Does this paper, using neural nets, prove industrialization is irrelevant to global warming? Recently, a paper was published by Abbot and Morahasy (2017) - see specifically Fig. 2. The thesis of the paper is to train an artificial neural network (ANN) on the temperature time series for pre-industrial ages. Then do forecasting with the ANN to predict the temperature time series in the 20th century. Because the ANN was trained on pre-industrial time series, then we can say that industrialization is irrelevant to global warming.

This goes completely contrary to the IPCC AR5 technical summary, which shows graphs that global warming is due to anthropogenic causes. See page 74 of the latter report.

So which do you trust and why?

The paper is deeply flawed from both the climate science and machine learning perspectives.  The most obvious being the most eye-catching claim that equilibrium climate sensitivity is approximately 0.6C, which if true would overturn our understanding of the climate system.  However the paper doesn't actually explain how this figure of 0.6C is obtained from a "largest deviation" of 0.2C, it is basically just a hand-wave.  Also the largest deviation is not 0.2, this is the largest average (mean absolute) deviation seen in the proxies, and you can have a mean absolute deviation without there being a trend that you could relate to increased GHG concentrations and hence estimate ECS.  More importantly, this would give an estimate of transient climate sensitivity, not equilibrium climate sensitivity, and you can't reliably estimate ECS (which is global) from regional or sub-regional proxy records.

Approaches such as the one taken in this paper, which seek to see how much of the data can be attributed to "climate cycles" with the remainder being taken as the anthropogenic component are inherently biased towards low estimates of ECS.  This is because of omitted variable bias; because the anthropogenic forcing signals are not included in the model, if the net effect of independent changes in the forcings is correlated with a sinusoidal component, they will be wrongly attributed to these climate cycles, when in fact they are produced by the forcings.  Models like this can only be used to estimate lower bounds on ECS, likewise if you make a model using the forcings as inputs and treat the residual as being "natural variability" it will tend to over-estimate ECS, giving an upper bound estimate.  The  Abbot and Morahasy paper cites a similar paper by Loehle, but sadly does not also cite the comment paper (of which I was the lead author, note the corregendum).  This is poor scholarship, and sadly  Abbot and Morahasy have gone on to make many of the same basic mistakes (but with a more complicated model), which is a shame.

Rather than using the original datasets (many of which are freely available) the authors chose to digitise images of the datasets instead.  This seems somewhat bizarre, and Gavin Schmidt points out via twitter that in at least one case the dataset has not been scaled or aligned correctly (andends at 1965, and so does not include the recent warming where anthropogenic contributions are most evident).  It also transpires that Figures 5 and 9 are identical.

The paper says "However, superior fitting to the temperature proxies are obtained by using the sine wave components and composite as input data. This was established by comparing the spectral analysis composite method versus the ANN method for the training periods.".   Evaluating performance on the training data is a classic error in the use of machine learning that people used to make all the time in the late 1980s and 90s, but is rarely seen today.  If you have two nested models (one can be implemented as a special case of the other) of different complexities, then the more complex model will always have a lower training set error, if only because it has more capacity to memorize the random noise in the data, but that doesn't mean it is the more accurate model.  For that you need out-of-sample comparisons, which are absent from the paper.

There is no handling of uncertainty in the model (for instance the periods of the cyclic components are not known exactly, cycles with slightly different periodicities will explain the observations almost as well), and likewise there will be uncertainty in the parameters of the neural net, but none of this is propagated through to give the uncertainty in the estimate of ECS.  As seen in the comment on the Loehle paper, this can be substantial.

Table 13 seems to suggest that paleoclimate studies give lower ECS estimates than GCMs, which suggests a rather selective view of the paleoclimate studies, which generally indicate high ECS IIRC.

The study also has problems with too many degrees of researcher freedom (e.g. how was the particular subset of proxies chosen?) and there is a lot of (automated) exploration of model architectures and feature selection, which is often a recipe for over-fitting in model selection.  It is also not clear why the observation should be a non-linear function of the cyclic variables (especially given that the cycles were obtained from the data by linear analysis).


Which chemicals in smog obscure visibility? I know that smog is generally a mixture of various chemicals, such as peroxyacetyl nitrate (PAN) and ozone. I also know that smog obscures visibility.

My question is two-fold:

What chemical in smog generally obscures visibility (discounting aerosols)?
Is there a relationship between the concentrations of the chemical and the optical depth/visibility of the smog?

Winter and Summer smog

There are two types of smog:

winter smog:

high emissions of soot and of $SO_2$ through heating with wood, coal, etc.
$SO_2$ reacts to sulfuric acid => formation of particulate matter => reduced visibility

summer smog (photochemical smog):

strong sunlight and emissions of $NO_X$, $CO$ and VOCs
emissions of primary particulate matter not necessary
reaction of these air pollutants to other gaseous air pollutants (PAN, $O_3$, $HNO_3$) through photo-oxidation
photo-oxidation of various VOCs => lump together to ultra-fine particles (secondary PM) => particles grow

Species that impact visibility

We 'need' the gaseous air pollutants to form secondary aerosol particles. The reduced visibility during winter and summer smog events is caused by these secondary aerosol particles (they scatter the light and, by this process, reduce visibility). The gaseous air pollutants might contribute to reduced visibility but their contribution is negligible compared to the aerosol impact.

Contribution of different aerosol species

The composition as well as the size distribution of the aerosol particles is important to determine the aerosol's optical properties. If you look into mass concentrations, a given mass of fine particles extincts more light than the same mass of coarse particles. If you look into composition (inorganic components), nitrate extincts more light than sea salt and sulfate. The extinction of organic aerosol depends on their composition (I have no idea which factors/species are relevant there).

If you are interested in further literature on the impact of the particle composition on the light extinction you might look into Pitchford et al. (2007). I didn't find a publication which quantifies the contribution of different particulate compositions/species to light extinction for smog. However, Pitchford et al. (2007) deals with light extinction for calculating the optical thickness from model data.


What evidence is backing the claim that the CO₂ we're releasing in the atmosphere is the main cause of climate change? There's a lot of evidence that:

mankind is putting a lot of CO2 in the atmosphere
CO2 levels are currently rising
CO2 contributes to the green-house effect, which contributes to increase earth temperature
the earth temperature has been increasing in the past decades

There's also evidence that:

CO2 levels have been going up and down for as long as we can look at them without human intervention. E.g. this NASA graph spanning 400.000 years
global temperature is still inside the bounds of normal cyclical Holocene variations (as seen on wikipedia)
earth temperature has been going up and down for millions of years, obviously without human intervention, as seen on the same Wikipedia page

The first set of facts I listed proves without a doubt that some of our activity is causing an increase of temperature of some unknown magnitude, but not much more. When confronted with the second set of facts I listed, scientists usually reiterate the first four facts, and add that there's a huge consensus among scientists (97% !) that human activity is the main driver of climate change, which is certainly the case, but is obviously not a proof.

They also say that reducing our CO2 emissions won't hurt anyway and that a 2 °C temperature increase would be catastrophic. This is a very good reason to act, but this still doesn't prove anything.

Digging in the research, the main evidence I've seen relies on the fact that our models can't explain the current change in temperature without taking into account human activity. When opposed that those models could be wrong, the usual answer is that we know they work because they explain past changes, but this not a very strong point since those models have been calibrated using past data (in the financial world, this is a well-known issue with models trying to predict stocks changes)

The other piece of evidence is that the other factors we know about (solar activity, volcano activity, changes in earth orbit, deforestation changing the energy reflected by some of the landmass, human-released aerosols reflecting more energy, etc... ) don't seem to be behind the recent increase in temperature. So the increase must be mainly caused by the anthropogenic CO2 , for lack of a better explanation. This is a strong point, but isn't a proof per se.

Are there other, possibly stronger points to support the claim that the CO2 human activity is releasing in the atmosphere is the main driver of climate change?

What evidence is backing the claim that the C02 we're releasing in the
  atmosphere is the main cause of climate change?

As you said in your comment:

  I agree that, if the proof is too complicated to be understood by a
  layman, your only choice is to rely on scientific consensus

Complication regarding proof or evidence based consensus in science is tricky.   Should we accept things that we don't understand, that scientists say are so, like the standard model or should we doubt them.   That's a philosophical can of worms that I'd rather not open, but I can say this, if you can't follow the science, perhaps you shouldn't take a side.  Your time would be better spent learning than doubting.   There is no wisdom in naked skepticism.

That's something many skeptics would be wise to learn.   Skepticism is both great and useless at the same time.   Bart Simpson's a skeptic.   The dumbest kid in the class can say "I'm skeptical about that", and he can answer every question with those 4 words, but he'll never get any smarter.

Applied skepticism is where it's at, and to apply skepticism, you need to understand the argument(s).  Good skepticism requires understanding and, after understanding the argument, then you can intelligently apply skepticism.   Empty doubt is useless.  Good skeptics need to be smart.

This is one argument as to why man made climate science is likely true.   Because there are no good skeptical arguments against it.   Urban heat island - debunked.   Cosmic rays - studied, but no evidence found.   It's the sun?   No, we measure solar output, we'd know.   Mars is getting warmer?  That's incidental.   We're still warming from the last ice age - actually, the opposite is true, we're in a cooling period.  Got any others?   The climate change deniers have figured out that they don't need science to sell their seeds of doubt, they're just selling doubt, but selling doubt isn't a scientific argument.

  What evidence is backing the claim that the C02 is the main cause of
  climate change?

A quick google search will answer this question for you.  Read some of those, and if you still have questions, come back and ask.   This really, really, really has been answered, again and again and again and again.   If you have trouble, I can post some explanations for you.

