Is it short or is it long?

To expand the question:

Is the global ecosystem resilient to complete annihiliation? As long as there is some life left, is it likely to prevail? Let's say some catastrophe strikes and wipes out everything but bacteria - are we likely to see complex life ever again? I know there are debates about the Great Filter, but is there any consensus? What are the most popular contenders?

Mass extinctions are selective: not all living organisms will be affected by it to the same extent. Meaning also that various groups will recover from it at various speed: a group from which half of the species were exterminated by the event will most probably take longer to recover (i. e. reach its pre-event diversity) than a group for which only 10% of the species are gone. And a group for which 95% of the diversity is gone is likely to never fully recover its initial diversity.

If you are looking at the recovery of the ecosystem/biome as a whole, then what is likely to happen is that the extinct species left whole ecological niches vacant, meaning that this vacuum is likely to be quickly filled by new species (either species group that already existed and were already occupying this ecospace but were dominated by the now-extinct species or brand new species group). On that subject, one has to realise also that the recovery of a trophic level of an ecosystem is dependent on the recovery of the others (i. e. and to simplify, recovery of apex predators depends of the recovery of grazers, which depends on the recovery of primary producers etc.), so a mass extinction affecting primarily the primary producers might need longer to recover than one affecting mainly the apex predators.

So is 10 Myr a short amount of time to recover from a mass extinction? I'll say that one would expect ecological recovery to be faster than that (see for instance the speed at which milieux disturbed by glacial episodes recover during interglacials, or the speed at which new islands get colonised). But for the complete recovery of global diversity (in particular for an event supposedly wiping out 90% of life diversity) i'd have expected it to take longer than 10 Myr. In the second article you link, the authors estimate that the recovery of the terrestrial ecosystem is fast by comparison with how long it took to colonise the land in the first place (i. e. 100 Myrs). But all the evolutionary adaptations needed to function on land do not need to be re-evolved, so it seems rational to expect it to take a shorter time than those 100 Myrs... Otherwise the probable reason the news article you linked considered it to be a long recovery time was to emphasise the fact that the article show that it took longer because of ripple effects of the Permo-Triassic event during the early Triassic that slowed down the recovery.

In a review of mass extinction recovery predating those two articles, Erwin (1998) estimated the duration of the recovery from the End Ordovician, Frasian-Fammenian, end-Permian, end-Triassic and K/T extinction events (I mention here only the so-called "Big Five" extinctions) to, respectively, 7, 3, "3 to 9?", 3 and 2 millions years. With those number in mind, then indeed 10 Myrs is a long recovery.

The same article also had this to say about the definition of mass extinction recovery:

  How does one define a recovery? Mass extinctions create new ecological opportunities, and the common-sense definition of a recovery interval encompasses the rapid diversification by surviving lineages following the end of the extinction and ending with either the waning of the rapid, postextinction diversification or the return of normally functioning communities. Normal is hard to quantify, however, even without the extensive disruptions associated with some mass extinctions. Moreover, different clades recover at different rates and the same clade can recover at different rates in different regions. If we accept the recovery as beginning with an increase in evolutionary rates, this usefully distinguishes an immediate, postextinction survival interval, dominated by surviving lineages, from the often exuberant diversifications of the subsequent recovery phase. An alternative definition relies on the 're-establishment of pre-extinction isotopic values and ecosystems that are essentially equivalent to those that existed before the extinction'. Here the emphasis lies equally on the physical environment and the ecosystem recovery.
  Douglas H. Erwing, 1998. The end and the beginning:
  recoveries from mass extinctions, Trends in Evolution and Ecology.

Finally, evolution is non-repeatable: so to answer your question "Let's say some catastrophe strikes and wipes out everything but bacteria - are we likely to see complex life ever again", the answer is that if all eukaryotes are wiped out then no eukaryotes is likely to reappear, but another "complex" group can appear anew (though bacteria are already very complex if you ask me). Similarly if life is completely wiped out I don't think it is reasonable to think it will reappear (in particular because the Hadean/Archean conditions that saw its appearance do not exist anymore).


What kind of tooth is this? Please help me identify this tooth and the era its from. I found it in Panama City Beach Florida. Its cold and hard when i bite it. It looks very old. Possibly a shark tooth?

It looks very much like a shark tooth, but it looks like it’s weathered and worn. It may have spent a good deal of time buried below the sand, being slowly ground by the sand and tide action. Eventually it became dislodged and after a while of being worn smoother it washed up and you found it.


