What is the (average) velocity of ocean currents? Does anybody know where to find statistical (average, standard deviation) data on velocities of ocean currents, such as

Equatorial countercurrent North of Madagascar
Agulhas current
East Australia current
Gulf stream East of Florida is about $2\,\frac{m}{s}$ (the only figure I have found)
South equatorial current North of South America
Kuroshio current
Antarctic circumpolar current (Strait of Magellan)
North equatorial (Philippines)
etc.

I have found time series data by NOAA (link), but no "postprocessed" values. Is such data available?

This is not meant to be a comprehensive answer:

Sometimes the easiest way to calculate the velocity of an ocean current is to take the published transport of the current and divide by the total depth of the current.

For instance, for the Agulhas Current, you can take Figure 2 from Casal et al. (2009) (below) and extract the velocities based on the depth of each area. Also in their Figure 6, there are several vertical sections of velocity across the current.

Also, you can obtain vertical sections of velocity for the same current (Agulhas) in earlier publications: Bryden et al. 2005 (Figure 8 and 9). Or in newer publications: Beal & Elipot (2016).

The main issue is that you will need to do a bit of digging around for each of the currents you list.


Has there ever been a case where we have found what appears to be a prehistoric fossil but have no way of dating it? I find that when ever I learn of a new fossil, the age of said fossil is always mentioned. This perplexes me given how intuitively rare it seems to have radioactive material to date a formation. I know that Paleontologists also use other fossils in the formation to date a new fossils however surely there have been cases where we have found new fossils that we have no way of knowing the age?

The short answer is no, because we always have some constraint of how old something is.  Sometimes we have fossils with large date error bars, and often we do not know for how long that species existed. A large date range constraint in some cases, like archeology, might not be useful. If the specimen is taken without noting the location it was taken from, then we have no context to date it, which is a big reason not to plunder paleontological sites.

For dating a fossil, the context of the rock layer, other fossils, cross-cutting units, and location is key.  Geologists must use a combination of absolute and relative age dating techniques.  Geologists examine the rock layer from which the fossil was found and compare that to other rock layers that stratigraphically correlate to it.  They use basic relative dating approaches, including:

Principle of Superposition: older layers on bottom, younger layers on top
Principle of Cross Cutting Relationships: if a feature (like igneous intrusions and faults) cuts through a layer, then that feature is younger than the layer
Principle of Original Horizontality: Layers are deposited in a horizontal fashion
Principle of Lateral Continuity: Layers are general deposited in a laterally continuous manner until they pinch out; if you see a canyon and similar layer on either side, you can assume it was previously continuous and the canyon is younger.
Principle of Faunal Succession: The presence or absence groups of fossils can be used to hone in on the time period

There are a wide variety of absolute dating techniques, each with its own time and medium constraints. Radiometric dating, fission track dating, and paleomagnetic approaches are typically restricted to igneous rocks. For radiometric dating, only a small quantity of isotopes are needed for a measurable date. Igneous rocks contain usable quantities of minerals like zircon that are good at holding atoms of uranium and other elements useful in for the absolute age-dating technique. Geologists use absolute dates of rocks that can be dated in combination with relative dating techniques to constrain the age of a rock layer that cannot be dated with absolute techniques.

Fossil morphology must also be considered to determine if you are really looking at a new species or just a special case of a previously identified species. Sometimes, evolutionary approaches can be applied to help place the specimen into a timeline.

Figuring out the temporal extent of a species takes more time and multiple discoveries of samples of that species to better constrain that extent.

A combination of approaches and techniques can help paleontologists be detectives in determining the age of specimen. Like other sciences, geology is social in the sense that it relies on the culmination of the work of many, with multiple lines of complementary pieces of information, to come to a conclusive age.

Here are some great articles related to your question:

DiMaggio, E. and Tripathy-Lang, A., 2019, How Do Scientists Date Fossils?: Smithsonian Magazine, online: https://www.smithsonianmag.com/smithsonian-institution/how-do-scientists-date-fossils-180972391/
Peppe, D. J. and Deino, A. L., 2013, Dating Rocks and Fossils Using Geologic Methods: Nature Education Knowledge vol. 4, no. 10:1, online: https://www.nature.com/scitable/knowledge/library/dating-rocks-and-fossils-using-geologic-methods-107924044/

Here is an example of an "undatable" fossil, where the age could "only" be constrained by 2 million years:

Yong, E., 2015, Why Don't We Know the Age of the New Ancient Human?: The Atlantic, online: https://www.theatlantic.com/science/archive/2015/09/why-dont-we-know-the-age-of-the-new-human-ancestor-homo-naledi/405148/


Calculate precipitation from WRF model output From WRF output file,

I find 3 variables related to the precipitation (unit: mm)

1. Precipitation

variable name: pr
unit:$kg/(m^{2}s^1)$
variable: RAINC+RAINNC
comments: $dt(RAINC+RAINNC)/DT$

2. Max hourly precipitation rate

variable name: prhmax
unit:$kg/(m^{2}s^1)$
variable: RAINC, RAINNC or RAINMAX1Hclwrf
comments: $MAX(dtsum()/DT)$

3. Convective precipitation

variable name: prc
unit:$kg/(m^{2}s^1)$
variable: RAINC
comments: $d_t(RAINC)/DT $

My task:

  Summarize the amount of days which precipitation > 0.254 mm

What variable should I use for further analysis?

Any advice would be appreciated.

Use (1) Precipitation, as it is the sum of convective and non-convective precipitation, integrate it over one day, voilà.

converting [$kg/(m^2 s)$] (precip):
$$ precip [kg/(m^2 s)] \cdot dt [s] \cdot \frac{1}{ \rho_w [kg/(m^3)]} \cdot 1000 [mm/m] = total\_precip [mm]$$

where $\rho_w$ is the density of water.

Practically the last two factors cancel.


Is the Earth heated up by the tides? Reading about moons of other planets they often get heated up by the tides so for example Io and Europe of Jupiter get friction by which eruptions and liquid water can arise. But is there also an effect on Earth due to the tides of the moon and sun? If so how many degrees is the Earth heated up?

A good estimate of the lunar tidal energy dissipated into the oceans is 2.5 Terawatts (Munk, 1997; Le Provost & Lyard, 1997). The value estimated comes mainly from two different sources: from harmonic calculations and from altimetry estimates using satellite observations (e.g., Topex/Poseidon).

The input of energy into the coastal ocean is not uniform and has a peak in the South Atlantic Ocean, while the energy is dissipated by bottom friction in the coastal ocean and mainly in the North Atlantic Ocean (Le Provost & Lyard, 1997).

Source: Nature: Egbert & Ray, 2000. Estimates of tidal energy dissipation.

Egbert & Ray (2000) showed that a fraction of the dissipation (1 TW) takes place in the deep ocean in areas of, generally near areas of rough topography. Maintaining ocean stratification and the large scale thermohaline circulation (the commonly known "Conveyor Belt") requires around 2 TW to provide enough mixing (Munk & Wunsch, 1998). Therefore, the tides provide about half of that energy with the other half coming from wind forcing.

Here is a summary figure from Munk & Wunsch, 1998.

The repercussion of this fact are given by Wunsch (2000):

  ...it was only recently recognized that the need for an energy source to sustain the vertical mixing (lifting dense water through lighter) has important consequences. The difficulties of driving fluid motions by surface heating and evaporation mean that a mechanical source of energy must control not only the directly wind-driven flows, but also the deep-water components of the meridional overturning circulation.

  ... changes in tidal distributions and the consequent mixing would need to be understood over geological time. During the Last Glacial Maximum, the sea level was about 130 metres lower than today. This configuration removed much of the present regions of shallow-water energy dissipation and changed the deep-ocean tides, presumably affecting oceanic heat transport. Over longer periods in the past, the entire continental configuration was different, with radically different tidal distributions and mixing. It appears that the tides are, surprisingly, an intricate part of the story of climate change, as is the history of the lunar orbit.


Why is the jet stream stronger in winter? I notice on a website talking about the jet stream https://www.weather.gov/jetstream/jet

It says:

  The winds blow from west to east in jet streams but the flow often shifts to the north and south. Jet streams follow the boundaries between hot and cold air. Since these hot and cold air boundaries are most pronounced in winter, jet streams are the strongest for both the northern and southern hemisphere winters.

Why are these hot and cold air boundaries mostly pronounced in winter?

I'll look at the climates of the town of Inuvik In Canada's Northwest Territory at a latitude of 68°21′42″N against that of Mexico City at a latitude of 19°26'N. In July, the daily mean temperatures are 14.1°C in Inuvik and 18.2°C in Mexico City — a difference of 4.1°C.

Compare that small difference with the daily mean temperatures in January of -26.9°C in Inuvik and 14.6°C in Mexico City – a huge difference of 41.5°. That factor of ten increase in the temperature difference in winter over summer drives a lot more north-south circulation in the winter compared to the summer, which in turn makes the jet streams stronger in winter compared to summer.


Is this a rock with metal or gold? I found these really hard rock while i was excavating. It caught my attention the different colors.

If it's really hard, I'd tend toward an iron base mineral of some kind. Gold is not very hard. Just hedging bets, you should always bet iron because its so common.

It also doesn't look like any gold ore I've ever seen, but I've only ever seen pictures. I understand that gold ore usually has free and unattached veins (looks like lovely yellow gold stuck in a rock), while the small remaining minority is wrapped up in pyrite or something else by as much as 1 oz gold to 1 ton rock (not very profitable outside of industrial mining). Unless there's literal tons of it, I'd just carry on with your business.

I'm not sure what lab testing would cost or even how available such services are, but if you can find something cheap enough and they also promise anonymity (you want privacy if you're sitting on a literal gold mine), might be worth quelling the curiosity.

A quick google search found this site: How to Test for Gold Ore - Sciencing. The page promises to be an accurate, at-home testing method for identifying gold ore. You would need some acids (I guess you can just buy those) and gold testing wires (which might be expensive).


Are there resources for determining what percentage of the earth's surface is occupied by air conditioned spaces? EDIT: My goal with this question was to better understand the impact of cooling systems on local urban environments, but its been pointed out I am asking the incorrect questions for the answer's Im looking for. So this can be disregarded, but I'm not deleting as deleting questions seems to be frowned upon.

I am exploring some ideas regarding the impact of urbanization on the climate and our environment. My basic thought process is that the vast majority of homes and work places have some form of air conditioning(I understand many parts of the world dont, but from estimates I saw the global average is still quite high). And as I understand it air conditioning functions to displace heat(and slight heat generation from the energy usage). Like putting a brick in a bucket causes the water level to rise so too does the outside heat level rise when the heat from inside buildings is displaced.

What I am looking to find out is if there is a way to determine what percentage of the planet's land surface is covered by buildings occupied by humans to determine what percentage of the world is displacing heat from the inside of those buildings(and the area that space occupies) to outside(all the other area)

I understand not every building has air conditioning and will not being using that figure to make a determination(as my previous post had people suggesting). I am simply looking for a good place to start before adding control variables.