  CO2 levels have been going up and down for as long as we can look at
  them without human intervention. Eg this NASA graph spanning 400.000
  years

The primary drivers are the milankovich cycle, which leads to the ice-age cycle and feedback mechanisms.  Colder oceans absorb more CO2, warmer oceans release CO2.   CO2 and global temperature have an effect on each other, each driving the other forward or backward depending on how much ice-cover the Earth has.   This is a well understood feedback mechanism that in no way contradicts climate change theory, in fact, they go hand in hand.

  global temperature is still inside the bounds of normal cyclical
  Halocene variations (as seen on wikipedia)

Yes, but the rate of increase is NOT within the bounds of normal Holocene variation.   Also, there is a relation between northern hemisphere summer insolation and temperature.   The direction of the Northern Hemisphere summer insolation is downward right now.  That suggests, without human influence, Earth should be cooling right now, it's not.  It's warming rapidly.

You can say "but the Earth was just as warm 7,000 years ago", and that's about right, but the orbit was different and Earth should have been warmer 7,000 years ago.

  earth temperature has been going up and down for millions of years,
  obviously without human intervention, as seen on the same wikipedia
  page

Hundreds of thousands of years:   Milankovich Cycles

2/5/10/50/100 million years . . . Isthmus of Panama, Himalayas, drifting of Antarctica, Glaciation of Greenland, variation in plant life.

There can be many causes of natural climate change.   One of the ways we know that the current climate change is man made is that we can rule out causes, for example, ocean currents didn't suddenly change in the late 80s.  No new land bridges formed.   Causes are testable and causes have signatures.  CO2 or greenhouse gas driven climate change has a measurable signature.   It's not just that temperature is rising but where it's rising that helps answer these questions, poles vs equator, land vs oceans, upper atmosphere vs lower.

  scientists usually reiterate the first four facts

If you'd read even one scientific study, you'd know this isn't true.  Journalists might mostly reiterate your first four facts, not scientists.

  we know they work because they explain past changes, but this not a
  very strong point since those models have been calibrated using past
  data

There's a principal in science called the double-blind study, where you set up two equal experiments, with one variation and you don't know which experiment has the variation and you study the effects.    This is a good scientific approach but it's not always possible.

You can study the effects of smoking by letting one group smoke and another group not and compare the two groups, but we can't build other Earths to study one with burning fossil fuels and one without - models are all we have.   How accurately the models predict what will happen by 2100 is hard to say, but inaccurate models are better than none.   Take a financial advisory firm that runs models and one that doesn't - and you tell me which one will be right more often.

There's also much more consistency with planet Earth than there is with financial models.  The solar energy the Earth receives year to year varies by less than 0.1%.  Global could cover varies by perhaps 1%-2% year to year.  Snowfall cover varies maybe a little more, volcanic ash comes and goes, but generally leaves the atmosphere pretty quickly, even the largest volcanoes only trigger cooling for a small number of years.   The Earth absorbs heat from sunshine with a small percentage coming from internal heat and volcanoes and it loses heat by radiation.   There are thermodynamic laws that govern heat transfer.    That means the Earth is pretty consistent, having roughly the same orbit around the same star.   By comparison, financial models try to estimate something that's a few orders of magnitude more volatile.

Modeling isn't easy, but it beats blind guessing like the Patriots beating the Jets.   That's true in both studying climate change and in finance.

So, how do we know it's man-made?
Look at the signature.

Earth is warmed by the sun during the day and it radiates energy away at night.   The atmosphere acts like a shield, blocking some of the solar energy from reaching the surface and a blanket catching some of the radiation leaving Earth.

Climate change gases like SO2 and very fine volcanic ash thicken the shield, cooling the Earth - see year without summer.   Climate change gases like CO2 thicken the blanket.   Water is also a greenhouse gas so where CO2 has the biggest effect is low absolute humidity regions like the poles.

Other changes, like albedo, the effect is in visible light, not infra-red.   Ocean current changes are easy to detect because the effects are visible on location.   A stronger mid-atlantic current = warmer European winter.   The climate effects of El Nino, which warms the Earth, are many, but they are well documented.

Heat-trapping greenhouse gas has a signature.   The lower atmosphere warms, the upper atmosphere cools, the tropopause rises and the troposphere loses mass.   The warming can be modeled based on greenhouse gas to be largely polar and the comparing temperature by time of day, the Earth warms most at night, where a hotter sun would do the opposite and warm the Earth during the day and that's where you'd see the larger variation.

Your question implies that scientists ignore all the other possibilities.   Nothing could be further from the Truth.   Scientists (on average) appreciate possibilities and will rarely dismiss valid alternative explanations.   While the theory was first proposed in the 1900s, modern climate change theory had a rebirth in the 1950s, and was the subject of much study through the 60s, 70s and 80s.   It was met, not with immediate acceptance, but decades of skepticism.   It's only now accepted because the evidence in favor is very strong and the evidence for alternate explanations is hovering close to zero.   Decades of research, models that aren't perfect, but fit both matching what's happened so far and going backward, and the signature of the warming matching what is expected from CO2 and the counter theories all failing.    The evidence is very very strong.

All it would take to disprove manmade climate change theory is one unexplained cold year - just one.  One year like the 1970s without a volcano to cause it and the theory is dead.  That hasn't happened.  We've had nothing but warm years for a few decades now.    You could also disprove it by showing a signature that doesn't fit with CO2.  The opportunity (and funding) to disprove climate change is enormous, but you can't disprove a truth, not scientifically.   If it was false, it wouldn't be that hard to show scientific evidence that disproved it.  It's not like this is Rosalind Franklin who worked out how to take photographs of the DNA molecule and she was reluctant to share them with other scientists who'd take the credit for her work.  This is the Earth.  The data, the evidence is out there.  The means to disprove man made climate change - if it was disprovable, are available, and the funding to disprove it is available and significant and they have nothing.   All the evidence still points towards man made climate change theory being right.

(too long?  too preachy?)


Is the momentum of a volcano's high-velocity ejecta mostly due to expanding gas? When I was very young I was always amazed that water didn't come shooting up out of the first ice-fishing hole of the season, due to the weight of all the ice. It doesn't, because the weight of the same volume of liquid water would be even heavier. Ice floats, and the thicker the ice, the lower the level of water sits down inside the hole.

There is no additional hydrostatic pressure in the water beyond that due to gravity, because if there were, the ice would have been slowly pushed up to a new equilibrium position fairly quickly.

If I extended this thinking to volcanism, I'd wonder why volcanos can sometimes have high velocity ejecta, and also build cones from liquid that rise high above the local surface. I am guessing that the height of the cone represents effects due to hydrostatic pressure beyond that due to the weight of material above (rock being less flexible than ice) but the high speed ejecta that falls far from the cone is accelerated by gas coming out of solution.

Is the momentum of a volcano's high-velocity ejecta mostly due to expanding gas?

above: Example of an ice-fishing hole, from here.

The ejecta and their momentum appear to be entirely the product of the dissolved gasses in magma, according to this page on Physicochemical Controls on Eruption Style on the How Volcanoes Work pages of the Geology Department of San Diego State University:

  The amount of dissolved gas in the magma provides the driving force
  for explosive eruptions. The viscosity of the magma, however, is also
  an important factor in determining whether an eruption will be
  explosive or nonexplosive. A low-viscosity magma, like basalt, will
  allow the escaping gases to migrate rapidly through the magma and
  escape to the surface. However, if the magma is viscous, like
  rhyolite, its high polymerization will impede the upward mobility of
  the gas bubbles. As gas continues to exsolve from the viscous melt,
  the bubbles will be prevented from rapid escape, thus increasing the
  overall pressure on the magma column until the gas ejects explosively
  from the volcano. As a general rule, therefore, nonexplosive eruptions
  are typical of basaltic-to-andesitic magmas which have low viscosities
  and low gas contents, whereas explosive eruptions are typical of
  andesitic-to-rhyolitic magmas which have high viscosities and high gas
  contents.

A similar description is offered by Stephen A. Nelson, associate professor in the Department of Earth & Environmental Sciences at Tulane University:

  At depth in the Earth nearly all magmas contain gas dissolved in the
  liquid, but the gas forms a separate vapor phase when pressure is
  decreased as magma rises toward the surface of the Earth.   This is
  similar to carbonated beverages which are bottled at high pressure.
  The high pressure keeps the gas in solution in the liquid, but when
  pressure is decreased, like when you open the can or bottle, the gas
  comes out of solution and forms a separate gas phase that you see as
  bubbles.   Gas gives magmas their explosive character, because volume
  of gas expands as pressure is reduced.

So the gross extrusion of magma from the earth is not innately gas-dependent (though gas influences the composition of the magma), but the violent processes are caused more by gas coming out of solution and forming pressurized bubbles than gas or magma being under pressure, if that makes sense.


What is a "tar shower?" I'm reading about Sodom and Gomorrah on Wikipedia when I come across this:
"One such idea is that the Dead Sea was devastated by an earthquake between 2100 and 1900 BCE. This might have unleashed showers of steaming tar."

What is a "tar shower?"  Are there any documented cases of this?  When I googled this, it went to the visual dictionary referenced in the Wikipedia article, which didn't explain the concept either.

Natural oil seeps are not unusual, the light components evaporate leaving "tar". Then an earthquake could cause a release of gas which if in just the right location could blow the tar into the air.  Normally the gas escapes through the tar and throws it only a very shot distance, like an inch.


How long would it take for Mars to cool after asteroid impact? As someone interested in terraforming, the main obstacle to colonizing Mars is the lack of a magnetosphere and Atmosphere. To create a magnetosphere of sufficient magnitude the Martian core must be reignited. There are several ways to do this, some of which involve using electric current to restart the core, but the most feasible way it seems would be to take an asteroid of sufficient size and slingshot it into Mars. Doing so would reignite the core resulting in increased volcanic activity, the formation of a thick and stable atmosphere, etc.