Gnomonic projection of a curves with constant latitude If we consider gnomonic projection, what are projections of curves with constant latitude. For example, we know that great circles are projected to straight lines. So, equator should be projected on a straight line, right? What about curves with constant latitude in general?

Edit: We use North pole as a tangent point.

Circles!

Well, some of them, anyway.

You can plot any azimuthal projection in polar coordinates, where the radius is a function of the angular distance from the center point.

So where two points' angular distances are the same, their radii are the same, and the projection of any locus of constant angular distance from the center point is a circle, if it appears at all.

Since you said that the tangent point is a pole, that means that parallels (lines of constant latitude) are those lines of constant angular distance. Ergo, Northern Hemisphere parallels appear as circles.

(Wikimedia Commons)

Since the Gnomonic projection can show only a single hemisphere, the Equator and parallels in the Southern hemisphere can't appear at all -- they would be an infinite distance from the center point.

The polar orientation of the projection even takes away  complications resulting from the earth's not being a perfect sphere -- the radius formula changes a little, but the equal results from the same input remain.


What are the striations or ridges in the eastern Pacific Ocean? Messing around on Google Earth recently I noticed a number of striations in the Eastern Pacific. These appear in an East-West orientation and seem to start on the North and South American continental shelves, and extend for roughly half the Pacific Ocean. For example one of these striations start in Santa Rosa Island off California and ends at Hawaii. These striations also appear to be roughly equally spaced at 8 degree intervals. The North and South American striations are angled with respect to each other and seem to converge at roughly Tahiti.

What causes these? I'm a fascinated novice.

EDIT

Some images to make things clearer (North Pole is top left):

Note the regularly spaced East-West parallel striations starting from the Equator and stepping north. In fact the striation on the Equator covers the entire Pacific.

Here a closer shot also shows fainter striations fanning out from Los Angeles:

They are fracture zones.

I've annotated your image with the names of these very long, tectonically important features. They even have names, such as the Mendocino Fracture Zone:

I also labelled some survey tracks (rather subtle, very straight, very regular in width), which are data artifacts — these are the things you noticed radiating from the vicinity of Los Angeles.

There are yet other types of linear feature on the sea floor:

Transform faults are strike-slip faults connecting segments of spreading centres in the oceanic crust.
The spreading centres themselves.
Roughly linear archipelagos like Hawaii.
The long, curved trenches at convergent plate margins.

Images from Google Maps. Note: I edited this answer substantially after the OP clarified the question... and I learned about the difference between transform faults and fracture zones.


Why do loose, soft soils amplify earthquake vibrations rather than dampening them? Areas where the buildings are built on top of a deep layer of loose sediments are widely recognised as being more prone to earthquake damage (all else being equal) than areas where the bedrock is shallow and building foundations can easily be dug down to it, because the loose sediment cover amplifies the vibrations from earthquakes, increasing the amount of damage they cause.  Why is this?  Intuitively, one would expect that, since the vibrations from an earthquake originate in the bedrock or deeper, buildings bolted directly to bedrock would be the worst-affected, and having a thick sediment layer would dampen the vibrations considerably.

So why do soft sediments amplify earthquake vibrations, when one would expect the opposite effect?

I think there are a few more options than bedrock/loose.  But I owned a house 3 miles from the San Andreas fault, and a geophysical engineer explained it to me like this after telling me earthquake insurance would be a waste of money.

The worst situation is landfill, like the Marina district in San Francisco that took much of the brunt of the 89 quake.  That is just loose sand and gravel, and when shaken it acts like a liquid - in fact, they call it liquefication.  The foundation shifts and sinks in it, like if you had a jar of sand and gravel and put a heavy rock on top and shook it.

However, if you are on bedrock - or something tightly bound above it (like Franciscan shale), you get all the shaking transmitted, but the earth stays in place under and around the foundation.

Earthquake damage can happen a few ways: from shaking up and down as well as sideways.  The Mendocino quake in the 90s (I think) had more side-to-side movement than ever seen before, and house held together but slid off their foundations.  After that they upped the degree to which house are bolted to the foundation to avoid lateral shifts.

I am not sure soft soil 'amplifies' the shaking.  There are a bunch of failure modes in buildings: they can come off the foundation; the foundation can shift and sink; the shaking can cause framing to collapse (which is why they put in shear walls); etc.

Incidentally, wood structures often do better because they can flex.  You'll never see a real brick house being built in a seismic zone anymore.

In the end, it is about making the building live through the accelerations, and the hardest thing to deal with is loose soil that itself moves and flows under the structure.


