Do man-made machines take natural Nitrogen out of the atmosphere and in turn cause global warming? I read in Wikipedia that, "Natural Nitrogen, Dinitrogen forms about 78% of Earth's atmosphere. Dinitrogen is the most abundant uncombined element in the atmosphere."

Do man-made machines destroy the natural Nitrogen, the extremely strong triple bond in elemental nitrogen (N≡N), turning natural Nitrogen into other compounds, molecules?

Does man-made fractional distillation, Nitrogen gas generators, and membranes take natural Nitrogen out of the atmosphere or ionosphere, causing global warming?

The short answer is that using atmospheric nitrogen as a feedstock for industrial processes doesn't really affect the climate per se. It does mess with the environment (primarily through deposition of nitrogen fertiliser) but this is a separate issue.

The problem from a climate point of view, is that the process is virtually certain to emit a lot of greenhouse gasses (primarily CO2 from fossil fuel powered machinery)


Statistical weather prediction Assuming I have time evolution of air temperature, air pressure, wind speed, wind direction, relative humidity and cloudiness, how can I predict weather based on this information?

I know that high air pressure increases chance of more concentrated sunlight and low air pressure increases chance of precipitation. I know that a decrease in temperature increases chance of snow or ice and also of low relative humidity and vice versa. I also know that higher wind speed means higher chance of a storm and that certain directions of wind can cause a change in temperature.

However I don't know what meteorological parameters I could predict with a combination of these variables. How would I predict the weather based on the time evolution of these variables?

You need a model. You could try to use Bayes theorem to build a model based upon conditional probabilities. See this reference from NOAA about weather forecasting: Probability Forecasting - Primer .

If I were to try to build a Bayesian model for weather forecasting, with the intention of using a limited data set of observations I had collected myself, I would look into existing software frameworks to see if I could use one of these. For example, the Infer.NET framework is available for free, and has several examples which would be a good starting point for learning about probabilistic modeling.


What was the Earth's continent's positions 10000 years ago, or 11700 years ago, AKA when the late Pleistocene epoch was coming to an end? In many articles online, geologists and geographers have described and depicted the theorized locations of all our continental plates with great detail and illustration, providing pictures, time-lapse videos, etc. as per Wegener's theory. But nowhere have I found online any article, paper, illustration, picture, or even a single comment, mention, or note talking about our continents' positions 10000 years ago, AKA, when the last ice age was just getting over. So please can someone answer this?

The reason that you have not seen any diagram showing the position of the continents 10K years before present (ybp) is that the plates move so slowly that there would not be a perceptual difference on the scale of a world map. The Atlantic is spreading about a half centimeter per year. So 10,000 years will have moved Europe away from North America by 5000 cm, or 50 meters.

An additional reason is that most models of continental drift have the sub-oceanic magnetic banding due to geomagnetic reversals as their guide for "recent" positions of the plates.  The latest geomagnetic reversal, the Brunhes–Matuyama reversal, occurred 780K ybp.  This is long before your 10K ybp point of interest and so any interpolated data would be suspect.


Thermohaline: Why is cold and dense seawater salty when warm water holds more dissolved salts? I read that thermohaline circulation is caused by cold and saline water sinking, while warm and less dense water rises. link

I understand that saline water is more dense, as there is a higher mass due to dissolved salts.

However, decreasing the temperature of water decreases the solubility, so in theory, shouldn't cold water hold less salt than warm water?

Vice-versa, shouldn't warm equatorial water increase in density as it is able to hold more salt?

Warm water does hold more salt - at saturation, but seawater isn't even close to saturation. Surface sea water gets warm, starts to evaporate (hence clouds) and therefore gets denser. So it sinks to the ocean floor, where it cools down to about 4 deg Celsius, and gets denser still. But it still is a very long way from being saturated with salt, so 'how much salt the water can hold' doesn't come into it.


With humans out of the equation, what could cause forest fire? Absent human activity, what does cause forest fires? I mean aside from lightning strikes, which are usually accompanied by water in the form of rain, and very rare events like volcanic eruptions or meteor impacts?

Wildfires are mainly caused by humans (or their technology) and lightning. Lightning is the most prolific natural source.  There really aren't many other sources in most areas, unless there is volcanic activity or a meteor strike as you mention.  There are also occasional cases of wildfire when peat dries out.
During a hot-dry summer, it can take several days of rain to moisten vegetation enough so that the fire danger is curtailed.  If there is a little rain accompanied by lightning, it is probably much less than what is needed to lower the fire potential (dryness of vegetation).

Furthermore, lightning strikes are not "usually accompanied by rain".  In the Pacific Northwest, for example, there are several lightning-caused wildfires every summer in areas where summer rain is quite scarce.  This is discussed a little in Wikipedia:

  The term dry lightning is used in Australia, Canada and the United States for lightning that occurs with no precipitation at the surface. This type of lightning is the most common natural cause of wildfires. Pyrocumulus clouds produce lightning for the same reason that it is produced by cumulonimbus clouds.


