Are mantle plumes distributed around the core randomly or in a known pattern? Background:

The theory of mantle plumes is useful (although controversial) in explaining the occurrence of intra-plate volcanoes.  The website here suggests that "hotspots" exist in fixed locations relative to one another in the core, and thus on a planet like Mars, where there are no tectonic plates, massive volcanoes will form above these "hotspots", but on Earth moving tectonic plates give rise to strings of volcanoes above underlying "hotspots".  The quote below is from the linked website:

  The image on the right shows some of the other "hot spots" scattered
  about the floor of the Pacific Ocean. It is intriguing, that portions
  of island chains of similar age are parallel to each other. This
  suggest that the "hot spots" themselves remain mostly fixed with
  respect to each other, otherwise the chains might be expect to be
  curvilinear, or trend in different directions as the "hot spots"
  generating them moved independantly.

Question:

Assuming that mantle plumes remain in fixed locations relative to one another at the core, is there any known pattern for how these mantle plumes are distributed relative to one another (or to fixed landmarks, e.g. axis of rotation), or do they appear to be distributed randomly?

First of all, the idea of a fixed "hotspot" reference frame is (albeit reluctantly) falling out of favour on a geological timescale; see e.g. http://onlinelibrary.wiley.com/doi/10.1029/GM121p0339/summary ("As studies of plate motions have advanced, however, it has become clear that the global hotspots do not stay fixed relative to each other...") and http://adsabs.harvard.edu/abs/2010AGUFM.U51A0010S ("Hotspot reference frames can only be confidently tied back to about 130 Ma and there is evidence that mantle plumes have moved relative to each other.") Global Moving Hotspot Reference Frames are in the process of being built, see e.g. http://adsabs.harvard.edu/abs/2010AGUFMGP24A..03D

Secondly, identifiable patterns in the distribution of mantle plumes are an area of active research: this year's EGU medal for outstanding young scientist was awarded to Rhodri Davies for his work in this area. Key to most arguments are the presence of Large Low Shear Velocity Provinces (LLSVPs) in the lower mantle, historically assumed to be "slab graveyards" (thermochemical piles created when subducting slabs pool in the lower mantle). The suggestion that these areas were both chemically and thermally distinct from surrounding mantle focussed attention on their margins as a highly probable location for the formation of mantle plumes. However, recent findings (by and cited extensively by Rhodri Davies) increasingly support the idea that these piles are thermal features only, with no chemical difference to surrounding mantle.

Rhodri Davies' research revisits past studies that found hotspots were concentrated along the edges of LLSVPs, and has thoroughly demonstrated that these conclusions are not robust, e.g. to choice of hotspot catalogue, prescribed angular search tolerance (between surface expression and imaged margin), (arbitrary) depth of analysis, and (arbitrary) shear-wave velocity contour. Via Monte Carlo simulations he rules out hotspots being drawn from the margins of the Pacific LLSVP, but cannot rule out the possibility that hotspots are preferentially drawn from the entire areal extent of LLSVPs in both the Pacific and the Atlantic.

RD & his team conclude that present-day hotspot locations are controlled by ancient subduction, rather than the current margins of LLSVPs - which are demonstrated via dynamical simulations to be mobile, even in the presence of dense chemical heterogeneity.

(As a side note, both "hotspots" and "mantle plume" are contested terminology, it's true - but the vast majority of geoscientists believe that mantle plumes do exist. There is complexity to that view, in that the consensus does not require all intraplate volcanism to be the result of atypically hot mantle -- but the idea that mantle plumes simply do not exist, as espoused by mantleplumes.org, does not have wide acceptance.)


Difference between pyrite oxidation and dissolution I've seen papers use oxidation and dissolution of pyrite. Are these two processes the same? I was always under the impression that pyrite does not dissolve easily. What is the difference between oxidation and dissolution of pyrite?

Oxidation and dissolution are not the same processes, but they are related when discussing the breakdown of pyrite in near surface environments.

Dissolution is a process(*1) in which the chemical components of a solid become part of a liquid, in the liquid state. For example, take fresh water and salt. Now dissolve the salt in the fresh water. Instead of having NaCl and H2O, you now have H2O with Na+ and Cl- ions floating in it, not solid anymore. This is not something happens easily with pyrite. You can't just dump FeS2 in water and expect to have Fe2+ and S(2)- in the water. This is because the sulfur is in the reduced state, as sulfide. The more soluble form of sulfur is sulfate, the oxidised form.

Oxidation is a process in which a compound or element bonds with (more) oxygen(*2). In order to dissolve pyrite, you have to convert the insoluble sulfide to soluble sulfate. In your previous question you noted the oxidation reaction for pyrite:

$\ce{FeS2(s) + 15/4 O2(aq) + 7/2 H2O → Fe(OH)3(s) + 4H+(aq) + 2SO4^2-(aq)}$

You start with pyrite in the solid form, and you end up with sulfate (sulfur bonded to four oxygens). The leftover iron is deposited as insoluble iron oxides and hydroxides (basically - rust), and you're also generating a bunch of protons that make everything acidic (i.e. acid mine drainage).

*1 - strictly speaking, dissolution doesn't have to be a solid in a liquid. It can be anything in anything.

*2 - actually oxidation is an electron transfer reaction and can occur with no oxygen involved at all.


What is the cause of temporary smell and black color of underground water? We have a well (about 1200KM away from sea and 60 meter deep), the water when taken out has slightly dark color and has smell. But strangely in about 12 hours the smell and black color vanishes and water becomes odorless and clear without leaving any residues.

What can be possible cause, are there any known underground impurities that change with something like sunlight or air exposure?

Organic impurities and sulfides don't disappear like this, can someone help with details of this kind of water impurity.

This is due to the presence of iron sulfide in the water. The iron sulfide oxidizes and goes into solution. Ferrous iron oxidizes to ferric iron. Depending on the water chemistry, this commonly precipitates out as orange-coloured iron oxyhydroxide, but that does not seem to be occuring in your case, otherwise you would see it. When it does happen, the pH of the water drops, as seen in acid mine drainage.

The sulfide may be volatilized as hydrogen sulfide which smells, or it too may oxidize and volatilize as sulfur dioxide (rotten egg smell). It can continue to oxidize to sulfate.

The iron sulfide may be present in the aquifer or it may be formed by microbial activity in your well. In the latter case, treating the well with bleach can solve the problem, at least temporarily. Be sure to treat all the piping, too. If possible, install a backflow preventer so water doesn't flow back down the well.


Antarctic and arctic meltwater is "bad" because it's dark, but why is transparent liquid on white stuff so dark? The Washington Post's Antarctic heat wave melted 20 percent of an island’s snow cover in days, caused melt ponds to proliferate includes the figure below of meltwater ponds on top of snow/ice.

The article is a good read, but my question is one of optics, namely what makes a pond of meltwater (essentially pure water) on top of something so white become so dark?

It increases sunlight absorption and heating, which in this case is "bad" but what's the physics or phenomena behind this that makes these so dark in the first place?

If I understand correctly, even shallow ponds or puddles of water can significantly reduce albedo, increase absorption and induce further melting, sometimes in a "runaway" manner. So I don't think it's bulk absorption by the water or contaminants, I think there's something more interesting going on.

  Melt ponds on the Antarctic Peninsula’s George VI Ice Shelf on Jan. 19, 2020. (NASA)

Water has lowest EM absorption in the blue part of light spectrum and increases rapidly  towards both UV and red parts of spectrum.

As a result in visible light water is blue. Same goes for the ice as it has very similar absorption spectrum.

While there is a lot of white in the picture, all of it is a thin snow cover on top of blue ice. Once the snow melts you get a blue water on top of thick layer of transparent blue ice that combined absorb most of the light making ponds looks exceptionally dark. Water would be so much lighter in colour if, for example, instead of transparent ice, you'd have sand on the bottom.


What type of rock formed first on earth and which rock is the oldest? It could be sedimantary or metamorphic rock or intrusive igneous rock

Does look a bit like a homework question..

First rock

Igneous rocks would have formed first, obviously, although if we consider the pre-Mars-forming collision Earth, then the process of cold accretion could have initially formed metamorphic rocks at the center of the early planetoid..

And that planetoid would have to be considered sedimentary, formed out of dust particles.

So what the first rock is depends on how you define Earth, or the point at which a specific planetoid would be positively identified as Earth.

Oldest Rock

First, are we talking about the oldest identifiable mineral grain (Zircons, about 4.4 billion years old), or the oldest complete rock (Isua Greenstone Belt, Greenland, 3.8 billion years). The first may qualify as part of a sedimentary rock, the second is metamorphic - but with a volcanic original rock.

And, of course, there could well be a meteorite out there - yet to be discovered or dated - that originates from outside the solar system and is therefore older than the solar system. That would qualify as the oldest rock on the planet.


What are the latest developments about global stilling? I recently learn about "global stilling", i.e. the fact that surface wind speed tends to decrease since the 80s. It was in this article, but it's from 2010. The Wikipedia page also seems a bit outdated, as it mentions the STILLING project as "current" (it ended in 2018). Said project has only one publication, although interesting (it suggests that part of the trend is an artefact from anemometers not ageing well!). So I was wondering what were the latest developments in this field? Do we now have a better idea of what could cause this phenomenon?

It seems to be a thing of the past. Apparently around 2010 the 30 years calming trend reversed. Since then, wind speeds and wave heights are picking up quickly, possibly in a decadal variation pattern.
Young et. al. 2010 Global Trends in Wind Speed and Wave Height
Possible application for the planning of wind turbines:
Zhenzhong Zeng et.al. 2019 A reversal in global terrestrial stilling and its implications for wind energy production
From the abstract of the latter:

... we use wind data from in situ stations worldwide to show that the stilling reversed around 2010 and that global wind speeds over land have recovered. We illustrate that decadal-scale variations of near-surface wind are probably determined by internal decadal ocean–atmosphere oscillations, rather than by vegetation growth and/or urbanization as hypothesized previously. ...