Does anyone have any resources to find out where one might come by these figures?

Additionally if someone has a possibly better method to find out the information I'm looking for I would love suggestions.

I would dispute the idea that the "vast majority" of the world's buildings have air con; in fact, considering that a large proportion of the world's buildings are either (a) in hitherto cool places; or (b) in undeveloped places, I would imagine that it's probably a minority. But I don't have figures on this.

The main part of the question, though, is about the proportion of the earth's surface that is built on. That could be approached as a GIS exercise, and would be reasonably easy to do in places like the UK that have freely-available maps that show all buildings... and very much harder to do in parts of the world that don't.

This study made an estimate (from various data sources, including nighttime lighting) that about 3% of the Earth's land area is "urban". That certainly doesn't include all buildings, but it also includes urban spaces that are not buildings, so it may serve as a useful first approximation.

Depending on your objective, you might find it more useful to stop thinking specifically about air conditioning and instead ask about heat produced by buildings. All buildings produce heat, whether this is from heating, cooling, or other energy use. As a proxy for this net heat production you could simply look at the buildings' energy consumption.


Resources for learning the technical parts of atmospheric modeling I'm a computer/atmospheric science undergrad and I'm trying to get into atmospheric modeling. Any recommendations for resources to get going or to learn about approaches? I can handle fairly technical stuff so don't be shy.

For fundamentals on numerical methods applied in atmosphere and ocean modeling, see the GARP publication by Mesinger and Arakawa: Numerical Methods Used in Atmospheric Models. This old, but certainly not outdated text provides the basics on time and space discretization and stability, with particular focus on solving advection equations, and gravity-inertia wave (read: shallow water) equations, and is relatively easy to digest. A must read for any meteorologist or oceanographer using or developing numerical models.

Then, an excellent textbook by Dale Durran, Numerical Methods for Fluid Dynamics: with Applications in Geophysics maintains similar application focus as Mesinger and Arakawa, but expanded with more numerical algorithms and in-depth analysis. It covers the basics as well, so it can be used as a stand-alone text.

There are many other more general CFD textbooks that contain material applicable to ocean and atmosphere modeling. The majority are more geared towards mechanical engineering applications, so you may need to apply a filter (hur hur).

On the other hand, if you are more interested in physics parameterization schemes used in atmosphere models, such as cumulus convection, microphysics, or boundary layer parameterization schemes, a book by David Stensrud, Parameterization Schemes: Keys to Understanding Numerical Weather Prediction Models, is an excellent summary of current state-of-the-art. It covers a wide area of unresolved physical processes in the atmosphere, so it does not go into too many details - if you are interested in fully understanding a particular scheme, you will need to follow the reference chain and read the particular papers on the topic. I highly recommend this one if you are interested in gaining an overall understanding of parameterizing atmospheric physics processes.


What are the technical solutions to measure $\ce{CO2}$ emissions? I'm currently at COP24 (United Nations Climate Change Conference) in Katowice, Poland.

(some editing since I took a screenshot of my laptop)
I've asked some guys about $\ce{CO2}$ emissions but very few have sufficient technical knowledge.
My assumption is that they assume the data is right.

Some Google-fu:
https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions#how-do-we-measure-or-estimate-co2-emissions

More recent energy statistics are sourced from the UN Statistical Office, which compiles data from official national statistical publications and annual questionnaires.

https://www.thenakedscientists.com/articles/questions/how-do-you-measure-carbon-dioxide-emissions

The Intergovernmental Panel on Climate Change has published a five-volume set of guidelines that all the countries now use, as part of the UN Framework Convention on climate change, for estimating emissions on all greenhouse gases and it does produce uniformity across countries.
Although there are some large power plants in which they actually put measurement devices in the smoke stack and can measure the amount of CO2 that comes out, that is unusual.

About measuring $\ce{CO2}$ in the atmosphere, we have a satellite for that: https://climate.nasa.gov/climate_resources/99/graphic-measuring-carbon-dioxide-from-space/
About air quality index - https://en.wikipedia.org/wiki/Air_quality_index - we have a number of standards for that (shame there are multiple standards)
About new $\ce{CO2}$ emissions - what are the scientific ways to measure that?

In addition to satellite measurements of carbon dioxide, there are numerous ground based stations that also measure carbon dioxide: Italy, Hawaii, Australia, just to name a few.

If you want to catch carbon dioxide emitting cheaters, a dense network of such ground based stations would be needed around the world. The measurements would need to combined with meteorological data, particularly wind directions and strength. I imagine this would also require significant computer modelling to analyze all this data in a timely manner. This would need to be operated by a totally independent organization with lots of money. This will be difficult to achieve.

Alternatively, and probably more costly would be to have a constellation of satellites in geostationary orbit around the Earth constantly measuring atmospheric concentrations of carbon dioxide. As with the ground based stations, the data would need to be combined with meteorological data and processed via a computer model.

Monitoring compliance will not be cheap or easy.


Free periodical satellite/aerial imagery There is a company called Planet Labs which sells daily satellite imagery covering the whole globe that can be used for various research  like agriculture, forestry etc. I wonder if there is a free equivalent of Planet Labs that offers periodically captured satellite or aerial imagery with decent resolution possibly on global scale or at least on regional scale (whole country). Do maybe NASA or ESA offer something periodical with decent coverage and resolution?

There are a wide ranging of publically available satellite images with different spatial and temporal resolutions. Notably Landsat (https://earthexplorer.usgs.gov/) and Sentinel (https://scihub.copernicus.eu/dhus/#/home) come to mind.
If you are interested in analysing remote sensing products at a global or regional scale, Google Earth Engine (https://developers.google.com/earth-engine) may be a useful tool for you. GEE can directly access Landsat and Sentinel products at no cost to the user.
I hope this information is of use to you.


How to write 'number of ...' in a unit? Q: Which unit is attached to 'number of particles per volume' (e.g. of the atmosphere)? The questions focuses on the 'number of' and not on the 'volume'.

The units [#/m3], [particles/m3] and [1/m3] are used in publications. Neither [#/m3] nor [particles/m3] are SI compliant. However, [1/m3] would be SI compliant but it looks ... incomplete.

edit 1:
The particles are of different size and composition. Converting the number of particles into another unit is not reasonable for my application.

In my experience $[m^{-3}]$ or $[cm^{-3}]$ as number density is very well understood throughout the communities of both earth, solar-system as well as exoplanetary scientists.

Take for example the recently published The atmosphere of Pluto as observed by New Horizons which in fig. 3 shows the derived atmospheric composition of Pluto from occultation measurments in $[cm^{-3}]$ with some model curves:

 (Property of G. R. Gladstone et. al 2016 and the New Horizons Science team)

The density in this unit is just a very natural and convenient outcome of the used occultation-inversion techniques. Thus of course the units are sometimes simply the result of the context in which a work is done, and as other commentators stated, a mole could be used.
However I'd argue that $[cm^{-3}]$ is sufficiently simple to be understood in any context and adding moles just makes things unnecessary confusing as it suggests numbers to have a unit, which they don't.
It just physically makes no sense.


Where did the daily temperature variation go? Currently central and northern Europe are experiencing a very cold, false-spring like weather phenomenon.

When i look at local weather charts, the daily temperature cycle seems to be completely gone, and replaced by a constant -8°C to -10°C, see below for an example of southern Sweden.

Taking a look at ventusky.com we also see that the cold air is being advected from colder regions in Europe to southern Sweden, as seen in this screencap:

Other locations don't display this behaviour any more:
The farther south I look, i.e. Berlin and Munich, the stronger the daily fluctuations get again, see both for comparison:

This 'constant temperature' seems odd enough for me to ask the question:

Is the constant temperature here in southern Sweden for a few days a lucky coincidence of temperature advection sources, or is this a known phenomenon and there is some interesting physics behind this?

There are (at least) five factors at play here:

the cold air advection from the north east has driven temperatures down
the cloud cover traps longwave radiation sort of like a blanket, keeping the night time temperatures from dropping
also, the cloud cover prevents solar radiation from reaching the surface and warming it
the relative humidity is near 100%, indicating that the dew point is nearly the same as the air temperature.  Dew point serves as a minimum possible temperature, so this also prevents the air temperature from dropping
precipitation traveling through the lower atmosphere will evaporate, having two effects: cooling the atmosphere and maintaining a high dew point

(5) is only really a factor during the day when temperatures would normally be on the rise.  The precipitation will keep the diurnal heating to a minimum.


Reversing the desertification What will be the effect on a desert-like area if it is covered with millions of umbrella-like structures like the following one?

Would it play any positive role in reversing the desertification?

It would depend on the reflectivity of the material used - a lighter color will reflect more solar radiation and help cool an area fairly quickly , but it would take longer for the area covered with such structures to experience changes in  poleward. energy transport. The poleward heat transport determines where the jet streams are located and how far north and south tropical rains (intertropical convergence zone) move. Thus, whilst the structures would cool the area, there would likely be insufficient rainfall to re-establish substantial plant life and reverse desertification.

In short, because of the need for water and the mesoscale weather patterns in a desert, shading the deserts would have little effect on the rate of desertification.


St. Elmo's Fire not dangerous? I know that St. Elmo's Fire is a form of plasma that occurs during thunderstorms that is similar to lightning because it is formed by a difference in charges.

But why isn't it dangerous if St. Elmo's Fire is around you?

For one, the fact that there is a charge difference usually means an electric shock, whether that is a tiny bit of static electricity from touching metal or a lightning strike. Yet St. Elmo's Fire is caused by a charge difference but doesn't give you an electric shock.

Also if there is a charge difference around you, lightning is more likely to strike you, even if you are as low as you can be. This can lead to heart problems such as tachycardia, fibrillation, or asystole. It can also cause uncontrollable muscle movements which itself can be dangerous because if your muscles are out of control you can end up anywhere. Muscles being out of control can also mean things like vomiting, lots of mechanical digestion, high blood pressure and more from involuntary muscles being out of control. In any case it is dangerous to have voluntary or involuntary muscles out of control. It can also cause nervous system problems, in particular excitation toxicity from positive charges continously reaching neurons until they don't send a signal.

So with all the health problems that can result and the difference in charges itself without an electric shock, why is St. Elmo's Fire not dangerous?

As you say in your question, ball lightening and and St Elmo's Fire are related to thunderstorm activity (e.g., Griwr'ev et al, 1991). Grigor’ev et al (1999) worked out a formula for the charge on small drops of water (which is a bit complicated for a simple answer), but suffice to say the total voltage involved  is high when you scale from one drop to millions. For example ~30kV per cubic centimetre is in the literature for initiating Ball Lightening, and lower for St Elmo's Fire because the coronal discharge nucleates on pointed or sharp objects.