Are there locations on Earth that only have one season? I am looking for locations/places/countries that only have one season.

By seasons, I mean a large varying change in temperature and precipitation caused by the climate in the region. I am not looking for abnormal weather.

Due to the obliquity of the Earth, no place would truly have a single season, which in this answer is taken as having consistent conditions, particularly in terms of temperature and precipitation.

An environment that would qualify as having minimal seasonality are in the equatorial tropics, which according to the article Climatic seasonality, resource bottlenecks,
and abundance of rainforest birds:
implications for global climate change (Williams and Middleton, 2008) due to the almost consistent insolation, as shown below:

Image source - the blue line represents the yearly trends across the year for  equatorial regions.

Although, according to the article, the temperature remains fairly constant, precipitation can have alternating wet and dry periods, and can affected by other climatic factors (depending on location) such as El Niño, monsoons etc.

However, according to the Köppen climate classification system, the closest environment that would have minimal seasonality is classified as Af, which are warm moist rainforest, located in the areas shown below:

Image source

An example of a location in such an environment is the city of Andagoya, Colombia, South America, (latitude 5N, elevation 65m) which has the following annual temperature and precipitation:

Image source: Climate Classification and Climatic Regions of the World, which describes the classification Af as lying within the influence of the Intertropical Convergence Zone (ITCZ) and experiencing very little variation in temperature and precipitation throughout the year.


Can a Humidity Differential move PM2.5 Pollution? Observations

There is a higher level of PM2.5 pollution outside of the house. Readings are in the 80-150 range due to wildfires. (PM2.5 levels determined by sensors in PurpleAir.com's sensor network)
Using a handheld air monitor that can measure PM2.5 readings were taken indoors.
Most rooms in the house are reading +/- 40, but one room read 450
smokey haze could be seen in the room during the highest readings (what alerted us to the problem)
relative humidity outside is typically low (30-40%)
the room with the high reading (450 PM2.5) has

high humidity (80-90%) to support tropical plants
windows from the 1990s (older, don't seal well)
an attic access panel that allows some air movement
no fans that would draw in air from outside or push air outside
room is long and skinny (40'x15') with windows along the long axis and has a door halfway down the 40' axis
one end has higher humidity (where the humidifier is)

putting 3 small HEPA filters in the room can reduce PM2.5 to 5 in about an hour. After about 10 hours, readings of PM2.5 are much higher 80-400
if we reduce the PM2.5 to under 10 and close the door halfway along the 40' axis of the room, the lower humidity side of the door stays free of PM2.5 whereas the PM2.5 on the higher humidity side of the door continues to increase.
there is no internal source of PM2.5 - this only started this week as smoke has blown into the area

Q: what's the likelihood that the humidity differential between indoors and outdoors is "pumping" air and effectively pulling smoke indoors?
Q. What's the likelihood of the humidity differential being able to concentrate the smoke indoors (there have been no readings outside that come close to the 450 PM2.5 that was seen indoors, could the humidity differential be "pumping" pollution indoors and concentrating it)?
Q. what else might be contributing or causing this?

Humidity or recent rain plays a huge difference in air pollution. Seattle has less air pollution, because the effect of heavy rain and water accumulating on particles 'wash" the air. In hotter, drier Los Angeles the pollution stays in the air longer because there's less moisture to weigh it down. Mold, spores, dust and allergens do thrive in humidity but those aren't Pollutants in the classical industrial sense.


How are giant sinkholes filled up? There are a few impressive photographs of giant sinkholes that appeared in cities, such as this one:

However, followup information (e.g. Guatemalan sinkhole) or photographs on how these kind of sinkholes are filled up is hard to find. What approaches may be taken to "repair" or filling up these?

If dumping more earth or materials into them is ineffective due to underground-water, how can they be covered up properly without causing another collapse?

How Japan Filled That Ginormous Sinkhole In Just One Week:
The Fukuoka sinkhole measuring 8,700 square feet (808 square meter), 65 foot (20 m) deep: they poured a mixture of soil, water, and cement into the hole—they use more than 7,100 cubic meters of the stuff in all. YouTube timelapse.

How To Fix a Giant Sinkhole about the two in Guatemala: The first from 2007 one they filled with a soil cement made from cement, limestone, and water known locally as lodocreto ("mudcrete").

  It's not clear whether cement is the best option, however. A 6,500-cubic-foot wad of concrete may serve to concentrate water runoff in other areas, leading to more sinkholes. Many engineers prefer the graded-filter technique, in which the hole is filled with a layer of boulders, then a layer of smaller rocks, and, finally, a layer of gravel. This fills the hole, more or less, while permitting water to drain through the area.