It seems to be the perfect solution despite the fact that doing so would be a long term investment. I was wondering - based on what we know of the Earth's development - how long would it take Mars to cool after an asteroid impact of sufficient size? are we talking millions or billions of years?

It would be interesting to read peer reviewed scientific papers that discuss the feasibility of "restarting Mars' core" via an asteroid impact. Some links would be appreciated.

I am very sceptical that it could be achieved in such a manner. Small asteroid impacts would change the topography of the surface by creating new craters and spraying crater ejecta over the surface.

Impacts from extremely large asteroids would only create larger craters or possibly blast out large chunks of Mars and even destroy the planet: such as a collision with Ceres.

One of the flaws I see in trying to "restart the core" is how to keep a solid inner core within a molten outer core, while at the same time creating relative movement between the two.

The Earth's magnetic field exist because its solid inner iron-nickel core and the metallic molten outer core move relative to one another creating a geodynamo. Without a solid core and relative movement between the two the only thing that will be achieved will be a molten core without a magnetic field.

If it were possible to remelt the core of Mars, a magnetic field would not be created by simply remelting the core.

The other flaw I see is that if it were possible to remelt the core, the core will expand due to thermal expansion. This will then increase ground stresses within the overlying rock which will result in cracking of the overlying rock and the generation of Mars-quakes.

Another flaw I see is concerns the energy required to remelt the core. A significant volume of core would need to be remelted. That would require a lot of energy over a prolonged period of time. The effect of an asteroid impact would dissipate quickly.


How to run earth system, land surface and climate models? I am interested in earth system models, land surface models and climate prediction models. I found a lot of online information on different models, including CIMP5, and the Earth System Modeling Framework. I also found a lot of articles using these models.

I would like to run and experiment with these models on my own computer. However, I could not find any clear installation guides or code examples on how to run these models. I would like to have a step by step instruction how to install the model, how to include the input data, how to run the model and how to view the output. There must be decent tutorials somewhere out there. I am particularly interested in models using Normalized Difference Vegetation Index (NDVI) and Leaf area index (LAI) data.

For the time being it should be something that can be run on a desktop computer or in a virtual machine, but I also have access to more powerful clusters.

As alluded to in some of the comments, all of the CMIP5 models will have been run on supercomputers, and it takes a lot of effort to get one of them running on a new platform, even for a team who know both the model and platform well already.  In addition to that, many of those models are closed-source and are not generally available to an individual researcher.  However, there are several older models such as MITgcm and EdGCM that it might well be possible to get running on a cluster.  It's something I've thought about but never quite got around to.  One group have even been
running CESM on Amazon's EC2 service.

Depending on what aspect of leaf phenology you're interested in, you may need to run quite long simulations (e.g., several centuries), which is prohibitive with a full ESM.  You can make a lot of progress in this area by running just the land surface components.  This is several orders of magnitude simpler than running an ESM: the source codes are often freely available where their host ESM code is not, and they can be run globally on desktop machines or clusters.  Some example land surface models you might want to look into:

Community Land Model (CLM) (used in CCSM, US)
JULES (used in HadGEM, UK)
CABLE (used in ACCESS, Aus)
ORCHIDEE (used in IPSL-CM5, Fr)
SURFEX (used in CNRM-CM5, Fr)

Each of these will require a set of forcing boundary conditions, and there are several commonly used by the land community:

GSWP3
WFDEI
CRU-NCEP
Princeton

If you go down the land surface route (and I suggest that's a good place to start), you should probably just pick a model and ask it's community directly about the details of getting it running.  In my experience, several of them have very good tutorials especially for people with a bit of Linux experience.


SPI (Standardized Precipitation Index) for 40 years seasonal mean I am working with SPI (Standardized Precipitation Index) and in particular I am interested in obtaining the seasonal mean observation over a period of 40 years.

The meteorological season I am considering is Winter and therefore the months of December-January-February.

The point is that for each location and for time scale I am using, the overall seasonal SPI winter mean should = ~0.

Is that possible?

I am expecting that the annual SPI averages would be = 0, because of the definition of SPI, but not for the overall seasonal mean.

The SPI statistic can be considered a standard normally distributed random variable $SPI \sim N(0,1)$. Thus the expected value, or mean, of the SPI statistic is $0$, and its standard deviation and variance are $1$.

If the mean of the distribution is zero, then by the central limit theorem, you would expect that the limit of your sample mean (the mean of ~40 years of data) would approach zero as your sample got larger. So yes, it is both possible and expected.

What may be causing your confusion is that SPI can be calculated for different time sets. If you are analyzing month by month, then I would assume that your dataset is divided by month. In that case, the SPI is calculated individually for each month, so that the mean of any month or set of months over many years would tend to zero, as per the last paragraph.

It would not make sense to calculate a monthly SPI from a 12-month mean divided by 12 (to give you a mean per month on an annual basis) In seasonal wet-dry climates you would have massively negative SPI value in the dry season, and highly positive numbers in the wet season. The monthly means are individually given an SPI statistic to allow apples-to-apples comparisons with the same month in other years.


Are these plane trails seen from satellite Here are photos from West of Normandy, at 7-9am after sunrise on the 14th of may, from the visible satellite. It's a bit strange that they are visible from space, they are 2-3 miles wide? Are they jet engine trails?
To see the original images you can rewrite the time on these hyperlinks to 8-15 etc...

https://archives.meteo60.fr/images_sat_vis/2019/semestre1/Sat_vis_20190514-08h00.png <-hours

Under the right conditions (in a basic sense, locally high relative humidity; see also this discussion on this site regarding contrail formation), the clouds initially formed by contrails may persist for hours and spread outwards to form larger areas of cirrus cloud. Additionally, NASA's Contrail Education Project website has some specific examples here showing the evolution of contrails and associated clouds over the course of a day, with extremely similar visual properties to those shown in the question. They also provide some discussion describing how large these clouds must be compared to what a typical weather satellite "sees":

  In order to be seen, a contrail must be wide enough (and long enough) to change the brightness of a satellite pixel. Each pixel covers a portion of the Earth. The size of that area is determined by the resolution of the satellite instrument. Typical weather satellites, such as you see on the news, have pixels that might be 8 km, 4 km, or 1 km on a side. To show up in such an image, a contrail must be nearly 1 km wide!

In other words, yes, they are contrails (or more accurately, persistent clouds originating from contrails) as observed by satellite.


Software for sediment transport modeling I am doing a paper about coastal processes and I was told that I should include a sediment transport modeling to further examine my geophysical findings. I was reading in the net and found that Delft3D Suite seems to be the best option, however I have no funding to pay for a license because it is all science.

Does anyone have software suggestions to model coarse sediment transport?

I think the best option for sediment transport modeling is the Community Sediment Transport Modeling System (CSTMS) package that was developed for ROMS. CSTMS was created by a group of sediment transport modelers lead by the USGS. One of the many benefits is that it is open-source and, thus, free. The model was designed for realistic simulations of processes causing sediment transport in the coastal ocean (estuaries, nearshore regions, and the continental shelf). Details on the package and its implementation are found in Warner et al (2008). The people from FVCOM implemented this package.

The most up-to-date version of the sediment transport module is part of the Coupled Ocean – Atmosphere – Wave – Sediment Transport (COAWST) modeling system. A good description of the model and its capabilities is given in Warner et al. (2010). The code can be downloaded from here.

The current version of CSTMS can model both cohesive (mud) and non-cohesive sediment (sand) sediments, bedload transport and sediment deposition and erosion caused by waves and currents.


Which component in a 3-component Sp receiver function is the actual Sp RF? In a 3-component Sp RF I have the green's function in P,SV, and SH. The actual component to the RF that shows the Sp conversion (the one always published in the literature), which would represent as a negative phase around the LAB and a big positive one over the Moho, would have to be the P component...right? I have three components to these RFs, but they were never labeled, two of them have the zero lag arrival at the same exact time while the third has its zero lag arrival occur about 3 seconds before the other two. Remember this is an Sp RF!

As an S wave in an non-isotropic (i.e. Earth) media would have some level of energy in two components, SV and SH (albeit the SH is always a lower SNR given the Earth is not actually isotropic), it completely makes sense that the two components in the receiver function that happen to have the zero lag direct arrival of the wave at the EXACT same time would have to be the SV and SH components.

Given that one of these two has a much lower SNR I could also argue which one is SV and which one is SH. Furthermore, since the only remaining component has its direct arrival occur BEFORE the other two I should naturally conclude this to be the P component! ....but this is where it gets complicated....this supposed P component does not have a clear positive spike where the Moho should be and a clear negative spike where the LAB should be.....the supposed SV component does....

I feel like I am just standing at the door before I walk in and learn an incredibly powerful lesson about the Earth, but I also feel like I want someone to walk through with me and tell me I'm on the right track in terms of my thinking....so am I??

I am not sure I clearly understand the question, but here is a quote from the paper that I looked at a while ago about S Receiver Functions.

From: Yuan, Xiaohui, Rainer Kind, Xueqing Li, and Rongjiang Wang. " The S Receiver Functions: Synthetics and Data Example ." Geophysical Journal International 165.2 (May, 2006): 555-564:

"Here we briefly summarize the processing steps for generating S receiver functions. The ZNE-component seismograms of S and SKS waves are rotated firstly into the ZRT system with the back azimuth determined by locations of the receiver and earthquake. The ZRT components are further ro-tated into the P-SV-SH system with the incidence angle determined by minimizing the amplitudes at time of S/SKS arrival on the P component. Waveforms are visually selected to avoid the confusing of S and SKS phases. Data with strong interference of S and SKS are excluded. A window of S/SKS waves on the SV component is deconvolved from the P component for source equalization. For direct comparison with the P receiver functions, we need to reverse the time axis as well as the amplitudes of the S receiver functions.Move-out correction is then applied for all the PRFs, SRFs and SKSRFs, with a reference slowness of 6.4 s deg−1 and the IASP91 model as reference."