If you troll physics forums about demonstrating St Elmo's fire in a laboratory setting, you'll see that it is actually quite dangerous, due to the high voltage. Most suggestions by physics teachers are to demonstrate the effect in neon gas, rather than air, and within glass bulbs. So one answer to your question is that the effect can be dangerous, e.g., when creating conditions of coronal discharge in an experimental setting.

What about in a natural setting? You can read in Griwr'ev et. al (1991) about several hundred reports of St Elmo's Fire sightings, but it isn't mentioned whether anyone has been 'within' the effect. However, St Elmo's Fire was observed on the Hindenburg shortly before it exploded (Robinson, 1964); not that this was the likely 'spark' that caused the explosion, but part of the prelude.

I can't find any verified reports of people immersed in St Elmo's Fire during my quick review of published literature, or non-peer reviewed sources like Scientific American and Wikipedia. There is an interesting reference in Wikipedia to Tesla managing to light up some butterflies with one of his coils, though!

Griwr'ev, A. I., I. D. Griwr'eva, and S. Shiryaeva. "Ball lightning and St. Elmo's fire as forms of thunderstorm activity." (1991)

Grigor’ev, A. I., and S. O. Shiryaeva. "Critical conditions for instability of a highly charged oblate spheroidal drop." Technical Physics 44.7 (1999): 745-749.

Robinson, Douglas. LZ-129 Hindenburg. New York: Arco Publishing Co, 1964.


How much of the Earth's surface was covered with water during the Mesozoic? When the Earth was at its warmest, and there were no ice caps at all, not even during the winter, and thermal expansion meant a certain amount of water took up more space, what ratio of Earth's surface was covered in water?
Also, how much more expansive was water back then? 5% or so?

At that time there were large areas of shallow seas, so small differences in elevation could lead to large differences in water area. I doubt that the elevations are well enough known to estimate the area precisely.
https://dinosaurpictures.org/ancient-earth/#90
The coefficient of expansion of water is only $207 \times 10^{-6}/K$. 15 degrees would give 0.3%.


Is there an estimation how much organic matter there is still in the ground? Oil, gas and coal are produced from organic matter. But is there an estimation how much is there still under the Earth's surface?

There are estimates produced my the major coal, gas and oil producing nations, but there are large error bars for some of them.

Wikipedia has oil, gas and coal split down by country - well worth a read of this or the CIA World Factbook, especially on the description of the various categories of oil reserves (Proven and Unproven and the various estimation methods used to work out how much is actually likely to be retrievable) but in summary:

World Coal Reserves - 909,064,000,000 tonnes
World gas reserves -  175,400,000,000,000 cubic metres
World oil reserves -  1,324,000,000,000 barrels

Now these numbers may not mean very much unless aligned with production and usage rates.


How would weather change on a tidally-locked terrestrial planet? On Earth, weather is very much affected by the Earth's rotation around its axis and around the Sun. Even locations that are almost on the equator do have strong annual variations in precipitation and other characteristics. On the other hand, on a tidally-locked planet (TLP), there are no cycles. The star is still on one place on the sky. From the point of view of the global circulation models, which are most often used for studies of the climate of TLP, this is an ideal steady state.

My question is: What weather changes and cycles should one expect on tidally-locked planets, where no astronomical cycle acts as external forcing? Would the weather in a particular location change at all?

My best estimate on what would happen is the following:
 - At the twilight zone there would be tremendously fierce and constant windstorms as the heavier cold air rushed from the dark side to displace the lighter air warmed by the Sun.
 - Additionally, the wind patterns would generally align themselves towards and away from the twilight zone.
 - Over a millennia, the storms would probably carve canyons and deep scars into the face of the planet along the twilight zone.
 - Relative calm would be found in the area closest to the Sun as well as farthest from the Sun.
 - If the planet were inhabited, the inhabitant would probably be locked to either the light side or the dark side unless they had some method of navigating through or around the storms.
 - I don't know if it would rain or not, but if it did, it would definitely only rain on the side facing the Sun, as the other side would be perpetually frozen.

I'm not a meteorologist, this is just a thought exercise, so I don't know how accurate any of this is (although I do have some basic knowledge of meteorology).

EDIT: I found this wikipedia article, which seems to support my theories.

  Due to differential heating, it was argued, a tidally locked planet would experience fierce winds blowing continually towards the night side[citation needed] with permanent torrential rain at the point directly facing the local star, the subsolar point. In the opinion of one author this makes complex life improbable. Plant life would have to adapt to the constant gale, for example by anchoring securely into the soil and sprouting long flexible leaves that do not snap. Animals would rely on infrared vision, as signaling by calls or scents would be difficult over the din of the planet-wide gale. Underwater life would, however, be protected from fierce winds and flares, and vast blooms of black photosynthetic plankton and algae could support the sea life.


Difference between isotherms and isotheres I encounter both similar terms while reading, isotherms and isotheres. Could someone help distinguish and explain to me the difference between them?

The general term isotherm refers to a line of equal or constant temperature, while isothere refers more specifically to lines of constant average summer temperature.

For what it's worth, coming from a background in forecasting and research centered around active weather rather than longer-term climate, isotherm is an extremely commonly-used term in weather discussions but I can't recall ever seeing isothere used in practice before now.


Books for learning applied seismic geophysics I am a software developer trying to learn applied geophysics. Specifically I am interested in seismic attributes. I have a strong background in mathematics and signal processing and therefore grasp the theory quite easily. However the geology and the applied part is a problem for me. What i would like is a book/tutorial that takes the reader trough very detailed concrete examples with no theory whatsoever. Any suggestions?

Here's a list of resources I've compiled before. Between them, maybe you'll find what you're after:

Some important geophysics papers and books: Must-read geophysics.
Six books about seismic interpretation — most of these include something about seismic attributes.
Six books about seismic analysis — more quantitative, and usually with lots of theory. I especially recommend Simm & Bacon.

I recommend learning what you can about rocks — their genesis, their properties, and especially their acoustic and elastic behaviour. If possible, go and see outcrops or at least cores. If possible, take classes in sedimentology, petrology, or even reservoir engineering.

You need to read about integrated interpretation; here are some other phrases to look for: well ties, phase estimation, spectral decomposition, seismic inversion, pre-stack seismic analysis, AVO. I recommend subscribing to CSEG Recorder, EAGE First Break and SEG Leading Edge.

Good luck in your quest!


Relation between molecular mass and retention of a gas on a planet An Introduction to Our Dynamic Planet under section 2.4 "The origins of the atmosphere and hydrosphere"(Page 80) says on the topic of gases escaping from our atmosphere as:

Different gases have different molecular masses, so their average velocities are
different at a given temperature. In order for a planetary body to retain a particular
gas in its atmosphere for a period of time of the same order as the age of the Solar
System, the average velocity of the molecules in the gas should be less than about
one-sixth of the escape velocity. (If the average velocity exceeds one-sixth of the
escape velocity, a significant proportion of molecules will be moving faster, and will
be lost.) This condition is achieved on only a few planets and satellites.

I didn't really understand where did this " one-sixth of the escape velocity" figure come up from. Is there some rigorous mathematical derivation or physical significance of this figure? In the previous page, the book had introduced the concept of how the velocities of molecules for a gas follow the normal distribution, and only those molecules which have velocities greater than or equal to the escape velocity of a planet can leave the surface(the formula for which was also shown). But I wasn't able to link this with the paragraph mentioned above. Any derivation/logic for this one-sixth figure would be welcome

I didn't really understand where did this "one-sixth of the escape velocity" figure come up from.

The "one-sixth of the escape velocity" a ballpark number. As a general rule, three sigma events (events that are three standard deviations from the mean) happen all the time, while twelve sigma events are so very, very rare that they can essentially be ruled out. Six sigma events are rare but do happen. In a logarithmic sense, six is halfway between three and twelve.
A bit less hand-waving, it can be shown that the Jean's escape flux (which is what your text is addressing) is proportional to $v_s \, (1+\left(v_e/v_s\right)^2)\,\exp\left({-\,\left(v_e/v_s\right)^2}\right)$ , where $v_s$ is the expected value of the magnitude of the three-dimensional velocity of the gas at the top of the exobase and $v_e$ is the escape velocity at the top of the exobase. That factor of $\exp\left({-\,\left(v_e/v_s\right)^2}\right)$ means that Jean's escape is extremely sensitive to changes in $v_s$.


Extracting Regional Data from ERA5 This is coming from a newcomer, so please be kind.

As I delve into the world of meteo data and reanalysis for the first time, I found that acquiring weather data is a lengthy process, so I'm shouting out for some help to get me started with it.

What is the recommended workflow to acquire ERA5 data for a region of interest (ROI) for a few surface variables (precip, soilmoisutre, tempmin, solar rad)?

Is there an API that connects me (R, Python, Curl) to the ERA5 database?
Do I need to download whole (global) files even if my ROI is always within the same country? If so, are we talking about 100GB, 1,000GB or 10,000GB of data for 6 variables, whole historical?

Seems like there are plenty of tools to extract ROI data from grib files. What is the recommended tool to learn in 2019?

Is CDO the most appropriate tool for the job?
Any Python/R packages that can extract and plot these data in an efficient way?

Thanks and let me know how to complement the info above

To me I am not sure why the subset option should not work with a python script. According to me it does work. Here is a sample script.

import cdsapi

c = cdsapi.Client()

c.retrieve(
'reanalysis-era5-single-levels',
{
    'variable':'total_precipitation',
    'product_type':'reanalysis',
    'year':'2010',
    'month':'04',
    'day':'07',
    'area':'60/0/0/100',
    'time':[
        '00:00','01:00','02:00',
        '03:00','04:00','05:00',
        '06:00','07:00','08:00',
        '09:00','10:00','11:00',
        '12:00','13:00','14:00',
        '15:00','16:00','17:00',
        '18:00','19:00','20:00',
        '21:00','22:00','23:00'
    ],
    'format':'netcdf'
},
'precip.nc')

UPDATE
In response to some of the comments raised by @Nemesi - with this CDS Python API
There is no need to use CDO or NCO to subset the data. The API itself takes care of it for you using the keyword area. Once you specify the bounding box the data that goes get downloaded is the bounding box boundaries you specify. There is also NO programmatic subsetting of global data. Right now the CDS web interface does not allow you to do subsetting(the problem is being fixed as I write according to Copernicus support). But that is not really a problem. Since OP's requirement is one of automating the process the CDS Python Web API fills the purpose. In this context subset is the same as ROI or region of interest.

Here is what I had to do get this to work. I had to install the cdsapi for python. One can do this using pip (I usually do it - python3.6 setup.py install since I do not have conda). Then create a .cdsapirc(on Linux and other UNIX flavors it should be under the main home directory. Create this file wherever you have the $HOME variable defined) which should be like this -

url: https://cds.climate.copernicus.eu/api/v2
key: {UID}:{API key}
verify:0

The values of UID and API key you should get when you register at the new CDS web interface site.

And then just run it.