How much net carbon can coral sequester? So I am wondering how much carbon any given coral can sequester given that carbon dioxide dissolves in water and forms carbonic acid, and coral uses that carbonic acid in their own calcification process given by this equation.

$$\ce{Ca^{2+} +2HCO3- -> CaCO3 + H2O + CO2}$$

Given the amount of concentration of carbon dioxide that is in the atmosphere currently, how much net carbon can one coral organism sequester per year?

Just as a note, I am not talking about coral reefs as a whole, but just one coral organism. Obviously a lot of assumptions must be made, so please just include them in your answer please. Thank you!

Corals usually grow 1cm every year, some as slow as 2mm, some faster.

Coral sand density is about 1.5g /cm2, it's not the best estimate of coral weight. So, a coral organism of 10cm^2 produces 150 grams of CaCO3 every year, and 1m2 of coral can absorb 15 kilos.

CO2 is 44.01 g/mol
CaCO3 is 100.0869 g/mol

15kg * .44 is the absorbtion of CO2 of a coral organism of 1m2 surface area.
that's 6.6kg.

A car produces about 6 tons of CO2 every year.

Coral reefs are estimated to cover 284,300 km2 (109,800 sq mi), just under 0.1% of the oceans' surface area.

There are 1 billion cars, and 9 billion tons of antropogenic CO2.


CMIP5 multi-model ensemble, can it be shown as ensemble average? Let’s say I have got 15 CMIP5 models’ outputs of a given variable e.g. temperature, for RCP6.5 (2020-2100) run.

I want to plot how the temperature will change in the future 2020-2100 (scatter plot, x = time and y = temperature).

Instead of showing all the 15 models outputs can I just simply show the CMIP5 multi-model ensemble average?

i.e. instead of 15 lines into one plot I show only one line (the average).

Is this correct?
Will a reviewer reject this approach?

Thanks

That is valid. You can show the average (or median if there is a reason to get rid of outliers), but it would be VERY misleading and arguably wrong if you don't show also the uncertainty associated  with that mean solution.
However, the whole point of getting the mean of many values is to reduce  the uncertainty. Therefore, just plotting a shaded area covering the range over which the original lines were distributed, would be an overestimation of the uncertainty (here I'm assuming that each original line have no uncertainty, which is wrong, but if you have that uncertainty data it can also be included).
A standard way to estimate the uncertainty of the average of many lines (a.k.a Time series) is calculating bootstrap confidence intervals.

Here is an example from a paper I recently submitted:

The mean of all those black lines is the blue line. To expose the spread of the data I decided to show all the original lines. But, if I were to show this to a general audience, I would get rid of the thin black lines and show the mean (blue) and the confidence intervals (pink shades).
Those shades mean that with a 90% confidence the mean should fall within the dark pink shading, and with a 99% confidence within the light pink shading. Giving a sense of how much you can trust the blue line.


Why haven't weeds overtaken the entire planet? Given how rapidly weed plants spread and grow, choking out all other plant life, how come after millions of years we haven't ended with forests full of thistle or pokeweed, as opposed to pines or oak trees?

A weed is just a plant where you do not want it. Totally a matter of context. Tumbleweeds are non-native, introduced centuries ago. I assume you mean the invasive species of plants that have been spread by humans and are disrupting ecologies throughout most of the world

Until recently, these plants we consider weeds were limited in their range to home environments simply by geographic barriers and surrounding unfriendly environments. And the natural consumers, parasites and competitors in the home environments had adjusted to these plants and kept them in check.

When non-native plants are introduced into a new environment by humans, most of them do not thrive, but occasionally a plant is wildly successful. Eventually the potential consumers, parasites and competitors in that new environment will adjust through evolution. But the tragedy is that many or most of the original species will be destroyed before that balance is restored in a new, way more simplified form. The landscape itself may be totally changed. Removal of a key original species can cause great change too: How Wolves Change Rivers.

Not only will many ecologies be reduced to much simpler versions, even if they eventually conquer the invasive plant, those simplified ecologies will closely resemble each other, if their geography is similar, even if on the other side of the world. If humans were to totally stop transplanting invasive species (collapse of civilization?), diversity would return after millions of years. We know this from Extinction Events.

So to answer you question, weeds before human intervention generally did not take over in their home environments because the potential weeds and their natural consumers, parasites and competitors all evolved together in a quasi-equilibrium. Now, however, most ecologies throughout the world are out of equilibrium because of environmental change and/or invasive species. This will inevitably lead to simplified, usually less robust, weedy ecologies throughout the world. That reduction in diversity might as well be considered a permanent situation compared to the timescale of civilization.