Similar observations of an increasing trend over ocean surfaces, overlapping with the period of global stilling over land.
Ching Wei Zheng et.al. 2016 Global oceanic wind speed trends
Can only read the abstract of the latter. Would be interesting to investigate further the reason for the differing observation and modelling of sea- and land-wind speeds during the term.


How thin is our atmosphere relative to the size of Earth? According to the GRC NASA website, Earth's atmosphere is a thin sheet of air extending from the surface of the Earth to the edge of space. Some videos on youtube also point out that if the Earth is the size of an apple, its atmosphere is just as thick as the apple's skin. But when we look at some diagrams, Earth's atmosphere is thick. For instance, when someone says that the atmosphere is a thin sheet of air, does he/she take in to account the thick layer thermosphere or exosphere? Or is it just that the diagrams we commonly see have inaccurate visual representation?

The answer to your question depends on where one defines the edge of the atmosphere.
The Earth's atmosphere is layered. The thickness, density of composition of each layer varies. The five layers are:

Exosphere: 700 to 10,000 km (440 to 6,200 miles)
Thermosphere: 80 to 700 km (50 to 440 miles)
Mesosphere: 50 to 80 km (31 to 50 miles)
Stratosphere: 12 to 50 km (7 to 31 miles)
Troposphere: 0 to 12 km (0 to 7 miles)

Being the outermost layer, the exosphere is the layer with the most nebulous upper boundary. It is also the layer with the lowest density and it is primarily composed of very low density hydrogen and helium, particularly in the outer/upper reaches.
Because of the low density of the exosphere and also because the Karman Line, which is 100 km above the Earth, which the line designated where Earth ends and outer space begins, the exosphere is sometimes ignored.
So if one accepts the top of the Thermosphere as being the effective upper boundary of the atmosphere the effective thickness of the atmosphere is only 700 km compared the radius of the Earth, which is 6370 km.


tectonic faults catalog for plot I looking for a catalog (ideally in a ASCII file) of the major tectonic faults on earth, in order to plot some of them on a map

Any suggestion ?

A good database of tectonic plates is available at the Institute for Geophysics of the University of Texas. The database includes present conditions and past and future conditions. They provide ASCII files in their ftp site.
 Source

Another option is the data from Peter Bird at UCLA that he described in his article "An updated digital model of plate boundaries", $G^3$, 2003. He provides the data in ASCII format in their ftp site (they include a readme file with the description of the data).


The seriousness of global warming/ climate change? Why is such an emphasis placed on sea level rise?? As this can be devastating in itself, it can be looked at as a great economic opportunity to put people to work preparing our coastal areas for the inevitable, but slowly progressing future situation.

Isn't the disruption of ocean currents (as portrayed in "Day After Tomorrow" or in Peter Ward's Medea hypothesis (hydrogen sulfide poisoning)) even more serious?

There are also major consequences such as fresh water shortage, ocean acidification, decrease in biodiversity, etc. etc. Some of the worst consequences may be ones we haven't even thought of yet.

I feel that we are oversimplifying the message to the public by focusing on sea level rise. Am I wrong??

Try asking Pacific Islanders that question.  Most Pacific islands are only a few meters above sea. Some have already had their fresh water sources, destroyed by rising sea levels. Most of these people are in danger of losing the land beneath their feet & becoming environmental refugees.

Then there is Bangladesh, a low lying country, without any hard rock, where gravel is made by baking clay. It already is losing significant parts of the country to coastal erosion, some of which was farmland.

If you're not concerned about Pacific islanders or Bangladeshis, then how about Europeans? Significant portions of the Netherlands are already below sea level, sustained by a system of dykes and sea walls. Some of theses are in danger of being overwhelmed by rising oceans and the land being lost.

If you're not concerned about Europeans, then how about Americans? Will Americans want to pay for system of sea walls to protect New Orleans? It already has issues trying to build a wall along its border with Mexico, but that's another issue.

Rising sea levels will inundate land with salty sea water and it cause the lose of softer coastal terrain to erosion, such as limestone cliff terrain in Britain.

The other thing that rarely gets mentioned is the affect that lost coastal habitats, such as mangroves, will have on non-human life. As if human life is the only form of life that matters on the planet and that nature is irrelevant. Humans need nature more than nature needs humans. Some of these habitats are critical to the some fish species and other life forms.


Velocity from time and depth seismic images I have a seismic dataset that contains a depth-migrated seismic (amplitude) volume in depth and then the exact same volume converted to time using the migration velocities. Unfortunately, I do not have the velocity volume used to do the conversion.

How can I extract the velocity volume using only these two (amplitude) volumes?

Since the signals are exactly the same, just stretched and squeezed, I believe the solution will require something like dynamic time warping but I don't have enough experience with this to make it work.

Since each trace in the volume is converted independently, this reduces to a 1D problem. An optimal solution for a single trace can be used to solve the entire 3D volume (unless there is a lot of error and then we can have lateral instability, but I can live with that).

I will eventually need to code it in MATLAB for application on sgy-formatted data.

Disclaimer: It a very crude way to do it.! Take it as the last resort.

It assumes that you know velocity for the shallower reflectors/layers. I will explain for one reflector and you can extend for deeper reflectors.

Step 1. You slice out the reflector event (in a trace) you want to find the velocity for.

Step 2. Take a correlation with the respective trace in other time/depth domain part and find the max correlation time/depth. Here you may assume this time corresponds to the respective depth so you get total travel time.

Step 3. At this point you know the interval velocities for layers at the shallower depth, so you can find out the interval velocity for this layer.

You start from the top and continue to bottom side. You may treat it as layer stripping.


Snow from Fire: Could graupel, or even snow, fall from pyrocumulus clouds? Pyrocumulus clouds often form in areas that experience prolonged fire conditions, particularly forest fires, but are also associated with volcanic eruptions and even nuclear explosions.  This question focuses on forest fire origins.

An example of what one looks from above, is below:

Caption: Pyrocumulus cloud, above the Oregon Gulch fire in Oregon & California, 2014. Aircraft is a F-15C Eagle. Image source

The general idea of how pyrocumulus clouds are formed is quite well known, and its relationship with a 'firestorm' is, in a simplistic way, is shown below:

Caption: Firestorm: fire (1), updraft (2), strong gusty winds (3) (A) pyrocumulonimbus cloud.Image source

Pyrocumulus and related pyroconvective clouds have been known to have caused severe hail to fall.  An example reported in the Earth Observatory: Russian Firestorm: Finding a Fire Cloud from Space, from the Canberra, Australia fires:

  Called pyrocumulonimbus clouds, the clouds are capable of dangerous lightning, hail, and strong winds. One such firestorm in 2003 pelted Canberra, Australia, with large, soot-darkened hail, produced a damaging tornado

(Point of reference: Canberra is Australia's capital city, I was there at the time).

Could graupel, or even snow, fall from pyrocumulus clouds?

(It would be good if examples from real life or models could be provided, if possible)

It is likely snowing somewhere in these clouds and graupel exist transiently on their way to becoming hail, but its not likely that you will see either at the surface.

You can make a first order approximation of a pyrocumulus cloud by putting a very strong heat source at the surface in an environment otherwise favorable for severe convection.  What you'll observe is that parcels will easily reach the LFC and you will have tons of CAPE owing to the high surface temperature.  The maximum theoretical updraft velocity is a function of CAPE and so we can expect exceptionally strong updrafts.  This can be confirmed by the observation of severe hail falling from these clouds -- the weight the hailstones can attain increases with updraft velocity.  Because we can observe hail we know that normal moist processes we expect in cumulonimbus clouds are working.

In any mid-latitude cumulonimbus cloud the precipitation starts out as snow. What we experience on the ground is dependent on the temperature profile and this snow either makes it to the surface, melts to be become rain,  melts then becomes supercooled (freezing rain) or melts and refreezes (sleet).  Another option is that the precipitation sublimates or evaporates and never reaches the ground.  The fire driving the storm is likely producing a warm, dry environment at low levels and promoting evaporation of any precipitation.

Graupel will exist as riming and accretion processes are at work, but because of the strong updraft you will end up with hail production and hail at the surface.

To take this approximation into reality you also need to take into account how the fire is modifying the low and mid levels and what kind of aerosols are being emitted by the fire.  The aerosol content could play heavily into the microphysics and precipitation production, but this is not my area of expertise so I won't speculate on the possibilities.


Lightning activity day curve - why it has high and narrow peak? Atmospheric potential gradient changes during the day, as different areas of lightning activity come under Sun.

This illustration from "The Carnegie Curve" by R. Giles Harrison shows contribution of different regions.

Why region curves are so narrow and high - about 6 hours wide if lightning storms go day and night? As I understand most of cloud energy is stored in latent steam heat, so why sunlight makes such big contribution?

I think the simple answer to your question is that sunlight widens the potential area for storms by producing a better convective environment, whereas nocturnal storms are highly localized based on climatological factors.
While a minority of storms do occur overnight due to local mesoscale features such as nocturnal low-level jets, the majority of storms will occur because of convective forcing. To have a convective environment, you have to have a parcel of air that is warmer than that of the environment it is traveling through, and that is what gives you lift. The easiest way for that to happen is to have parcels rise up from the ground at the peak heating of the day while the ground is much warmer than the air above it.
In an older (and still infinitely useful) thought process of meteorology, there is a temperature known as the "convective temperature" that can be gotten from a Skew-T diagram. It takes into account the dewpoint and vertical temperature profile of the atmosphere and produces a temperature at which the surface level has to get to in order to set off thunderstorms. The best way to get to and beyond that temperature is through the heating of the sun. Additionally, when the air is warmed through heating from the sun it makes the environment ripe for convective initiation through triggers such as fronts.