Here the key parameter is the  area

and the first two values are starting latitude and longitude followed by the ending latitude and  longitude. When I viewed the downloaded netCDF file using ncdump it did have the right bounding box values. Now you could change it to GRIB format if you so wish but I think the basic format of the script does not change.

Here is a plot of the subset of the precipitation for a specific instant in a 24 hour period.

Here is the code that plots it (I use matplotlib and cartopy)

from netCDF4 import Dataset,num2date
import cartopy.crs as ccrs
from cartopy.mpl.ticker import LongitudeFormatter, LatitudeFormatter
from cartopy.util import add_cyclic_point
import matplotlib as mpl
mpl.rcParams['mathtext.default'] = 'regular'
import matplotlib.pyplot as plt
import numpy as np

file = "precip.nc"
nc_pvFile = Dataset(file,'r')
lats = nc_pvFile.variables['latitude'][:]  # extract/copy the data
lons = nc_pvFile.variables['longitude'][:]
lats = lats[:].squeeze()
lons = lons[:].squeeze()

preciPlot = nc_pvFile.variables['tp'][:]

pp = preciPlot[0,:,:]

ax1 = plt.axes(projection=ccrs.PlateCarree(central_longitude=180))
clevs = np.arange(min(pp.flatten()),max(pp.flatten())*1000,1)

shear_fill = ax1.contourf(lons,lats,pp*1000,clevs,
                      transform=ccrs.PlateCarree(),cmap=plt.get_cmap('hsv'),
                                                                      linewidth=(10,),levels=100,extend='both')

ax1.coastlines()
ax1.gridlines()
ax1.set_xticks([0, 10,20,30,40,50,60,70,80,90,100], crs=ccrs.PlateCarree())
ax1.set_yticks([0, 10,20,30,40,50,60], crs=ccrs.PlateCarree())
lon_formatter = LongitudeFormatter(zero_direction_label=True,
                               number_format='.0f')
lat_formatter = LatitudeFormatter()
ax1.xaxis.set_major_formatter(lon_formatter)
ax1.yaxis.set_major_formatter(lat_formatter)
cbar = plt.colorbar(shear_fill, orientation='horizontal')
plt.title('Total precipitation', fontsize=16)
plt.savefig('precip_era.png')


Inconsistency between topographic survey and Google Earth For a piece of land in Peru (Zone 18K), I was provided the following UTM coordinates (showing just one): 140800 E 8176337 N. However, when I look up the site on Google Earth, while the N coordinate is identical, the E one is 779875.

Anybody know what the issue might be?

It's almost certainly a difference in the UTM zones.

In most zones, the minimum easting value is 160,000 mE and the max is 834,000 mE (at the equator). People sometimes use the 'wrong' zone (i.e. not the zone that the location is actually in) if it's more convenient to use a neighbouring zone for some reason. For instance, maybe I have coordinates for 100 points but a few are in a neighbouring zone; it's probably easier to tolerate the location inaccuracy than to reference them to a different UTM zone.

The other thing that can create discrepancies is different datums (e.g. WGS84 in Google Earth, and some other probably local datum for your survey), but that's not what's going on here.

To sum up, it looks like the coordinates you were given are referenced to Zone 19K, to the east of Zone 18K, so the easting is smaller than the usual minimum. The correctly referenced Zone 18K coordinate is the one in Google Earth.

Last thing: I just want to connect with this related question.

EDIT: Conversion

Converting to the correct coordinates is a little risky without knowing exactly how the original coordinates were arrived at. But if they were indeed simply given in UTM Zone 19, then a round-trip conversion via lat-lon shows that they are equivalent to 781493.139 mE, 8177491.483 mN in UTM Zone 18.

We can confirm this with PyProj using the zones' EPSG codes:

>>> import pyproj
>>> x, y = 140800, 8176337  # Zone 19S we think
>>> utm18_wgs84 = pp.Proj(init='epsg:32718')
>>> utm19_wgs84 = pp.Proj(init='epsg:32719')
>>> pyproj.transform(utm19_wgs84, utm18_wgs84, x, y)
(781493.1384182497, 8177491.482738381)

So, if that's what originally happened, these new coordinates are what you want.


How did Earth's plate tectonics start? Plate tectonics is a theory which describes Earth's lithosphere as being composed of distinct plates which are able to move atop of the underlying asthenosphere.  At plate boundaries, this movement can give rise to convergent boundaries where subduction may occur, divergent boundaries, where molten lava rises to fill the gaps between diverging plates, or sliding plates at transform boundaries.

While I understand why we have come to adopt this theory, what I am less clear about is why  Earth's lithosphere is composed of such distinct plates in the first place, and is it possible for existing plates to split into two distinct plates?  Is there a theory on how the Earth's plates were initially formed?

Is there a theory on how the Earth's plates were initially formed?

The answer to this is has roots in another question you asked about the differences between continental crust and oceanic crust. Carlson et al. (2014) just put out an excellent review of what we know about Earth and how it formed through time. I am using it as a guide and source for much of this post.

Just recently an age of a zircon was determined to be 4.374 Ga (Valley et al., 2014) using U-Pb geochronology. The age of the Earth is 4.54 ± 0.05 Ga. This new result suggests that granitic and felsic magma was already present on Earth only after ~160 million years after the Earth formed. Some other interesting dates is the Moon formation between 4.4 to 4.45 Ga and, based on xenon isotopes, the separation of the atmosphere from the solid Earth is thought to happen around 4.45 Ga.

After the formation of the Earth, the core formed, thereby creating a metallic inner core and the primitive outer mantle. The Earth began to cool and differentiate and thereby form a crust. Different models suggest a range of possibilities such as a quasi-stable quench crust of peridotitic/komatiitic composition (Smith, J.V., 1981) to a very evolved composition approaching tonalite (Harrison,T.A., 2009).

The question now is this crust now a plate or rather, similar to the lithosphere as we know it today?  The lithosphere is defined as the brittle outer layer of the Earth and plates are segments of the lithosphere and the base of it is called the Mohorovičić discontinuity, which generally defines the contact between the lithosphere and the upper mantle. It is interesting to think about when these features may have formed as the Earth's outer crust is forming.

There is an entire GSA Special Paper volume on the subject of 'When Did Plate Tectonics Begin on Planet Earth?'. There is a range of evidence suggesting that plate tectonics as we know it today initiated at the latest around ~3 Ga to as late as ~1 Ga (Condie & Kröner, 2008). Below is a table from that paper that outlines indicators of plate tectonics.

The outer crust of Earth is likely not stationary, but possibly being dragged along the paths of mantle convection. These brittle segments begins colliding into one another and building upwards while other portions are subducted beneath other plate segments. The convecting mantle causes mantle material to be brought up from depth to conditions at lower pressures, which cause the mantle to melt (this is called adiabatic melting).

There was a paper just recently published in Nature by Bercovici and Ricard(2014) where they try to answer the question as to why we see geological evidence of proto-subduction at 4 Ga with for prominent subduction features appearing around 3 Ga. I suggest reading the abstract on the papers website but they suggest that ...

  when sufficient lithospheric damage combines with transiet mantle
  flow and migrating proto-subduction, it leads to the accumulation of
  weak plate boundaries and eventually to fully formed tectonic plates
  driven by subduction alone. - Bercovici and Ricard (2014)

On the composition of the crust...

The most incompatible elements in the mantle (e.g. lithophile elements [K,Na, Nd] and high field strength elements [U,Th]) will go into the liquid melt and move towards the surface of the Earth and either erupt on the surface or be stored in a magma chamber and further fractionate or differentiate to more felsic magma compositions.

Through time, all of these processes will generate different pieces of crust formed from different sources and at varying conditions and later become altered due to either chemical or physical metamorphism. Each of the continents we have today are pieced together from the separation and collision of other tectonic plates. For example, Pangaea was formed due to the collision of many different plates, I am not sure if Pangaea was then considered one giant plate, but it then broke apart and separated.

  Is it possible for existing plates to split into two distinct plates?

The East African Rift is currently a divergent boundary within the African Plate. So the answer is yes.


Does "wind" include the air molecules involved, or merely the kinetic energy? This question is about a riddle in which the statement "I am weightless" was made, and the answer was "wind".

I want to know, by definition, does the wind include the air being moved, and thus have a weight, or is it only the kinetic energy, and thus doesn't have a weight.

Kinetic energy is the work needed to accelerate a mass. Wind defined as the velocity air (not the same as energy, as noted in comment).

However, the air moved by wind is a good example of kinetic energy, molecules are accelerated by a difference in pressure and moved. When the pressure difference decreases, the movement of molecules stop. So yes, the wind moves matter with weight.

However, weights of gases are somehow difficult to sense, as any gas would replace the weight of the air that normally surrounds us. The weight of the air can therefore be understood as the pressure generated by the weight of all the air above. Air particles moves from high pressure to low pressure and so the wind is formed.

A way to show how efficiently the wind is actually moving the air masses, is to consider how the wind can transport solid matter, sailing boats, wind mills and even sand and rocks. For example the Harmattan, a wind from the North that transport huge amounts of dust from Sahara to the coast of West Africa and the Atlantic Ocean. Other air borne sediments can form thick formations of Loess or other aeoloian formations as sand dunes. Also consider how the wind can move clouds and how all water in rivers and lakes therefore have been transported by the wind.

I hope that this, very simplified answer will make you more interested in meteorology and Earth science in general.


Why have "ozone-depleting substances" led to a third of all global warming and half of arctic sea ice loss? According to the Phys.org article "Ozone-depleting substances caused half of late 20th-century Arctic warming, says study" (emphasis added):

  A study published today in Nature Climate Change by researchers at Columbia University examines the greenhouse warming effects of ozone-depleting substances and finds that they caused about a third of all global warming from 1955 to 2005, and half of Arctic warming and sea ice loss during that period. They thus acted as a strong supplement to carbon dioxide, the most pervasive greenhouse gas; their effects have since started to fade, as they are no longer produced and slowly dissolve.

Questions:

Do these "ozone-depleting substances" also have infrared-absorbing greenhouse impact unrelated to their ozone-depleting chemistry, or is the story more complex?
Why the different fractions; 1/3 of all global warming but 1/2 of arctic sea ice loss?

The Global warming potential (GWP) describes how much global warming a particular gas may induce in a particular time period.  It is often expressed in terms of CO₂-equivalent.  The best known greenhouse gases are carbon dioxide (CO₂), methane (CH₄), and water vapour (H₂O).  Water vapour is short lived and therefore its emission is not a primary climate change contributor (but it is a strong secondary contributor through the water vapour feedback).  However, there are other greenhouse gases that are, per unit volume, extremely strong.  Some of those are CFCs and HFCs.

Wikipedia quotes various IPCC reports and summarises the 20-year global warming potential of some greenhouse gases (emphasis mine):

CO₂: 1 (by definition)
Methane: 86
Nitrous oxide (N₂O): 268
HFC-134a: 3790
CFC-11: 7020

The GWP is a result of a combination of the strength of radiative forcing and atmospheric lifetime.  The radiative forcing is about 20,000 times stronger, due to those complicated molecules having lots of rotational and vibrational states that can absorb IR radiation.  Fortunately, their lifetime is also shorter, resulting in an estimated GWP of around 7000-11000 for commonly used CFCs.