Does this help?


How did Great-Britain separate from France? Looking at continental plates both France and GB lie on the Earasian plate. Now those plates moves and created our continents of today out of Pangea.

But a lot of pictures shows that France and GB were once stuck together. Also their shapes looks like they fit together.
But if they lie on the same plate how is it possible that those contries are now separated? Is it possible that the oceans eroded land between them so they became separate?

Or is it possible that in one plate there were plenty of little continental drifts too; if that is true what is the difference between a continental drift and drift within plates. Or is it even possible that GB lies on its own plate?

Picture taken from the hi-res drawing at Here's what Pangea looks like mapped with modern political borders

"Is it possible that the oceans eroded land between them so they became separated"? Yes, sort of, but it isn't a simple story. There are several factors: (1) Rivers eroded much of the English channel, mostly during the last ice age when sea level was up to 120 metres below the present level. The Rhine actually flowed (and eroded) much further out into what is now the English channel. (2) Some have argued - though I'm not sure that I agree with them - that at least part of the English Channel was cut by glaciers. However, the main British ice sheet was further north than the channel. (3) There is sound evidence that an ice dam collapsed, resulting in a huge glacial lake outburst, which would certainly have resulted in major erosion. (4) The Alpine orogeny of late Mesozoic / early Cenozoic age, created a compressive zone across much of northern Europe, thereby flexing low-angle folding. One of the major folds was the Wealden anticline, most of which is exposed in southern England, but to a lesser extent also in northern France. Tension fractures in this anticline created an area of weakness and enhanced erosion across what is now the eastern English Channel.

Could microplate tectonics have contributed? Good question. Certainly it is possible for the jostling of major plates to splinter off microplates, or even mesoplates - examples being the Aegean region, and the rotation of Iberia, respectively. I don't have any information on the deep geology of the Western English channel, but I suspect that tectonic thinning of the crust in that area may have contributed to subsidence and subsequent flooding.


How to estimate size of cloud formation Looking up at say a cumulus cloud at a height of 2km which covers say 10 degrees of the visible sky, what is the easiest way to estimate its rough size at its base?

Simply put, how large is the arc of visible sky viewed from the surface?

Three methods spring to mind:

1) If you can really estimate both the width in degrees and distance to the cloud, you can draw a triangle and use trigonometry to calculate the width.

2) The distance to the cloud you may estiamte from the cloud type. But both height and width in degrees are uncertain numbers. Instead you can estimate cloud sizes by looking at planes passing through them. If you time how long it takes a plane to pass through a cloud, you can multiply that with its cruising speed to get the width of the cloud. The cruising speed (typically 500km/h) can be found via say, the Flightradar24 app.

3) Using that app, you can also track the plane in real-time to map out not only the length of the cloud, but what land it is covering. No need to time the plane or know its speed.

By following a plane on the app until it goes under the horizon at your location, you get a feel for "how far away the horizon is", for clouds at that plane's altitude. high-altitude clouds and aurora at the horizon will be much farther away than low-altitude clouds.


Prevailing Winds: Is the speed relevant? The Wikipedia entry for prevailing winds notes (in my understanding) that the prevailing wind direction is determined solely by the mode of the directions. They note another qualifier called 'dominant wind' which should give the direction of the strongest wind.

However, it feels a bit counter-intuitive that if we had (an example) over 8h a wind from the east at 2m/s and after that a 10m/s wind from the north for 4h, that the prevailing wind direction would still be east.

Based on the above example, would the prevailing wind direction be east?

Is the term 'dominant wind' (with a northerly direction) used in common meteorology, and would that be (in the above example) northerly?

Part of the complication goes to two separate definitions for the word:

prevailing:

  To be frequent (Miriam-Webster)

The most frequent, the most occurring wind direction in your example, even if weak, is east.  So that would be the prevailing wind, as that's the definition we generally use in meteorology.

So don't think of it as

  Having superior power or influence (Dictionary.com)

as indeed, that'd become a bit more subjective of a concept.

Sometimes you may hear about the average direction (which would be east-northeast in your example).  So perhaps that's more what you're wishing for?  Of course if you have an east wind for half the day and a west wind for half the day, the average wind direction would be either north or south.  Or, if instead of treating direction and speed differently, you took the vector average... you'd have a mean windspeed of nothing!

Looks like this MathSE question fairly discusses some of the benefits and troubles with different methods of summarizing wind direction... which line up closely with the more general disparities of each of mean, median, and mode.

Alternatively, wind roses can be much more informative and enticing.  They give both an indication of the directions (by the length of the bars in each direction) and the intensity (color coded).  You can find things, such as: in Colorado Springs in May (as shown below), winds aren't from the southwest very often... but when they are, they tend to be fairly strong (whereas when winds are from about east, as is more common, they're typically quite light):

Looks like you can make some pretty snazzy/customizable recent wind rose plots of locations around the world at the Iowa Environmental Mesonet site.

But the take home is: in meteorology we typically define prevailing wind as simply the most common direction, with no consideration of the speed distribution.


What type of mammal does this fossil tooth belong to? The fossil tooth was found western South Dakota in the early 1980s.
I can't be sure on the location.  It might have been collected from Belle Reservoir, near Belle Fourche, Butte County, South Dakota, USA.
What type of mammal does this fossil tooth belong to?

It's an entelodont, South Dakota is famous for it's Oligocene mammalian faunas which include entelodonts such as Archaeotherium and Daeodon.

here is an http://i.ebayimg.com/images/i/181202162847-0-1/s-l1000.jpg for comparison:

Thanks to the guys at fossilforum, they knew in less than a day. this question could have stayed on here for a year so i was impatient.


Does gravity increase the closer to the core you get? Or does the mantle and crust above you counteract the increase at one point and it actually decreases?

The below figure, taken from Wikipedia shows a model of the free fall acceleration, i.e., 'gravity'. The left-most point corresponds to the center of the Earth; then further right at $6.3\cdot1000$ km you are at the Earth's surface; and then further out you move into space. You can follow the blue line for PREM to get an idea of the average (expected) gravity. As you see, the gravity actually increases slightly within the Earth (reaching a maximum at the core-mantle boundary), but tapers down within the core.

To make this kind of calculations, you must think of the Earth like an onion: made up of many concentric spheres. Whenever you move a bit deeper into the Earth, you strip off all the layers you've crossed. As you get closer to the center of the Earth, there are fewer and fewer layers, and eventually, there's nothing left at the center! The reason why gravity goes up ever so slightly within the Earth is that you get close to the much denser core material. If the density of the Earth were constant (per the green 'constant density' line), the gravity would just decrease linearly.

See the other answer and the discussion below for some more details on the math and procedures required to make these calculations.


Why do high tides vary month to month? I've noticed that some ‘highest‘  high tides in one month are bigger than the highest high-tide of previous months. Why is this so?

The dynamics of the tides are quite complex. The main idea is that gravity from the Moon and the Sun affect water (and everything else) on Earth. The issue is that there are several motions that alter the distance between the 3 systems and those motions cause interactions between the different frequencies involved. The Equilibrium Theory of Tides separates the different effects into a set of constituents by conducting a harmonic analysis. The relevant periods are:

the lunar day (period of lunar rotation), 24.84 mean solar hours.
the sidereal month (period of lunar declination), 27.32 mean solar days.
the tropical year (period of solar declination), 365.24 mean solar days.
the period of the lunar perigee, 8.85 years (1 year = 365.2421988 days).
the period of the lunar node, 18.61 years.
the period of the solar perihelion, 20940 years.

The explanation of each constituent can be rather complex (some examples in this other answer). The different amplitudes in a day and the spring-neap cycle are related to the combination of the main lunar and solar effects.

The differences in high/low tide from month to month are related to the next two main frequencies of oscillation. Mainly, the variations in Earth-Sun distance associated occurring in a period of tropical year. The lunar distance also contributes to these differences, but its cycle is much longer (~9 years). Also, the spring-neap cycle (with a frequency of half a lunar month ~13.5 days) will occur at different times of the month and can lead to differences in tidal amplitude if you compare the tides measured the same day of consecutive months.

(Source www.niwa.co.nz)


How does water still exist on the Earth? Almost all the theories that explain the origin of Earth says, it was way hot back then.

That means It was in a lava state in its early days. Then gradually cooled down to the current state.

If this is the case how did the earth retain this much of water on its surface?

Lava doesn't destroy water it evaporates it into steam.  This steam rises high into the atmosphere, cools and condenses into rain which it falls back onto the Earth's surface where it gets hot again, evaporates and rises.   This isn't too different than how rain is made today, except that the evaporation process is slower and mostly driven by sunlight, wind, running rivers and by plant transpiration, not as much by a scorching hot surface.

Rain is a very efficient form of heat transfer.  Water evaporating very efficiently cools the surface.   I read or heard somewhere, don't remember where, so take with a grain of salt, but I heard that the Earth rained constantly for millions of years when the planet was young and the surface was hot.

To thermally split water into Hydrogen and Oxygen, the temperature needs to be about 2,000 degrees C.  Lava isn't that hot, though it's possible that the very young earth might have been hot enough to actually destroy some water and turn it into it's elements, Oxygen and Hydrogen, some of which would have recombined, and some of the hydrogen could have been lost as Earth's gravity is too low to retain all of it's hydrogen, but for the most part, Lava doesn't destroy water it simply evaporates it.  It's also possible that some other chemical interactions would absorb and change the chemical property of some of the water, but for the most part, Lava just turns water it into steam, which is still water, just in a different state, like how Ice is still water, just not liquid.