Why is there so much oil in Saudi Arabia, Venezuela and Canada, but almost none in Europe? Why do some countries have a lot of oil reserves, while some others don't?

I wouldn't say there's 'almost none' in Europe, but the global distribution of petroleum is uneven. The reason is that petroleum systems need a convergence of conditions that is relatively rare.

For a start, the comment about the inappropriateness of a political map for this purpose is spot on. This USGS map of global petroleum systems, and non-petroleum-rich basins, is much better — apart from the fact that it perversely omits the USA's substantial endowment:

These 'petroleum systems' are essentially modern or ancient sedimentary basins with a particular combination of features. I'll refer to a previous answer about a specific region: Why would there be no hydrocarbons in the Sveconorwegian belt? Paraphrasing, and self-plagiarizing, here's what you need for a hydrocarbon (oil or gas) accumulation:

  A kerogen-rich source rock that has been 'cooked' to thermal maturity. So you need lots of organic matter, burial, and time.
  A migration pathway from the source to a trapping configuration, and time for this to have happened.
  A structural or stratigraphic trap, such as an anticline, and the geological conditions that have preserved it since filling.
  A reservoir rock — a porous and permeable rock. Usually this is a sedimentary rock (like sandstone, which there's lots of in Saudi!).

  Only 'conventional' hydrocarbon deposits, such as you might find in
  the North Sea, Saudi Arabia, or the Gulf of Mexico, need all these
  conditions. 'Shale gas' is basically just a mature source rock — we
  can extract hydrocarbons from it by fracking, for example.

So the map of global petroleum resources is a map of places where these criteria converge. Certain deltas are prolific (Mississippi, Niger), because you have rapid burial of sand and organic material. In other places, one or more of the conditions has not been met. Much of Canada, for example, is exposed basement granite: none of the components are there.

The unevenness is exacerbated by the Pareto distribution of system productivity — as with most natural things, we have a few giants, and a long tail. So the WCSB and Saudi stick out as anomalous, making the distribution even more 'lumpy'.


Calculate the number of model grid cells covering a specific country What is the best method of calculating the number of model grid cells (e.g. of climate models) covering a specific country? For example, if I wanted to know how many 2 degree grid cells are in the United Kingdom, how would I go about it? At present I use the mapping toolbox in matlab and add a 2 degree grid and calculate manually. Is there a better way of doing this? Any advice is appreciated.

Here is a simple 'back of the napkin' idea for Python:

Get a shapefile of the borders and use Python to create a polygon of the borders.
Use mpl_toolkits to convert the climate model to X and Y coordinates
Check to see if the model grid points are within the Polygon


Could Earth have had a greater axial tilt? In thinking about the question, Why is earth's axis tilted?, and reading articles about Earth's axial tilt, I came across the website Snowball Earth which describes an alternate theory for global glaciation proposed by George Williams, from the University of Adelaide - what is proposed is that the Earth had a considerably higher axial obliquity (greater than 54°) up to about 600 million years ago.

Professor Williams proposes that this could be a mechanism for Snowball Earth events and cites the 'explosion' of life occurring after the axial tilt stabilised, thus causing the seasonal changes to become less severe with lower obliquity.

This is related to the question What sort of climate zones would be present if Earth was tilted like Uranus?, but asks the question if there is evidence that Earth did have a greater axial obliquity in the Proterozoic?

There is no evidence that Earth had a much greater axial tilt so long ago.  To my knowledge, the evidence for changes in the axial tilt of the Earth is based on ocean sediment cores (see http://en.wikipedia.org/wiki/James_Hays ) and ice cores ( see http://en.wikipedia.org/wiki/Milankovitch_cycles#Axial_tilt_.28obliquity.29 ).  However, these only go back 100s of thousands of years.  There is no record that I know of that could be used to assess the axial tilt of Earth 100s of millions of years ago.  However, you could speculate that after the collision that Earth had that led to our moon, the axial tilt could have been much greater as a result.  However, all records that I have seen show that the axial tilt fluctuates from 22.1 to 24.5 degrees.


