Megathrust earthquakes on subduction zones I am a beginner in geology and earthquake studies, and learning about subduction zones recently.

Question is: do large earthquakes (sometimes referred to as megathrust quakes) occur on any point in the Subduction zone? For example, the Indo-Australian plate subducts underneath the Burma microplate, and the Sunda plate. So does the megathrust quake occur anywhere along this zone or is it limited to certain areas within the subduction zone?

Another related one is what is the different b/w earth quake and rupture process that happens after an earth quake. Example: in some articles about the 2004 Northern-Sumatra quake, I read that "the rupture continued northward for nearly 1000 km".

Megathrust is not a particularly well defined term but in my experience it generally refers to very large earthquakes that occur on the subduction interface.

The subduction interface is the main surface which separates the overriding plate from the subducting plate and is where most of the convergence is accomodated.

(image source)

Earthquakes occur on the subduction interface when the two plates are locked together (referred to as strong coupling) and cannot move past each other, leading to accumulation of strain which is eventually released in an earthquake. The amount of coupling on the subduction interface can vary strongly along its length. Chlieh et al., 2008 says this about the Sumatran megathrust:

  Near the equator, the megathrust is locked over a narrow width of only a few tens of kilometers. In contrast, the locked fault zone is up to about 175 km wide in areas where great interplate earthquakes have occurred in the past.

Some subduction interfaces are thought to be almost entirely decoupled and do not generate megathrust earthquakes but large earthquakes can still occur on splay faults in the accretionary prism (Shaw et al., 2008).

With regards to the second part of the question, earthquakes are seismic waves generated by rupturing of rocks in response to accumulated stress. Every earthquake creates a rupture patch with a certain area. The 2004 Sumatra earthquake had a rupture patch that was over 1300 km long which is enormous, hence why it had a such a large magnitude. The rupture started at the southern end of the fault and propagated northwards at 2-3 km/s, taking around 9 minutes to fully rupture. The epicentre is the location of the initial rupture.

The seismic moment of an earthquake ($\mathrm{M_0}$ is related to the area of the rupture patch ($\mathrm{A}$), the average displacement on the fault ($\mathrm{D}$) and the friction coefficient on the fault plane ($\mu$) by: $$\mathrm{M_0 = \mu A D}$$


Is there a name for these "pouring" clouds? I snapped this photo with my phone flat against the window of a bus, facing south while traveling west across a bridge in New Taipei City. I'd say it was at about 24.995N, 121.438E. It was about 14:00 local time, 28-05-2017, a cool day, roughly 20C outdoors but I don't know the temperature in the mountains. The overall bluish/greenish hue is the result of the tinting of the bus' window.

Is there a name for this "pouring clouds" effect?

The term used by the American Meteorological Society is orographic fog. A perhaps more descriptive name is "orographic waterfall cloud".

Prevailing winds can force air to flow upwards over rising terrain. The rising air cools more or less adiabatically, and this can in turn result in clouds. The nature of the orographic clouds (orographic: "related to mountains") that result vary greatly.

In arid regions, orographic clouds can form lenticular clouds that look amazingly like UFOs (three links). Unstable conditions can result in wave clouds, where an obstruction causes a cloud after cloud after cloud downwind of the obstruction. Even icebergs can cause wave clouds. Another form of orographic cloud is a banner cloud, where a cloud flies like a banner downwind of a mountain:

Source: https://commons.wikimedia.org/wiki/File:Banner_clouds.jpg . Copyright Zacharie Grossen, license CC BY-SA 3.0

This is getting closer to an orographic fog. Climbers on the Matterhorn oftentimes experience that cloud, firsthand. Even closer to home is Table Mountain near Cape Town, South Africa.

Source: https://commons.wikimedia.org/wiki/File:Cape_Town,_Table_Mountain,_Table_Cloth.jpg. Copyright KodachromeFan, license CC BY-SA 3.0

This is an orographic fog. (Table Mountain can also create some rather spectacular lenticular clouds.) Another example of an orographic fog is detailed in the article "Waterfall-like Orographic Clouds".

The conditions needed to form an orographic fog include

Prevailing winds that force air to blow upwards over an obstruction, with the orographic fog flowing downwind from the obstruction.
The flowing air must be sufficiently humid. Without this condition, you might see a very cool looking lenticular cloud, but you won't see a banner cloud or an orographic fog.
The flowing air must be sufficiently cool. Humid air at the same pressure and temperature of arid air is less dense than is that arid air. The flowing humid air has to be fairly cool for the flow to be downward downwind of the obstruction.
The flow has to be fairly slow (low Reynolds number) and uniform (low Froude number). Otherwise, a wave cloud or banner cloud will result.


What are the guidelines for constructing variable names that follow CF conventions? I am attempting to develop variable names following Unidata's climate forecasting (CF) variable naming guidelines, but for biological variables used to parameterize and evaluate land surface and ecosystem models (See a first draft on Google drive). However, I can not find the documentation for these guidelines.

Until early 2014, the guidelines were here: http://cf-pcmdi.llnl.gov/, but now there is a link to http://cfconventions.org/, and then a list of standard names, but the guidelines page that this points to does not (currently) exist.

I think it would be helpful here to have a link to the appropriate documentation, but also a summary of the guidelines (i.e., how to construct variable names that are consistent with the CF approach). In addition, any feedback on the standard_name field in my draft would be appreciated.

Possible this is not what you need, but here's an archive of the Guidelines for Construction of CF Standard Names, which is "Version 1, 3 December 2008" and was cached on July 28, 2013; guessing that the page has not been updated since December 2008.

Also, the source code repository for CF Conventions website you linked to (cf-convention.github.io) is viewable from here; if you had questions about the status of the site, you might try contacting the developer listed on Github for the project; their email is listed on their Github profile.

UPDATE: Here's the contact info for the CEDA Data Scientist; their "main role in CEDA is the development of metadata standards, particularly the CF (Climate and Forecast) metadata conventions."


ERA-Interim how to select only grid-points over land area? I am using ERA-Interim data, e.g. total precipitation, and I want to take only observations over land areas.

How can I filter the ERA-Interim dataset of precipitation to get only observations in grid-points over land?

Is there any specific method I should apply?
Maybe CDO can help?

Thanks

The simplest way is to download another variable in which data is only available over the ocean, such as Sea Surface Temperature (SST). You should be able to download it in the very same way you do with precipitation (let us call it PREC hereafter).

Then, you can use any software that handles this type of data (Matlab, Python, NCL, GrADS...) to mask out the ocean cells. The logics is to assign a missing value (NaN) in PREC, where SST is not a missing value, to get the land-only PREC (PRECL). Or the other way around: keep the values of PREC where SST has missing values.

Imagine SST and PREC are 2D fields, that is, PREC=PREC(y,x) and SST=SST(y,x), where y and x are indices for latitude and longitude coordinates. In Python, the code should read something like the following, given that you have PREC, SST fields and the lat and lon arrays of coordinates as Numpy arrays.

import numpy as np

# Initialize variable with shape of PREC, filled with missing values:
PRECL = np.zeros(np.shape(PREC))
PRECL.fill(np.nan)

# Check the content of each cell in SST, to decide about PRECL:
for x in range(len(lon)):
    for y in range(len(lat)):
        if np.isnan(SST[y,x]):
            PRECL[y,x] = PREC[y,x]
        else:
            PRECL[y,x] = np.nan


Could the current climate change events cause long-term problems in the viability of Earth to sustain life? There are a lot of reports on the consequences of climate change for the relative short term. From what I understand, in the next 100 years or so, we will face:

global floods of coastal areas, causing large-scale migrations;
desertification of desert-adjacent regions, leading to more migrations and less arable land;
more and longer periods of drought and heatwave, leading to failed crops and hunger epidemics;
changes in local climate, leading to changes in biodiversity and possibly introduction of pathogens in areas that before were inhospitable to the carrier;
...

I might be totally mistaken here, but while these things are definitely cause for serious concern and good reasons to take action, they don't seem like they could cause the end of life on Earth as some people claim, or even the extinction of Humanity. I'm fairly sure that even though loads of people might die due to the consequences of climate change, humanity as a species would probably survive. I might be wrong though.

Could climate change lead to the extinction of humanity?

There is one scenario in which climate change could render the Earth inhospitable to life in general, which would be a runaway greenhouse effect.  In a runaway greenhouse effect, the Earth would get so hot that the oceans start to evaporate, adding more water vapour (powerful greenhouse gas) to the atmosphere, which will make it hotter yet, until Earth ends up like Venus.
However, the current scientific consensus is that a runaway greenhouse effect as a consequence of anthropogenic global warming is not possible.

Life in general will almost certainly go on, and most consider it unlikely that the survival of humanity itself is at risk as a direct consequence of climate change.  Many other species, however, will likely disappear, as has been widely documented in the scientific literature.  As an example, complicated ecosystems depend on coral reefs, and as things stand, there may not be any coral reefs left by the end or even the middle of the century.  This will be disastrous for significant subpopulations of humanity (I've heard in a talk last week than 400 million people depend on fish supported by ecosystems around coral reefs), but it will not by itself cause the extinction of mankind.


If a prevailing wind traveled due east in the Northern Hemisphere, would the Coriolis Effect act on the water? I am in a Marine Environmental Science II class, and we are discussing the Ekman Spiral. As I understand, the Coriolis Effect does not occur when whatever is observed does not change latitude. So, if a wind above the ocean in the Northern Hemisphere were to hypothetically blow due East, with no change in latitude, would the water under the wind still be deflected to the right in the form of the Ekman Spiral?

Thanks in advance!

The Coriolis Effect occurs in all directions equally, even straight zonal (east-west) winds.

Many indeed struggle with this idea - this Physics SE question has a fair explanation as to why.

As arkaia commented, the total deflection magnitude is $f=2{\omega}\cdot{\sin(latitude)}$, which is an orthogonal vector change (and as such shows up as terms in both the zonal and meridional velocity equations).

So there's still deflection to the right (in the NH) equally regardless of which direction the air/water is flowing (except that in such a feature, deeper water is moving slower, so deflects by less magnitude... but still matching in regards to the proportion in comparison to the velocity).  Otherwise the result would not be a spiral... but only at most a 90° decaying curve, since as the water begins to turn towards a more zonal direction, the angle of deflection would start to decrease, until at some height the water is moving easterly (or westerly) (such as at height labeled 3 in this diagram), and the water below it wouldn't turn further.  So the direction independence of Coriolis is vital to there being Ekman spirals at all.