ERA5 mean evaporation rates data - Why is that negative? Please, let me know if this question is too technical/specific for Earth Science. In case, I will remove it and eventually post it elsewhere.

I am processing some data extracted from ERA5 to set up a large scale hydrological model. We are calculating the evapotranspiration using the typical P-M formula, using as input the usual variables: wind speed, solar radiation, temperature, pressure, relative humidity and so on. In order to check the consistency of our calculations with the  variables provided by the ECMWF, I downloaded also some evaporation related variables. I'm struggling to understand the data related to the mean evaporation rate variable data. ERA5 are available at hourly time steps at ~0.28 degrees spatial resolution. For the mean evaporation rate, Minimum, Mean, and Maximum values are provided expressed in kg x sqmt x sec-1. Data look like this:

The ncdump is the following:

and plotting the mean values for a hour during the day, would look like this:

What looks not clear to me is why the mean evaporation rate is negative: I would expect a positive value in the wet regions and zero over the deserts. I tried to look at the ERA5 data documentation, but the issue is not addressed there. Am I misinterpreting something?

Just leaving this for future readers. I finally found in some ECMWF documentation (referring to a different variable) that: "The ECMWF Integrated Forecasting System convention is that downward fluxes are positive. Therefore, negative values indicate evaporation and positive values indicate condensation". This applies also to other variables.
Thanks to Daniel and Spencer for their help.


Language to modernize a scientific Fortran codebase Dear earth science community,
I am seeking a language to modernize a large Fortran project that works with geospatial NetCDF files.
The requirements for this language include:

A rock-solid NetCDF library (we do not want to reinvent the wheel).
Excellent support for vectors and matrices (e.g. via operator overloading or something similar).
Native performance is needed (compiled or JIT-compiled).
Must be open-source.
Ideally, simple bindings with Fortran (not a strict requirement).

Python +numpy isn't really an option because of customized number-crunching with native performance.
Even if numpy is implemented in C, the project includes custom algorithms that operate on matrices, and we do not want to write those in C.
I know that Python could be optimized by calling into C or Fortran, but I just don't think that such optimization is going to happen with our team. Therefore, I am seeking a language that is "fast by default". Julia seems to deliver much better on this "fast by default" promise, whereas Python is more like "fast if you have the right optimizations in place".
Matlab is a non-starter because of its proprietary license.
C is a non-starter because it does almost nothing to "modernize" a Fortran codebase.
Go is probably not sufficiently well-established for scientific computing?
Julia could be a promising option because it combines the ease of Python with native performance.
Kotlin might be interesting because it combines the strength of the JVM with the possibility to compile to native code.
Swift would be a great language, but I am not sure whether it is sufficiently mature for my targeted domain.
C++20 and Rust are additional options that might be interesting, but I fear the complexity of those languages (remember that this is for earth scientists, not computer scientists).
Which options would you prefer for a gradual Fortran replacement with NetCDF files?

The modern language you are looking for is called modern Fortran 2018. Fortran 2008 and 2018 have everything a numerical computing project would need and so many features that many other languages mentioned here lack (including extremely pleasant array-syntax which has inspired all other languages such as MATLAB, Python, R, Julia, ..., even C++ numerical libraries). It is the only language that has native built-in parallelism and is the only language, along with C, for which the official MPI parallelism standard is released. It has also excellent vendor support for GPU parallel computing and as I heard in SC18, some vendors like NVIDIA/PGI have already started implementing the native parallelism features of Fortran via GPUs.
Modern Fortran is a high-level language comparable to MATLAB and Python, yet 100-500 times faster than both (https://modelingguru.nasa.gov/docs/DOC-2783). Using Coarray Fortran you can seamlessly parallelize your code with minimal effort to run it from your laptop to the largest supercomputers in the world. No other language has such capability at the moment. Fortran is also the only language that has all levels of parallelism, from instruction level to vectorized, concurrent, and coarray-distributed parallel computing. If such features are not considered "modern", perhaps "post-modern" would be a better description.
Fortran has been a reliable lasting language for almost 3 quarters of a century and has excellent highly-optimized compiler support (Intel, GNU, NAG, IBM, PGI/NVIDIA, ...). If you want to write code that lasts decades, then port your FORTRAN77 code to modern Fortran with minimal effort and save yourself time, energy, money, and computational power.
A good start with modern parallel object-oriented Fortran is "Modern Fortran Explained: Incorporating Fortran 2018" by Metcalf et al.
If you decide to port your code effortlessly to modern Fortran, you can also get help from the official Fortran language website https://fortran-lang.org/ and the community of programmers on Fortran discourse: https://fortran-lang.discourse.group/
Update Nov 17, 2020
Just yesterday NVIDIA released a news post on its GPU implementation of the concurrent features of Fortran 2008 / 2018. Users can now write code in pure modern Fortran and let the compiler automatically offload it to GPUs for thousands-way parallelism.
What is the relevance and importance of this achievement? The same Fortran code that a user writes can now be parallelized via GPUs, distributed CPUs, OpenMP threads, or auto-parallelization features of the Fortran compiler depending on the user's platform and compiler choice. All of that complexity is hidden from the user. No need for preprocessing and conditional compilations anymore. This further enhances the excellent existing portability of Fortran programs across platforms and architectures.


How many extreme shifts in climate has Earth gone through in its existence? As the Earth formed, it went through cycles of essentially hotter and colder periods. Extremely volcanic times and ice ages, in feedback loops contributing to one another. CO2 swinging from high to low back and forth, all the while islands and landforms are evolving. In some ways it's like a ripple effect moving through the Earth as it came to be the shape it is today, still with an evolving climate and form.

How many extreme temperature and activity cycles has the Earth (or at least the surface of it) gone through since its formation? I understand there might be some uncertainty since this is over the scale of hundreds of millions of years. If the question can be answered clearer within a limited geological time period please do apply that boundary and answer for a more recent time period.

I'd also be interested to learn about any kinds of measurements or cutting edge topics or research questions that would help us learn about these cycles in the past.

As I finished writing this question I did find one answer. I'll ask anyway and see if anyone has more info to contribute.

From the Wikipedia page on Ice Ages, there's this Timeline of life including a list of ice ages on left side.

Based on this, there were 7 ice ages in the past 4.5 billion years (apx age of the Earth). Were there also 7 major periods of high volcanic activity?


Why does the Hadley cell descend at 30 degrees? George Hadley's initial model of the Hadley cell described air as being heated at the equator, ascending, and then moving aloft pole-wards where it would cool and descend.  Meanwhile surface air would move towards the equator to take the place of the rising hot air there, forming a giant Hadley cell, as in the picture below:

However the modern conception of the Hadley cell is one where air ascends at the equator while air at an angle of 30° latitude descends, with winds moving towards the equator on the surface, and with winds moving towards the poles aloft to complete the cell.  The modern conception of the Polar cell also works in the same manner, with the difference being that the expanding air hot air in this cell originates from 60° latitude, rather than from the equator.

Why is it that the air in the Hadley cell descends at 30° latitude, as opposed to continuing all the way to the poles as Hadley had initially suggested, and why does air then rise again at 60° latitude forming the Polar cell?

The Hadley cell was proposed and works only for a non-rotating earth. When we consider the earth's spin, we have to consider the Coriolis force as well. Because of this force air cannot travel in one unhindered cell from the equator to pole or back. So there must be an odd number of cells together so that the air rising and falling in the adjacent cells is oriented in the proper direction. Considering the various observations of the Easterly and Westerly trade winds a 3 cell model best explains our atmospheric circulation. The location of the majority of earth's driest and arid regions are located in the areas underneath the descending branches of the Hadley circulation around 30 degrees latitude, which also supports the 3 cell model.

Also watch this video which gives a great explanation to all of your questions with the help of practical experiment and animations.
Atmospheric Circulation Video


Website that contains the maps of atmospheric pressure and wind speeds Is there a website that contains the maps of atmospheric pressure and wind speeds for specific climatic events such as hurricanes day after day ?

Check out this beta data portal from the Cooperative Institute for Meteorological Satellite Studies / University of Wisconsin-Madison
CIMSS Tropical Cyclones
Data Archive http://tropic.ssec.wisc.edu/archive/  .

However, my favorite source of information is the Regional and Mesoscale Meteorology Branch (RAMMB) of NOAA/NESDIS http://rammb.cira.colostate.edu/products/tc_realtime/

And there are good summaries here:
https://www.tropicalstormrisk.com/hislink.html

and another good general source of information is from the National Hurricane Center http://www.nhc.noaa.gov/data/


How to determine how long ago a rock was broken? I know that there are techniques that help scientists determine the age of a rock. But is it also possible to determine how long ago a rock was broken? For example, how could we date the formation of the fracture surface in the photograph below?

There is a technique called "Exposure Dating". Using e.g. cosmogenic nuclides (they are produced in the first metre or so of the surface of a rock which is exposed to cosmic rays, i.e. on the surface of the earth), it is possible to estimate the amount of time that the rock was exposed.

With some assumptions, you can get an exposure age of the fracture surface (or at least some information about it) since the fracture surface was exposed to cosmic rays only recently, whereas the rest of the surface was exposed to it long before.

The specific sample is probably too small though. This technique is useful to date the retreat of glaciers (they shield cosmic rays from the underlying bedrock), fault scarps, or the time a meteorite spent flying in space from its parent body to the earth.


Why is the Ring of Fire there? The Ring of Fire goes through the places that have the most earthquakes. Why is the Ring of Fire there, not somewhere else?

Any help would be appreciated!

This question is very similar to: Why does the "Ring of Fire" pretty much define "Pacific Rim"

The high levels of volcanoes and earthquakes are primarily due to subduction. So why is the Pacific surrounded by subduction zones?