Color of ocean waters and Ekman pumping - what is the connection? Is there a connection between the colors of oceanic waters near the coast and Ekman pumping? Along the coastal areas of the Bay of Bengal where I live, occasionally during the monsoon, the colors of the waters become aquamarine, only to become sky blue in color a few hours later as the sea breeze sets in.
Can this be explained by coastal upwelling?  If this is due to Ekman pumping where does EP take place? Over equatorial waters and is then pushed north due to a coastal current?
The phenomenon has been observed during both the Indian monsoons- the south west monsoon as well as the north east monsoon i.e. that the seasonal shift in wind direction does not impact the appearance of the aquamarine color.

The width of the patch is between 200-300 meters from the coast and it is oriented parallel to the coast. Closer to the coast the color is dark greenish brown and as you go further into the open sea it is aquamarine green. There are occasional dark blue "patches"(dark blue bands) which I am presuming is phytoplankton.

Few more personal observations. It appears that the aquamarine color usually manifests itself during the mornings (when there is no breeze whatsoever). The sea presents extremely gentle waves when the aquamarine color is visible. Does that mean that the origin of the aquamarine color is "non - local" ?

The relationship of the observed "aquamarine color" near the coast and the Ekman pumping in the open ocean, while possible is rather unlikely. Ekman pumping is confined to the areas affected by the cyclonic wind stress curl and by definition it is mostly effective in the open ocean, where there is no bottom boundary effect. The color of the coastal waters is likely more affected by the upwelling-favorable wind creating upwelling conditions that provide nutrients to the coastal areas. The fact that the color is affected by the sea-breeze is even more justification for the upwelling mechanism. While transport of nutrient-rich waters to the coastal areas is not uncommon, the time scales associated with primary production especially in coastal areas are quite fast and tend to use the open-ocean nutrients in short time scales.

Phytoplankton changes especially on the order of hours are more likely associated with purely coastal processes. While there might be an input of open-ocean nutrients to the coastal areas, the coastal primary production tends to differ from open-ocean communities and tend to respond rapidly to extra nutrients.

The aquamarine color could be the result of many coastal processes. Without knowing the area, I don't feel qualified to make a strong case about the causes. Reasons for the color could include 1) vertical phytoplankton migrations that settle to the bottom/lower water column when the breeze comes up; 2) the sea breeze resulting on a local near-shore downwelling; 3) a breakdown of the stratification by the breeze that mixes down the surface layers; 4) regional features (e.g., sea level pressure gradient) that become active when the breeze is occurring. Too many unknowns for me. It would be good to know the extent and duration of the "aquamarine color" patch, the width and slope of the continental shelf in the area and the ind and stratification conditions in the near-shore and coastal areas.


Oscillations in the Keeling curve? I'm having a slightly difficult time understanding the Keeling curve, pictured here:

I understand that carbon dioxide (ppm) is increasing with respect to time, but why is there an oscillation between the summer months and winter months? I have two guesses but I'm not sure if they are correct:

Changes in density due to temperature?
More plants in the summer, resulting in less carbon.

Are these guesses correct?

Photosynthesis increase in the northern hemisphere spring, especially in the Siberian Taiga, and carbon dioxide decrease in atmosphere. During autumn and winter, decomposition of plant material and increased combustion, bring more carbon dioxide to the atmosphere. Measurements from e.g. the South Pole shows the same pattern, but much less and in opposite phase.  As the temperate and boreal landmass are larger on the northern hemisphere, the oscillation is also larger.

It's well explained here. Also check ESRL and CDIAC for more stations and downloadable data sets.


Why do wind speeds often jump from 20 knots to 40 knots Looking at the BBC weather forecasts I've often noticed that strong winds will often be over 40 knots (for the UK at least). Most of the time (nearly always) the wind will jump from 18-22 knots to over 40 from one hours forecast to the next. I don't often ever see wind speeds in the high 20s or 30s. Why is this the case? I looked at the Weibull distribution but this doesn't seem to apply.

This is an (annoying) artefact of BBC weather forecasts, and not an actual feature of the weather.

At low wind speeds, the speed shown is the expected average speed.

At higher wind speeds, the speed shown is the maximum expected gust.

It changes over when the maximum expected gust is 40 mph (not knots). You can tell the difference because average wind speeds have a white background, and gusts have a black background. I tried to post example screenshots, but I couldn't find any location with a >40mph forecast today ;-)

There is a little bit of explanation about half way down this page: https://www.bbc.com/weather/about/17185651


How can I learn to make mesoscale/synoptic analyses of major weather events? With the tornado outbreak in southern Georgia and northern/central Florida on Sunday that has tragically resulted in significant loss of life, eyes are once again on the weather. I was particularly impressed by the synoptic analysis done by the Capital Weather Gang over at the Washington Post.