When there is snow on the ground, can a hurricane still form? Where there is snow on the ground, it is a clear indicator that winter in near or already here. Meaning the oceans waters will be colder. But can hurricanes still form in such weather?

First off, hurricanes form in tropical seas over warm water. In general, they form in places where it never snows at all. Also, they form over the ocean, and it is hard to have snow on the ground in the ocean. So in that sense, the answer is: No, hurricanes cannot form in a place where there is snow on the ground.

However, you may mean to ask can a hurricane show up to a place where there is snow on the ground. This is a little more difficult.

Wikipedia's off-season Atlantic hurricane page lists 21 hurricanes that formed in Dec-Feb. Of special interest is the 1952 Groundhog day tropical storm which hit Cape Cod on Feb 4th and Maine Feb 5th of that year. Hyannis, MA had 2 inches of snow on Jan 28th of that year, which melted by Feb 1st (temp data found here). It dropped to 30 degrees F the night of the 3rd before the hurricane hit.
The airport in Bangor, ME had snowfall the 28th and 29th of January which persisted on the ground until the 3rd of February. The night of the 4th dropped to 21 degrees F before the hurricane hit on the 5th.

In both cases, temperatures got into the 40s and heavy precipitation while the storm was passing assuredly melted the snow on the ground. But in that sense of your question: Yes, hurricanes can strike somewhere with snow on the ground, although the warm air and rainfall of the hurricane will probably melt that snow.


Performing time-frequency analysis (FTAN) I am trying to do ambient noise tomography and I am quite confused on how to perform time-frequency analysis (FTAN) as shown in figure 13b and 13d of this paper by Bensen et al.. I am using Python and Obspy to do analysis. The closest I can find is time-frequency representation from Obspy but I'm not sure if they show the same thing. My question is how can I make similars FTAN figures from a signal?

Any help would be appreciated. Thank you.

If you are flexible with your choice in software, I would strongly recommend using Bob Herrmann's Computer Programs in Seismology for this work. http://www.eas.slu.edu/eqc/eqccps.html. This software package has nice workflows for doing ambient noise tomography and will save you a lot of time over python. For example, you can relatively quickly do group/phase velocity dispersion curve picks. It is also fairly easy to QC your data. Look at the documentation for 'Surface Wave Dispersion - Receiver Function Inversion' on http://www.eas.slu.edu/eqc/eqc_cps/CPS/CPS330.html for more details.

If you must use python, I would suggest writing your own Time-Frequency code as obspy's implementation is not very thoroughly documented, and you still need to get from Obspy's representation to dispersion curves. This will take some time, especially if you want a nice GUI for picking. This is why I recommenced the aforementioned software.


What is a typical value of the Péclet number for internal waves? Defining the Péclet number as:

$Pe = \frac{U \lambda}{\kappa}$

Where $U$ is the characteristic fluid velocity, $\lambda$ is the wavelength of the internal wave and $\kappa$ is the turbulent eddy diffusivity. I found in Moum et al. (2003) that measurements show the mean of turbulent eddy diffusivity in Internal Solitary Waves is $\kappa = 0.005$ m$^2$ s$^{-1}$, and a typical velocity is $U = 0.6$ m s$^{-1}$. So for a $1000$ m wave I arrive at a Péclet number:

$Pe = 120,000$

In your experience is that a typical value that you have observed?

I don't have personal experience with this situation, but reading around suggests it depends what kind of mixing you are talking about, for example whether it is vertical or horizontal.

Looking around for recent examples, I see Chao et al. (2007) had a value of 4.0 m2/s for horizontal diffusivity. This larger value would give you a smaller Péclet number of 150. Your use of wavelength for the characteristic length suggests you might be more interested in that dimension?

Chao et al. used ~10–5 m2/s for vertical diffusivity, and I find Bogucki et al. and Lien et al. using ~10–2 m2/s and ~10–2 m2/s respectively. Those are not too distant from your number, and it looks like Moum et al. are talking about vertical mixing. However in this case I am not sure you want to use horizontal length and velocity; you might consider asking about this in Physics.SE, using the fluid-dynamics tag.

In any case, as we hone our intuition about such things, I like this quote from Durran (1999):

  The Péclet number is completely analogous to the more familiar
  Reynolds number, which is the ratio of momentum advection to momentum
  diffusion. The difference between the Péclet and Reynolds numbers is
  due to the difference in the diffusivities of heat [or mass] and
  momentum. [My addition]

I like this because it suggests that some of the same intuition we have about Re may apply to Pe too, especially the fact that it can vary by several orders of magnitude (from here):

Whale swimming at 10 m/s, Re = 3 × 108
Duck flying at 20 m/s, Re = 3 × 105
Copepod swimming at 0.2 m/s, Re = 3 × 102
Larva swimming at 0.001 m/s, Re = 3 × 10–1
Bacterium swimming at 0.00001 m/s, Re = 1 × 10–5

Reference
Shenn-Yu Chao et al., 2007, Assessing the West Ridge of Luzon Strait as an Internal
Wave Mediator, Journal of Oceanography, Vol. 63, pp. 897 to 911, 2007. Available online.
Durran, D, 1999, Numerical Methods for Wave Equations in Geophysical Fluid Dynamics. Springer. Google Books.


What causes some plates to move faster than others? Why do some tectonic plates move faster than others?  Is it due to friction between the plates, the driving forces on the plates, or both?  If it is driving forces, what makes the driving forces on some plates stronger than on others?

The driving forces of plate tectonics has long been debated. Several mechanisms have been proposed, mainly ridge push, mantle drag, and slab pull (see this page from the British Geological Survey). However, there is now a good agreement that slab pull is the main driving force of plate tectonics. It means that it is the subducting plate which controls the velocity of the plate's movement. And the rate at which a plate sinks depends mostly on its age/temperature/density: older plates are cooler/denser, thus they sink at a higher velocity than younger plates.


Can earthquakes contribute to Antarctic ice loss? I read about the earthquake that took place in Japan in 2011, led to some small calving events in Antarctica (link). So, it makes me think if there is a big earthquake near or in Antarctica, can it lead to big calving events, like  loosing a whole floating ice shelf (event comparable to the Larsen ice shelf collapse)? Such an event can be very important, as ice shelves control the flow of ice from the various ice streams. And losing one leads to a significant speed up in the ice loss from the antarctic ice sheet.

Or the somewhat plastic nature of ice makes it much resistant to a big Tsunami or earthquake, to the point that we don't need to consider it as a possibility at all.

I did some background study, and found there are not many active seismic regions near Antarctica as such. But there had been some big quakes in the nearby region in the past few decades.

UPDATE: Found a recent news article "Faraway Earthquake Triggered Antarctica Icequakes". It doesn't answers the question, but provides more insight to the topic. You can also listen to this very cool audio Antarctic Icequakes Triggered By Earthquake in Chile

There are two ways in which earthquakes could affect the Antarctic ice sheet, either by occurring on the Antarctic continent or by occurring elsewhere and sending tsunami-type waves towards the ice sheet/continent.

Seismic activity occurs all the time on Antarctica. Particularly the West-Antarctic Ice Sheet (WAIS) is located over seismically active zones although such occur under the East Antarctic Ice Sheet (EAIS) as well. In the case of WAIS, subglacial volcanoes have been inferred from geophysical measurements. It is possible that such activity but also elevated geothermal heat fluxes, typical of seismically active areas, contribute to making the subglacial thermal regime temperate (at the melting temperature). This means the ice flow can, at least partially decouple from the bed and slide causing larger ice fluxes. Such behaviour is known from WAIS but is observed to be a part of the dynamic setup of the ice sheet and does not seem to change fluxes on time frames that we can observe directly or through investigations of indirect evidence of past flow variations. In short, there is no clear evidence that seismic activity in Antarctica directly causes major changes in ice loss.

Tsunamis reaching Antarctica could conceivably cause break off of larger ice bergs or larger numbers of ice bergs at the fringes of the ice sheet. Ice berg calving in Antarctica is largely through ice shelves, which are floating parts of the ice sheet. These ice shelves are part of the natural way in which the ice sheet looses mass so a momentary acceleration due to tsunami-type waves is conceivable. But, the main question will be of this momentary acceleration of calving simply causes ice that would calve anyway within some period is shed more quickly resulting in a period of quiescence as the shelf recuperates and resumes normal "operations*. This is unclear because we are dealing with processes that have to be seen over long time spans. The loss of an immense ice berg, such as occasionally reported in media, may not have that much significance in the long-term.

There are studies indicating larger ice fluxes out from specific outlets in Antarctica. How these may be influenced by direct or indirect seismic activity has not been investigated. Ice in glaciers and ice sheets behaves plasticly, which means it can accommodate external forcing to some extent by plastic deformation, and also elastically. As an example, lake ice may bend when waves propagate in the underlying water but can also cause breakage under certain circumstances (wave amplitude and frequency). It is hence conceivable that increased breakage can occur if circumstances are just right but it is not at all clear that such activity would cause anything but momentary acceleration of processes that would be shadowed by the longer term trends caused by climatic forcing.


What theories exist connecting volcano temperatures to eruption probabilities? Wikipedia names thermal monitoring as one of the methods for predicting volcanic eruptions. I was able to find some papers (First, Second) on such thermometry and while they are challenging (I retired from physics years ago), I will consult them for the methods.

What I completely fail to find information on, is how current thermal behavior is supposed to be linked to future eruptions (other than: "it’s getting hotter, that could be magma rising upwards"). I realize we don’t have complete theories, but I hope you can tell me what kinds of ansatzes there are.

I have not heard of complete theories connecting volcano temperatures to eruption possibilities either. If you mean subsurface magma temperatures, it is uncommon for there to be direct observations / readings for a particular volcano. Fumarolic temperatures, on the other hand, are directly indicative of current volcanic activity and are much more easily measured (example). In addition, geochemical analysis of fumarolic gases can be related to eruption probability (example, example).

Even in models of magma ascent, temperature differences are not the main focus, but rather pressure differences are (example). This is directly related to g.z.'s comment that volatile content certainly can be a dominant eruptive trigger.