Think back to Pangaea. This was a supercontinent that formed in the late Palaeozoic. Virtually all of the Earth's land masses were concentrated in one large supercontinent. When this broke up, the new continents moved away from each other. Fast forward 200Ma or so, and you find that the continents have moved so far apart that they are now converging on a point on the other side of the planet - the continents are moving towards each other! Hence the remains of the super ocean (which was actually multiple ocean plates - today's Pacific & Nazca plates, plus the Farrallon plate (RIP),etc ) is shrinking as the continental plates move towards it. This destruction of the ocean plate(s) occurs at subduction zones.

This is a big picture generalisation. Not all of the Pacific's boundaries are marked with subduction zones (e.g. North America has two large strike slip systems + a new spreading ridge). Also, not all of the continents are converging on each other. Africa is doing a pirouette, India is moving northwards, etc.


Is there any natural phenomenon that can account for the 100 fold faster CO2 rate increase? "Based on the best historical data that we have available CO2 is probably increasing at a rate at of least 100 times faster than at any time in the last 800,000 years." Pieter Tans lead scientist of NOAA's Global Greenhouse Gas Reference Network.

Peter Tans approved the above verbatim quote to be directly attributed to him. I contacted him by email today on the basis of this material:

“The rate of CO2 growth over the last decade is 100 to 200 times faster than what the Earth experienced during the transition from the last Ice Age,” Pieter Tans, lead scientist of NOAA’s Global Greenhouse Gas Reference Network, said in a statement. “This is a real shock to the atmosphere.”

The annual rate of increase in atmospheric carbon dioxide over the past 60 years is about 100 times faster than previous natural increases, such as those that occurred at the end of the last ice age 11,000-17,000 years ago.

https://e360.yale.edu/digest/co2-levels-continue-to-increase-at-record-rate
https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide

There are things that could do it, but they would be very noticeable.

A whole string of thousands of the largest volcanic eruptions to ever occur on earth. Volcanoes can briefly match human output, but volcanoes only erupt for a few minutes or hours. you would need the equivalent of mount St Helens erupting continuously for 70 years.
The burning if every forest on the planet. I'm sure humans would notice such a firestorm, and I;m not even sure if that would be enough.
The slow extinction of photosynthetic algae. without the bulk of photosynthesis to convert co2 into oxygen it could build up. Of course we monitor this so it would not go unnoticed. More importantly oxygen levels would also drop dramatically which it hasn't. https://scied.ucar.edu/imagecontent/carbon-cycle-diagram-ipcc
The ignition and continuous burning of millions of miles of exposed coal beds. You would need to burn approximately ~3 teratons of coal. coal beds can be ignited by natural causes but we would notice a coal fire larger than a continent.
A drop in sea level by hundreds of feet would do it. large sea level drop cause outgassing of methane and co2, from wetlands and sea muds. but again New York would notice it if long island stopped being an island.

Some of these have actually happen in earth's geologic history just none recently, and not as consistently as we have managed (at least not since life evolved). Really scientists have spent a lot of time and money looking for other causes, and no one has found any. Scientists concluded it was human activity by eliminating every other conceivable cause.


Landsat 8 acquisition time and date The the meta data text file that comes with Landsat scenes, contains an acquisition date and a scene center time in successive lines. I wanted to know if the image is recorded at the scene center time on the date of aquisition.

According to page 43 of the Landsat Products Description Document the acquisition time is GMT when there is a "Z" behind the time.


What's the difference between uptake and adsorption of gas into aerosols In the area of atmospheric chemistry, I have learned that the heterogeneous oxidation of SO2 is one of the important pathways for sulfate formation. The reactions of SO2 oxidation in mineral, soot particles have been confirmed.

The adsorption or uptake of SO2 on the particle surface" is the initial process of the transformation. I have heard that adsorption is the surface-based process of gases or ions and create a film wiki reference.

What's the difference between the adsorption and uptake processes?

Adsorption is adhesion of thin film of liquid or gas on solid substance and the host solid substance does not form chemical bond with deposited material. Uptake is entering of material into substance, end product of which is a solution. Uptake generally happens in liquid host substances but it is also possible for solid host substance to uptake the gas or liquid.

In context of aerosols, the term adsorption is used when solid aerosol particles like dust, soot, ice, etc. are interacting with gases. The term uptake is used when liquid aerosol particle are interacting with gases.

Reference
http://glossary.ametsoc.org/wiki/Adsorption


How do we know the speed of S-waves (shear waves) in the Earth's inner core? Has this been measured? Wikipedia's Seismic wave includes the plot below of the speed of S and P waves as a function of depth in the Earth. In the region of the outer core the speed of S-waves or shear waves is shown to be zero but really they are evanescent and so the velocity is probably complex.

Then at the inner core boundary the speed of S-waves is shown again down to the center of the Earth, fairly flat near 4 km/sec.

Is the speed of shear waves in the Earth's inner core a measured quantity or is this just deduced? If it's measured, how do these shear waves get to the core if they can not propagate through the outer core?

 Source

If waves would travel only through a medium while keeping their form (i.e., P-waves remain P-waves and S-waves remain S-waves), you would obtain something a bit like this video: https://www.youtube.com/watch?v=YctV5crEXyM .

However, standard models for wave propagation are more complicated than that. Upon hitting an interface, P-waves both reflect off and refract into the other material. And if this happens at a bit of an angle, it even generates a reflected and a refracted S-wave (if the material allows it!). Something like this image:

What you see is a P-wave that comes towards an interface between two different media (Vp=P-wave velocity, Vs=S-wave velocity, \rho=density). After hitting the interface, it creates 4 new waves! Two P-waves, two S-waves. A similar figure can be made for an S-wave hitting an interface.

So we can follow a hypothetical wave-path as follows:

There is a P-wave generated at the Earth's surface that travels down from the crust to the mantle (creating 4 new wave modes as in the figure above; we follow the transmitted P-wave that goes down),
That wavefront travels from the mantle to the outer core (which creates 3 wave modes because there is no transmitted S-wave! We follow the transmitted P-wave the goes down).
That wavefront travels from the outer core into the inner core (which creates 3 wave modes, because there is no reflected S-wave; We follow the transmitted S-wave that goes down).
The S-wave travels through the center of the Earth back up to the interface between inner core and outer core (creating 3 wave modes, because there is no transmitted S-wave; We follow the P-wave that goes up).
The P-wave travels through the outer core and hits the interface with the mantle (which creates 3 wave modes because there is no reflected S-wave; We follow the P-wave that goes up).
This P-wave further travels to the Earth's crust and surface (creating more wave-modes in the process), and is measured there.

You can see some of these effects in this nice video: https://www.youtube.com/watch?v=j7eoxizmC1I that I put in the comments also. It shows P-waves in green and S-waves in red. You can see how complicated the total wavefield becomes because every interface creates new waves...so it'll be a bit hard to see the particular wavefront I described above, but you can see the general picture.

On this snapshot you see the P-wave (in green) generating an S-wave (in red) in the inner core.

So -- S-waves can exist in the inner core even when the outer core doesn't support them (because waves modes convert, as it's called, at interfaces), and their presence can be measured at the surface. I think that answers your question mostly.

Then, of course, there is still the question of how you'd measure the speed of the S-waves in the inner core, which is rather complicated. These days, it is done by assuming some seismic model of the earth (choosing V_p, V_s, and \rho everywhere within the Earth), and modeling seismic events such as on the linked YouTube video. Then you compare real recordings against your modeled data. If there are particular misfits, you create a new model and you iterate this procedure until your model fits the recorded data 'well'.

So is the shear-wave in the inner core a measured quantity or a deduced quantity? That requires a very careful definition of those terms, so I won't answer that question! Regardless, there exists a shear-wave velocity for the inner core that describes and explains recorded data very well.


Is it possible to obtain the richter grade of an earthquake with the data of an accelerometer? I have an accelerometer on a table that gives me the $x$, $y$, and $z$ axis acceleration in $m/s^2$ when I move the table. Is there a formula or method to pass this data to a earthquake grade in a Richter Rank?

The Richter Number is a measure of total energy released in an earthquake.  To calculate it, even roughly, you need to know the epicenter of the earthquake (that needs at least three measurements from three locations) and the length and intensity of the shaking to determine the energy contained in the waveform.  All you seem to have with your accelerometer is the peak intensity of the shaking at a single point.  So the answer is no.


Regarding the melting glaciers and icebergs, why isn't the extra water vapor in the atmosphere mentioned in discussions of global warming? As is reported on the major news networks, many glaciers and big icebergs are melting, which reportedly causes a tremendous increase in the amount of water vapor in the atmosphere.

Now a lot of water vapor and the increasing heat from the sun powers stronger storms and greater inequalities in the distribution of water throughout the world. Therefore, there are more incidences of drought in some places and big flooding in others. I think it all relates back to the fact there are millions of tons more water vapor in the atmosphere. This, added with the Sun's heating, will make more intense storms.

My question is, given all the talk of global warming and instabilities in the weather why isn't the fact that there is a tremendous amount of extra water vapor in the atmosphere ever mentioned on the news or on other TV shows?

Extra water doesn't mean extra water vapor. Even without this EXTRA water, the water vapor levels will increase, in the current warming world. As its the temperature rise that is making the water turn to vapor.

  As temperature rises, evaporation increases and more water vapour accumulates in the atmosphere. As a greenhouse gas, the water absorbs more heat, further warming the air and causing more evaporation. When CO2 is added to the atmosphere, as a greenhouse gas it has a warming effect. This causes more water to evaporate and warm the air to a higher, stabilized level. So the warming from CO2 has an amplified effect. Water vapor is infact the largest positive feedback in the climate system (Soden 2005). - Skeptical Science

Intensification of the water cycle hence, is a product of rise in temperature, rather than the water content. Of course we need water to evaporate, but the increase in the water content doesn't correlate to increased water vapor. It might play some role locally in small ponds and seasonal rivers which get dry during summers, but on a global scale with most of our evaporation occurring over oceans (86% of global evaporation), its not significant enough.