Update:

On the comments below, that's on the Earth Science/Astronomy border, but there are a fair bit of unknowns on how much atmosphere and water the Earth has lost to the Solar Wind.   One estimate says the Earth is losing about 90,000 tons of hydrogen every year.   Source.  Since that hydrogen effectively comes from split water molecules by UV rays high in the atmosphere and by mass, Water is about 8 parts Oxygen to 1 part hydrogen, then 810,000 tons of water is converted to 720,000 tons of Oxygen every year.    If we multiply that by 4 billion, just cause, you know, why not run the numbers, assuming consistency, over that time, the Earth has lost 3,240 trillion tons of water and added 2,880 trillion tons of Oxygen.  Consistency is a big if, but these numbers seem reasonable enough to work with.

The oceans contain about 1.4 million trillion tons of water so the estimated 3,240 trillion tons of water lost is irrelevant, less than 1/400th of the Ocean water at the current rate of loss.

Oxygen is different.   2,880 trillion tons of Oxygen is more Oxygen than is currently in the Earth's atmosphere, but much of the Earth Oxygen formed in the upper atmosphere combined with other elements like Iron in the oceans or Methane gas, or helped form the planet's granite, so even though the solar radiation should have produced lots of Oxygen from water over time and Hydrogen that was lost, the amount of water is negligible and the Oxygen has been useful in many ways.

But I digress as those are current estimates not historical ones.   The solar wind, while it does blow hydrogen off the Earth and in effect removing water from the Earth, the effect is slow enough that it's a minimal change.

But the Earth's magnetic field wasn't always there and it isn't as old as the early and late heavy bombardment periods.  Our magnetic field is thought to be about 3.5 billion years old.  Source.  So it's entirely possible that the Young Earth lost a significant amount of water prior to the magnetic field.   Venus has no magnetic field to speak of but it's retained it's atmosphere's heavy elements but very little of it's water.   Mars is much smaller, so it's less good at retaining it's atmosphere than Venus.   Nobody knows how much atmosphere and water the young Earth lost to space.

It's entirely possible Earth lost a pretty good share of it's water to the Sun's UV rays prior to it's magnetic field, and in part due to it's high temperature, but I don't think anyone had a good guess on the precise numbers.  To return to the question above, Magma on the surface isn't a big factor unless it's hot enough to split water into individual molecules.   It's the temperature of the upper atmosphere, the atmospheric escape velocity, the solar wind and magnetic field are the larger factors.


Where can I find weather data on ambient outside illumination? I am looking to analyze outside lighting data and its implications on human health regionally, but I can't seem to find a ubiquitous database that contains outside lux illumination data throughout the continental US. This is essential to my study and seems to be measurable, but virtually nonexistent on each climactic database I request from.

Any help is appreciated,

Thank you.

One direction to look in might be the various GIS systems that exist to forecast the amount of light that will reach photovoltaic (solar panel) installations. I don't know about the US, but I would be very surprised if there isn't one - try googling for "PV GIS" or similar.

Now, that will give you insolation (illuminance) in W/m2. It may be further broken down into direct and indirect insolation (that's direct sunlight and diffuse light from the sky or clouds), or it may be a single global figure.

Since you're after the information in lux rather than W/m2, you'll need to convert it. This will necessarily be an approximate process, but so long as you don't need very high accuracy it should be quite doable. Lux is at base a measurement of power density, just like W/m2, but it's modified by a frequency-dependent function that represents the sensitivity of human vision. So you'll need to assume a spectrum for the sunlight, and then apply the conversion curve (which is an international standard, and hopefully available on the internet).


How do archaeologists address time dilation when analyzing carbon dating results? It is a proven fact that the gravitational force exerted upon an object directly affects that objects experience of time; the greater the gravity, the slower time passes, and visa versa. While the rate of radioactive decay may be nearly absolute, the gravitational environment in which that decay took place dictates how time was experienced by the decaying atom.
    Gravitational environment differs with respect to altitude, and would also differ based on the weight and density of material in which an object was located. Furthermore, gentle gravitational waves ripple across the face of this planet every day, creating the weather of our atmosphere. It is also highly probable that the earth has experienced a myriad of intense gravitational events over its history, during unstable periods of solar radiation, and from the ripples of other catastrophic cosmic events.
    I am very curious to read any research in this area.

For all intents and purposes, the Earth represents one frame of reference, as @kwinkunks states. Therefore no effect.

Yes the gravitational field on top of a mountain is slightly less than at sea level. This is very small though. Variations in gravity over the Earth's surface typically vary at most by a few hundred milligals (ie. "one part in 10,000" order of magnitude).

I doubt you would be able to measure General Relativistic effects due to such small field changes (even integrated over 10,000 years) - and even if you could, they are much smaller than other sources of error (e.g. the atmospheric C14 curve, and sampling errors).


Is Earth inhospitable? It's thought that, shortly after Earth was done being refurbished resurfaced during the Late Heavy Bombardment, life abio-generated almost as soon as it was able to. The short delay led to speculation that: in the right conditions, life arises fairly easily; and, under that assumption, many "lifeforms" arose alongside one another, perhaps some subsisting even today.

Earth, to the standards of the lifeform(s) that won out, is pretty hospitable--perhaps because life made it that way, altering the chemical properties of the atmosphere and terrain. Life thrives in nearly every remote nook and cranny of the planet.

Is there any thinking out there into why abiogenesis may have stopped? Is the process expected/hypothesized to be ongoing concurrently, in the present day? If life came to be so rapidly, why isn't it still coming, especially given Earth's apparent suitability?

(Perhaps our form of life, by its pervasion and alterations to Earth's condition, truly "won out," monopolizing on Earthly resources in such a way that bars newcomers from developing to compete and bars us from detecting their remnants, should they exist?)

I think that your question is not really answerable.  But perhaps the reasons it's not answerable are themselves interesting.  There are two parts to this answer:

why do we think abiogenisis is likely?
is Earth, today, hospitable for organisms which originate through abiogenesis, if it is likely?

My answer to the first part is, I think, more well-founded than my answer to the second (I'm a physicist not a biologist!).

Is abiogenesis likely?

Well, we have exactly one example of a planet we can study closely with life on it (indeed there is only one example of a planet that we know has life at all at present), and life has been there for such a long time and has modified the environment of that planet so extensively that I think speculation about how life originated on that planet is, well, speculation.  That doesn't mean it's not interesting or that there might not be plausible and attractive hypotheses.

As an example it's tempting to argue that, because life originated on Earth almost as soon as it could, and disregarding panspermia, that abiogenesis must therefore be very common.  That argument is wrong.  There are a huge number of potentially-earthlike planets: this paper (arXiv version) claims that around 10% of stars may have a planet that is about the same size as Earth and gets around the same amount of sunlight as Earth.  There may be around $10^{24}$ stars in the observable universe: based on this paper (arXiv) there may be around $2\times 10^{12}$ galaxies and assuming each galaxy has $10^{12}$ stars we get $2\times 10^{23}$ stars.  So this means perhaps $2\times 10^{22}$ potentially-earthlike-planets.  All we know is that life originated on one of those planets, somehow (and abiogenesis is only one of at least two options), and it did so rather early.  What does that tell us?  Well, statisticians can play games and those games are probably reasonable, but it doesn't tell us, for sure, that the chance of that happening is higher than $1/10^{22}$.

This argument is related to the anthropic principle which I find rather unappealing in terms of explanatory power: I find the idea that the fine-structure constant must be what it is because otherwise we would not be here to measure it unappealing for instance.  But the anthropic principle is nevertheless not an idea that can be ruled out in general: we know life evolved on Earth because we're here to observe it, but this doesn't, yet, tell us anything about the probability of life evolving elsewhere: the universe could have just thrown a $10^{22}$-sided dice $10^{22}$ times and come up with the side that says 'life' once.

This doesn't mean that abiogenisis can't be really common, or even that it not likely that it is, it just means that we don't know that it is.  With luck this will change in the relatively near future, as we begin to be able to observe expolanets which convincingly have life.  Then we'll be able to use statistics in a more useful way.

How hospitable is Earth, today?

Well, let's assume abiogenisis is common, what can we say about Earth's hospitability to new life generated that way?  Well, we know that organisms on Earth are continually under attack by other organisms and things which may be organisms (I'm not a biologist, I'm not sure if viruses count as organisms or not).  And we know that these attacks can be pretty successful: for instance when Cortés invaded what is now Mexico the population was around 25-30 million, 50 years later it was around 3 million, and most of this decline happened due to disease (Wikipedia).

So life on Earth exists in this continual arms-race: things try to attack organisms and organisms develop hugely sophisticated immune systems to deal with those attacks.  We're living, right now, through an example of what happens when an agent attacks us for which our immune system is not yet prepared: fortunately it's not going to kill that many of us.

So let's propose that abiogenesis happens on Earth, now.  There are really two options.

Whatever appears is, say, RNA-based, and as such is recognisable by the existing warring factions.  It has no defences and gets promptly attacked and eaten.
Whatever appears is based on some significantly different chemistry.  But whatever it is, it's harvesting energy from somewhere and making it into itself.  As soon as it starts harvesting enough energy it becomes interesting to existing organisms who would be quite interested in getting that energy for themselves, who pretty quickly evolve to being able to do so and eat it.

The third option is that whatever it is turns out to be so efficient in some way that it wins the fight with the existing stuff.  I suspect, without any kind of proof, that this option is absurdly unlikely to happen.

I think what is more likely to happen is that, any time some new way of chemically stashing energy happens, it becomes attractive to existing organisms, who evolve to be able to harvest that energy and do so, long before whatever thing has happened could be described as 'alive'.

In summary: Earth is almost certainly not currently hospitable to newly-generated life, at all, because the existing life will eat it, one way or the other.


Are sandstorms like regular storms? What's the difference between sandstorms and regular storms? Are they more than just strong wind within deserts?