Hudson Bay Has Low Gravity? Is there lower gravity at the Hudson Bay? How does this happen? And where exactly is this because I might want to go.

Gravitational acceleration does vary.  It tends to be strongest at the poles and weakest at the equator, this is due to the oblate shape of the Earth which means that at the Equator you are further from the centre, and gravity decreases the further you are.

Also the spinning of the Earth makes gravity seem less at the Equator.  The combination of these effects causes felt gravity to vary from about 9.77 $\frac{N}{kg}$ at the Equator to 9.83 $\frac{N}{kg}$ as you travel from the equator to the pole (a difference of about 0.6% in weight).

On top of this there are local variations in gravity, which are called gravitational anomalies. They are caused by the structure of the rocks in a particular location.  There is a large scale anomaly over the Hudson Bay region, and so gravity there is slightly weaker than you would expect at its latitude. Gravitation anomalies are generally due some combination of two mechanisms:

The massive ice sheet that covered Canada during the Ice Age pushed mass down and south. Now that the ice has gone, the rocks are rebounding back but the mass has still been pushed aside. Less mass means less gravity.
There are mantle plumes - hot spots like Yellowstone and cold spots where the mantle sinks.  Hot spots tend to have high gravity and cold ones tend to have lower gravity.

These two effects combine in the Hudson Bay region to give a distinct gravitational anomaly.  However the difference is tiny. There is still lower gravity in Florida than in Hudson, simply because Florida is closer to the Equator (and thus further from the Earth's center). And you still wouldn't notice the difference between the strongest gravity and the weakest. It is much too small to feel (though pole vaulters still could have a small gain [1 or 2 cm] if they compete in countries close to the Equator). It is absolutely not the case that there is any part of Caanda where you can float or experience "half the strength of gravity".


Why is this area apparently unpopulated in the great Buenos Aires, what is it? I'm not sure if I can ask this question here but it is the only Stack Exchange community where I saw the tag Geography. I was reading about the great Buenos Aires and I saw this night satellital picture. There is this big area apparently unpopulated or with little population surrounded by the metropolis. What is it? Why is it apparently unpopulated?

“Campo de Mayo is a military base located in Greater Buenos Aires, Argentina, 30 km (19 mi) northwest of Buenos Aires”.
                                               Wikipediawikipedia


What geophysical knowledge have we learned by the construction of IceCube? The IceCube is a particle detector at the South Pole that records neutrino interactions. It has lead to many fascinating new discoveries in the field of astrophysics (e.g., 1, 2) and it was awarded "Breakthrough of the Year 2013" by Physics World. My question is whether the process of installation and operation of such an extensive array has provided any new knowledge of the geophysical characteristics of the Antarctic.

IceCube was initiated as the Antarctic Muon And Neutrino Detector Array (AMANDA) project. Since the sensor array involved drilling deep holes vertically into the Antarctic ice sheet by melting ice, no ice cores were retrieved. The bore holes have, however, been used to construct temperature profiles through the Antarctic ice sheet published in a paper in PNAS. Gathering information of internal temperature is important to understand, for example, basal geothermal heat fluxes and estimating whether or not the ice sheet base is at the melting point and can support liquid water.

In the glaciological literature, very little has been published but then the projects AMANDA and IceCube have never focussed on such questions.

Price et al. (2002) Temperature profile for glacial ice at the South Pole: Implications for life in a nearby subglacial lake. PNAS, 99, (12), 7844-7847. https://doi.org/10.1073/pnas.082238999


Project Mogul: Does upper atmosphere indeed have a sound waveguide channel? While the project was deemed a failure (see below), does the upper atmospheric acoustic waveguide exist?
What are the propagation losses for low-frequency sounds?
Where can one find further information on the acoustical characteristics of the upper atmosphere?

PROJECT MOGUL

Project MOGUL was first conceived by Dr. Maurice Ewing of Columbia University, NY, and Woods Hole Oceanographic Institution, MA. Dr. Ewing had conducted considerable research for the Navy during World War II, studying, among other things, the "sound channel" in the ocean. He proved that explosions could be heard thousands of miles away with underwater microphones placed at a predetermined depth within the sound channel. He theorized that since sound waves generated by explosions could be carried by currents deep within the ocean, they might be similarly transmitted within a sound channel in the upper atmosphere. The military application of this theory was the long-range detection of sound waves generated by Soviet nuclear detonations and the acoustical signatures of ballistic missiles as they traversed the upper atmosphere. He presented his theory to General Carl Spaatz, Chief of Staff of the Army Air Forces, in the fall Of 1945. ...
...By December 1948, serious concerns had arisen regarding the feasibility of the project as first conceived. Even though the principle on which the project was based was determined to be sound, questions concerning cost, security, and practicality were discussed-that ultimately led to the disbandment of the project, and Project MOGUL as first conceived was never put into operational use. ...
...The primary scientist for MOGUL was Dr. James Peoples, assisted by Albert P. Crary, the Field Operations Director. Both scientists had previous associations with Dr. Ewing: Dr. Peoples at Columbia, and A.P. Crary at Woods Hole. Both scientists were assigned to MOGUL for the entire length of the project. ...

References

Wikipedia on Project Mogul
A background document on Mogul from Berkeley - a lecture course by Prof.Muller.

More than a year later, I'm doing a preliminary literature survey (noting that infrasound propagation is used in nuke test ban treaty verification):

https://dx.doi.org/10.1016/0012-8252(77)90063-0 W.L. Jones. Waves in the atmosphere; Atmospheric infrasound and gravity waves, their generation and propagation. (1977)
https://dx.doi.org/10.1111/j.1365-246x.2011.04975.x Green et al. Infrasound radiated by the Gerdec and Chelopechene explosions: propagation along unexpected paths. (2011)
https://dx.doi.org/10.1111/j.1365-246x.2010.04925.x Groot-Hedlin, Hedlin, Walker. Finite difference synthesis of infrasound propagation through a windy, viscous atmosphere: application to a bolide explosion detected by seismic networks. (2011)
https://dx.doi.org/10.1029/2011jd017014 Evers et al. Anomalous infrasound propagation in a hot stratosphere and the existence of extremely small shadow zones. (2012)
https://dx.doi.org/10.1121/1.1903454 Liszka. Long-distance propagation of infrasound from artificial sources. (1974)
https://dx.doi.org/10.3390/ani3020349 Kelley, Garstang. On the possible detection of lightning storms by elephants. (2013) (courtesy of casey)

... and a ton of others. When I have enough time, will study. Others may surely use the leads I collected to post an answer before that.

Things to keep in mind: anomalous propagation, whether acoustic or electromagnetic, below the surface or above it, is based on speed inversions. Whenever there are countervailing trends in salinity (for water)/water content (for air), density, and temperature, natural waveguides may exist.


Synoptic weather predictibility under climate change scenarios Under climate change scenarios, it is quite certain that high latitude regions will experience more warming than at low latitudes. For example, in winter the reduced area of sea ice and snow cover should have the amplifying effect for temperature rising over polar region. Thus the meridional temperature gradient would also be reduced, so as the baroclinicity. Baroclinicity is important in theories concerning synoptic weather forecast in mid-latitudes.

Is there an estimate, and if yes how much climate change will reduce synoptic weather predictability? How will predictability be affected in springtime for mid-latitudes?

Are you referring to mid-latitude cyclones, or a different synoptic weather event?

Baroclinicity is one factor of synoptic climatology in the mid-latitudes, but it's hardly the only one. Since meteorologists are moving away from traditional forecasting parameters and heading toward a more radar-focused and statistical inference model, it won't have an impact on the "predictability" of synoptic weather. Remember, our advances in science may be the only thing outpacing climate change, and that's a damn good thing.

One more thing: Psychics predict, scientists project.


How did this rock dome (pictured) form? I saw this rock formation near Hveravellir, Iceland. It is probably of volcanic origin and looks like a dome. It is nearly symmetric and appears to consist of hardened lava maybe, with several very big cracks that divide it into sections. It is quite far away from the lava flows of the old, very flat Strytur volcano that is about 2 km away.

I have several hypotheses of my own, but I am not a geologist. Could it be a small "failed volcano"?

The vast majority of magma never even makes it out to the surface - most is simply crystallised at depth in magma chambers which dead-end several kilometres below the surface, or are injected as dykes or sills within the host strata.

By OrbitalPete, posted on reddit.com

If magma rose up below that mound it probably got closer than several kilometres to the surface; and the theory could be tested with one drill hole. I'm assuming the mound itself is not lava as such but bedrock that's been forced up.


Are we going to enter a mini ice age by 2030? According to this article, a mini ice age could hit Earth by 2030

Mini Ice Age could hit Earth by 2030

and according to this video

    NASA admits mini ice age coming faster than anticipated.

  All continents are now showing signs of cooling

    Mini Ice Age by 2021 not 2024, Every Continent Will be Affected

Mini ice age by 2021 not 2024

Are we going to enter a mini ice age in the next decade, and if so, when?

These claims originate with a paper by a mathematician named Valentina Zharkova and others, who studied a correlation between solar magnetic fields and sunspots.  Based on the last three solar cycles, her model predicted that the next several solar cycles will be less intense than typical (i.e. fewer sunspots), which implies lower radiant output.

Here is an article addressing the claims and explaining why it's not something to worry about.  Some key points include:

The paper only addresses solar activity, and does not mention the impact that lower solar radiation would have on earth.  Climate scientists have looked at the impact that a Maunder Minimum would have, and found that the cooling effect of reduced solar output is less than the warming effect of increased greenhouse gases, so the net effect is that the earth will continue to warm even if the predictions turn out to be correct.

The cooling associated with the Maunder Minimum was not entirely due to the lower sunspot numbers.  There is evidence that massive volcanic eruptions played a significant role in the cooling.

Claims that the earth is already cooling because there may be fewer sunspots 5 or 15 years from now simply make no sense, and  global temperature measurements  clearly show that there is not a cooling trend.


Is there a general equation to know how big of an area is affected by an earthquake? If you visit USGS earthquakes listing, you get 3 points of information for each earthquake: Location, depth, magnitude. My question is, is there a way to approximate how big of an area is affected? Like if an earthquake happens 20km from San Francisco, how strong does it have to be for someone in SF to be able to feel it?