So coming to your question. First of all its not like water vapor is never mentioned -

  As global temperatures rise, the atmosphere then holds more moisture ... Therefore there is more water vapor available to fall as rain, snow. - thinkprogress.org - September 5

  Global warming is moistening the atmosphere - The Guardian - August 13

And if you notice, all the recent news about melting glaciers has been in connected to some recent developments and observations in form of published papers at reputed journals. NASA even conducted a press conference explaining their latest research, which led to a series of news articles on the topic. So, i'm quite sure if there are some significant developments in terms of water vapor research, it will make the news as well.


What is the oldest sediment? Sedimentary rocks in Akilia or at Hudson Bay have been proposed as the oldest in the world. My question is not related to rocks, but rather to sediment while still forming sedimentary deposits but before lithification (rock formation). While it might be difficult to put a clear limit between "sediments","lithified sediments" and "sedimentary rock", the question is what is the oldest sedimentary deposit on Earth still under sedimentary processes?

According to page 86 of Exploring the World Ocean:

  In December 1989, ODP scientists drilled Hole 801C
  and recovered Jurassic-age rocks and sediments, about
  170–165 million years old, from the Pigafetta Basin in
  the western Pacific, near the Mariana Islands. Sediments
  of nearly identical age had been found previously from
  the Deep Sea Drilling Project Hole 534A, located on the
  Blake-Bahama basin in the central Atlantic. These sediments
  and the rocks on which they rest are among the
  oldest oceanic crust found in the world ocean.

There is a more-detailed discussion at Site 801: Sedimentology and Biostratigraphy


3 Billion years ago, the earth is covered with Carbon Dioxide. Where did it go? Oxygen gas began to appear on the earth surface about 2 billion years ago by photosynthesis. Carbon Dioxide was converted into carbohydrates in the process. Where did these carbohydrates go?
If they were converted into coal, oil, and natural gas over millions of years, then by releasing them back to the atmosphere in a couple of hundred years by combustion, we are definitely changing the atmospheric composition. This will definitely change the climate. This argument for climate change seems easy to understand and bulletproof. However, I have not heard this argument mentioned by the media. Why?

It went into:

Limestone

Mostly made out of calcium carbonate (CaCO3)

Coal

Oil and gas

Living biomass

Subducted into the mantle

Occasionally coming back as diamonds

Or as volcanic gas

All images public domain from here


Why are there both climate regions from axial tilt and weather cells? So Earth has an axial tilt and that creates weather regions. For example, approximately 23 degrees north and south, approximately the same as the planets axial tilt, will give you the tropics. This creates a band around the Earth of warm wet climate. But then there are these climate cells as well. The Hadley cell occurs at 30 degrees north and south. This apparently creates low pressure and high pressure zones of hot air rising, condensing with rain, falling and cooling, etc.
So what the difference between the 23 degrees and the 30 degrees? I thought that tropics are created because of at 23 degrees tilt which also causes seasons? But then they are also created because of Hadley cells? They seem to have the same effect with 2 completely different systems. Why are there both? And what happens between 23 and 30 degrees?

Generally speaking, the tropics are a geographical term. It's the area on the surface of the planet where at least once a year the Sun passes directly overhead.
It has relation to climate, but even then within the tropical region you have a variety of climate zones from rain-forests all the way to savannas and deserts. Being in tropical region only ensures that it's generally warm all year round, other parameters define the actual climate type. Take a look here at the range of climate types available in the tropics.
Now, coming to Hadley cells and how they relate to tropics - they are not directly related to one another, i.e. one of them is not used to define the other.
In Hadley cell the humid air rises and moves north or south depending whether it started north or south of the equator and then sinks to the surface at around 30 degrees north and south of equator. So they are both dependent on the same factors, namely the simple fact that it's generally hot in the tropical region.
What happens between 23 and 30 degrees really depends on where in the world you are. If you're between 23 and 30 degrees in North Africa, it's very unpleasant, because Sahara is right there. Other places are different depending on their own geographical and climate parameters.


Is this scientific explanation of The Bible flood accurate? I googled "the flood and freshwater fish" and came up with this question Christianity StackExchange: How did Noah preserve fresh water fish?.

The writer makes a lot of claims like how the salinity of the oceans was lower in 2500BC  (time of the flood), how an experiment found that saltwater fish and freshwater fish can live in the same environment (he didn't provide a reference) etc...

My questions are:

What was the ocean salinity around 2500 BC, and could freshwater fish tolerate that level of salinity?
If the ocean was much less saline, is it possible to have increased to present day levels in 4500 years?

Fishing through the links mentioned over at Christianity SE, I netted this scientific paper about freshwater and marine fish: Why are there so few fish in the sea?. Apparently the bulk (96%) of marine species have a single freshwater ancestor species extant 300 Mya (300 million years ago). Descendants of this species did not enter the ocean until about 180 Mya, with the greatest diversification and subsequent dominance of the oceans starting 110 Mya. Another fact: only 4% of current fish species can thrive in both saltwater and freshwater (e.g., salmon, trout, ...).

To get anywhere near a hypothetical event equivalent to Noah's flood would require accepting dozens of counterfactual assumptions, and a total misunderstanding of geology, evolution, paleontology, not to mention conservation of mass (where did all the water come from?).

But to address the narrow issue of survival of fish, one could imagine that the flood happened so rapidly as to create a very thick layer of freshwater on top of the saltwater. Freshwater is considerably lighter than saltwater, and would "float" on the saltwater. Marine mammals would be okay in freshwater for a few days. Then the waters could recede (where did all the water go to?), and maybe enough freshwater species would end up in the new freshwater lakes and streams.

As far as the Ocean being less salty, there is no evidence for that. A lower salinity is postulated to fit into the theories of the Young Earth proponents. Paleosalinity is a complex study. You can browse through these references here and here.

A flood such as this would have enormous, I would say overwhelming, geological, geographical, and paleontological evidence left behind, which in fact does not exist. But everything is possible with miracles.

You may be interested in this paper: An Abrupt Drowning of the Black Sea Shelf which led to this book NOAH'S FLOOD: The New Scientific Discoveries About the Event That Changed History


What was the first rock in the rock cycle? I am an undergraduate student but I am a tutor at a High School, and one student asked me. Attempting to explain the rock cycle "if one rock turns into the other then which came first" my gut is telling me probably igneous (given Earth geologic past.) Resources online have different opinions. Am I right in my assumption?

which came first

That's actually a very hard question. The most simple answer would indeed be igneous. Here's why:

Sedimentary rocks (in the sense of rock cycle) comes from pre-existing igneous or metamorphic rocks, so you need to have had them first.
Metamorphic rocks, by definition, are rocks that form from other kinds of rocks (be it igneous or metamorphic).
Igneous rocks form by melting of other rocks. Now here is the catch - what do you consider "other rocks"? The first igneous rocks on Earth (or to be exact - the proto-Earth) likely formed by impact melting of various small planetary bodies hitting each other and coalescing to form the Earth. These planetesimals formed by condensation of gas from the solar nebula, before Earth even existed, and before the rock cycle began.

So yes, igneous rocks were here first. The rocks (or material, if you wish) that existed before the igneous rocks do not fit into the traditional igneous/sedimentary/metamorphic definitions.

However, note that the rules of the rock cycle aren't written in stone (pun intended). What about evaporites? Rocks such as halite or gypsum beds form on the surface on the Earth, and their constituents aren't derived directly from either igneous or metamorphic rocks. What about sandstones that form by weathering of former sandstones? What about igneous rocks that form by partial melting of metamorphic rocks, and then melt again without ever reaching the surface to become sedimentary rocks? And my favourite one: pyroclastic rocks. Are they sedimentary or igneous? One textbook quips that they're igneous going up, and sedimentary going down.


Upon breaking apart andesite, what do you get? I'm aware that andesite consists of about 60 percent silica and as for minerals, pretty sure it's usually pyroxene and plagioclase. What form would these take on if they were to be separated? Especially interesting, I think, is what would happen to the silica: would it be in its "commercial" powdered form?

By definition andesite is mainly plagioclase (mostly variety andesine),and pyroxene with either quartz or olivine (not both), and minor amounts of magnetite, ilmenite, zircon, apatite, possibly biotite mica, and maybe a few traces of rarer minerals. The pyroxene is probably a mixture of orthopyroxene and augite. In addition to plagioclase there may be small quantities of other, more alkaline feldspars.

Andesite is chemically about 60+/-3% silica, SiO2, but the amount of free silica is very small, if present at all - at most 2 or 3 percent. So no, you won't extract commercial powdered silica. Better than 99.9% pure silica is found very abundantly in some quartzites, a common sedimentary rock. So nobody is going to try to extract silica from other silicates.


Earthquake severity during supereruption at Yellowstone caldera? Theoretically, I ponder what type and strength a supereruption would generate, say for example at the Yellowstone caldera? The last supereruption was roughly 70,000 years ago when Toba erupted. It's claimed that this single event bottlenecked our species and nearly ended us? My curiosity is more towards the effects in the immediate vicinity of the collapse, in particular the seismic effects and their severity? Large quakes and tsunamis if near ocean?

Volcanic earthquakes aren't actually all that strong. That's quite easily understandable by just looking at length scales: In the largest earthquakes that happen on earth, tens of kilometers of subduction zones rupture at once, releasing the stress that has built up from two plates moving past each other (but being locked) for decades.

Even large calderas cannot produce faults of this length that are sufficiently long and linear and can rupture in the same quake. Consequently, earthquakes in volcanic zones are usually much smaller than the largest ones we experience on earth.

The global effects of supereruptions are not due to earthquakes or tsunamis, but due to the gases, ash and sulphur that ends up in the atmosphere and that leads to global cooling for several years.