So to answer your first question: yes, ozone-depleting CFCs have a very strong greenhouse gas potential independent of their ozone-depleting properties.  Their replacement, HCFCs, are much more gentle to ozone but still very strong greenhouse gases.

I'm not sure why their effect is relatively stronger in the Arctic.  The research article you linked provides some ideas:

  It is also legitimate to ask whether such a large contribution of ODS to Arctic warming might be an artefact of the CAM5LE model.
  (...)
  In addition to a larger RF, two factors produce an enhanced Arctic warming with increasing ODS in CAM5LE: (1) a stronger lapse rate feedback (which is positive for the Arctic, confirming previous work) and (2) a weaker negative net cloud feedback (with contributions from both long and short waves).

Note that the article seems to entirely ignore that HFCs are not phased out at all — HFCs have largely replaces CFCs because they don't destroy ozone, but still have a strong GWP.  I find that a rather serious omission because it strongly undermines their conclusion that the phase-out of ODS, which is well under way, will substantially mitigate Arctic warming (the article groups HFCs together with CFCs, which makes sense for GWP but not for ozone depletion).


At what altitude a ballon is no longer pushed by the wind? In 1960, NASA launched the "Echo 1A" balloon which had amongst its objectives to test the triangulation principle with satellites.
I wonder why we don't have more "ballon" satellites for our GPS system : they are really less expensive to operate. The only problem I see is the wind, which makes their localisation quite unpredictable. At which altitude a balloon would not be affected by the wind?

In the range where a balloon can fly, there is always wind.

The NASA Echo 1A satellite was used to test the satellite triangulation. GPS works in some other way...

The GPS system used active satellites (non-pasive as Echo 1A) that constantly supplies their position, their time and additional coding information. So the satellite position should be known and corrected constantly. With a balloon constellation it will be very difficult.

Supposing that we can install all the equipment in a balloon, the top we could reach will be 53 km. The actual Navstar GPS constellation it is working at 20.200 km from our surface. So it means that we will need a lot of balloons in order to create a similar network, with a lot of ground stations to manage it.

Even if that point could be possible, there will be additional problems, as the areas with no islands or no continents when additional ground stations should be required to correct the signal and position.

The actual GPS satellite geometry was decided in order to reduce the number of satellites with the maximum cover.


Have the seasons always been? Has the Earth had it's wobble that causes the seasonal variation in solar energy in the northern and southern hemispheres for it's entire history? Is this variation evident in the geologic record or is it an open question? Could a meteor impact like that which killed the dinosaurs 66 million years ago have altered or created the wobble? Are there any factors dampening or increasing the seasonal wobble over time?

Has the Earth had it's wobble that causes the seasonal variation in solar energy in the northern and southern hemispheres for it's entire history?

First it depends on how you define the "entire history" of the earth. There was a pre-earth that was hit by a Mars sized body. The collision fragments ultimately collapsed into the present earth and moon. Exactly how massive the pre-earth was and its orbital parameters are "unknown", meaning we know the parameters with much less precision than we know the parameters today.

Second there are two factors here. The seasonal (yearly variation) is caused mostly by the earth's axial tilt even though the distance between the earth and sun varies a bit since the earth's orbit is an ellipse rather than a circle. However the wobble of the earth is better better described as the precession of the earth's axis and it currently has a period of about 26,000 years.

  Is this variation evident in the geologic record or is it an open question?

There is evidence in geological record for season and precession changes for the present earth.

Isotopic composition of glacial ice and ocean sediments reflect yearly temperature variations. The yearly temperature changes also cause seasonal changes in the distribution of the earth's weight which effect the precession and tilt.

Lava cools leaving imprints of the instantaneous magnetic field of the earth over geological time. The interaction of the magnetic field drift and reversal, the precession of the earth, the axial tilt of the earth, and the plate movement of the earth is not well understood. It is basically governed by chaotic system interactions. For example plate movement can cause earthquakes which are as of yet unpredictable.

Again what the precession and tilt were like for the "pre-earth" is mostly a mystery.

  Could a meteor impact like that which killed the dinosaurs 66 million years ago have altered or created the wobble?

The impact that created the moon was with a Mars sized body and definitely effect the earth's precession and tilt.

  Are there any factors dampening or increasing the seasonal wobble over time?

Moon damps the tilt over geologic time. The instantaneous flow of the liquid magma inside the earth may increase or decrease the precession and/or tilt, but as the earth cools the overall effect is to decrease both.


Carbon dioxide on Mars, Venus and Earth Earth's atmosphere is 0.038% carbon dioxide. Mars's atmosphere is 95.3% carbon dioxide. Venus's atmosphere is 96.5% carbon dioxide.

If Earth's climate is controlled by CO2, then why is Mars so cold in comparison to Venus? Mars is very cold (average about –60°C) and Venus is very hot (+460°C).

Firstly, Mars is farther away from the sun than Venus or Earth, so it gets less heat from the sun. Secondly, Venus & Earth are volcanically active, whereas Mars is volcanically inert. Thirdly, the atmosphere on Mars is much thinner than those on Venus and Earth.

The density of the atmosphere on Venus is approximately $65\ \mathrm{kg/m}^3$, whereas, the density of Earth's atmosphere is $1.217\ \mathrm{kg/m}^3$ and the density of Mars's atmosphere is $0.02\ \mathrm{kg/m}^3$. Earth's atmosphere is 60 times denser than that of Mars; Venus's atmosphere is over 3000 times denser.

With such a thin atmosphere on Mars, there is little atmospheric mass to retain heat, despite the atmosphere being composed of 95.3 percent carbon dioxide.


What are seasonal and perennial ponds? I stumbled upon these terms in a text related to Pisciculture (fish farming).
I've looked on Google and Google-books but I couldn't find any type of definition.

P.S. Please let me know if I posted it in the right community.

Seasonal ponds are ponds that only exist for part of the year. Jamesqf covered it well in his comment. There is just a wide variety of terms explaining the same thing. The terms were originally used more for streams (Perennial water), but it has slid into broader usage.


What is the definition of "ground-up shell"? The archeologists use the term "ground-up shell" to designate a type of temper used for pottery. What is this material? Earth containing fossilized mollusk shells? I noticed the term is also used in texts about oysters.

I'm not sure this is the best place to ask.

Ground-up shell means just that - shells that have been ground (reduced to small particles or powder by crushing it).

Shell tempering is one of the hallmarks of Mississippian cultural practices. It is often characterized by the adoption and use of riverine, usually mussel shells, (or more rarely marine) shell-tempering agents in the clay paste.

Read more here: https://www.revolvy.com/main/index.php?s=Shell%20tempered%20pottery&item_type=topic


Is there a special name for along-course elevation profiles of rivers, and where you can you find them? Was discussing the terrain and rivers of Europe today with my father and it became apparent that a graph of the elevation versus course of a river would offer interesting insight, including a quick summary into the elevation of various cities of interest along the course, and some loose feel for the possible speed of the river in various spots.

I did find one image fitting the general theme of what I was looking for regarding the upper Mississippi River at an Army Corp of Engineer's website:

But I didn't have any subsequent luck in Googling the terms used there, nor on any additional terms, for rivers like the Rhine and Danube.

Are these along-course cross-sections made enough that there's a name for them?

And if so, is there any resource where such images can readily be found for major rivers worldwide?

I guess there are multiple names, but I know it as the river's "long profile", and it is used in academic papers (one example here and a search in google scholar here). But you can find similar diagrams under names like the river's height profile, longitudinal profile, longitudinal map or geographic profile. These last two are the ones used in an Australian government web page that have many of those profiles for all major rivers in Australia, with the cities along the river and other information. I'm not aware of a global repository of long profiles.

The following picture is from the same link pointed above (from Geography AS Notes)

A quick search for "Danube long profile" put the following image in the second position of the results

Taken from here


What does it mean for waves to "feel" the bottom? While typically waves are said to "feel" the bottom when the depth of the water is less than half the wavelength, what does it mean for the waves to "feel"?

Furthermore, why does this happen at the depth of half the wavelength?

In water wave physics, when we say that the wave "feels" the bottom, we mean that the water depth affects the properties of the wave.

The dispersion relationship for water waves is:

$$
\omega^2 = gk \tanh{(kd)}
$$

where $\omega$ is the wave frequency, $k$ is the wavenumber, $d$ is the mean water depth, and $g$ is gravitational acceleration. We distinguish "shallow" and "deep" water waves by the value of $kd$, which includes both the wavenumber and the water depth:

Shallow water waves when $kd < 0.3$;
Intermediate water waves when $0.3 < kd < 3$;
Deep water waves when $kd > 3$.

Thus, a long swell wave may act as a shallow water wave in depths of 10 m, but also a very short wave may act as a deep water wave in depths of 1 m.

How are these limits for $kd$ obtained? The tangent hyperbolic function has some convenient properties for the limiting values of its argument:

For deep water waves, $kd$ is very large, so $\tanh{(kd)} \rightarrow 1$. The dispersion relationship then reduces to:

$$
\omega^2 = gk
$$

Phase and group speeds are then:

$$
C_p = \dfrac{\omega}{k} = \sqrt{\dfrac{g}{k}}
$$

$$
C_g = \dfrac{\partial \omega}{\partial k} = \dfrac{1}{2}\sqrt{\dfrac{g}{k}}
$$

Notice that $C_p$ and $C_g$ are not a function of water depth, thus it is said that deep water waves don't "feel" the bottom.

On the other hand, for shallow water waves, $kd$ is small (approximately 0.3 or less), and $\tanh{(kd)} \rightarrow kd$. The dispersion relationship is now:

$$
\omega^2 = gk^2d
$$

and phase and group speeds are functions of water depth:

$$
C_p = \dfrac{\omega}{k} = \sqrt{gd}
$$

$$
C_g = \dfrac{\partial \omega}{\partial k} = \sqrt{gd}
$$

So, why is it said that the waves "feel" the bottom at the water depth of half wavelength?

$$
kd = k  \dfrac{\lambda}{2} = k \dfrac{2\pi}{2k} = \pi
$$

and this is approximately the value below which the regime transitions from deep water to intermediate water, i.e. $\tanh{(kd)} \approx 1$ does not hold anymore.


Great circle in UTM coordinates I've got a question about calculation of great circles in Cartesian coordinates:

Is it possible to compute points along a great circle in UTM coordinates, i.e. given two points P1(easting1, northing1) and P2 (easting2, northing2) is there a formula to get waypoints along the geodesic connecting the two (without converting to geographical coordinates and back)?

Any help is appreciated! Thanks!