No, there isn't, because the area affected depends on so many factors, some of them unknowable. Magnitude, cause, depth, geology (which may be very variable in different parts of the area) etc. Besides which, the easiest way to tell which areas are affected is to monitor reports from observers. In the final analysis, the data that aid agencies want to know is which areas ARE affected rather than which might theoretically be affected if all relevant factors were known, which they rarely will be.


What is the largest hurricane possible? With Earth getting hotter and hurricanes also getting larger I wonder; Is there a limit on how big a hurricane can physically get?

I am going to take an educated guess here because it is not possible(AFAIK) to accurately predict with any known skill what several decades into the future would be like.
Given that premise the largest hurricane in the future could be the size of the tropical extent of the Pacific Ocean or the Atlantic Ocean(wherever that begins and ends). Here I am only considering the Northern(or Southern) tropical extent of the Pacific or Atlantic Ocean because as we know a tropical cyclone cannot cross the equator as explained in this in depth answer Impossible or improbable? Hurricane crossing the equator. The thought process behind this idea is that hurricanes(tropical cyclones) dissipate on coming contact with land. Hence the maximum area of the largest cyclone in the future would  have to be the ocean body maximum tropical extent(typically sea surface temperature (SST) greater than 27 degrees centigrade). Just in case if people are wondering why just the tropical extent and why not more than that ? It is because once you enter into mid latitude regions frontal processes could kick in(cold core cyclones-as an example -Can a tropical cyclone form in mid latitude oceanic waters?)
So if the tropical extent of the biggest oceans increases in the future one can imagine a very large possibly synoptic scale tropical cyclone.
Here I am excluding the North Indian Ocean basin because it does not have the surface area to compete with the North Pacific or North Atlantic
Secondly from this popular science article -How strong can a Hurricane get? and this one Are Category 6 Hurricanes coming soon ?

By the end of the 21st century, human-caused global warming will likely increase hurricane intensity, on average, by 2 to 11 percent, according to a review by NOAA's Geophysical Fluid Dynamics Laboratory, revised on Aug. 30, 2017.

followed by

But physics dictates there must be a limit. Based on ocean and atmospheric conditions on Earth nowadays, the estimated maximum potential for hurricanes is about 190 mph (305 km/h), according to a 1998 calculation by Kerry Emanuel, a climatologist at the Massachusetts Institute of Technology.
This upper limit is not absolute, however. It can change due to changes in climate. Scientists predict that as global warming continues, the maximum potential hurricane intensity will go up. They disagree, however, on what the increase will be.

So theoretically a Category 6 Hurricane could have speeds of more than 200 mph.But scientists disagree on these calculations and i am going to leave it at that.


How much energy does Earth surface radiate at night per square meter? I am finding lots of information about Earth's energy budget, about how objects emit infrared radiation based on heat, and lots of related things, but nothing helping me figure out how much energy is actually being emitted by the ground at night.

At night, the ground will still be emitting electromagnetic energy. The amount of energy being emitted will vary based on many factors. Information that helps with many different types of land in various conditions would be great, but for my case I'm focusing on a stereotypical grassy plain in an area which has been between 5C-40C (40F-100F) for the past weeks.

Ultimately I'd like to have a rough ballpark figure of watts per square meter.

In response to @Michael's comment:

  The amount of energy emitted by night depends on how much it receives during the day, water content, length and type of grass and other vegetation, how many "past weeks" have there been, and what was the temperature of the ground when the relevant period began.

During a sunny day the ground is said to receive approximately 1 kilowatt per square meter.

Assume grass of 10cm-50cm (about a half foot to a couple feet). There have been thousands of past weeks. Since we need to get picky let's say the temperature has been a constant 10C (50F) every hour of every night and 15C (60F) every hour of every day for the last thousand years except for the 1 or 2 hours day/night transition where the temperature adjusts linearly back and forth if that makes the exercise easier. And the average annual rainfall of this location is 100cm (40in), rain was coming regularly at that rate until 4 days ago. In the last 4 days, it has rained once, yesterday afternoon dropping about 1cm (half-inch), and the water table is generally about 5 feet under ground level.

The dirt is completely covered and appears as you would expect if you Googled an image of a grassy meadow. For example, the picture I've added at the bottom of the question.

In my opinion, however, the best answer would not just say "The ground emits 10 watts per square meter under those exact conditions!" (even that would be useful though) but would instead say "The type of grass actually makes a significant difference that can throw off even a ballpark estimate, as the difference between grass type A and grass type B produces a whopping half-order-of-magnitude difference in final results due to the way their outer material insulates them! And the difference between wet grass and dry grass is actually 2 orders of magnitude! If I were to simply pick a random, reasonable scenario of ABC it would be within the order of magnitude of 0.1 to 1 watts per square meter, and that's on the high end."

For anything else that matters feel free to simply pick a reasonable value and mention (even if only in a few words) why it matters and if your pick produces a high, low, or mid-range estimate.

I'm not sure how accurate you need, but beginning NASA's global 398.2 watts per square meter estimate from their energy budget a rounding down based on temperature variation should give a pretty good estimate.    A lot of people have a problem with that number because it's more energy than we get from the sun, but that's because our atmosphere is a kind of blanket that traps heat, which warms the Earth above it's planetary eqilibrium temperature.

It's also (but less so), higher because Earth is warmed from below as well as above.

Diurnal temperature variation is between highest day temperature and coldest night temperature and you're looking for average.  Using that number won't give a correct answer, but using, perhaps 1/2 that number might be in the range and that's over land.   The diurnal temperature variation over water is much lower.

So, 288 Kelvin Earth, say 12 degree variation day to night, so 294 / 282.  Ratio of 1.0425, to the 4th power means 18% more heat is radiated from land during the day than at night.   Adjust the temperature if you think mine is off.    That's 18% x 29% of the surface area.

For oceans, 71% of the surface area the temperature variation is smaller, say 2.5 degrees.   289.25 / 286.75, ratio of 1.0087.   4th power, means the oceans radiate about 3.5% more energy during the day than at night.

(18% x 29%) + (3.5% x 79%) = about 7.7%

So if Earth's surface radiation global average is about 398.2 w/m^2, then the day/night numbers work out to about 7.7% variation between them, or +/- 15.5 degrees, about 413.7 watts/m^2 during the day and about 382.7 at night.    That's a pretty good estimate I think.   I'm open to a better estimate if someone can think of a way to do it.


How is the mass of the Earth determined? According to textbook knowledge, the mass of the Earth is about $6 × 10^{24}\,\mathrm{kg}$.  How is this number determined when one cannot just weight the Earth using regular scales?

According to Newton's Law of Gravity based on attractive force (gravitational force) that two masses exert on each other:
$$F=\frac{GmM}{r^2}$$
Where:

$F$ is the gravitational force
$G = 6.67 \times 10^{-11}\ \mathrm{m}^3\ \mathrm{kg}^{-1}\ \mathrm{s}^{-2}$ is a constant of proportionality
$M$ and $m$ are the two masses exerting the forces
$r$ is the distance between the two centers of mass.

From Newton's second law of motion:
$$F=ma$$
Where:

$F$ is the force applied to an object
$m$ is the mass of the object
$a$ is its acceleration due to the force.

Equating both the equations:
$$F = \frac{GmM}{r^2} = ma$$
$$\frac{GM}{r^2}= a$$ (The $m$'s canceled out.)
Now solve for $M$, the mass of the Earth.
$$M = \frac{ar^2}{G}$$
Where $a = 9.8\ \mathrm{m}\ \mathrm{s}^{-2}$, $r = 6.4 \times 10^6\ \mathrm{m}$, and $G = 6.67 \times 10^{-11}\ \mathrm{m}^3\ \mathrm{kg}^{-1}\ \mathrm{s}^{-2}$.
$$M = 9.8 \times (6.4 \times 10^6)^2/(6.67 \times 10^{-11})\ \mathrm{kg}$$

Hence,
$M = 6.0 \times 10^{24}\ \mathrm{kg}$


Why is at high altitude more light from oxygen in the auroras while it is heavier than nitrogen? In an other recent question is said that because of diffusion and thermal causes oxygen and nitrogen are mixed. Nevertheless oxygen is a little bit heavier than oxygen so it should be lower in the atmosphere.

In an other question I read:

"This is why there is a color differential with altitude; at high altitude oxygen red dominates, then oxygen green and nitrogen blue/red, then finally nitrogen blue/red when collisions prevent oxygen from emitting anything."

What causes the beautiful Auroras on the north and south magnetic poles?

So my question is why is at high altitude more aurora from oxygen while concerning diffusing it shouldn't make a difference and because of oxygen is heavier it should be lower.

But in case of an aurora it is higher, so why is that? What makes all the differences in auroras?

The visible emissions from atomic oxygen take place between the fine structure levels of the ground state, and transitions between these states are not quantum-mechanically allowed by electric-dipole radiation. These "forbidden" transitions take much more time to occur, proceeding by magnetic dipole or electric-quadripole radiation. As a result the atom spends a long time in the excited state (~1sec for the 557.7 nm transition, and ~200 s for the 630 nm transition), during which time the atom can make collisions and deactivate without radiating. However, the emissions from molecular nitrogen take place between dipole-allowed transitions, and spend only ns to micro-seconds in the excited state before radiating. Thus, they survive to radiate even in high collision conditions (i.e. low altitudes).

The frequency of collisions an atom or molecule makes increases with decreasing altitude. In addition, the higher the energy of the auroral electrons (2 keV to 20 keV), the lower in the atmosphere they deposit the energy (150 km to 90 km). If there are low energy electrons in the aurora, the emission occurs at very high altitude and both the excited atomic oxygen and the molecular nitrogen make few collisions. Thus they both radiate, but at these altitudes there is more atomic oxygen than molecular nitrogen and the reds and greens of atomic oxygen dominate.

As the auroral energies increase and the electrons deposit their energy at lower altitudes, collisions are much more frequent and the atomic oxygen excited states do not live long enough to radiate. This kills off the green and red emissions at low altitudes. However, the molecular nitrogen, with its short excited state lifetimes, continues to radiate and the lower border of the aurora turns pinkish-purple with the nitrogen emissions.


How to tell if fog is made out of water droplets or ice crystals? I understand that clouds can be made out of water droplets and/or ice crystals. And that fog is nothing else than low-lying clouds.

However, I've experienced fog in a wide ranges of temperatures. I like mountaineering and you often get fog high in the mountains. I've been lucky enough to visit the high mountains of Antarctica and I've also experienced fog there at very low temperatures.