I've always found this kind of mesoscale "tale of the tape" analysis to be interesting. Accuweather has made these kinds of analyses/maps, see 3/2/12.

I would like to be able to look at upper-air and surface charts, and be able to explain the weather. How can I do that? What would I have to learn?

Through lots of studying of NWS upper air and surface charts, nullschool.net maps, and reading Cliff Mass's blog, I was able to draw some crude Microsoft Paint renditions of the basic summer weather pattern in the Pacific Northwest:

Furthermore, I was also to depict a map of the atmospheric conditions during the 4/27/2011 tornado outbreak, utilizing William Smith's excellent analysis (you'll want to click on the image for a larger resolution):

But I want to learn how to do this on my own. I want to be able to look at charts, and use the charts to make an analysis of a weather event. I'll give you a good example of what I want to do:

During the early morning hours of July 7th, 1999, thunderstorms erupted over southwestern British Columbia and interior sections of WA near the Strait of Juan de Fuca. I know this because I lived through them, I was 7 years old at the time and they kept me up all night. NWS radar archives did not register any precipitation, but Plymouth State University's archives did. Plymouth State's archives also have upper-air analyses; the 00Z 7 Jul 99 analysis shows the shortwave trough draped from the Puget Sound up to southern Vancouver Island. What I want to do is to learn how to forecast the weather at a basic level, then apply this knowledge and look at the upper air, mid-level, and surface analyses, then be able to put them all together to understand this event occurred. I then want to apply this knowledge to be able to predict or analyze other convective thunderstorm events or other major weather events. Other people have recommended reading the content at theweatherprediction.com.

Thank you.

You're definitely on the right path with wanting to dig into raw data yourself.  RAP has always been a pretty solid source of useful basic data.

But in terms of making sense of the data, it indeed will take some practice. You can feel like you're not getting it at all, but suddenly pieces will start to click, much like riding a bike.

Basically, you need to start building from those that know these things.  As such, one good insight can be in reading NWS forecast discussions, which you can find among the rich data at kamala.cod.edu or in one big set at this NWS link.

But, at least in terms of storms, I think the place to start has to be the same place that the CWG article relied upon: the Storm Prediction Center.  Specifically:

Convective outlooks will explain the day's weather picture and large key features
Mesoscale discussions offer insight into the finer details that make all the difference, ones which even the most seasoned meteorologists may not always recognize.
Then the mesoanalysis tool allows you to dig more into the data yourself and see overlays of a deep variety of parameters.  But the tool that may be right down your alley may be the composite map generator tool, which allows you to combine just the noteworthy parts of the key elements onto one image and see how they line up.
And then the Severe Weather Events Archive allows you to dig into a great deal of past events, and the Outbreaks Browser lets you see the bigger events in a very sharp, graphical way.

And there's plenty of other great things there too; climatologies, publications, education pages, etc.  Now, obviously the majority of this information focuses most directly on severe weather setups (though the SPC does actually also issue winter weather mesoscale discussions [the WPC now does heavy rain MDs, and of course the NHC does the main discussions on tropical systems]), and only regard US events.  But these tools can really help even those interested more in other areas and topics get a better understanding of the bigger picture, which sync up well into just about every topic of synoptic and mesoscale meteorology, regardless of location.

Now, in terms of helping you personally narrow down onto the key elements, so that you could make your own composite map... the classic ingredients necessary for thunderstorms (also see here) can be a good starting point:

Instability... the predisposition of rising air to continue rising.  Basically warm (and moist) surface air and anomalously cold air aloft.
Moisture... high dewpoints create clouds more readily, form them at lower heights (important for tornadoes), and produce more precipitation/energy for storms.  Plus it helps the instability.
Trigger... something to get the air moving to rise so that the ingredients can be realized.  There are a WIDE range of possibilities here.  Important ones for storms include fronts, the dryline, vorticity advection aloft (incoming vort maxes you see spinning around on water vapor imagery), favorable jet streak quadrants, strong temperature advection (e.g. low-level jets), outflow boundaries, seabreezes/lakebreezes/riverbreezes, gravity waves, diffluence aloft, terrain/orographic lift, horizontal convection rolls/cloud streets, isentropic upglide, and differential heating boundaries.  Suffice to say there are a lot of options in play, though some are more common than others.  But you'd be surprised how quickly you can get used to finding them with practice.  (And it's really a pity there isn't greater information/graphics/videos/explanations on some of those topics... perhaps some of these will eventually work their way here to be questions that can encourage a better, clearer reference to form)

And finally, to really ramp up severe weather, and also primary to tornado threat, you add in ingredient four...