The UTM coordinate system, is a kind of Transverse Mercator projection separated in longitude bands and restricted in latitud extent such that the distortions associated with the projection remain small. Also, the UTM coordinate system is conformal projection. Therefore, it preserves the angles. That means that within the UTM zones, a straight line in UTM projection is a good approximation great circle over the relatively short distances that could be found in a UTM zone. If you don't need great accuracy, you can just trace the straight line between P1 and P2.

The following plot shows the maximum deviation that a straight line have from a great circle. In this case P1 the red dot at the Equator and Longitude 3°E, and the maximum deviation is calculated for all points in the displayed box of 6°x6°.

While the differences remain small within distances of few hundred kilometers, bigger differences can be found over larger distances, specially if P1 and P2 are in different UTM zones.

If your application requires larger distances, you shouldn't use UTM projection. Alternatively, if you your application require greater accuracy over distances suitable for UTM projection, you can calculate the great circle trajectory, but I don't know any direct formulas.

What I have used, which I know is not what you are asking for, are some Matlab functions to convert to and from UTM coordinates and another that computes great circle tracks in geographic coordinates:

function [lat, lon] = greatCircle(P1,P2,N)
%GREATCIRCLE compute points along the great circle arc connecting points P1
%and P2
%   P1, P2 format: [lat,lon]
%   N: Number of points along the great circle arc

        lat1=P1(1);
        lon1=P1(2);

        lat2=P2(1);
        lon2=P2(2);

        lon12=lon2-lon1;

        a1=atan2d(cosd(lat2).*sind(lon12),(cosd(lat1)*sind(lat2)-sind(lat1)*cosd(lat1).*cosd(lon12)));
        %a2=atan2d(cosd(lat1).*sind(lon12),(-cosd(lat2)*sind(lat1)+sind(lat2)*cosd(lat1).*cosd(lon12)));

        a0=atand(sind(a1).*cosd(lat1)./sqrt((cosd(a1).^2)+(sind(a1).^2).*(sind(lat1).^2)));

        sigma01=atan2d(tand(lat1),cosd(a1));
        sigma12=atan2d(sqrt((cosd(lat1)*sind(lat2)-sind(lat1)*cosd(lat2)*cosd(lon12))^2+(cosd(lat2)*sind(lon12))^2),(sind(lat1)*sind(lat2)+cosd(lat1)*cosd(lat2)*cosd(lon12)));
        sigma02=sigma01+sigma12;

        lon01=atan2d(sind(a0)*sind(sigma01),cosd(sigma01));
        lon0=lon1-lon01;

        sigma=linspace(sigma01,sigma02,N);

        lat=atan2d(cosd(a0)*sind(sigma),sqrt(cosd(sigma).^2+sind(a0)^2*sind(sigma).^2));
        lon=wrapTo360(atan2d(sind(a0)*sind(sigma),cosd(sigma))+lon0);
end

And for the conversions:

function  [x,y,utmzone] = deg2utm(Lat,Lon,Huso)
% -------------------------------------------------------------------------
% [x,y,utmzone] = deg2utm(Lat,Lon)
%
% Description: Function to convert lat/lon vectors into UTM coordinates (WGS84).
% Some code has been extracted from UTM.m function by Gabriel Ruiz Martinez.
%
% Inputs:
%    Lat: Latitude vector.   Degrees.  +ddd.ddddd  WGS84
%    Lon: Longitude vector.  Degrees.  +ddd.ddddd  WGS84
%
% Outputs:
%    x, y , utmzone.   See example
%
% Example 1:
%    Lat=[40.3154333; 46.283900; 37.577833; 28.645650; 38.855550; 25.061783];
%    Lon=[-3.4857166; 7.8012333; -119.95525; -17.759533; -94.7990166; 121.640266];
%    [x,y,utmzone] = deg2utm(Lat,Lon);
%    fprintf('%7.0f ',x)
%       458731  407653  239027  230253  343898  362850
%    fprintf('%7.0f ',y)
%      4462881 5126290 4163083 3171843 4302285 2772478
%    utmzone =
%       30 T
%       32 T
%       11 S
%       28 R
%       15 S
%       51 R
%
% Example 2: If you have Lat/Lon coordinates in Degrees, Minutes and Seconds
%    LatDMS=[40 18 55.56; 46 17 2.04];
%    LonDMS=[-3 29  8.58;  7 48 4.44];
%    Lat=dms2deg(mat2dms(LatDMS)); %convert into degrees
%    Lon=dms2deg(mat2dms(LonDMS)); %convert into degrees
%    [x,y,utmzone] = deg2utm(Lat,Lon)
%
% Author:
%   Rafael Palacios
%   Universidad Pontificia Comillas
%   Madrid, Spain
% Version: Apr/06, Jun/06, Aug/06, Aug/06
% Aug/06: fixed a problem (found by Rodolphe Dewarrat) related to southern
%    hemisphere coordinates.
% Aug/06: corrected m-Lint warnings
%-------------------------------------------------------------------------

% Argument checking
%
error(nargchk(2, 3, nargin));  %2 arguments required
CHuso=true;
if nargin==3
    CHuso=false;
end
n1=length(Lat);
n2=length(Lon);
if (n1~=n2)
   error('Lat and Lon vectors should have the same length');
end

% Memory pre-allocation
%
x=zeros(n1,1);
y=zeros(n1,1);
utmzone(n1,:)='60 X';

% Main Loop
%
for i=1:n1
   la=Lat(i);
   lo=Lon(i);

   sa = 6378137.000000 ; sb = 6356752.314245;

   %e = ( ( ( sa ^ 2 ) - ( sb ^ 2 ) ) ^ 0.5 ) / sa;
   e2 = ( ( ( sa ^ 2 ) - ( sb ^ 2 ) ) ^ 0.5 ) / sb;
   e2cuadrada = e2 ^ 2;
   c = ( sa ^ 2 ) / sb;
   %alpha = ( sa - sb ) / sa;             %f
   %ablandamiento = 1 / alpha;   % 1/f

   lat = la * ( pi / 180 );
   lon = lo * ( pi / 180 );
    if CHuso
        Huso = fix( ( lo / 6 ) + 31);
    end
   S = ( ( Huso * 6 ) - 183 );
   deltaS = lon - ( S * ( pi / 180 ) );

   if (la<-72), Letra='C';
   elseif (la<-64), Letra='D';
   elseif (la<-56), Letra='E';
   elseif (la<-48), Letra='F';
   elseif (la<-40), Letra='G';
   elseif (la<-32), Letra='H';
   elseif (la<-24), Letra='J';
   elseif (la<-16), Letra='K';
   elseif (la<-8), Letra='L';
   elseif (la<0), Letra='M';
   elseif (la<8), Letra='N';
   elseif (la<16), Letra='P';
   elseif (la<24), Letra='Q';
   elseif (la<32), Letra='R';
   elseif (la<40), Letra='S';
   elseif (la<48), Letra='T';
   elseif (la<56), Letra='U';
   elseif (la<64), Letra='V';
   elseif (la<72), Letra='W';
   else Letra='X';
   end

   a = cos(lat) * sin(deltaS);
   epsilon = 0.5 * log( ( 1 +  a) / ( 1 - a ) );
   nu = atan( tan(lat) / cos(deltaS) ) - lat;
   v = ( c / ( ( 1 + ( e2cuadrada * ( cos(lat) ) ^ 2 ) ) ) ^ 0.5 ) * 0.9996;
   ta = ( e2cuadrada / 2 ) * epsilon ^ 2 * ( cos(lat) ) ^ 2;
   a1 = sin( 2 * lat );
   a2 = a1 * ( cos(lat) ) ^ 2;
   j2 = lat + ( a1 / 2 );
   j4 = ( ( 3 * j2 ) + a2 ) / 4;
   j6 = ( ( 5 * j4 ) + ( a2 * ( cos(lat) ) ^ 2) ) / 3;
   alfa = ( 3 / 4 ) * e2cuadrada;
   beta = ( 5 / 3 ) * alfa ^ 2;
   gama = ( 35 / 27 ) * alfa ^ 3;
   Bm = 0.9996 * c * ( lat - alfa * j2 + beta * j4 - gama * j6 );
   xx = epsilon * v * ( 1 + ( ta / 3 ) ) + 500000;
   yy = nu * v * ( 1 + ta ) + Bm;

   if (yy<0)
       yy=9999999+yy;
   end

   x(i)=xx;
   y(i)=yy;
   utmzone(i,:)=sprintf('%02d %c',Huso,Letra);
end

and

function  [Lat,Lon] = utm2deg(xx,yy,utmzone)
% -------------------------------------------------------------------------
% [Lat,Lon] = utm2deg(x,y,utmzone)
%
% Description: Function to convert vectors of UTM coordinates into Lat/Lon vectors (WGS84).
% Some code has been extracted from UTMIP.m function by Gabriel Ruiz Martinez.
%
% Inputs:
%    x, y , utmzone.
%
% Outputs:
%    Lat: Latitude vector.   Degrees.  +ddd.ddddd  WGS84
%    Lon: Longitude vector.  Degrees.  +ddd.ddddd  WGS84
%
% Example 1:
% x=[ 458731;  407653;  239027;  230253;  343898;  362850];
% y=[4462881; 5126290; 4163083; 3171843; 4302285; 2772478];
% utmzone=['30 T'; '32 T'; '11 S'; '28 R'; '15 S'; '51 R'];
% [Lat, Lon]=utm2deg(x,y,utmzone);
% fprintf('%11.6f ',lat)
%    40.315430   46.283902   37.577834   28.645647   38.855552   25.061780
% fprintf('%11.6f ',lon)
%    -3.485713    7.801235 -119.955246  -17.759537  -94.799019  121.640266
%
% Example 2: If you need Lat/Lon coordinates in Degrees, Minutes and Seconds
% [Lat, Lon]=utm2deg(x,y,utmzone);
% LatDMS=dms2mat(deg2dms(Lat))
%LatDMS =
%    40.00         18.00         55.55
%    46.00         17.00          2.01
%    37.00         34.00         40.17
%    28.00         38.00         44.33
%    38.00         51.00         19.96
%    25.00          3.00         42.41
% LonDMS=dms2mat(deg2dms(Lon))
%LonDMS =
%    -3.00         29.00          8.61
%     7.00         48.00          4.40
%  -119.00         57.00         18.93
%   -17.00         45.00         34.33
%   -94.00         47.00         56.47
%   121.00         38.00         24.96
%
% Author:
%   Rafael Palacios
%   Universidad Pontificia Comillas
%   Madrid, Spain
% Version: Apr/06, Jun/06, Aug/06
% Aug/06: corrected m-Lint warnings
%-------------------------------------------------------------------------

% Argument checking
%
error(nargchk(3, 3, nargin)); %3 arguments required
n1=length(xx);
n2=length(yy);
n3=size(utmzone,1);
if (n1~=n2 || n1~=n3)
   error('x,y and utmzone vectors should have the same number or rows');
end
c=size(utmzone,2);
if (c~=4)
   error('utmzone should be a vector of strings like "30 T"');
end