This answer (in the comments) and the fog wikipedia article mention that ice fog happens only at extremely low temperatures (-35 or -40 C). But I think I've experienced fog at those temperatures too. Some times, with the right light I've seen the air filled with tiny crystals, but I wouldn't call that fog, because it is very thin.

Then, as far as I can tell, all thick fogs feel and look the same. No matter if they are made out of ice crystals or water droplets. Is that right? Or is there a way to differentiate between ice/water fogs?

Or maybe contrary to what I think, I've never experienced frozen fog.
But: would I notice the difference if I were to ever experience it? How would they feel/look different?

Finally, if somebody also knows why water droplets can stay liquid in clouds down to -30°C, it would be great to learn about that too.

This doesn't aim to be a complete answer, but after putting a juicy bounty at Aviation SE on the question "Can pilots tell if a cloud or fog is made out of water droplets or ice crystals when flying through it?", the answer seem to be: No, they can't. And all the things to look at to detect ice clouds doesn't seem to be useful if you don't have a plane at hand. There is nothing like "there is a special refraction pattern around the lights on the wings", or such.

So far it seem like ice and water clouds are indistinguishable.


Where can I find papers on the geology of the Wastach Range in Utah I am looking for papers on the stratigraphy, geochronology and/or compositional make up of the Wastach Range and its formations. I prefer a broad overview paper and I can't seem to find one. Any help is appreciated.

This report on the stratigraphy is probably a good place to start.

Additonally, searching Google Scholar for Wasatch Range geochronology brings up a number of papers on the geochronology of specific formations if you are interested in that.


What causes ringing effect when using corner filter? I used the corner filter (band pass) with this frequency values (8,10,45,50). I get ringing effect on the data. my questions are:

what is the name of this effect and the cause?
should be removed and how?
3.on what basis the frequency values should be chosen?
what are the visual features of seismic data make us decided the processing steps.

After filter:

Before filter:

Filtering is always a convolution of the signal. What you are doing in the frequency domain will also be manifested in the time domain. A sharp edge in frequency domain will create a long convolution in time domain.

Ormsby (or trapezoidal) filters cause strong ringing if the slope is steep due to the Gibbs effect. To reduce the ringing, make the slopes more gentle (eg 6, 12, 45, 60) or try to taper the filter slopes.

However, it appears that you are using a strong AGC. Check if the ringing is actually a problem before smoothening the filter.

Some of the ringings will also disappear if you intend to F/K filter the direct waves.


Storing borehole interval data (logs) in netcdf I have a number of datasets that describe geological properties as intervals down a borehole (e.g. unit codes, sample results)

In a database, or a flat ASCII file, I would describe these with a from and a to column, and then have a column for each observation type.

What (if any) is the guidance for storing this kind of data that represents an interval within a netCDF. I've checked the CF Conventions, notably the section on discrete sampling geometries but haven't been able to find anything.

The more I think about it, intuitively, it seems like the wrong file format but maybe I'm wrong.

tl;dr

I would suggest considering the borehole measurements as a vertical profile. In terms of the CF Convention it would be a featureType profile, which is described in the discrete sampling geometries section.

I didn't include all reference to the relevant sections in the CF Conventions below. Just comment if import things are missing.

Example netCDF

netcdf borehole_01 {
dimensions:
      z = 8 ;
      profile = 1 ;
      nv = 2 ;

variables:
    int profile(profile) ;
          profile:cf_role = "profile_id";
    double time(profile);
        time:standard_name = "time";
        time:long_name = "time" ;
        time:units = "days since 1970-01-01 00:00:00" ;
    float lon(profile);
        lon:standard_name = "longitude";
        lon:long_name = "longitude" ;
        lon:units = "degrees_east" ;
    float lat(profile);
        lat:standard_name = "latitude";
        lat:long_name = "latitude" ;
        lat:units = "degrees_north" ;
    float z(z) ;
        z:standard_name = "depth";
        z:long_name = "depth below ..." ;
        z:units = "m" ;
        z:positive = "down" ;
        z:axis = "Z" ;
        z:bounds = "z_bnds" ;
    float z_bnds(z, nv) ;
    float temp(profile, z) ;
        temp:standard_name = "soil_temperature" ;
        temp:long_name = "soil_temperature" ;
        temp:units = "K" ;
        temp:coordinates = "time lon lat z" ;
        temp:cell_methods = "z: mean" ;

// global attributes:
        :featureType = "profile";

data:

 z = 5, 15, 25, 45, 55, 70, 90, 150 ;

 z_bnds =
  0, 10,
  10, 20,
  20, 30,
  40, 50,
  50, 60,
  60, 80,
  80, 100,
  100, 200 ;

 temp = 279.4, 278.8, 278.3, 277.0, 277.1, 276.9, 277.0, 279.2 ;
}

Explanation

The variable temp is an example for a data variable in the file.

Basic depth information

Please see CF Conventions section 7.1 Cell Boundaries for details.

z_bnds provides the boundaries of intervals over which the temperature is averaged. The attribute bounds of variable z points to these boundary data. In this example, I wrote the average depth of each interval into the z variable. However, this is no requirement (as far as I know). It might be also the upper or lower depth of each interval or another depth in between. z_bnds automatically inherits all relevant attributs from z. Therefore, it has no own units and standard_name attributes.

As you can see in the data for z_bnds (or in the table below), it is possible to skip depth ranges (between depth invertal 3 and 4) and to have differently spaced intervals (e.g. interval 6 compared to previous intervals).

| **depth interval** | **minimum** | **maximum** |
|--------------------|-------------|-------------|
| 1                  | 0           | 10          |
| 2                  | 10          | 20          |
| 3                  | 20          | *30*        |
| 4                  | *40*        | 50          |
| 5                  | 50          | 60          |
| 6                  | *60*        | *80*        |
| 7                  | 80          | 100         |
| 8                  | 100         | 200         |

Connecting data variables proberly to the vertical coordinate

Please see CF Conventions section 7.3 Cell Methods for details on the first paragraph and section 5.2 Two-Dimensional Latitude, Longitude, Coordinate Variables for details on the second paragraph.

The value z: mean of the attribute cell_methods of variable temp tells us that the temperature is an average value in z-direction over the interval provided in z_bnds. The latter (over the interval provided in z_bnds) is implicitely assumed.

The value time lon lat z of the coordinates attribute of variable temp indicates that the variables time, lon, lat and z provided temporal and spatial dimensions to each value of temp. Really proper software should be able to map each value of temp a the correspondinc time, lat and lon values via the dimension profile. However, implementing this properly is hard work. Therefore, most software package won't recognize it or might even have issues with it. I your software package throws errors, one first step should be to remove the attribute coordinates.

Setting global attributes

Please see CF Conventions section Features and feature types for details

The global attribute featureType is mandatory when we have a discret sampling geometry.

Several boreholes with different depth intervals

For details on coordinate variables and auxiliary coordinate variables please have a look into sections 1.2 Terminology and 5 Coordinate System

Via the dimension profile we could save several boreholes in one file. In the current situation, the samplings depths of each borehole would be the same. One could make the variable z and z_bnds dependent on profile to provide depth intervals for each borehole. However, then we needed to rename the variables z and z_bnds because a variable might only have the same name of a dimension, if the variable is onedimensional and only depends on this dimension (a coordiante variable). When a variable like the depth depends on two dimensions, it becomes and auxiliary coordinate variable and has to have a different names. Thus, we would have double depth(profile, z) instead of z(z) and double depth_bnds(profile, z, nv) instead of z_bnds(z, nv). The temp:coordiantes would have a value of time lat lon depth (because depth is the vertical coordinates) but temp:cell_methods would remain z: mean (because we calculate average in z-direction).


What, if any, scientific value do global soundscapes have? Seems like the Earth Day related crowd sourcing project to create the first global soundscape by encouraging smartphone owners around the world to download and use an app developed to record the sounds around them is interesting, though it's unclear what scientific value it would have. Is there any scientific value to understanding soundscapes on a global basis?

Remote sensing using passive sonar and seismograms, which are
  acoustic or near-acoustic signals, works on the principle of the
  inverse problem. While the object or phenomenon of interest (the
  state) may not be directly measured, there exists some other variable
  that can be detected and measured (the observation), which may be
  related to the object of interest through the use of a data-derived
  computer model.

  Soundscape ecology is the study of sound within a landscape and
  its effect on organisms. Sounds may be generated by organisms
  (biophony), by the physical environment (geophony), or by humans
  (anthrophony). Soundscape ecologists seek to understand how these
  different sound sources interact across spatial scales and through
  time. Variation in soundscapes may have wide-ranging ecological
  effects as organisms often obtain information from environmental
  sounds. Soundscape ecologists use recording devices, audio tools, and
  elements of traditional ecological analyses to study soundscape
  structure. Increasingly, anthrophony, sometimes referred to in older,
  more archaic terminology as anthropogenic noise dominates soundscapes,
  and this type of noise pollution or disturbance has a negative impact
  on a wide range of organisms. The preservation of natural soundscapes
  is now a recognized conservation goal.

  Source: Wikipedia links referenced above.


Half of Earth with most landmass About 71% of the Earth's surface is covered with water and the remaining 29% is landmass*. If you could theoretically cut the planet in half, with the objective of producing a half with the most landmass possible (and another with the most water possible), where would the cut be? More specifically, where would the centers (in the surface) of both halves be located?

You would have to cut somewhere along this circle:

The only landmass here is New Zealand, eastern Australia, eastern PNG, western North America and some Pacific islands. I'm pretty sure you can tweak it a bit, but that's the basic idea.
Notice that this actually shows less than a half because of the relatively low altitude. If you "zoom out" infinitely you'll get some more Australia and more America in this, but it's still going to be mostly ocean.


If an asteroid strikes a glacier, does it make a print on the land below? If an asteroid strikes a glacier, does it make a print on the land below? For example, a 10 km wide asteroid on a 2 km thick glacier, or a 2 km wide asteroid on a 2 km thick glacier.

A 10 km asteroid would not only obliterate the section of glacier it hit, but also create a huge crater at the impact site!

The asteroid that created the Vredefort crater in South Africa is estimated to have been 10 to 15 km in diameter. It is also estimated that the initial crater created by the impact, some 2 billion years ago before it was eroded, was 300 km in diameter.