Wind shear... different winds at different height.  A combination of how much directional difference there is and how much speed difference.  Significantly impacted by upper level jet streaks, low-level jets, and the direction of the surface flow is.

This may sound like a ton.  But taking a second look at that Accuweather graphic, it's those same ingredients:

So with those basics to start at, the pictures have a pattern to them.  And then when you add in the finer details discussed, you can really find the deeper things you won't on the more basic composites.  You can see what really DID make all the difference.  In the end, it's an investigative science, a continual game of making and refining theories, and it's something you only get better at with practice.  Even top meteorologists still don't always have the answers; I don't know whether anyone has come up with a perfect explanation yet for why the supercells on Sunday in Central Florida didn't produce prolific tornadoes.  Forecasts do still fail.  And so we're always trying to better clear up the details of each past event, so that we'll be better at the next one.

A couple final links... it seems like this journal article might be fairly interesting and approachable for you... and then websites like Stormtrack can be a really great asset, as that's where quite a few chasers/meteorologists often congregate to discuss big weather events.  The more time you spend looking at this stuff, engaging in conversation, challenging the reasoning you/others have, and learning, the better you'll be able to form a clearer picture of what's going on.  A much better picture than any news article will ever give!


How do long rivers exist? I was recently on a long-haul flight over Siberia and it struck me as rather remarkable that something like the Lena River could exist. It seems very surprising that there's a route from some random spot near Lake Baikal over 2,800 miles or so to the Arctic Ocean, which is downhill all the way. Likewise, the Missouri River tells us that there's an even longer downhill-only route from some place in Montana to the Gulf of Mexico.

But these things certainly do exist and it's a pattern repeated all over the world: the great majority of the Earth's surface is drained by rivers that run downhill to the sea. They don't get stuck and they don't seem to form huge numbers of lakes where they have to flood an area to raise the water level over some barrier. I'm aware of endorheic basins, which don't drain to the ocean but they only cover about 18% of the land surface, mostly in central Asia.

Is the existence of long downhill routes more likely than I imagined? (I can't tell if I think it's more likely in mountainous areas than in flatter areas, which suggests I have poor intuition about this) Or is it just a coincidence of our planet? Did the rivers make the downhill paths themselves?

Well, I can only agree that it is indeed amazing and it doesn't get less amazing when some geology, hydrology and geomorphology is added to the the amazement.

All precipitation that falls on land must flow back to the oceans somehow, and unless it evaporates it will flow in rivers or as groundwater towards a lower hydrostatic level. Water can not flow uphill, so it follows (and crafts) the slope in topography. Water will flow from mountains towards the ocean and due to geometric and morphological reasons, rivers joint to a drainage pattern due to the geology and topography.

Mountain ranges are often formed from orogeny, where tectonic plates collide. Rivers starts at high altitude, radiating out in all directions from mountains, but as collisions in the present continental settings are often on the rim of large plates (e.g Andes, Alps, Himalaya), and the rivers can't cross the range, it will have to travel the whole continental plate to reach ocean level. In the case of Asia, most large rivers starts in Himalaya (or other tectonic active regions, as Altai), in Europe large rivers starts in the Alps. In Africa, they start in the tectonic active rift zone.

This map shows the ocean drainage dividers. The border between the drainage areas are the line where rivers start.

Lakes could be understood as temporary stop in the flow, and it will quickly fill up with vegetation and sediments as the velocity of the water decreases. In a geologic context, lakes are never very old, Baikal being the oldest, 25 million years. Drainage patterns are often much older.

So why are some rivers so long? Because of tectonic uplifts and orogenies. The answer to your question 'Did the rivers make the downhill paths themselves?' is yes, as erosion works toward the peneplain (low relief).


I need help with these geode like rocks I found these rocks in my pasture and was excited because I thought I had found some geodes.  The rocks were in a sandy bank and looked like eggs sticking out of the bank.  I am located in Ness County Kansas.

This is what they looked like after I opened them.  There are no crystals but some had a round ball in  the center.  Others were just empty centers.

Hi:  Your rocks are not geodes but likely concretions.  The wiki article even mentions concretions from Kansas though the concretions described don't to me fit what I see in the images.  Better pictures and more description about the rocks would lead to better identification.  See Better rock ID requests

Wiki's Concretion Page


Why can't wave models model storm surge? I found this nice module here on MetEd that gives an overview of the WAVEWATCH wave model. In it, in the Introduction section, it is mentioned that WAVEWATCH cannot model storm surge or tsunamis. Is this true of all 3rd generation models? Can source terms be added to the energy balance equation to model these phenomena?