What are the evidences that the earth climate is getting warmer? Someone, who does not believe climate change asked me today --
How is it possible for us to conclude that the past five years are the hottest five years since record begun, since

There are only a limited number of locations where we measure temperature.
There is a wide range of difference in temperature even in a small area.

How would a meteorologist answer these questions?

Besides rising surface air temperatures other indicators of global warming include -

ocean surface temperatures rising
ocean temperature at varying depths rising
global average sea level rising
Arctic sea ice extent decreasing
Arctic sea ice thickness and average age decreasing
Glacier retreat
Earlier Spring snow melt
Borehole temperatures rising
Earlier budding time of various plants
Less new record low temperatures
More new record high temperatures
Greenland losing ice mass
Antarctica losing ice mass
and etc

Every possible way we can observe and measure the changes we should expect with global warming shows results consistent with actual global warming.
Global Average Temperature as the go to single simple measure is a statistical construct, derived mostly from about 7,000 long running and up to 30,000 current weather stations recording daily minimum and maximums. It is a way to reduce complex change to a single simple number, for convenience. That metric may be a construct but it is constructed to show the extent of change to those recorded temperatures. In one sense it isn't a direct measurement of "something", yet we can confidently expect this average to rise if the climate system is warming - and not rise if it is not.
These weather records allow other kinds of examination besides getting a global average temperature - mapping of regional changes, geographic ones and all the way down to the conditions at individual sites, including their suitability for inclusion in global temperature record calculations. Badly sited ones can be excluded, step temperature changes from changing location or changes to existing location can be adjusted for to achieve better accuracy.
These records don't exist in isolation - there is a broad understanding of climate and weather processes that goes with them. They are also supported by satellite data, such as microwave sounding that allow remote estimation of atmospheric temperatures; whilst they tend to show higher response to El Nino Southern Oscillation, the rates of warming are broadly consistent with weather station records.
It is a reliable observation that in between nearby weather stations sharing similar geography there are similar weather conditions, including similar maximum and minimum temperatures. Consistently different conditions in the spaces between would be noticed and we cannot expect such differences to be confined only in those between spaces; if there were significant variations in the temperatures and rates of change over time in the spaces between locations it would be happening at those locations as well and that would show up in the weather station records. What we find in those records is consistent with global warming.


Should Modis & LandSAT NDVI composites agree and why not? Modis takes daily images at coarse resolution (500m?) that are then lumped into 16-day composites.

LandSAT, let's say 8, takes roughly bi-weekly images at 30m (100m resampled to 30), and those are then lumped into 32-day composites.

Clouds aside, would you generally expect the two for the same time period to match?  In other words, if you aggregated the Landsat pixels by mean, ought you to get the same value of the corresponding Modis pixel?

Probably not, right?  Could you explain why?  Is it the 16 vs 32 days?  The world changes in two weeks?  Equipment differences?  Resampling algorithms?

Are there any Modis-LandSAT pairs of data that actually would match quite closely?

I can't comment yet, but I want to share this thought:

One challenge of the comparison is the co-registration of the data, so that really the same area on Earth's surface is compared.

In this article about the difference of MODIS and Landsat 7 NDVI, the authours put much effort in the co-registration to really compare the same area on the ground (but still there was a difference between the two sensors)


The Tambora eruption caused the "Year without a summer". How much would such an eruption today affect the output of solar pv on a global scale? Are there any estimates for the reduction of global solar insolation at the Earth's surface that a Tambora scale eruption would bring?

If our electrical power generation became heavily reliant on solar pv would it bring about a substantial reduction in output capacity?

Volcanic eruptions effectively inject large quantities of aerosols in the upper layers of the atmosphere, increasing Earth's albedo and reducing the intensity of the solar radiation reaching the surface. Such reduction would indeed lower the solar energy available to solar panels.

These effects of volcanic eruptions have been studied by Gao et al. (2008) and Crowley and Unterman (2013). Both studies were combined by the IPCC Working Group I during the assessment report 5 (2013), and summarized on the figure 8.18 (Chapter 8), together with other climatic forcings:

You can see that the largest drop in effective radiative forcing happens in 1815 as a consequence of the Tambora eruption.

Unfortunately, that event goes out the scale of the plot. However, the data is available on Table AII.1.2 of Annex II, were we can see that the minimum value indeed happens in 1815 and reaches –11.629 W/m².

Considering the typical amount of energy received from the Sun under clear skies at seal level is roughly 1,000 W/m², the irradiation drop produced by Tambora would represent a drop of about 1% on the energy reaching the Earth's surface. Of course, much larger local effects could be observed due to transient and more localized dense ash clouds.

Therefore, at a global scale, if a new "year without summer" where to happen, photovoltaic energy output would drop by ~1%.

Of course, larger effects would take place if the eruption happens to be close to the most important areas for photovoltaic energy production.


Why isn't the side of the earth facing the sun completely illuminated by sunlight from the north to the south pole every day of the year? We all know that the earth rotates every 24 hours, that it is tilted 23.5 degrees, that it circles the sun every 365 days, and that it is located approximately 148,600,000 km (92,333,000 miles) from the Sun.

We also know that we have 5 major circles of latitude, from north to South: the Arctic circle at 66.5 degrees north, the Tropic of Cancer at 23.5 north; the Equator at 0: the Tropic of Capricorn at 23.5 south, and the Antarctic Circle at 66.5 south.

I have read previous answers regarding questions similar to mine but feel that the question(s) were perhaps misinterpreted as to meaning why isn't Earths side opposite the sun illuminated given the sun's size, so I want to be more specific.

Why isn't the side of the earth facing the sun completely illuminated by sunlight from the north to the south pole every day of the year?

Because if the The Earths diameter is 12,740 km (7,917 miles) and the Sun's is 1,392,700 km (865,370 miles), or about 109 times greater, it would seem logical that the sun's rays would provide sunlight on the face of the Earth pointed towards the Sun, completely from the North Pole to the South Pole, and yet we know that it doesn't...  Why so?

If the diameter of the Sun is $R_S$, the diameter of the Earth is $R_E$, and the orbital radius of the Earth is $r$, as in the drawing below (sorry about the quality),  then you can do some geometry and compute $\theta$, which is the angle at which the light from the edge of the Sun's disk as seen from Earth is tangent to the Earth's surface referenced to a line between the centres of the Sun and the Earth.

The expression for $\theta$ comes out to be

$$\theta = \sin^{-1}\left(\frac{R_S - R_E}{r}\right)$$

(You get this by extending the tangent line and the line connecting the centres, realising that this makes two similar right triangles with the angle at the tip being $\theta$, and the base of the larger one being $R_S$, then working out what the hypotenuse of the larger triangle is, which gives you $\sin\theta$.)

Since $\theta$ is small we can just say $\sin \theta = \theta$ in the usual way, and plugging in values we get $\theta \approx 0.0046\,\mathrm{rad}$.

If the angle at which the Earth's rotation axis is tilted is more than $\theta$, then there will be a period of the year during which the poles are not illuminated as the point at which the Sun's light is tangent to the Earth's surface is sunward of the pole.  Well, the angle of tilt is $23.5^\circ \approx 0.41\,\mathrm{rad}$, which is about $90\theta$.


Rainbowish phenomenon outside my home I took a photo of an amazing sight I had never seen outside my home ( southern india ) but I could not tell if it was a rainbow type thing or an aurora borealis. Also if it was to be a sun dog , shouldn’t it have some curvature and symmetry .Can someone tell what this is and it’s reason of occurrence

Sun dogs are bright spots to one or both sides of the sun. They are a form of halo created by ice crystals in the atmosphere.

What you saw was most likely cloud iridescence, which is a phenomenon that occurs closed to either the moon of the sun. The iridescence is caused by diffraction created by water droplets or small ice crystals individually scattering light. Large crystals produce a halo, not iridescence.


Is it possible to infer the depth of a river from the shapes of the islands and the banks? Look at the photo below. Presumably, the river bed is a smooth shape. Therefore, it should be possible to infer the depth of the water from the photo, right?

I am not even an amateur of geo-science.

I am willing to listen to the experts.

The island morphology isn't necessarily an indication of the river's depth because the river can be bimodal, with shallows and deeply incised trenches. One thinks of the River Congo which has many islands, but depths of up to 220 metres in its main incised channel. That said, however, if the river has a multi-channel, heavily braided morphology, as in the Waimakariri in New Zealand, or the Brahmaputra in Assam, then one can be fairly certain that the intense sediment load would have filled in any deep pools (excluding local scour in sharp bends, caused by super-elevated flow). In such cases, one may assume a shallow river profile, governed only by storm-flow peak stages.
Where there are few or no islands coupled with geomorphologic indications of rapid cut back or rejuvenation, such as the Mekong upstream of its delta, then one may suspect very deep channel profiles. In general though, islands and bank morphology are not reliable indicators of a river's cross section.


Will the ocean eventually erode all land? It seems as if the 'lowest energy' state for the Earth is to not have any mountains and that given enough time, the oceans would erode all land. Essentially it's an argument like entropy. And I mean in the far future, once tectonic activity has ceased.

Is this the case, and if so how long might it take? If it is not the case, why not?

Continents are made up of different, lighter materials than oceans and both continents and oceans "float" on the mantle. Continents are also thicker than oceans so erosion does not only need to take care of the ~5 km which is above sea level but it should also erode away the continental root (which can be several 10's of kilometers until the continental crust is actually slightly thinner than oceanic crusts are today.

However tectonics is not the only source of topography which can easily be seen if we look at Mars where a hotspot has created an enormous mountain on a tectonically inactive planet.

So if you want to end up with a topography free planet you need to shut down all possible mantle plumes too.


Querying Seismic Databases I'm trying to find 3-component records of the P-wave arrivals of a variety of earthquakes at seismic stations (specific earthquakes or stations aren't important, I just want a small library of these arrivals for a machine learning project). I expected there would be labeled databases of this kind of thing where I could simply browse by earthquake or station and download the data. However the request process appears much more complicated and honestly I'm very confused.