There are two types of dust storms.

The first, a dust storm or "sandstorm", is associated with a synoptic scale feature (like a low pressure system).  Strong winds along air mass boundaries (i.e. cold front) create clouds of dust as sand, dust, or other particulates become suspended by turbulent eddies near the surface and aloft.

The second, the infamous "haboob" is associated with the cold pool of thunderstorms.  In the American desert southwest, during the summer monsoon, numerous thunderstorms develop. These thunderstorms produce rain or virga that cools the atmosphere beneath the thunderstorm as it evaporates.  Cool air sinks into what is known as a 'cold pool'. Cold pools generally strengthen as a thunderstorm decays.  Cold pools are air masses of cooler than environment air that spreads out like a pancake in all directions from beneath the thunderstorm.  These cold pools can create wind gust fronts between 40 and 70mph. Similar to larger dust storms, sand, dust or other particulates become suspended in the air and create the wall of dust.


Where on Earth does the atmosphere have the most $O_2$ concentration? Is there a map that shows the average oxygen concentration in the atmosphere? Seems to me that it would be where the most plants are but I wonder if population and industry make a difference in oxygen levels in a given area?

You may find bigger O2 levels at the upper layer of rich oceans -biologically talking-. There is Henry's Law, an equilibrium between gas pressures/concentrations of the ocean and the atmosphere, so you might find it at the contact between an ocean bacterial rich system and the atmosphere, but maybe on arboreal forests at light.

I have no data about O2 levels at both suggestions, atmosphere/ocean contact at a rich ocean system & a very rich arboreal forest on hot season. Just a caution for a possibly answer from a botanic. There may be maps about O2 levels at ocean surface but that at NASA and so and I am a student with no access to Science papers Muze and don't know how to get them. For arboreal system they can give you absolute maximum O2 levels registered, and then comparison.

The maximum level will happen at a certain time, and even I think satellites can measure gas levels the layer to search is about 1mm or so. maybe doing a comparison between highest O2 levels measured at the interface of a rich estuary or so and a tropical forest coming from local studies we find a non exactly answer but giving the environment where to find it and an approximate concentration.

There are those ozone/O3 layers with a very high concentration at industry zones,but i guess you ask for O2 gas. There are also hyperbolic conditions,eg at a Erlenmeyer flask of a lab, but I guess you are asking for levels on Earth's Atmosphere sensu stricto at a relative big atmosphere's surface/volume. I think others will appreciate more the question if you write eg "higher O2 concentration measured on an Earth's Atmosphere area despite labs or natural micro-layers" or something like that if that's you want to mean. Also sensu stricto more oxygen no matches with saturation (saturation is function of Temperature and Pressure).


Does snow melt on ice? I looked up nearly everywhere on the internet, but couldn't find any evidence that snow wouldn't melt because of ice. When I look it up, it instead tells me how salt can melt snow. I'm NOT looking up on salt!

This is the best weather-related StackExchange I could find, so I posted this question on this website. Also, I live in a hot desert climate, so it'd be hard to test it out in real life.

Yes, a layer of snow on top of ice can melt in some circumstances. For example, one active area of climate research involves analyzing the optical properties of sea ice as they relate to incoming solar radiation. In some studies (e.g., Ehn et al. 2004) this involves snow layered on top of ice, with the snow explicitly melting (and later refreezing) over the diurnal heating cycle in some cases.

As a more specific recent illustration, this phenomenon was also reported for the Canadian Lowell Glacier in July 2018 by NASA. Abnormally warm air temperatures (up to 29°C/84°F, according to nearby surface observations) over several days resulted in the melting of surface snow while the deeper ice below remained intact - a process referred to as ablation.


What principles do we consider when selecting an air pollution monitor location? I'm working on a project aiming at finding some potential point as a new air pollutant monitor site for a city to measure $SO_2$, $NO_2$, $PM_{2.5}$, etc.
After modeling the surface concentration of the area, here is my select standard:

The violation situation

  Finding the area which exceed the local air quality standard most in the modeling area.

The representation area

  Each modeling grid concentration is a time-series dataframe. Compute the
  spatial correlation coefficient (r) between one grid with surroundings area,
  we can get each grid's represent area assuming there is a cut-off coefficient $r_c$.

For example, 3 grid i, j, k in the city.
$r_(ij) > r_c$ → $grid_i$ can represent the  temporal variation of   $grid_j$
$r_(ik) < r_c$ → $grid_i$ can't represent the  temporal variation of $grid_k$
Population density

  Considering the environmental exposure healthy risks, I add the pop-ind data for each concentration grid

Here is my question

Are these principle enough for a monitoring site?
How to combine the results from the analysis based on multi-air pollutant data?
( In practice, one monitoring site often measure various air pollutants simultaneously, but my method is based on a specific type of air pollutant owing to the different emission source & chemical  reactivity)
Combining each site, We can get a monitoring network, how to estimate the network's strengths and weaknesses?

Each one of the monitor siting examples you list has a different purpose.  As you have listed, a monitor will be sited for air regulatory compliance purposes (e.g. determining the highest concentrations downwind of a major source), understanding the region (e.g. representative site in well-mixed location), or health exposure risks (e.g. densely populated areas). From a health and regulatory perspective, those types of site locations are sufficient.  However, you may want to consider other monitor site locations in your network that will help to evaluate the performance of the air quality model and assess the importance of various sources:

Monitors at a variety of elevations, so that vertical mixing can be evaluated (or use sondes)
Monitors both upwind and downwind of major sources, so that their contributions can be determined to a greater accuracy than represented in the original emissions inventory.
Monitors behind complex terrain, which affects transport, and can be difficult to model correctly.

Air quality modeling helps to fill in the gaps left by monitoring networks, since they are expensive to site and maintain.  Monitor networks are relatively sparse compared to the number of major source and receptor locations.  So, it is important to carefully consider each site location and pick ones that satisfy multiple criteria.  Satellite retrievals and local testimonials can be used to evaluate the initial value of your network.  However, you will benefit from quality controlling your model in the areas where your model performs poorly.

For reference, here is an example of how modeling and air monitors can be used together to make quality forecasts.  Environment and Climate Change Canada’s FireWork air quality (AQ) forecast system for North America with wildfire emissions has a post process called UMOS-AQ (see below).  The Canadian researchers built a system that modifies their air quality predictions based on recent surface monitor model/observations comparisons.  The Regional Air Quality Deterministic Prediction System (RAQDPS)uses GEM-MACH (Global Environmental Multi-scale - Modelling Air quality and CHemistry) and BlueSky Canada.  Here is a paper that describes the process.

  The RAQDPS includes other components besides GEM-MACH. One postprocessing product is the Updateable Model Output Statistics for Air Quality (UMOS-AQ) package, which applies statistics for bias correction to compensate for systematic AQ model errors and account for unresolved subgrid-scale phenomena at particular locations, namely the locations of AQ measurement stations (Wilson and Vallée, 2002; Antonopoulos et al., 2010; Moran et al., 2012). Hourly model forecasts of both pollutant concentrations and meteorological quantities at specific locations are combined with available hourly surface AQ measurements to generate location-specific hourly statistical forecasts for areas where AQ is measured. The location-specific O3, PM2.5, and NO2 concentrations calculated by UMOS-AQ are also the ones used in the calculation of the AQHI values that are disseminated to the public.


Is the "Kartenhoff" meteorite real? In the Bond movie "Spectre", there is a scene with a large meteorite on a stand:

Is this meteorite real, or is it based on a real meteorite? Are there actually any meteorites this large and perfect?

The story told in the movie about the meteorite is fictional. Here is a quote:

  The Kartenhoff, the oldest in human possession. The very meteorite
  which made this crater.

The Kartenhoff is a fictional meteorite (I found few sources about the movie saying so, this is the most comprehensive one). It is not the oldest known to humans, and it didn't make the crater shown in the movie. That crater is in fact the Gara Medouar, a crater-like formation created by erosion NOT a meteorite (here more info about it). This link will take you to a view of it on Google Maps.

All the above make me think that the object shown in the movie is not a real meteorite (maybe not even a real object and just crated digitally), however it is definitely inspired in a real one. As it have the color of an iron meteorite and its characteristic regmaglypts (indentations on the surface of a meteorite created by ablation while falling through the atmosphere). As mention by Trond Hansen in the comments, perhaps ir was inspired by the Willamette Meteorite. With 15 ton in weight, it is much larger than the one on the movie (it is 3x2 m) but have a remarkably similar shape and general aspect.

(Picture from Wikipedia commons, originally here)

In terms of shape, iron meteorites (that are a small fraction of all existing meteorites), tend to have very irregular shapes. Therefore, to find one as "perfect" as the one in the movie is unlikely, but not imposible. A Google Images search for iron meteorite, would show you in a glimpse the vast diversity of shapes, been generally irregular.

Now when it comes to size, they can be much larger than that. Some examples are the "El Chaco" meteorite found in Campo del Cielo, Argentina, weighting 37 ton.

(image taken from DESTINO INFINITO)

Or the largest iron meteorite know, the Hoba meteorite, with 66 tons.

(image taken from TripAdvisor and submitted by user huys25)

The reason we found meteorites up to about that size only, is because they are small enough to suffer a significant slow-down when falling though the atmosphere. Larger meteorites hit the surface so fast that the energy released vaporize the meteorite, so only the crater is left with no traces of the impacting body.


Newton's estimate of the age of the Earth I was reading many articles about estimates of the age of the Earth throughout the ages. I was dumbfounded when I read that Newton, arguably one of the greatest scientists ever to have ‘calculated’ the age of the earth, estimated that the Earth was created in 4000 BCE. Johannes Kepler arrived at a similar result. Which methods did these scientists use to arrive at such conclusions?