Yes. Spectral wave models cannot model storm surge because the wave energy balance equation that they integrate does not describe the physical processes associated with storm surge.

Wave models solve the wave energy balance equation:

$$
\dfrac{\partial E}{\partial t}
+ \dfrac{\partial (c_gE)}{\partial x}
+ \dfrac{\partial (\dot{k}E)}{\partial k}
+ \dfrac{\partial (\dot{\theta} E)}{\partial \theta}
= \rho_w g\sum S_i(x,k,\theta)
$$
where the terms on the LHS represent local change in time and advection of energy in geographical ($x$), wavenumber ($k$), and directional ($\theta$) space, respectively. The source terms $S_i$ on the RHS determine the growth and decay of wave energy due to wind input, wave dissipation, and non-linear wave-wave interactions.

While mean water depth, wind forcing, and background Eulerian currents all affect the evolution of wave energy, the wave energy balance equation only solves for the statistical distribution of wave energy and its change in time. It does not provide information about the change of mean water level or Eulerian currents. The simplest equation set necessary to explicitly model surge are the single-layer (2-D) shallow water equations:

$$
\dfrac{d\mathbf{u}}{dt}=-g\nabla\eta + \dfrac{1}{\rho_w} \dfrac{\partial \boldsymbol{\tau}}{\partial z}
$$

$$
\dfrac{\partial \eta}{\partial t} = -\nabla \cdot (\mathbf{u}(H+\eta))
$$
where $\mathbf{u}$ is the Eulerian velocity and $\eta$ is the displacement from the mean water level $H$. $\nabla$ is the horizontal gradient operator. $\dfrac{\partial \boldsymbol{\tau}}{\partial z}$ is the vertical stress gradient that forces the flow - essentially the difference between surface and bottom stresses. The momentum equation describes how the flow velocity changes due to horizontal pressure gradient and surface forcing (stress). The mass continuity equation describes how the water elevation changes due to divergence of the flow. For spatial scales larger than 10 km or so, Earth's rotation becomes important and the RHS of the momentum equation must include the Coriolis acceleration.

Another requirement for the model to simulate storm surge is to allow for wetting and drying. What this means is that the land cells, which are originally above mean water level, and thus not part of the model solution, can become wet once the water level reaches their height and "submerges" them. These grid cells then become part of the model solution. While this may sound obvious and physically intuitive, implementing a wetting-and-drying scheme in a model is a non-trivial challenge regarding software design.

When the wave and surge models are coupled, the Eulerian velocity field $\mathbf{u}$ is mainly forced by wave dissipation, and less by wind directly. The surface elevation changes in response, and together with Eulerian velocity feeds back to the wave model.


Relationship between atmospheric density and atmospheric pressure? I am slightly confused as to how the following statement is true:

As the density of the Earth’s atmosphere decreases, the average atmospheric surface pressure remains the same

As dictated by the equation $P = \rho R_mT$, where P is pressure ρ is density, T is temperature, and Rm is the univeral gas constant divided by the molar mass, there should be a relationship between density and pressure. What is incorrect about my understanding of fundamental concepts?

There are two fundamental gas laws that need to be understood:

Boyle's Law which states     ${P_1.V_1 = P_2.V_2}$

From this formula if volume increases pressure decreases and vice versa

The second law is Charles's Law which states ${V_1/V_2 = T_1/T_2}$   or    ${V_1/T_1 = V_2/T_2}$

This law states that if the temperature increases there must be a corresponding increase in volume of the gas and vice versa. Another way of looking at it is if the volume drops so must the temperature and vice versa.

The ideal gas law that you mention in your question can be also be written as:

${PV = mRT}$

Where:

P is pressure,
V is volume
m is mass
R is the universal gas constant
T is temperature

Now, density, ${ρ = m/V}$

Which leads to the equation you used:

${P = ρRT}$

One of the primary ways the atmosphere changes is via changes in temperature. The atmosphere on the side of the Earth facing the Sun warms up, while the atmosphere of the other side of the Earth cools.

According to Charles's Law, for the side facing the Sun, the increase in temperature will cause the volume to increase. An increase in volume will reduce the density, because mass doesn't change. With an increase in temperature and a decrease in density the pressure will remain unchanged.