To date, this is the largest recognized asteroid crater on Earth. The crater that was produced by the dinosaur extinction asteroid, in the Yucatan (Chicxulub) was only 180 km in diameter. Interestingly, the asteroid that created that crater was also estimated to be 10 to 15 km in diameter.

The Gosses Bluff Crater, in Australia, is 22 km in diameter and it is estimated to have been created by an asteroid 1 km in diameter. The rim of the crater is still 150 m above the surrounding desert.

Any sizable asteroid will vaporize the section of glacier it hits and create a large crater at the impact site.


why we don't have solar eclipse every month? The moon takes about a month to orbit around the Earth. So why we don't have solar eclipse every month?

The moon's orbit is at a slight angle from the plane of earth's orbit around the sun, so it doesn't always hit the right spot, as described on NASA's Total Solar Eclipse 2017 site:

  Eclipses only occur if the Moon is located within 0.5 degrees of the
  plane of the ecliptic, on a line that passes through the center of the
  Sun and the Earth. The Moon travels along an orbit that is inclined by
  5 degrees to the ecliptic plane, so there are only two opportunities
  each month when it passes through the plane of the ecliptic. These
  points are called the ascending and descending nodes. Eclipses of the
  Sun only occur if new moon occurs when the Moon is near of one of
  these nodes. A similar argument explains why lunar eclipses do not
  occur every full moon at the node opposite the Sun from the Earth.


is there any technique developed that can estimate depth of bedrock? I am looking for some technique or machine developed to estimate how deep is a hard rock starting around 100 meter below earth surface. If somebody wants to estimate how deep is that hard rock, how can they know is there any method implemented and used around the world?

A small scale seismic survey as well.

I remember as students we found the water table using a 100m refraction line and a sledge hammer sound source. Scale that up from ~5m to 100m you're going to need a longer line and a larger sound source. Reflection might also become more convenient. Still a lot smaller than a typical 2d survey line though!


Are the Olympic Mountains (in Washington state) geologically unique? So it is my understanding the Washington's Olympic Mountains are basaltic mountains. The reason is that they formed from the upthrust of Ocean crust rather than continental crust as the Farallon plate was pushed under the North American plate. Are there any other mountain ranges (worldwide), particularly coastal ranges made of basalt oceanic crust, that have roughly the same geology?

Short answer: yes, there are other mountains which contains oceanic crust in their lithologies.

The process you described as "the upthrust of ocean crust" is called obduction. The resulting rock sequence is called an ophiolite. As you can see here, there is quite a lot of them around the world! One of the most studied is the Oman ophiolite. I have seen the Chenaillet ophiolite in the French Alps, it's quite spectacular.

Note that ophiolites usually include not only basalts (often in form of pillow lavas, typical of emplacement under the ocean), but also other oceanic crust lithologies such as gabbros, and even the underlying lithospheric mantle, often as serpentinite (a peridotite altered by water).

Edit:

I found a  Guide to the Geology of Olympic National Park on the USGS website. Unfortunately some links are dead, but you can still find lots of information on the range's lithology and formation. The page on "basalt and its associated rocks" mentions the presence of gabbro (a magmatic rock with the same composition as basalt but a crystalline texture due to slower cooling), but not that of any mantle rock. According to this other page on "colliding plates and Olympic rocks", the basalt is not from the oceanic crust itself but rather from a submarine volcano emplaced avove the plate (fig. 26). So, the Olympic Mountains would not be an ophiolite per se, but rather an accretionary wedge, i.e. "a thick wedge of rocks produced by the progressive offscraping of ocean floor sediments during subduction and their accretion to the continental margin" (excerpt from the guide's preface).


Why don't dewdrops form on a cloudy night? The reason behind the non- formation of dewdrops on a cloudy night is the non-attainment of below dew point temperatures. It happens as the outgoing longwave radiation (OLR) is not allowed to escape due to cloud cover.

My question is: How the clouds do this, exactly? Do they absorb OLR or they just reflect it back to earth therby not allowing the earth temperature to go below dew point?

My second question is about the formation of dew drops on a clear night. Why do the greenhouse gases that are implicated for global warming allow OLR to pass through to space?  Do the greenhouse gases somehow become transparent to OLR during nighttime on clear nights?

Clouds absorb thermal radiation and re-emit it, so that some of it comes back towards the Earth (Behind the Forecast: How clouds affect temperatures). During the day this warming effect is balanced by the cooling effect of blocking out the sunlight. They don't strictly speaking stop the formation of dew, but they make it less likely.

In the words of NASA's Climate for Kids pages, "It’s sort of like clouds are wrapping Earth in a big, warm blanket."

The 2nd question is about the effectiveness of greenhouse gases, and why we still get dew at night with all the extra greenhouse gases (GHGs) in the atmosphere. There are two parts to this. Firstly, the GHGs are not as effective as clouds when it comes to blocking the transmission of thermal radiation to space: they absorb in spectral bands related to the vibrational modes of the molecules in the gases, and there are gaps in these bands ("windows") which allow radiation to escape to space.

Secondly, dew formation depends not only on the temperature at night, but also on the near-surface humidity. The increase is GHGs is, as we know, warming the Earth and this also leads to an increase in the amount of water vapour in the atmosphere, because warmer air can carry more water. To get dew formation we need a change in the temperature between night and day -- and GHGs don't contribute directly to this.

There is an indirect effect which we see in nights getting warmer faster than days. There are several recent studies looking at the vapour pressure deficit (VPD) and showing an increase due to GHGs (e.g. Ficklin and Novick) -- VPD is a measure of the dryness of the air and an increases means less dew (though I have not found a reference that give direct evidence of reductions in the amount of dew). This drying of the night-time may also contribute to reduced harvests (Sadok and Jagadish).


Coral growth keeping up with sea level rise? On 11 sep 2016, the Australian Herald Sun placed an opinion piece by Andrew Bolt titled Drowning in cash: Pacific islands love this scare* about the $300 million** financial aid pledged by the Australian Prime Minister, Malcolm Turnbull, at a Pacific leaders’ forum in Micronesia last week (I guess that's this meeting), to help the Pacific “manage climate change and improve disaster resilience".

Bolt's critique is that these islands do not actually face much danger:

  The scare that these islands risk drowning as man-made warming melts our ice caps is wildly exaggerated.
  Professor Paul Kench, an Auckland University coastal geomorphologist, along with Australian scientists, has studied more than 600 coral reef islands.
  His findings: about 40 per cent have actually grown in size. Another 40 per cent stayed stable, and just 20 per cent have shrunk.
  Much of that is because coral islands, essentially living things, grow with rising seas, as well as with sand washed up by the waves.
  What’s more, populated islands can reclaim land.

Paul Kench's page at the University of Auckland lists several of his publications, and maybe the blog post refers to this one:
Destruction or persistence of coral atoll islands in the face of 20th and 21st century sea-level rise?
From the abstract:

  Here, we analyze the physical changes in over 200 islands on 12 atolls in the central and western Pacific in the past few decades when sea level in the region increased at rates three to four times the global average. Results show little evidence of heightened erosion or reduction in island size. Instead island shores have adjusted their position and morphology in response to human impacts such as seawall construction and to variations in climate–ocean processes.

The article is behind a paywall, so I cannot look at the actual study - the abstract does not mention anything about coral growth.

As far as I know, sea level rise is going to be much faster than coral can grow, plus we have the complication factor of reduced grow (or actual coral death) because of rising sea water acidity and temperature.

But it's still an intriguing question: Could there be a hint of truth in this, that coral growth could keep up with sea level rise?
Maybe with a little help from us?
Has this been investigated?

* You may have trouble following this link directly. In that case go to the start page, Andrew Bolt's blog, and look up the article there.
** Australian dollars, I assume. That would be US$ 227 million

I have worked as a climate-change specialist in many countries including those with coral atolls, such as the Maldives, Solomon Islands and Samoa. I have analysed, at first hand, both the the tide-gauge and satellite-based rates of sea level rise. Notwithstanding the non-scientific writings of that well-known journalist, Andrew Bolt, the demonstrable truth is that ocean acidification is real and unstopable for the foreseeable future. The sea surface is warming faster than expected a decade ago, and the rate of sea level rise is accelerating. In the southwest Pacific, which is particularly prone to El Nino intensification, these affects are even more alarming.

I point out that Bolt has zero scientific credentials, has never done any climate research, and is only able to make a living as a climate-skeptic writer because many Australians are, by nature, predisposed to enjoy 'contrary' arguments, irrespective of the science.

Much research has gone into coral growth over the last decade, particularly in peri-Australian waters. Current findings are that, under optimum conditions, the fastest growing corals can indeed grow fast enough to keep up with the current rates of sea level rise. However, this cannot continue indefinitely. The reef is a total ecosystem, of fast and slow growing corals, bryozoa, etc., which has an aggregate rate of growth of less than the rise of sea level. Fast growing pioneering corals eventually collapse if left to continue growing ahead of the rest of the biome. Note also the phrase "under optimum conditions". As Jan Doggen rightly points out, sea-surface warming beyond the optimum thermo-tolerance, acidification, and water pollution are all serious stress factors. Between them one can say that, apart from deep-water corals, there is hardly a coral reef on the planet that isn't  suffering from sub-optimal growth conditions.

There is another somewhat unexpected threat to corals: ordinary sun-cream from holidaymakers swimming near reefs. The common sun-cream component of oxy-benzone (present in most sun-creams) is toxic to corals at only about 60 parts per trillion. Globally, an estimated 10,000 tonnes of sun-screen ends up in the oceans, near corals, every year. This has a noticeable negative impact on the reef.

Taken altogether, this quadruple whammy bodes ill for the world's coral reefs. When the reefs die, and sea level rises there will be nothing to stop sub-tropical waves eroding the very land that some Pacific Islanders live on. Even islands with higher elevations still have fringing reefs. They are all in trouble, because sea level rise and higher erosion rates will force a retreat from the coast (hopefully planned), with massive social, environmental and economic disruption. So yes, they are absolutely justified in getting agitated about reef degradation!


Simulating the earths crust I would like to create a computer simulation which would fold two plane-ish surfaces into two crumpled-ish surfaces. This in order to simulate the earths crust movement and collisions resulting in mountain chains, vallies and hills etc.