The estimates of Newton and Kepler, and the similar estimates of dozens of their contemporaries, were produced by treating the Bible as a historically accurate document and deriving a chronology from it. I think that a detailed explanation of their techniques would be off-topic for Earth Science, but the Wikipedia page on the Ussher Chronology (which provides probably the most famous biblically-based estimate of the Earth's age) goes into reasonable detail about the methods used for such calculations.


No sedimentation without water? I just found a video on sedimentary rock formation, and to my surprise, it stated that this only could occur in water! I always thought that any layer of matter, if buried deep underneath more matter, could form a sediment and become new rock. Am I completely wrong, or was the video simply not covering all bases?

I did Google it and check Wikipedia, but with my limited knowledge of the field, the results were inconclusive.

Not all sediments are deposited in water, but water is important in the formation of most sedimentary rocks.

If we're just thinking about the deposition of the sediment, then we don't necessarily need water. Some counterexamples are:

Aeolian sandstones, such as the Lower Permian Rotliegend sandstone of the North Sea. These are deposited by wind, not water.
Some types of sedimentary breccia, which are chiefly deposited by gravity, not water.
Tuff, which are deposited by gravity and wind, not water. They also undergo substantial compaction and lithification with or without water.

But deposited sediment does not a rock make. Once deposited and if buried, most sediment undergoes compaction and diagenesis, eventually lithifying — a fancy word for turning into a rock. Below the water table, the shallow crust is saturated with (mostly) saline water, and processes like dissolution and cementation are necessarily aqueous. So it's fair to say that water is essential in the formation of sedimentary rocks, on Earth anyway.

Footnote

You were right to be skeptical, by the way; the video is introductory material apparently intended for grade school audience, so you can't treat it like a textbook. And you can't even take a textbook as 'truth', especially when it comes to slippery things like definitions. Sometimes generalizations and simplifications help, sometimes they don't.


How to predict when contrails are likely to form over a specific location using public data? I saw the image below used as a click-attractor to an unrelated story about tourism, but found a larger version here.

Contrails, or water condensation trails happen when planes pass through the atmosphere under certain atmospheric conditions, presumably related mostly to humidity, pressure, and temperature.

If I wanted to write a contrail predictor script that would poll public sources of atmospheric data and check locations (and altitudes) to see if they were currently substantially more prone to contrail formation now than on an average day, what public sources of data might I look at, and what parameters would be the most important?

Actual formation also requires air traffic of course, but that's askable on a different SE site.

Source

As described here, condensation of cloud particles (i.e., contrail formation) will occur if the mixing between hot and moist exhaust from an aircraft engine and ambient environmental air results in the mixed air exceeding the ice saturation vapor pressure as its temperature changes. A conceptual diagram of this mixing process is shown here, for exhaust (parcel A) and environmental air (parcel B) with generic temperatures and saturation vapor pressures is shown here:

However, this would require knowledge of these specific temperatures and corresponding saturation vapor pressures. More practically, contrail prediction often just assumes that the air at altitudes where jets typically cruise (commonly, though not always, above 8 km/26,000 ft and at air temperatures below -40°C) is near or above supersaturation with respect to ice. This assumption is used operationally, for example, in NASA's publicly-available persistent contrail forecast. Note that the first source indicates that low wind speeds are also useful in identifying likely regions of persistent contrails.

Several sources of data may be useful in constructing similar analyses or forecasts and comparing to what might be expected on an average day, based on the local climatology. Observational data from radiosondes (i.e., weather balloons with instruments measuring temperature, moisture, and winds) is available globally in near-real time. This provides actual measurements of weather conditions through the relevant altitudes for contrail formation, and is particularly useful if measurements are needed relatively close to a radiosonde launch site.

For broader coverage in both space and time, the US National Oceanic and Atmospheric Administration provides archives of past weather analyses and operational forecast model output that can be requested by the general public. These datasets contain gridded model output with common parameters at various levels through the atmosphere on a national to global scale. While these datasets do not strictly consist of observed measurements, they are useful for analyses extending beyond the relatively limited set of observations available in most circumstances. Output from various operational forecast models is available for near-current or future conditions, whereas the reanalysis datasets provide similar information obtained from model analyses of past weather.

For a given location, the reanalysis datasets can be used to identify climatological temperature, moisture, or wind characteristics for a given location and date or season. Information from radiosondes or model forecasts can then be used to identify how conditions at a near-current (or future) time compare to these "average" conditions.


Large Igneous Provinces are like Lunar Mare? Would Large Igneous Provinces like the Deccan Traps have looked like ancient lunar Mare from space? Glowing lava oceans shinning in the night?

Are these two things similar in nature? Would smoke from these regions fill the atmosphere with a haze that would hide the view from space?

I disagree with Michael about the "not as large as the lunar mare" part. Head and Wilson (1992) mention that the "total area of exposed mare deposits is about 6.3 millions km2" (17 % of the Moon's surface area). They estimated a total volume of 10 millions km3. The largest mare, Oceanus Procellarum, covers about 4 millions km2.

These values are quite comparable with Large Igneous Provinces (LIPs) in terms of area, and are even one order of magnitude lower in terms of volume. From the Encyclopedia of Volcanoes:

  The composite Ontong-Java-Manihiki-Hikurangi plateau covers 3.5
  million km2 with an estimated volume 59-77 million
  km3. [...] The Kerguelen plateau in the southern Indian
  Ocean is the second largest LIP, covering 2.3 million km2
  with a volume of 15 million km3 [...] Not all LIPs are
  oceanic plateaus; for example, the North Atlantic volcanic province,
  derived from a hot spot presently centered beneath Iceland, has an
  area of 1.3 million km2 [...] Also notable are the Deccan
  traps in India (1.8 million km2/9.3 million
  km3).

If lunar maria seem that large from Earth, it's only because the Moon is small!

But to know if lunar maria or LIPs would have looked like "glowing lava oceans shinning in the night", we need to look at emplacement rates rather than just areas and volumes. From the same chapter, one can calculate LIP emplacement rates of ~3-13 km3 per year. It may seem quite low (for comparison, ocean ridges quietly produce ~20 km3 per year), but it is an average output rate over a few million years. As noted on largeigneousprovinces.org, their might be pulses of magmatic activity, with peaks in production rate. This is exactly what's been inferred for lunar maria by Wilson and Head (2017): even if the average output rate has been calculated at a very low 0.01 km3 per year, they found that some flows could have been emplaced with rates up to 106 m3s-1!

As to whether this would have been visible from space: define "from space"! From low Earth orbit like the ISS? From the Moon itself? :)


What is this strange fossil I found? I found this weird fossil rock and I am wondering if anybody could help identify what could have made the imprint in it or what kind of rock it is?

Looks like a sand dollar fossil.  Note the pentagonal shape in the middle.

Source: fossilera.com


What is the cause of the jet streams? Jet streams are fast-flowing currents of air in our earth's atmosphere. An enormous amount of energy is necessary to keep a jet stream going. Where does this come from and why?

The subtropical jetstream
The subtropical jetstream can be explained with angular momentum arguments.  In an idealized circulation model of the atmosphere, there is a hadley cell that circulates upward at the equator, poleward along the tropical tropopause, downward around 30 N/S and equatorward at the surface.  Parcels rising at the equator have a fair bit of angular momentum from the rotation of the Earth.  As these parcels move poleward they tend to conserve this momentum and this manifests as a westerly wind.
The subtropical jet is weak in the summer (ITZC and maxmium solar heating disrupt the hadley cell in that hemisphere), strong in the winter and is generally fixed at around 30 N/S and at a higher altitude than the polar jet.
The polar jetstream
The polar jetstream draws its energy from horizontal temperature gradients in the lower troposphere as a consequence of the thermal wind.  To understand the thermal wind, consider a temperature gradient at the surface, cold toward the pole and warm toward the equator.  Over the cold air, heights of pressure levels will be lower than normal and over the warm air the heights will be higher than normal.  If you look at any pressure level this will result in a height gradient with higher heights toward the equatot.  This gradient will increase with height.  The geostrophic wind is proportional to the height gradient and thus increases with height.  The polar jet exists where these surface temperature gradients are strong but above them around 250 mb.
You will find the polar jet wandering around and associated with the strong surface fronts that come out out of the poles and into the mid-latitudes.  It will be stronger in the winter when the fronts are stronger.  During the summer the jet will remain at higher latitudes and in the winter can dip well into the mid-latitudes.


Are we at the beginning of a Heinrich Event? Does our current weather trend properly reflect a Heinrich Event?  It seems like the drastic weather swings are what I would expect but I realize that is not definitive.  I don't see the term bandied about as I would expect.  Are there other criteria missing?

Definitely not.

A Heinrich event requires massive ice sheets to grow and then collapse in the Northern hemisphere. The large outflow of icebergs that would result form such collapse would deliver fresh water and debris to the North Atlantic, which is what constitutes a Heinrich event. These events are detected by existence of deposits of ice rafted debris and dropstones in the sea floor.

Example of a dropstone carried by an iceberg, dropped on the sea floor, and then embedded in sea floor sediments (image taken from snowballearth.com)

Current ice masses in the Northern hemisphere are tiny compared with those that generated all recorded Heinrich events.

Something similar could happen now further south if East Antarctica collapses. However the circulation pattern in the Antarctic ocean limit significantly the distance that icebergs can travel.


Is there a map that displays every country at its correct relative size? I know that the standard Mercator projection is completely wrong when it comes to the relative sizes of countries (Greenland appears relatively much larger than in reality, for example). AFAIK they do this because the focus of Mercator isn't realism, but to keep routing working correctly (ships and airplanes for example).

But: is there a map that correctly displays the relative size of every country?