Is anyone familiar with how to query these databases?

Unless they are large or famous earthquakes, I doubt you will find the waveforms for specific earthquakes.

What you will find is a ton of seismic data: http://earthquake.usgs.gov/data/?source=sitenav

which you can request. Once you have requested (downloaded ect) the waveforms (probably in seed format) you will need to analyze the waveforms themselves to find specific earthquakes (request data from a time when you know there was an earthquake) and find the p/s/love ect wave yourself on the seismogram.

To read seed data, you can either find a matlab code or write your own! (Im sure there is a python equivalent at this point.)


What causes the Earth to have magnetic poles? A compass can tell me the directions of the Earth's North and South poles?  What is it about the Earth that produces this "polarity" such that a compass can pick it up?

The first thing that jumped into my head was the Earth's rotation, but if that is the explanation, why have I heard from people that the Earth's polarity can switch every million years or so?

Well, firstly it's important to recognise that the poles are merely the extremities of the shape of a magnetic field - the earth's magnetic field.  All magnetic fields have polarities as such.

However, you're asking why the field itself even exists, I gather.  In this case it's generated by electric currents in the conductive molten iron (and other metals) in the core of the earth, as a result of convection currents generated by escaping heat.   This is known as a geodynamo, and is one way of generating a magnetic field.  However, exactly why this occurs is still under investigation.

More is available in this Wiki piece - specifically on the physical origins of the earth's magnetic field.


GOES Visible Channel - asymmetry between morning and afternoon In the GOES-13 Visible channel, there seems to be a morning/afternoon asymmetry in the data. I'm wondering what might cause this.

In this example data, the morning is the lower branch, and the afternoon is the upper branch. The y-axis is the pixel level (0..255), the x-axis is the Sun's local altitude above the horizon. The location is the Gulf of St. Lawrence, on the east coast of Canada.

Latitude +46.94N, longitude -63.21W (not far from the center of the images below.)

Morning, 10am local time:

Afternoon, 4pm local time:

The absolute accuracy for GOES-13 visible channel is 5%, so 2% is well within the noise. http://noaasis.noaa.gov/NOAASIS/ml/imager.html


Are there known ore deposits under cities? Occasionally there are news about a major ore deposit for a specific commodity being found. Some of these recent discoveries are underground, and the "geophysics" aspect of their exploration is more important than the "geology" aspect.

This makes me wonder—are there any such known ore deposits that have been found under cities? Some examples might be "the largest gold deposit ever, under Buckingham Palace" or "diamond bearing kimberlite pipe under Central Park in New York".

One example of an ore deposit that runs under a city is the banded iron formation ore in Kiruna. In this case the ore has been mined outside of the city since the turn of the previous century. The ore has been found to run under the city and there are now plans to move the city more detailed information. This has led to a process where the city has to be re-established in a different location including moving a large number of historically significant buildings.

A similar situation is also present in Malmberget (about 120 km S of Kiruna), part of the twin town of Gällivare-Malmberget. In this case the plan is to have Malmberget inhabitants to move to Gällivare. The mining activities at Malmberget have resulted in several collapse features see images on this link. There is also some information in English on the Gällivare web-site.

In both cases there are significant restructuring of the societies. It is also worth noting that the definition of ore is economical which means that what is worth mining depends on market prices. In the case of Iron the market has been strong but has fluctuated significantly. The result is that the planning and decisions for a move such as these  are difficult since they are costly and depend on the market to be financially viable (it is the mining company that largely pays for the move).


Circular patterns at bottom of rock, is it a fossil? The image below was taken on a hike.  Circular patterns at bottom (it is flatter on this face and round otherwise) appear either man-made or possibly it is a fossil.

Any idea what this could be?

The face of the rock with the round center portion looks strongly like a Rugosa or Horn Coral.  I suggest it is a Rugosa coral because of the center with the radial lines out from the center and the clear edge surrounding the radial lines.  See https://en.wikipedia.org/wiki/Rugosa.


Will California become a subduction zone in the distant future California is one of the few places in the world that lie on a transform fault. My question is why considering the fact that North American Plate is moving westward shouldn't California be a subduction zone like the Entirety of the west coast of the Americas say for Canada. Why is that the North American plate is simply rubbing up against Pacific plate in here as well as Canada.

Before the transform process of the San Andreas Fault zone we know today, there was indeed a subduction zone event taking place in this same region near now coastal California during the late Jurassic to late Cretaceous periods.
Today the city of San Francisco physically represents the aftermath of the ancient clash of mighty tectonic titans as the city and surrounding land and oceanic areas consist of and exists on several terranes and melanges which accreted, or formed, during this time, which make up the assemblage known as the Franciscan Complex. These assemblages are an illustrative historical account of events that formed while the mighty Pacific Plate aggressively rammed its way in an easterly direction toward the equally colossal North American Plate. There was a key player who’s pretty much laid to rest now and that was the ancient tectonic Farallon Plate in this same region off of California before the - modern day, neverending, gorgeous, and ever-dynamic coastline. This ancient plate now rests somewhere underneath Utah or there about, theoretically. Although and obviously not as robust as either plate forcing it into its “Malachi crunch” (uh oh, now I’m dating my own “...Days”), it was sizable yet, so while it was forced to dive underneath the North American plate for as much as a mass apparently its size can be, until eventually becoming so plugged up and impeding its displacement from the ongoing movement of the Pacific Plate, forcing it to redirect its great energy force elsewhere. This systematic transition of backed up energy marks the birth of the famous, very active San Andreas transform fault! For more on SAF: https://geo.libretexts.org/Bookshelves/Geography_(Physical)/Supplemental_Materials%3A_Physical_Geography_(Lenkeit-Meezan)/08%3A_Shaping_the_Lithosphere/8.03%3A_Orogenesis%2C_Faults_and_Earthquakes
Equally fascinating is that the subduction of the Farallon Plate formed the Sierra Mountain Range orogenesis by way of folding and uplift, while tensional stress of the orogeny stretched things out on both Eastern and Western locations of the Sierra’s and “simultaneously” formed the Great Valley which California’s Central Valley of today was/is vastly part of, as well as the creation of the Great Basin on the far eastern side of the Sierra Nevada Mtn. Range.


Is this paper attributing a change in polar wander to climate change? After coming across this article here, and reading the paper here I came away with the impression that the authors were saying that polar wander is being affected by climate change due to mass rebalancing as ice caps melt. As I understand it, the magnetic field of Earth derives from the liquid outer core, and due to the sheer mass difference between the core and any surface mass losses, combined with the lost mass being rebalanced isostatically, such a theory seems on first glance improbable. Could someone with more knowledge perhaps explain how the proposed theory operates?

The term ‘polar wander’ is ambiguous. In this case it's got nothing to do with the magnetic poles, but rather with the Earth's spin axis. If you think about a desk globe mounted on an axle, the poles under consideration here are the points where the axle intersects the globe's surface.

The paper is essentially saying that climate changes are changing the distribution of ice and water on the surface of the planet, and this in turn is shifting the spin axis slightly. You're right that the mass of material on the Earth's surface is dwarfed by the mass under the surface; however, if you look at the paper you'll see that they're talking about miniscule shifts in the axis. The changes shown in Figure 1 are on the order of tens of mas (milliseconds of arc) over a few decades. One mas is one 3.6-millionth of a degree, or about 3.09 cm as measured on the Earth's surface. So, at least at first glance, the changes don't seem too implausible.

You mention isostatic response as another concern, but this is a slow process which doesn't really come into play on the decadal time scales considered in the paper. Fennoscandia and northern North America are still rebounding isostatically from the last ice age.


UAH and RSS Lower Troposphere data The UAH 6.0 and RSS lower troposphere data sets line up nearly perfectly and both show no significant warming for over 20 years.

What is the leading theory for what's going on? What explains this?

Firstly, the RSS and UAH datasets do not "line up nearly perfectly", the diagram below shows both products over the last 20 years (which appears to be what this question is actually about) here is the url used to generate it.

As you can see, they disagree quite considerable on the value of the trend.  UAH and RSS are different methods used to infer trophospheric temperatures from them MSU instrument carried aboard various weather satellites.  The reason why they differ is because they use different methods to deal with the various drifts and biases involved in the measurements, and the fact that we don't know exactly how this is best performed is what is known as structural uncertainty.  Note there are a couple of other similar products, but UAH and RSS are the main ones.

As to "no significant warming for over 20 years", this is the subject of a fair bit of discussion in the journals, but not nearly as much as in the blogsphere, and a lot of it stems from not understanding what the term "statistically significant" means (and more importantly, what it doesn't mean).  The key point is that "no significant warming" does not mean "there has been no warming" or that "the rate of warming has slowed".  Unfortunately the reasons for this are a little complicated, so I will start with a simple example.

Consider the usual statistical test for the bias of a coin, we start by stating the null and alternative hypotheses:

$H_0$ - null hypothesis, unbiased coin, probability of a head = p - 0.5.

$H_1$ - alternative hypothesis, biased coin, $p \neq 0.5$.

We then flip the coin $n$ times and count the number of heads, if the p-value is less than some pre-determined value, typically $\alpha = 0.05$, then we say that we can "reject the null hypothesis", implying that the data provides some support for our alternative hypothesis, $H_1$.

However, if we are unable to reject $H_0$, there are at least two reasons for this, it may be that $H_0$ is true, or it may be that $H_0$ is false but we haven't seen enough data yet to be confident of this.  For example, if we only toss the coin four times, then even if we get a head every time, we still won't be able to reject the null hypothesis as the p-value cannot be smaller than 0.0625.

The statistical power is the probability [in a frequentist sense] that the test correctly rejects the null hypothesis ($H_0$) when the alternative hypothesis ($H_1$) is true.  In this case, the statistical power of the test with only four flips is zero, because we can never reject $H_0$.