Is there any existing calculations or models for this? Are these models already put into computer simulations or are they just available on paper?

What is the math behind this?

I am afraid that you aren't being specific enough to really answer your question: What about mountain chians valleys and hills are you interested in? There are simple and complex models dating back from the 1960s to present. Are you interested in learning about the material properties of the crust, or just topography in general? What about weathering effects? What about the flow laws that govern the lower and middle crust (depending on who you talk to).

I would look into the field of dynamic topography and how that is calculated.

Two books that I think might be useful to read are Fowler and Tourcotte and Schubert, they will help give you an overview of geodynamics as a field, and what engineering solutions we apply to Earth. In the 1-D and 2-D flow sections there is much about the crust.

A good starting paper might be Bird 1991 (sorry, its probably behind a pay wall, but I couldn't find an open pdf on it).

As far as codes (and consquently mathematics) The two sections of CIG I would look at are S-T Dynamics and Mantle Convection.

I am sorry I couldn't provide a comprehensive answer, but I think the sources I've linked may give you a good start and thinking about this problem.


Differences between TEOS-10 and EOS-80 for salinity In 2009, the oceanographic community decided to adopt the Thermodynamic Equation Of Seawater - 2010 (www.teos-10.org) as the standard to calculate the properties of seawater. As part of that, they changed from the conductivity-based salinity (Practical Salinity, PSS-78, as part of the EOS-80) to Absolute Salinity (mass fraction of salt in seawater). What are the main differences between the two standards? Where in the world ocean should we expect to see the biggest differences between the two?

From my reading of the primer and manual, I would summarize the difference as follows. Practical salinity is calculated directly from the conductivity of seawater (which is what's most often measured by buoys, floats, and other autonomous systems) whereas absolute salinity is based on the density of the seawater. Practical salinity is essentially measuring the distribution of ions in the seawater. Absolute salinity is based on the mass of all non-H2O material, whether it's ions, gases, or solids. Relating salinity to mass, rather than conductivity, makes writing conservation equations much more straightforward; a dissolution of HCO$_3^-$ into H$^+$ and CO$_3^{2-}$ changes the practical salinity but not the absolute salinity. Basing salinity on mass also makes the thermodynamics much simpler, but I'll address that in your other question.

Differences between the practical and absolute salinities crop up where there are big differences in the composition of seawater, especially in its dissolved but non-ionic components. Page 14 of the manual (Fig 2) has some maps of what this looks like: Large deviations in the lower-salinity Pacific, and large deviations at depth where density and conductivity aren't so closely related. Absolute salinity can handle measurements of seawater composition in a way that practical salinity doesn't.


Interpreting some hydropower data. What does DSF mean in this context? This is the historical feed of the Keystone dam for October 2014:

www.swt-wc.usace.army.mil/chartbin/KEYSOct14.shtml

Here is the real time feed:

www.swt-wc.usace.army.mil/ops_hydropower/KEYShydro.html

I am having trouble understanding the "Releases DSF" Power/Total columns. What do these mean? I understand that DSF is day-second-feet but that is a unit of volume NOT flow rate. The real-time feed shows the flow rate in CFS (cubic feet/second). The dam is rated at around 70 MW. Do you think that the column in the historical data is mislabelled as Power when it should be Energy (MWh)?

I understand that Power = Height of Dam x Flow Rate x Efficiency and this makes sense in the real-time feed. However, I am having trouble reconciling the historical data with the real time data.

Bottom line: I want to know the power / energy generated at the dam historically and in real time.

I think the DSF releases are both measures of releases. Neither is a measure of power. They are both a measure of the amount of water released, in day-second-feet, as you say.

The total column is the measure of the total amount of water released (in DSF). The power column is the amount of water released in order to generate power (in DSF). The difference between those two numbers is the amount of water (in DSF) released down the spillways (rather than to generate power), as part of overflow prevention, maintenance, or other activity.

On the realtime feed, the column labelled power looks like mean power to me in MW: the dam rating is 70MW, and the power column maxes out at 70.267, so that does indeed look like MW. So that's the average over the quarter-hour. Multiply by 0.25 to get MWh.

footnote rant:
Feet? Seriously? Feet? Who uses feet? What's wrong with these people?


Why do meteorological seasons start earlier than astronomical seasons? In meteorology the seasons always start at the beginning of the month the astronomical seasons start.
The astronomical seasons start around the 21st in a month so I guess it would make more sense to start the meteorological season at the first day of the month following the start of the astronomical season.
Another more logical reason to do this: for example the meteorological winter start at December 1 and ends at February 28 (or 29) in the next year so meteorology actually measures in broken years. Should the meteorological winter start at January 1 and end at March 31 then all seasons do exactly fit in the same year.
So is there a reason why meteorologists do it this way or is it just arbitrarily chosen?

Meteorological seasons are based on temperature, whereas astronomical seasons are based on the position of the earth in relation to the sun.  So meteorological winter is the three coldest months of the year (December, January, and February) and meteorological summer is the three warmest months of the year (June, July, and August).  More information can be found on this NOAA web site.


What techniques are used to date asteroid impacts? How do scientists use data at the crater site to estimate when a meteorite or asteroid impacted the earth?

Several possible ways..

Stratigraphic (Local):

If the crater has been buried, just date the first rocks that are on top of the crater but not disturbed by it; this can be done using fossil-based dating if no good radiometric techniques are available.  This has the advantage of being unambiguous, but the problem could be, especially for land based craters, that there is a gap between crater formation and new sediment deposition.

Stratigraphic (Regional)

If you can find a layer of ejecta (famously the layer of Iridium-rich ejecta from the K-T impact) and relate it to your crater, then you can often date this very precisely, more so than the disturbed area around the crater itself.  This has the potential to be more accurate than any other method, but you have to be sure that the Iridium-rich layer you are dating actually corresponds to the crater.

Radiometric

A large impact will almost certainly melt some rock locally at the site of impact, resetting any radiometric 'clocks' in that rock. If you can locate this impact melt, then there are a variety of radiometric techniques that you can apply to it, depending on the mineralogy. Potassium-Argon would be an example.


Is ground level ozone dangerous to human health when other pollutants are not present, for example, at high altitudes? In mountainous areas there is often little or no air pollution such as particulate matter, sulphur/nitrogen dioxide etc. However, ground-level ozone is frequently more present at these higher altitudes. For example, in the Pyrenees mountains between France and Spain there is little or no pollution however they show high ozone readings. The Alps show the same situation.

Reference maps:

http://www.eea.europa.eu/themes/air/interactive#b_start=0
http://www.eea.europa.eu/themes/air/air-quality/map/airbase/air-quality-statistics-at-reporting-stations#content-core

Yes high ozone levels are bad for human health and plant development.

Integral to your question is the natural high ozone concentrations at altitudes where you are near the tropopause.  The stratosphere has a lot of ozone and it gets entrained to the air around high elevation mountains quite often.

You could read what the US EPA has to say about ground level ozone: http://www.epa.gov/airquality/ozonepollution/ which is relevant in terms of the health effects and the ecyosystem effects links.

It says: "Breathing ozone can trigger a variety of health problems including chest pain, coughing, throat irritation, and congestion. It can worsen bronchitis, emphysema, and asthma. Ground level ozone also can reduce lung function and inflame the linings of the lungs. Repeated exposure may permanently scar lung tissue."

The National Ambient Air Quality Standards for ozone is 75 ppbV for an 8-hr average.  This means that if a county has 4 days per year with exceedances of the 8-hr avg threshold (over a 3-yr average), the air quality does not meet the Federal standard.


Does the Columbia Basin, North Cascades and Idaho Panhandle/Clearwater get a lot of violent, rotating supercellular thunderstorms? Every storm season, supercells erupt in Montana and Wyoming. Wayward cold-core setups can trigger supercells or even long-tracked strong tornadoes in the Columbia/Willamette Valley and the rest of SW WA. Examples abound: 4/5/1972, 6/29/1989, 2/8/1993, 1/10/2008, 6/4/2009, 8/12/2014, 5/4/2017, the list goes on, and on, and on.

However, I'm asking about severe weather in the region directly wedged in between the two aforementioned regions; all of WA east of the Cascades (East Slopes, Yakima Valley, Palouse, etc. This includes the southern Okanagan and the Kootenays in B.C.), and northern Idaho. Spokane/Coeur d'Alene, Pullman/Moscow, Lewiston, Wenatchee, Kelowna, Penticton, etc. Maybe even down to Boise.

Is this an area that can have favorable conditions for rotating supercell storms (the kinds that can spawn significant tornadoes or drop monster hail), like in neighboring Montana, Wyoming, or the Deschutes Basin in central Oregon?

Such a region is on the leeside of the Cascades (which means capping inversions), and right in the firing line of monsoonal plumes from the Four Corners states, so to me it seems logical that (at least on paper) the northern reaches of the Inland Northwest can support supercellular development.

Addendum: I was asked to source my "Deschutes gets monster hail and significant tornadoes" statement. For hail: if you look at the SPC storm reports for May 4, 2017, you'll see that 1.75-2" hail was recorded in Bend, as well as the towns of Sisters OR and Madras OR, around 10:30-11:00 p.m. PDT (0530-0600Z) on the 4th. For the Pacific Northwest excluding Idaho, I'd say those are some pretty darned big hailstones, and qualify as "monster hail" in a relative sense. Supercelluar thunderstorms are also not unheard of in this area, like the July 9, 1995 supercell in Redmond OR. As for tornadoes, I was wrong. I checked the Tornado History Project map, and it looks like most tornadoes to hit the Beaver State are west of the Oregon Cascades.

Note: These inputs are of a meteorologist who has quite actively tracked severe
weather around the US for a couple
decades... but also hadn't spent as much time in or attention on the west and northwest of the country.  So there could could theoretically be some degree of unintended bias.  I've tried to use objective data where possible, but it's something to keep in mind, regardless.