Yes.
Every equal-area map displays all countries (and other areas) in their correct relative size. Inevitably, they don't show the correct shape (unless you're looking at a globe). Personally, my favourite projections are pseudocylidrical equal-area projections, such as:
Equal Earth projection

Mollweide projection

Eckert IV projection

Tobler hyperelliptical projection

There are others; see this list on Wikipedia.
The pseudocylindrical part means that lines of latitude are horizontal lines. I think that for any non-polar projection in the Earth sciences, this is a highly desirable property. A truly cylindrical projection means a projection onto a rectangle, but that just makes distortions even worse than they need to be.  There are other practical considerations, such as whether the poles are points or lines and whether the outer lines of longitude are ellipsoids or sinusoids, which differ between the various examples I've listed above.


Why do more tornadoes happen late in the day? According to the graph below, which appears to be sourced from the US National Oceanic and Atmospheric Administration, more tornadoes happen late in the day - why is this?

There are two factors at work here:

Actual occurrence of tornadoes,
Reports of tornadoes.

Tornadoes are primarily associated with supercell thunderstorms, though they can also be associated with landfalling tropical cyclones, squall lines and bow echoes.  Thunderstorms are favored in the afternoon to early evening hours as this is when integrated solar heating throughout the day has warmed the boundary layer enough to kickstart convection (through reaching the convective temperature or eroding the capping inversion).  Because of this, supercells are going to tend to initiate in the mid to late afternoon and if they produce tornadoes it will be in the timeframe maximized in your graph.

The tornado record is far from perfect and is based on verification of tornado damage.  That damage will only be surveyed if a potential tornado is reported or radar strongly suggested that one may have occurred.  A small tornado in the middle of nowhere from an unimpressive storm at night surely may exist, but a record of it may not.  This is also true of middle-of-nowhere tornadoes during the day, but those may have a slightly higher chance of being reported by a storm chaser.  No one smart chases at night.


Did the impact event that caused the Chicxulub-Crater definitively and single-handedly cause the Cretaceous-Paleogene extinction? Opinions abound on the web. What is the state of the current science regarding this theory and what is the best evidence? Is the theory gaining or losing traction? If it's losing what's the best of the alternatives? Perhaps there was more than one major cause. What changed peoples' minds either way pro or con?

No, it did not definitively single-handedly cause the KT mass extinction event. Around the same time, the Deccan Traps Large Igneous Province (India) was being emplaced. Flood volcanism has been associated with other mass extinctions, due to the impact on climate, sunlight at the surface, etc, of the output of huge volumes of sulphur-based gases.

The Chicxulub impact probably didn't hurt the extinction, but the large particulate material it distributed in the atmosphere would have sedimented out again entirely within a handful of years. Meanwhile, the Deccan Traps contain sediment layers intercalated between lava flows, some of which contain fossilised dinosaur eggs.

The reasons for mass extinctions (and whether they actually occur at all, as distinct identifiable events) remain poorly understood, but we're pretty sure the meteorite impact wasn't the only thing that did for the dinosaurs.


Percentage of dry land surface with sea level elevation lower than 1 km Being this my first questions on this .SE I hope that the topic is appropriate.

I've been told that 99% of the living species on earth live in between -200m and 800m above sea level, this made me just wonder how much of earth surface lies in this elevation span, but I couldn't find the answer googling.

1) Does anybody have a source to check what percentage of dry land has sea level elevation lower than 1 km (or 800m, or in between -200m and 800m...)?

2) How should I interpret the information given to me about the number of living species? I would just say for the 99% of the living species the intersection between the "natural habitat" and the altitude "-200m - 800m" is non empty, is it correct? Is there a source where I can check this information?

Thanks in advance!!

(Fig. 2.4 of Deep-Sea Biology: A Natural History of Organisms at the Deep-Sea Floor)

8.3% of the Earth's surface is above 1 kilometer.

This corresponds to about 29% of the land area.

So 71% of the land area is below 1 km.


When a tectonic plate subducts, does any of the subducted material melt, or is it just the mantle above the subducted slab that melts? I know that water released from oceanic crust causes melting of the mantle in subduction zones, but does any part of the subducted slab melt as well - such as the sediments on the slab or the basalt?  If so, how do we know what material was melted so deep in the subsurface?

This is a very good question Inkenbrandt. It is quite common for even some graduate students to think that the majority of partial-melting comes from the slab: when it is the the mantle above the fore-arc, in the volcanic region, where most of the partial melting occurs.

Lets think about this mathematically: you say yourself that you realize that subduction hydrates the mantle, lowering the solidus and allowing for more partial melting, so what happens to the slab? Well it has to dehydrate, making it much harder to melt the slab. So to answer your question: Probably a very small amount in the upper mantle, but if you are a mantle plume believer, the partial melting of a slab provides a great mechanism to 1) displace hot mantle so it rises and 2) a source of meltable material.  The hydration of the mantle from subduction happens on a much much faster timescale than the melting of a subducted slab. In this paper, the authors provide a mechanism for the volcanism in Yellowstone that relies on two things: the Farallon plate being ripped apart by rapid mantle flow and the cut off piece of the subducted slab to melt. Geochemical data supports this, and it turns out this is a very important paper.

I hope this answers your question. In geodynamic models interested in examining the melting structure at subduction zones, we largely ignore slab melting unless we are specifically looking at it. For almost everything else, it seems to be pretty negligible.


Are there any geology only related educational institutions? I'm not looking for college recommendations or which is the best, so I'm not asking for opinions on which institutions are the best. What I would like to know is if there are specific places that someone could go where they can just focus on geology related fields only. And only take classes that pertained to acquiring enough education to work in a geology related field.

Why would you limit yourself? You could just go to a regular university and enroll in the geology degree program. In some countries (like Germany) you would then only take courses necessary to become a geologist (including the math and physics you need to understand for it). In some other countries (e.g, the United States) you'd have to take other courses for "breadth requirements" as well, but most of your courses would still be in geology.

The fact that a regular university also offers courses in other areas doesn't really matter that much, or does it?


Is it possible to create clouds by pumping water into volcanoes? Suddenly, there is this idea in my mind that if an important effect of global warming is rainfall reduction and drought, is it possible to use volcanoes as water vaporizers (regardless of costs)?

Is it possible to create clouds by pumping water into volcanoes?

Maybe, but it's a really bad idea. Here's why:

Volcanoes are unexpected and change with time. You can waste two years building a facility that does it, only for the volcano to cease being active and become dormant. Alternatively, the volcano might blow up and destroy your infrastructure.
You actually need lava to do so. Very few volcanoes have persistent lava lakes. Two are in tropical islands (Vanuatu, Hawaii), two are in rainforests (Nicaragua, DRC), one is in Antarctica, and only one is in a desert where it would actually be somewhat useful (Ethiopia).
In the absence of a lava lake, you can pump the water into the underground magma chamber and hope that it escapes in the form of steam. This is a bad bad bad idea, because you can cause a phreatic or phreatomagmatic eruption. Here's an example:

https://youtu.be/hjOnh_QRd0A

You need water. If you have fresh water, you better use that water to solve the drought directly instead of pumping it into a volcano. If you're using sea water, you have the problem of laze. At the moment the opposite is happening: Kilauea in Hawaii is erupting lava that reaches the ocean. The reaction between the hot lava and the sea water creates releases acid into the air. Bad idea. Here's how it looks like:

https://youtu.be/8SF5LQO4T_4

If somehow you managed to avoid exploding the volcano or creating acid rain, you would rapidly cool the top layer of the lava, solidifying it into rock. Rock is a poor thermal conductor, so you're forming a lid on top of the lava, making the thing much less effective.

  if an important effect of global warming is rainfall reduction and
  drought...(regardless of costs)

Just use desalination. A very effective yet expensive way to get fresh water.


How does the composition of volcanic rock change as it makes its ascent towards the surface? A schematic for the fluid mechanics of a volcano is represented below.

Graciously borrowed from Figure 1 of the reference cited below

From the caption of that figure:

  During explosive eruptions, bubble walls rupture catastrophically at the
  fragmentation surface. The released gas expands rapidly and magma ascent changes from a viscous melt with suspended bubbles to a gas flow with suspended magma fragments.

My assumption is that this boundary between the magma column and the steam above it is critical to the crystallization of the minerals to form the volcanic rock.

Does the composition of the volcanic rock change drastically according to the distance between the magma column and the mouth of the volcano at the time the rock is formed?
(Or) do the rocks melt and recrystallize frequently as the boundary moves, only attaining their final composition before they are ejected into the air?
How important is the steam/air interface at the top of the volcano to the rock's formation?

I realize this is going to change based on the composition of the magma itself, but I'm looking for the behavior of an "average" rock species, though specific examples are great, too.

  Reference:

  Gonnermann, H.M. and Manga, M. (2007). The fluid mechanics inside a volcano. Annu. Rev. Fluid Mech, 39, 321–56. [PDF] [DOI].

Does the composition of the volcanic rock change drastically according to the distance between the magma column and the mouth of the volcano at the time the rock is formed?

The metal composition of the magma will not change drastically. By metal I mean the basic constituents of the rock: mostly silicon but also iron, calcium, aluminum, magnesium, etc. I will add that there are processes that can affect metal composition (chiefly mineral fractionation) but I think its influence is minor when you're talking the the uppermost part of the volcano where it erupts.

What can and does change is the volatile composition. The magma is depleted of gases. Take for example a bottle of coke. When you open it, the CO2 bubbles out. The coke itself remains coke, but its chemistry changes a bit (and it tastes bad) because the CO2 is out. The magma may also change oxidation state. This, together with the volatile degassing may eventually affect the minerals that crystallise from the magma.

  (Or) do the rocks melt and recrystallize frequently as the boundary moves, only attaining their final composition before they are ejected into the air?

No. Once a rock crystallises you are going to need quite a lot of energy to melt it again, and this is not a likely process to occur in a system open to the atmosphere where heat is free to leave the volcanic system.