% Memory pre-allocation
%
Lat=zeros(n1,1);
Lon=zeros(n1,1);

% Main Loop
%
for i=1:n1
   if (utmzone(i,4)>'X' || utmzone(i,4)<'C')
      fprintf('utm2deg: Warning utmzone should be a vector of strings like "30 T", not "30 t"\n');
   end
   if (utmzone(i,4)>'M')
      hemis='N';   % Northern hemisphere
   else
      hemis='S';
   end

   x=xx(i);
   y=yy(i);
   zone=str2double(utmzone(i,1:2));

   sa = 6378137.000000 ; sb = 6356752.314245;

%   e = ( ( ( sa ^ 2 ) - ( sb ^ 2 ) ) ^ 0.5 ) / sa;
   e2 = ( ( ( sa ^ 2 ) - ( sb ^ 2 ) ) ^ 0.5 ) / sb;
   e2cuadrada = e2 ^ 2;
   c = ( sa ^ 2 ) / sb;
%   alpha = ( sa - sb ) / sa;             %f
%   ablandamiento = 1 / alpha;   % 1/f

   X = x - 500000;

   if hemis == 'S' || hemis == 's'
       Y = y - 10000000;
   else
       Y = y;
   end

   S = ( ( zone * 6 ) - 183 );
   lat =  Y / ( 6366197.724 * 0.9996 );
   v = ( c / ( ( 1 + ( e2cuadrada * ( cos(lat) ) ^ 2 ) ) ) ^ 0.5 ) * 0.9996;
   a = X / v;
   a1 = sin( 2 * lat );
   a2 = a1 * ( cos(lat) ) ^ 2;
   j2 = lat + ( a1 / 2 );
   j4 = ( ( 3 * j2 ) + a2 ) / 4;
   j6 = ( ( 5 * j4 ) + ( a2 * ( cos(lat) ) ^ 2) ) / 3;
   alfa = ( 3 / 4 ) * e2cuadrada;
   beta = ( 5 / 3 ) * alfa ^ 2;
   gama = ( 35 / 27 ) * alfa ^ 3;
   Bm = 0.9996 * c * ( lat - alfa * j2 + beta * j4 - gama * j6 );
   b = ( Y - Bm ) / v;
   Epsi = ( ( e2cuadrada * a^ 2 ) / 2 ) * ( cos(lat) )^ 2;
   Eps = a * ( 1 - ( Epsi / 3 ) );
   nab = ( b * ( 1 - Epsi ) ) + lat;
   senoheps = ( exp(Eps) - exp(-Eps) ) / 2;
   Delt = atan(senoheps / (cos(nab) ) );
   TaO = atan(cos(Delt) * tan(nab));
   longitude = (Delt *(180 / pi ) ) + S;
   latitude = ( lat + ( 1 + e2cuadrada* (cos(lat)^ 2) - ( 3 / 2 ) * e2cuadrada * sin(lat) * cos(lat) * ( TaO - lat ) ) * ( TaO - lat ) ) * ...
                    (180 / pi);

   Lat(i)=latitude;
   Lon(i)=longitude;

end

I hope that helps.


Why does sea level correspond to boundary between oceanic and continental crust? Is it a coincidence? the first is determined by the amount of water on the Earth and the second comes from evolution of tectonic plates. Still, oceans seem to fill exactly the oceanic crust.

Sea-level only sort-of corresponds to the oceanic–continental crust boundary.

In depth, they don't correspond at all:

It's the same story at an active margin: the plate boundary at a subduction zone is buried several kilometres beneath a wedge of sediment:

What about spatially? As you can see from this map, they don't correspond all that well spatially either: they are commonly 100s of kilometres apart, sometimes more.

The difference, shaded grey in the map, is the continental shelf. It is sometimes emergent (e.g. at the end of the Permian, or during ice ages, when global sea-levels are low). It is sometimes, as now, flooded. The vertical change of ca. 100–250 m means a lateral change of 100s of km, because the shelf is almost flat.

OK, enough nit-picking, roughly speaking, why are the oceans on oceanic crust?

Continental crust is relatively thick and low density (ca. 2700 kg/m$^3$), compared to oceanic crust (25–70 km and ca. 2900 kg/m$^3$). So it 'floats' higher on the thin, dense mantle (7–10 km and ca. 3300 kg/m$^3$). When a new rift forms, it creates a depression and space for new oceanic-style crust. This is happening right now in the Gulf of California, the Baikal Rift Zone, and in the extensive East African Rift system. All of these places have large lakes and/or are extensively below sea-level. It's a divergent 'tear' in the continental crust, so intuitively we might expect a depression. As it fills with thin oceanic crust, the depression is maintained and eventually fills with ocean water.

Why is ocean crust so thin? I don't have a lot of expertise here, but I think it's determined by the relative rates of melting and cooling, and the heat balance at the ridge and subduction zones. There's a nice answer to this question on Reddit, complete with links. As insinuated in that thread, the thermo- and chemo-dynamics of the spreading centres and subduction zones are intimately related to the presence of the ocean, so together they make a complex system (indeed, the entire planet is a complex system), as @stali points out in his comments and answer.


Does the Earth 'Flare' like the Sun does? Solar Flares are a commonly discussed phenomenon, which have effects ranging from geomagnetic storms to radio disruptions to absolutely nothing noticeable.

Given that part of the core of the Earth is molten, and magnetic, is there any evidence either way of the core of the Earth producing 'geoflares' like Solar Flares?

The medium for a solar flare is plasma, so nothing like that occurs in the Earth's core. The outer core fluid is highly conductive and has a low viscosity, so changes may occur in the core's field, but the mantle has enough electrical conductivity to filter out the more rapid changes (those with periods of roughly a year or less). See Merrill and McElhinny pp 49-51 for details. However, geomagnetic jerks have been observed. These are abrupt changes in the second time derivative of the Earth's magnetic field. Sometimes they are global, although mantle filtering can delay the jerk by different amounts at different locations on the Earth's surface.


Need help understanding this satellite image of Larson C ice shelf The false color image below shows synthetic aperture radar imaging from ESA's Sentinel-1 satellite. The map from the 20-Jan-2017 BBC article Larsen ice crack continues to open up illustrates the same general area.

The Larson C Ice Shelf is the large blue-ish region in the middle of the false-color radar image, and is labeled as such. The crack is the thin lighter line just above the red arrow.

Moving diagonally upwards to the right, the gray region is labeled "Sea Ice". Is this just much thinner but mostly solid ice, or water with pieces of ice in it? While the ice shelf seems relatively uniform in tone, the gray sea ice area has a mottled pattern.

Also the boundary between the two regions has what looks to me like some kind of 3D effect - the black, ribbon-like variable width region separating the two. Is this an effect of shadowing from oblique incidence? Is this actually the sidewall height of the ice shelf?

There is also some discussion of radar imaging of sea ice in this answer.

above: Cropped and enlarged highlight from Sentinel-1 synthetic aperture radar image of the Larson C ice shelf, beginning of January 2017, found here. Image credit: ESA/EU/Copernicus

above: Sentinel-1 synthetic aperture radar image of the Larson C ice shelf, beginning of January 2017, found here. Open in separate viewer or tab for full size. The width of the image is roughly 300km, south is towards the lower right. Image credit: ESA/EU/Copernicus

above: Map of the region around the Larson C ice shelf, beginning of January 2017, from BBC here. Image credit: MIDAS Project, A. Luckman, Swansea University. Because it's difficult to read, I'll point out that Wales not shown in it's correct location - it's there for scale only.

I found a natural-color image of the same area: 68.28 South, 60.47 East, North is up, resolution is 130m/px, which makes the whole image about 100 km x 100 km. Looking at the image i'd say that:

sea ice is water with pieces of ice in it,
the boundary between the two regions is clear water, probably caused by winds and currents moving the floating ice away from the edge of the ice shelf.

I got the image at Sentinel Playground using 100% cloud filter, 0.3 gain and date selection of 2016-11-21.

EDIT: Added more info about the position, scale and orientation of the image.


Seismic AVO/AVA concepts I have a basic question concerning AVO, AVA, and reflections. What is the difference between AVO/AVA and obliquity factors from a given reflection from a point in the subsurface? If there is a technical difference, how is it accounted for during processing and amplitude conditioning?

While the terms are rarely used rigorously, AVO and AVA refer to slightly different versions of the same type of analysis.

The amplitude (and phase) of a seismic reflection varies with the offset distance between the source and receiver. Hence 'amplitude variation with offset', or AVO.

Strictly speaking, however, the variation — which is given by the Zoeppritz equations — is with the incidence or offset angle, often called $\theta$. That is, the reflectivity is a function of angle, not of distance. So 'amplitude variation with angle' (AVA) is arguably a better name for the phenomenon.

It turns out that the reflectivity varies linearly with respect to $\sin^2\theta$, so we often use that relationship instead, e.g. via the 2-term Shuey approximation:

$$R(\theta) = R(0) + G\sin^2\theta$$

where R is the reflectivity and $G$ is a function of P-wave velocity $V_\mathrm{P}$, S-wave velocity $V_\mathrm{S}$, and density $\rho$.

If we're being strict about the language, the practical difference in seismic analysis is that you'd perform AVO analysis on offset gathers or partial offset stacks (such as you might get directly from processing), and AVA analysis on angle gathers or partial angle stacks (which would require you to interpolate the offset-based data using a velocity model and ray-tracing).


What is a pre-monsoon shower? Is there any distinguishing feature between monsoon and pre-monsoon showers? While attending a lecture about monsoon, our professor mentioned about pre-monsoon showers. However, he never bothered to explain it. So, what is a pre-monsoon shower and what are its distinguishing features from monsoon showers?

Mango showers, or ‘mango rains’, is a colloquial term to describe the occurrence of pre-monsoon rainfall! Monsoon is prevailing wind due to seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea. Usually, the term monsoon is used to refer to the rainy phase of a seasonally changing pattern. They are notable across much of South and Southeast Asia, including India, and Cambodia.

https://en.wikipedia.org/wiki/Monsoon here is a helpful resource I used!

:)


How to find the top level of the planetary boundary layer in WRF? I am working on WRF_Chem, I would like to calculate the concentration of CO2 just in the Planetary boundary layer(I mean, I want to calculate CO2 from surface to top of PBL).in WRF How can I calculate the level of PBL.
in WRF we have (PBLH: the height of PBL but it doesn't inform us what is the top level of PBL compare all level of the model?).
my model has a 37vertical levels.
If I Know the level of PBL, I will calculate the pressure weight of its level and calculate the contribution of PBL concentration.
how can I find the concentration Of CO2 in PBL height considering the weight of PBL layer?
thank you for all your guidance.

Well, the variable PBLH should tell you the PBL height. If you want the level that the PBL is, I suggest modifying the Registry.EM_COMMON file.
Perhaps I can refer you to WRF-Python to help you with your calculation. For example, wrf.interplevel might be the function to use to interpolate to the PBL height. If you interpolate to fractions of the PBL height, you could one of the integration methods to sum up the number of fractions of the PBL height and get the average concentration of $\ce{CO2}$ in the PBL (also, divide by the PBL height to actually get the average).