In terms of "a lot", at least for tornadoes/hail, I'd suggest that nowhere west of the Rockies sees a lot truly:

Tornadoes [left], hail [right]... source: Storm Prediction Center SVRGIS page
I'd offer the idea that there of perhaps two notable reasons for that:

The lack of consistent and widespread surface wind fields favorable to tornadoes... due to a combination of the lack of the big lee cyclogenesis seen east of the Rockies, along with the complex topography.
The rarity of regular low-level moisture significant enough to allow for low LCLs.  The higher the storm base is above the ground, the less likely a tornado
[in figure 6 of Edwards and Thompson 2000, all the red boxes showing tornadoes are on the left side, which are lower LCLs]

The lack of rich low-level moisture is due in large part to the lack of accessibility from warmer moisture sources, particularly the Gulf of Mexico; the Rockies provide a barrier to much of the moisture reaching further west.
As you note, parts of Wyoming and Montana do see supercells and tornadoes a bit more often... but on a good topographic map, fair parts of those states are east of the Continental Divide, and so still on an "upsloping" area and thereby not blocked by sinking regions which prevent full moisture progress.  They're still less-tornado prone due to elevation and increased distance from moisture, but it does happen.
The desert southwest also does manage to get monsoon moisture sneaking around the terrain further south... but further north that monsoon moisture sees additional blocking by the more elevated terrain across Nevada and Utah.  (And in the southwest, a different key ingredient in tornadic supercell development is typically missing in the summer monsoon: upper-air winds sufficient for supercell development)
The Pacific Coast does see a few occasional tornadoes.  But from what I've seen, they typically form from smaller storms with much less classical and intense mesocyclones.  As you mention, they're a bit more in line with cold-core setups, which usually produce weaker short-lived tornadoes than classic supercells of the Plains and on east.  If you plug in the events you speak of into SPCs Severe Weather Events archive, [pick the date, then click Obs and Mesoanalysis on the left, then use the dropdowns to find various parameters]
you can see that CAPE was typically very meager (well short of 1000 J/kg) and the storm structure quite weak in reflectivity in comparison to a classic supercell, more indicative of such cold-core setups.
Capping inversions may be helpful to "keep the lid on the pot" if you have strong CAPE (and therefore quality moisture) and intense updrafts to erode the cap during the day.  But as it is, there isn't enough moisture typically for the cap to be a positive factor.
Quite a bit of the area you mentioned, such as Spokane, makes up one of the more arid regions of the country.  Further removed from the rain shadow of the Cascades, the Idaho Panhandle does get more precipitation, but it's mostly in cooler months that lack the deep convective development needed for supercells, probably because of the proximity of the Pacific high in summer months.  Further east in E ID/W MT, particularly in the Flathead Valley, there are occasional summer thunderstorms... but the storms may well be higher based due to the limited low-level moisture, and so have low potential of tornadic development.  For more on the climate complexities at play in the Idaho vicinity, check out this article from the Western Regional Climate Center.
In the end, the area you ask about is one of the weakest regions for supercell development in the entire United States.  The entire quarter of the country west of the Rockies isn't much better.  This page from Iowa State University will create an image showing the number of days since each pocket of the country (sorted by National Weather Service forecast office areas) last saw a tornado warning.  It shows that the Idaho Panhandle hasn't seen a tornado warning in over 10 years:

More than anywhere but northern California.
And another ISU page allows it to be shown that:

... Most spots in northern Idaho only see about one severe thunderstorm warning per year on average (versus 10-20 per year over Oklahoma).
So the danger of severe convective weather is remarkably low in that region of the country overall.


What causes clouds to appear blue? In a thunderstorm cloud about sunset time, I saw these clouds, including some (in the upper right) that were a unique shade of blue.  I don't think I've seen clouds quite that color before.  I tried to capture the color as best I could with a digital camera, though the blue is slightly washed out in the image.  I took these images facing East at sunset time, during summer.

Optically zooming in on the blue cloud:

This answer suggests that the sunlight should be missing those wavelengths ("at sunset, when only the red/yellow end of the spectrum hits") which is consistent with the brilliant warm colors to the left.  But...the cloud was a strong and unique shade of blue, different from the blue behind it.  How does this happen?  That is, what natural processes underly the occurrence?

(Although that question is on Physics.SE, there seem to be more questions about cloud appearances on this site.)

The true reflected colour of a cloud doesn't change from white unless there is serious pollution, such as Saharan dust, wildfire soot or industrial emissions. None of these produce a blue colour, so the question really becomes 'what reflected light looks blue', and that is a function of the direction of view (towards or away from the sun), the subject's perception of colour (which can be surprisingly deceptive), and how much atmospheric blue back-scatter the cloud is reflecting. The latter accounts for most of the 'blue cloud' that we see.


What is the simplest meteorological model to operate? For teaching purposes I am looking for an atmospheric model that can be easily installed and the input data can be easily read and prepared.
Preferably I would like to run a global low resolution simulation of ~5 years. Naturally, I know this model will not have high forecasting accuracy.
Is there a model that suits this criteria?

Thanks for the help!

I think you are asking a question with a variety of different constraints. I'll tackle a couple of them.

  What is the simplest atmospheric model to operate?

That would be the Zero-dimensional energy balance model. It has almost zero resolution and no temporal capacity.

  What is an atmospheric model that can be easily installed and run?

The Weather Research and Forecasting (WRF) model is a very flexible, limited area model. This model has successfully been run on what amounts to a child's toy.

  What is a global atmospheric model that can be run for a long period of time, but can easily be run?

While I have never run it myself, it sounds like you may be looking for SPEEDY. I have not heard it is the most numerically stable model, and I cannot attest to how easy it is to run. From the documentation, it seems like it can be run one year at a time, but I was once told that it is typically stable in the range of months or even days.

Atmospheric models are not like a game you can just install and run like MS Word or a game. With almost any atmospheric model, a knowledge of programming in a Linux/Unix framework is paramount.


Is it possible to kickstart an hypothetical frozen earth with 0.6 ice albedo to an earth with an atmosphere, with just the sun at current distance? Phase change of water at different pressures and temperatures tell us that with no atmospheric pressure 200 Kelvin (minus 73 Celcius) is enough to turn ice into vapor directly
Wouldn't that suggest that solar insolation at the distance of earth to the sun heating potential is enough to kickstart the hypothetical ice planet to a waterworld with an atmosphere? Even when averaging day/night?

The answer is no.
Explanation:
No atmosphere is equivalent to all molecules being able to evade to space (This happens on planets with low gravitational force). Thus also $H_2O$ molecules will evade and I guess that many molecules already evaded during the frozen state of the planet due to sublimation. So this could be the end of this answer.
But let's suppose for a moment, even if it is not realistic, that an atmosphere could form. Top of atmosphere power received from the sun is around $S_0 = 1368 \, \frac{\text{W}}{\text{m}^2} $ ($S_0$ being the solar constant). Assuming earth is a blackbody we can equate power received from the sun and power radiated from the hypothetical earth (see also Stefan-Boltzmann law).
$S_0(1-\alpha) \pi r^2 = \sigma T^4 4 \pi r^2$
$\alpha = 0.6$ is the albedo, $\sigma = 5.67 \cdot 10^{-8}$ is the Stefan-Boltzmann constant, $\pi = 3.1415$, $T$ is earths surface temperature and $r = 6371 \, \text{km}$ is earths radius. Simplifying and rearranging yields
$T = \left(\frac{S_0(1-\alpha)}{4\sigma}\right)^{\frac{1}{4}} \approx 222 \, \text{K} = -51.15°\text{C}$.
Taking a look at the phase diagram you provided, we see that at $222 \, \text{K}$ and low pressure water naturally occurs as gas. Given the assumption that an atmosphere could indeed form (for some magical reason someone increases gravtiy) the answer is yes an atmosphere could form.


What is this spaceship-shaped cloud? This tweet from the European Space Agency (ESA)'s Spanish account show a striking photo of a round, flat, "space-ship-shaped" cloud in an otherwise completely clear sky. The stars are out so I assume this is at night, possibly with a Moon.

Could this be real? If so, what kind of cloud is it? and how can it appear out in the open?

The image shown is a lenticular cloud, a type of cloud often observed around significant topographical features such as the mountain peaks shown in the photo. Depending on the local atmospheric moisture, they can occur on their own (as in this case), apart from other cloud features.

All cloud growth depends on the condensation of water resulting from air being cooled as it is lifted vertically by some forcing mechanism. However, these clouds are an exception to more typical cloud growth, which depends on the atmosphere having a tendency (or instability) for air to continue rising - and thereby condensing more liquid water - once forced upward.

Following the initial source cited above, lenticular clouds form in environments that are stable (i.e., not conducive) to these vertical motions, so upward motion is entirely driven by air forced over an obstacle - in this case, mountain terrain. From a horizontal view, the vertical motion forced by this obstacle commonly takes the form of a persistent wave pattern:  image source

This occurs downwind of the terrain feature, with clouds forming over the portion of the wave featuring upwards vertical motion. This becomes extremely evident when viewing time-lapse videos of this phenomenon.


[How deduce from shadows, the angulation of the Sun that the Sun is 15 degrees over horizon? At r/rbi, u/A11edge asked

Can anyone determine an hour when the photo was taken?
The author of the photo is suspected of spraying pesticides during daytime (which is illegal because it causes death of thousands of bees).
Location: somewhere in Poland

XauManKib answered

Judging by the photo, I can see three main aspects: the flowers, the shadows and the upper reflection of the Sun.
Considering the colour of the sky and the overall light, this is the afternoon.
The flowers in the picture are Cruciferae, and I thinks is white mustard, common in East Europe, that is flowering between April and May, this means that the sunset in Poland, is around 1930 hours and 2020 hours in that period.
Supported by the shadows, the angulation of the Sun is clear in the reflection present in the photo, that is raffigurating [I looked up on Wiktionary], except flares, the Sun as [typo for "is"] 15 degrees over the horizon, or about 40 minutes before the sunset.
The time in the photo is between 1850 and 1940 hours.

I never visited Poland and don't know anything on it. But can someone explain boldened paragraph like I'm 5 in Simple English? How  deduce all this?

There are "flares"?

"the angulation of the Sun is clear in the reflection present in the photo"? Can someone draw on the picture to indicate this?

How deduce the Sun is 15 degrees over the horizon?

How deduce "40 minutes before the sunset"?

If you look at the shadow of the tractor on the right side of the exhaust pipe you can see that this picture is taken in the early morning or a fairly short time before sunset.

It is not possible to give you a good estimate of what time the picture is taken as this depends on the time of year.

If the picture is taken in early april it is more than one hour before sunset and more than one hour after sunrise.

If the picture is taken in the middle of may it might be whitin one hour before sunset or one hour after sunrise.