So, if you want to claim that it is in some way a surprise that we can't reject the null hypothesis, you need to show that the power of the test is high, and in the case of the trends over the last 20 years, it isn't particularly high, as similar trendless periods ocurr both in the observations and in the model output, as shown by Easterling and Wehner.  For example the trend in RSS to 1997 is very similar to the trend from 1995 to the present day, and that is almost as long:

Part of the reason for this is that the RSS and UAH datasets are both very sensitive to ENSO, and the trend over the last 20 years is dominated by the 1998 El-Nino.

So how long do you need to get reasonable statistical power?  Well climatologists generally use a period of at least thirty years (IIRC this is a WMO guideline).  Santer el al performed a study and found that you would need at least 17 years of data for identifying human impacts on surface temperatures.  Note this is a bare minimum, and refers to the detection of a trend in a randomly chosen time period.  If you wait until a period of 17 years comes a long before making the argument for a hiatus, the assumptions of that analysis are violated by the fact that multiple hypothesis tests are being implicitly performed, and in practice you would need a much longer period.

Now are scientists ignoring the apparent "hiatus"?  No, there have been many studies analysing it, for instance Foster and Rahmstorf show that the apparent hiatus can be reasonably explained by ENSO and volcanic forcing, and so there is no real reason to suppose that there has been a pause in anthropogenic global warming, and the apparent hiatus is probably due to a redistribution of heat between the atmosphere and oceans.  There has even been a special issue of Nature Geosciences devoted to this topic.

UPDATE: @user1286792 notes in the comments below: "!UAH, and !RSS show it has been 21.5 years since there has been any tropospheric warming.".  This clearly isn't true, at least for UAH.  If you plot the trend since 1995, it is essentially the same as the long term trend since the start of the dataset.  The fact that the RSS trend for the last 20 years is very different is I suspect the reason skeptic blogs switched from using UAH to RSS, but as always don't believe everything you read on line, and woodfortrees is a great tool for checking things.  As I said, UAH and RSS vary considerably over the last 20 years in their trends and the reason for this is structural uncertainty.  That doesn't mean that either of them are right or wrong and if your argument is not valid for both, then you probably shouldn't be confident that it is true.  Basically the timescale is too short to reliably estimate the trend given the uncertainties in the data, including the structural uncertainties.

Caveat: I think WFT may be using a previous version of UAH, however this rather illustrates my point about the structural uncertainties, if successive updates to the algorithm make such large differences to the trends, that means the structural uncertainties are very large and we should take that into account when looking at the trends.  However, the basic point remains that (i) the trends are too short to expect the warming to be significant (ii) the apparent haitus is adequately explained by ENSO and volcanic forcing (iii) similar periods of little warming are seen in the output of GCMs, and so it is not entirely unexpected.


Is it feasible to 'harvest' the clathrates from the permafrost before they evaporate? We can see that there are large buildups of methane clathrates in permafrost regions.

Climate scientist James Hansen has predicted that the release of the permafrost methane clathrates could cause runaway climate change.

We know that some have related the Triassic Extinction event to the release of Permafrost Clathrates.

I know that there are various techniques to extract natural gas from shale and rock.

My question is: Is it feasible to 'harvest' the Clathrates from the permafrost before they evaporate?

No, it's not feasible. They are too dispersed, and any operation to harvest them would be too costly and inefficient, and would amount to vandalism on a gigantic scale. We just have to hope that the vast majority of tundra clathrates will remain un-melted, as will probably be the case. The last time they were melted on a massive scale may well have been the Permo-Triassic extinction event of 250 million years ago.The Arctic tundra is a vast natural wilderness full of valuable wildlife. Any ill-judged operation to remove clathrates would not only be grossly expensive and inefficient, but would have both taxpayers and environmentalists up in arms!

Assuming theories of the Permo-Triassic event are correct, it took the long term eruptions of the Siberian Traps super-volcano to release almost unimaginable quantities of CO2 into the air to trigger the melting of clathrates. Eruptions of super-volcanoes like the Siberian Traps 250 million years ago and the Deccan Traps 66 million years ago make modern volcanic eruptions, even Krakatoa (1883) or Tambora (1815), pale into insignificance.


Where can I find geomagnetic observations for the Indian Ocean region in 2017? I am looking for the geomagnetic data for the Indian Ocean region. The 3D data should correspond to longitude-latitude grids at hourly intervals.
The model data is easily available at NOAA but I need the observed values (satellite as well as surface observations) for the year 2017. I also checked the NOAA and USGS website but none of them are providing their data for the specific spatial domain.

For surface data, a good place to start is Intermagnet, a global network of geomagnetic observatories. Their data download page lets you filter by time span and region, and sample rates down to the second are available for some observatories. The data are direct observations from individual observatories at fixed locations, and are not averaged over a region. (You mention in a comment that you couldn't find a station for ‘the northern equatorial part of the region near India’; for this region I'd suggest Gan in the Maldives.)

For recent satellite data, the Swarm mission provides an excellent resource. This page gives instructions on how to download their freely available data sets. Registration is required, but as far as I can tell it's free and available to anyone. They've also got an excellent online visualization tool which lets you explore their data interactively.


Land's effect on winds and currents? If we did a thought experiment and imagined the Earth to be covered in a global ocean (ie. no land to slow winds or direct ocean currents) would winds and waves be perpetually enormous or would they come to some sort of equilibrium state?

A few thoughts - assuming like you say that the aqua-planet is the same size as earth, and all else being equal, it's best to consider the two major classes of waves:

Nondispersive wind generated waves: Here the maximum wave height is a function of wind speed (fetch). However, wind speed in general is not a function of wave height (unless you invoke concepts like walker-circulation from ENSO, but you wouldn't get ENSO since there are no continental boundaries).

The relationship between maximum wave height and fetch in deep water, can be described empirically as $$H_{max}=0.332 \sqrt{F}$$

So this all goes to say that it is impossible to determine $H_{max}$ without knowing something about the atmosphere dynamics. If you assume that the atmospheric dynamics are the same as on earth (in terms of storm statistics), then this little empirical relation would suggest wind generated wave heights should be no different for an equally sized aqua-planet. Larger planets do however have larger storms...

Eddies and planetary waves Eddies are waves, yet quite different from wind generated waves. While they certainly don't reach the impressive heights of wind-generated waves, their wavelengths are several orders of magnitude larger. And so technically, you could say they are in fact "bigger" waves. Along with eddies, there planetary waves such as Rossby waves and Kelvin waves. All these eddies and planetary waves are limited in size by the Rossby radius of deformation. Which is to say, their maximum size is effectively limited by the curvature of the earth.

Upshot To get larger wind generated waves, you need larger storms. Therefore you need a larger planet (e.g. great red spot on jupiter). To get larger planetary waves and eddies, you also need a larger planet! The reason that larger planets have both larger storms and larger planetary wave/eddies is the same ~ which is that the rossby radius is bigger for a bigger planet.

You might be interested to check out something called the "aqua planet experiment" project. These are general circulation models run on a hypothetical planet with no continent, they're all just atmosphere and ocean. The image below is cloud cover output from an aqua-planet simulation.


Creating a general log sheet for CTD and ADCP for fieldwork It is close to the deadline for conducting research on a research vessel for the Irish Sea (one month left). I'm currently a student and would like some descriptive observational data/variables needed to account for when recording measurements from CTD (conductivity, Temperature, Depth) and ADCP (Acoustic Doppler Current Profile) instruments. For both CTD and ADCP, what do I need from these devices to create a general log sheet suitable for all students (my crew) to record during the trip.

This answer might be a bit late but here are some common metadata variables that get recorded:

For a CTD:

Operator
Date and time
Start and end co-ordinates of station
Station Number
Sample depths (assuming you'll also be collecting water samples)

Here you can also record what the water samples are used for i.e. salinities, chemistry etc

Sea state
Vessel
File name

For the ADCP:

Start and end co-ordinates
Date and time
ADCP type
Set-up (sampling frequency, bin size)
Vessel
Operator
File name


What is the lowest latitude at which snow has been recorded at sea level? We have had some stations report snow that have not reported snow in the past 55 years at sea level. I have read that Tampico, Mexico at 22°N is one of the stations that has recorded snow in the tropics. What is the lowest latitude at which recent snowfall(as recorded by humans) has been recorded at sea level? Please note that the question is very specific to snowfall and not merely the lowest temperature recorded in the tropics (subzero)

The question is hemisphere agnostic.

According to the USA Today article Answers archive: Winter, snow, ice, the sea level snow closest to the equator in recorded history are as follows.

The record for either hemisphere was in 1654, in the Chinese city of Nanning (now near present day Beihai) recorded snow, it is situated at 21°29'N.  This cold period is included in the article Coherence of climatic reconstruction from historical
documents in China by different studies (Ge et al. 2008) as part of a historical document that stated:

  ‘The winter in the 11th year of Shunzhi (1654 A.D.) was
  severely cold

For reference, the USA Today article states that the Southern Hemisphere record was considerably further from the equator, occurring in Valparaiso, Chile (33°02'S) in 1977.

One major caveat to this answer (asides from the USAToday source) is the length of time that records have been kept - for China, it has been thousands of years - there is virtually no equivalent record keeping in many areas (particularly in the Southern Hemisphere) for that length of time.

Having said that, according to the Australian Bureau of Meteorology, snow has been recorded in the 1950's and 1960's, several hundred kilometres north of Brisbane, the furthest north was in the Clark Ranges, west of Mackay at a latitude of about 21°S- but these locations were considerably higher than sea level, so do not qualify.

From personal experience, I recall when I lived in the southern suburbs (at sea level) of Melbourne as a child, one winter there was snow - melted as it hit the ground - but that is at a latitude of 38.2°S

In geological history, it could be argued that snow may have preceded the glaciation at the equator during Snowball Earth events, if proven to be true.