Meaning of "Objectively analyzed" I've found that there may possibly be many meanings of "objectively analyzed" and "objective analysis" in modeling and data assimilation. What are some of the accepted meanings?

In my field of oceanography, objective analysis (OA) is often taken as a synonym of optimal interpolation (OI). (e.g. Emery & Thomson, Section 4.2; and in many lectures).

The same method is also referred to as objective mapping or Gauss-Markov smoothing. In this case OA is a least squared interpolation where the estimate is unbiased and the expected error is a minimum in the least squares sense.

In many other cases, objective analysis is taken to be a specific type of optimal interpolation. A good example is the group from University of Liege. In this case OI includes other methods like kriging, successive corrections or the Cressman method.

In my case, I tend to follow the nomenclature and suggestions by Ide et al. (1997).


Does usual city pollution have effects on relative humidity? I've noticed that in a rural area with low pollution the relative humidity is constantly lower than the humidity in a high polluted city. Is there any correlation between pollution and humidity?

By way of reference, "humidity depends on water vaporization and condensation, which, in turn, mainly depends on temperature".

From the information you have supplied in your comments. There are waters in Bucharest and forests in the suburbs, but no waters or forests where the country house is located.

From your information, Bucharest has a number of sources of atmospheric water vapour, the river that flows through it (evaporation of water) and the forests in the suburbs (transpiration of water). Additionally, motor vehicle exhausts will increase the humidity as water vapour is one of the products of the combustion of hydrocarbons.

The warmer the air, the greater its capacity to hold moisture. Cities tend to be warmer than rural areas due to the heat island effect, which is the result of modifying land surfaces and the generation of waste heat.

Humidity in the rural location will arise from evaporation of water in the soil and transpiration from crops or grasses. Such transpiration will produce less water vapour than forests. Additionally, the rural location will have significantly fewer cars producing water vapour in their exhausts. Consequently, the rural location will be less humid than the city.

The reason why Bucharest is more humid that the rural location has more to do with the greater availability and vaporization of water in Bucharest and the temperature of Bucharest than the amount of pollution in Bucharest.


Evidence for "earthquake storm" at the end of the Bronze Age The decline of the large population centers around the eastern Mediterranean at the end of the Bronze Age has been associated with a set of large earthquakes ("earthquake storm") occurring between 1300 BCE and 1150 BCE (e.g., late Minoan Crete Earthquakes). What evidence is there of such events? How can they explain the collapse of these civilizations?

Nur & Cline (2000) constructed a map of sites destroyed in the Aegean and Eastern Mediterranean region during the years 1225–1175 BCE. They also provided a map of earthquakes of magnitude above 6.5 that were measured during the XX century. They claimed that "virtually all of these Late Bronze Age sites lie within the affected (“high-shaking”) areas". They also showed evidence of earthquake damage in many of the main cities of the area and point out that:

  While such a ‘‘storm’’ is unlikely to have been the sole cause
  of the end of the Late Bronze Age in the Aegean and the Eastern Mediterranean, it may have interacted with the other forces at work in these areas c. 1200 BCE

The idea of an "earthquake storm" has been around at least since 1970. Ambraseys (1970) describe multiple "earthquake sequences" lasting around 40-50 years with "quiet periods of more than a century in a nearby fault system (the Anatolian fault zone).

In a study preceding the Nur & Cline work, Nur (1998) provided a possible explanation to connect earthquake damage with civilization collapse:

  The earthquake in this ca. 50 year long storm could have render many of the urban centers militarily vulnerable, thus inviting attacks not by powerful, distant Sea People, but by opportunistic indigenous or neighboring populations. These attack might have led in turn to the political and social collapse of the centres, followed by a dark age of recovery and rebuilding often lasting a few hundred years.

They also provide an example from the Old Testament: Jericho, that was attack by invaders after the city walls collapse.

A simple explanation of the potential set of events is given in this video.


What's the difference between cleavage and fracture? I see both terms refereing to fractures on crystals or minerals, so I wonder if they could be considered synonymous.

If no, what's the difference between both terms?

They are not synonymous.

Cleavage means breaking along planes defined by crystallographic directions. For example, cubic crystals like halite, NaCl, often cleave along directions that follow the cubic form. However, with a different bond strength, like fluorite $\ce{CaF2}$, the crystals cleave most easily along octahedral directions, similar to two pyramids sharing a base.

Fracture is when the break does not form along the crystallographic directions. It then can be grainy or conchoidal (like breaking glass).

Fracture is also used to describe the breaking of rocks as opposed to single crystals. In this case planar fracture follows the direction of forces that formed the rock.


What were CO2 levels in Carboniferous? What were CO2 levels in early and late Carboniferous, an what were mean levels? Who are the sources for these figures?

Carboniferous CO2 levels may not have been unlike today's. Evidence for this is primarily from long term geochemical modeling work, as there are few direct proxies of sufficient age.

I can easily cite one source, as it's from my own paper, but please check the reference list for the other datasets. http://dx.doi.org/10.1016/j.chemgeo.2013.10.012


Can thunderstorms be thought of as a heat engine? Or in other words, can they be seen as sources of heat transport?

If so, what can be thought of as the heat source, and what can be thought of as the heat sink?

Yes, they can.

Broadly speaking, most dynamical atmospheric phenomena are heat engines in one form or another. Ultimately the heat source is due to sunlight heating up the ground, and the cold sink is the upper atmosphere, which stays cold due to emitting thermal radiation into space. Large convection cells (such as tropical cyclones or the Hadley cells) act broadly like Carnot engines, adiabatically expanding packets of air as they're brought upwards from the ground to the upper atmosphere, then isothermally compressing them as they radiate into space, then adiabatically compressing them as they travel back down to the surface, and then isothermally expanding them as they pick up heat from the ground. (This description is a very rough approximation to the reality.) The net effect is to transfer heat from the ground to the upper atmosphere, while converting a small amount of that heat into kinetic energy, which keeps the whole thing moving.

Thunderstorms are quite an interesting case, because they are driven by latent heat as well as sensible heat. The air near the surface is not just warm but moist, due to evaporation and evapotranspiration from plants. As air rises it cools. Cool air can hold less moisture than warm air, so this can lead to condensation (i.e. the formation of clouds and rain). This condensation releases heat. A thunderstorm happens when condensation releases so much heat that the air starts to rise even faster, pulling more air up behind it. The moisture in this air then condenses, releasing more heat and pulling more air up, and so on. This is why thunderstorms often rise to a much greater height than the surrounding clouds.

Condensation releases heat, but evaporation uses up heat, which is why you feel cooler when you sweat. When water evaporates it takes heat away from the surface. That heat was put there by sunlight, and it gets released back again at the top of the thunderstorm. So a thunderstorm is part of a large-scale heat transport process that begins with evaporative cooling at the Earth's surface, and ends with the heat from condensation being transported into the upper atmosphere and ultimately radiated away into space.


What does "glacier collapse" mean? CNN's Mont Blanc glacier could collapse at any moment, Italy warns says:

A staggering 250,000 cubic meters (8.8 million cubic feet) of ice could break away from the Planpincieux glacier on the Grandes Jorasses mountain in the Mont Blanc massif, experts at the Valle d'Aosta regional government and the Fondazione Montagna Sicura (Safe Mountain Foundation) reported in an analysis published this week.
While it's impossible to predict the exact timing of the collapse, observations in August and September showed that the glacier was shifting at a speed of 50 to 60 centimeters (20 to 24 inches) a day, experts said.
"These phenomena once again show that the mountain is going through a phase of strong change due to climatic factors, therefore it is particularly vulnerable," Stefano Miserocchi, mayor of nearby Courmayeur, said in a statement. "In this case, it's a temperate glacier particularly sensitive to high temperatures."As a precautionary measure, Miserocchi ordered the closure of roads in the Val Ferret valley and the evacuation of mountain huts in the Rochefort area.

The caption of the image in the link (shown below) is labeled Figure 22, so presumably it's from some much larger report.
I'm curious about the choice of the word "collapse". What is it exactly that the glacier might do? Will it collapse in the same way that a Soufflé collapses, or is this more like an avalanche, or does the whole glacier just start sliding much faster, like several meters per day instead of several tens of centimeters currently?

The word collapse is not appropriate in the case of a hanging glacier such as the one you mention in your question. A hanging glacier is a glacier that terminates at a cliff edge. Since glacier ice is constantly moving towards the cliff, the terminus will occasionally lose sufficient support and detach from the glacier causing an ice avalanche. As long as the glacier feeds ice to the cliff edge ice avalanches will continue to occur. How often will largely depend on the ice velocity moving ice towards the cliff edge. This is thus a natural behaviour and not a collapse, or at least not named collapse in glaciology.
The word collapse is not a scientific term and does not have a unique definition in glaciology. In the case of an ice shelf that suddenly breaks apart such as the Larsen B (Rott et al. 1996) the term collapse has been used in articles. In this case the event was sudden and the entire ice shelf broke up and was lost during a few months. At the same time collapse is commonly used to describe other phenomena such as the loss of an ice sheet or part of an ice sheet (for example, Brendryen et al., 2020). Such a process is much slower than the ice shelf collapse, perhaps lasting many hundreds or thousands of years. But the word is used because it describes an irreversible event or development.
So coming back to the hanging glacier, its avalanches is an ongoing process and the word collapse gives the wrong impression. The glacier is not collapsing. Given climate warming the glacier will likely decrease in size and the avalanching change, possibly stop depending on the bedrock morphology on which the glacier sits. If the climate warming causes the glacier to completely melt away, then that could be considered a collapse of that glacier. But when you read different scientific articles on glaciers you will see the word used in many different ways so a tricky word to use in a good and consistent way.
References
Helmut Rott, Pedro Skvarca, Thomas Nagler, 1996 Rapid Collapse of Northern Larsen Ice Shelf, Antarctica. Science, 271 (5250) 788-792
Brendryen, J., Haflidason, H., Yokoyama, Y. et al. 2020 Eurasian Ice Sheet collapse was a major source of Meltwater Pulse 1A 14,600 years ago. Nat. Geosci. 13, 363–368.


Why are earthquake considered spot things? As far as i know earthquake is result of movement of earth crust layers and release of energy at these locations and movements at faults.

So i think its happens somehow along a line or in a wide almost flat layer.

But each earthquake is given a coordination and a depth as if its like a spot explosion.

Why is it like this? Are my assumptions wrong?

Faults and discontinuities within the Earth's crust are rarely smooth and any smooth parts are short in length.

The degree of roughness along a fault or any discontinuity varies in strength and magnitude. This causes stresses to build up unevenly along faults and discontinuities. When the stresses are too large for one rough patch to withstand there's a break and stress is released causing an earthquake. This is why earthquakes occur at a particular location.