Whether this was actually done with the 2010 one I could not find (yet). Even the Wikipedia entry on the 2010 sinkhole (which you are also refering to) says This section needs to be updated.

It seems to be closed now, look at this video fragment compared with the bottom picture here.

Note that 7000-8000 m3 sounds like a lot, but that is only 400-500 truck loads.

BTW (I know, that is not answering the question, but it was too nice to not add):Instead of filling them up you can also make a garden in them:

Photo credit: KnitSpirit/Flickr


The influence of special emissions (possibly coal mining activity) on particulate matters Based on multiple site sampling of airborne $PM_{2.5}$ and $PM_{10}$ , the elemental concentrations of the trace elements were analyzed.

I have found out in the site near surface coal mining zone presenting ~3-4 times of heavy metals ($As$, $Cd$ and $Pb$) compared to those of in other sites (~ 50 km away from the coal-production zone).

The receptor-oriented source apportionment tool was also applied, with a special factor could be identified which has high loading of element Cd, As, Pb.

Therefore, I infered that this factor might be attributed to coal mine dust.  Since Zn, Cd, Pb were all existed in coal seams as some minerals and they can be emitted in the coal mining, transportation activities.

Since there have been none similar research pointing out this factor, I was doubt about the rationality of my judgement.

More detailed description are depicted as follows:

(1) This factor was only show apperaent contribution on the site near coal mine area

(2) This factor can be produced in PMF analysis for both  $PM_{2.5}$ and $PM_{10}$ samples, respectively.  If I removed the dataset of the corresponding site, this factor will be gone in the source identification analysis.

Some "negative" information:

(1) The wind direction factor was also implemented. The source variability was not well in accordance with the wind field (As expected, the high contribution of coal mine dust should occurs in the time when the wind is coming from the direction of coal mining area)

(2) Combining with a prior knowledge, the source profile for coal mine dust (upper soil by wind-blown process) should enriched in coarse particles, while the high proportions of $As$, $Cd$, $Pb$ in $PM_{2.5}$/$PM_{10}$ were still founded in the coal-mining site.

The figures followed was the emission features of coal combustion and "coal mine dust"(inferred by myself).

I am not well satisfied with my interpretation on the apportionment results. I will be grateful if some researchers shed some light on this issue.

More information on the sampling sites

PM samples are simultaneously collected in six sites within the studied area in daily basis. As a energy base area, there are 8 coal-fired power stations within this area.

Site 1 was located near coal mine as the following figure.

More information on the source identification.

One factor can be identified in all sites, with high mass loading of Na, Cr, As, Zn, Pb. These trace elements existing in coal can be volatilized in high temperature combustion processes and then coagulated into solid phase in atmosphere.

The seasonal variability of this factor also show the trend of highest contribution in winter. It might indicate the increasing coal combustion for domestic heating which is common in north China.

Thus, I inferred this factor was the emission from coal combustion (coal-fired power/heating plant and domestic uses of bulk coal).

The other factor which was similar with the factor in the source profile. High mass loading of As, Cd, Pb was also founded. Meanwhile, this factor presented elevated contribution only at the site near surface coal mining zone.

Therefore, I thought this factor should be the emission of coal mining activity.

Information of the coal mining

Responding to first answer, I investigated the coal mining activity in this area. Here is an figure of  one of the coal strip mine and the coal is mined by mechanical cutting techniques.

The first thing to consider is, if it is not the adjacent coal mine, what other nearby sources could produce such a result. Is there a coal fired power station or a factory nearby. If there are no other likely sources then the coal mine is still the most likely candidate as the source of the dust and metal contaminants.

The other thing to consider is how is the coal being mined in the open pit and how is dust being generated by the coal mine.

The most likely method of mining the coal would require the use of explosives and blasting. This can create large clouds of dust that can be high and wide. If the wind was not blowing when a blast occurred the dust may have reached your sensors.

If the coal is mined by mechanical cutting techniques dust will still be generated, but not in the same quantities as blasting produces.

The other ways dust is generated is by vehicles travelling on unsealed roads - the tyres of the vehicle churn up the dust on the roads.

Dust can also be blown from trucks loaded with coal or from conveyor belts conveying coal to a dump site. The loading of trucks will also generate dust, as will the dumping of coal.

From experience, the only way to control dust is to constantly spray with water. Do you know if the mine uses any for of dust suppression?

It is well known that coal contains all types of contaminants, including metals such as cadmium and mercury. Different deposits have different types and degrees of contaminants.

From what you have presented, the coal mine is the most likely source of the dust and metal contamination.


Beringia - history of the region, periods of sea level fall/rise - paleogeography of Pleistocene I am trying to find any published (not wiki) source of information about how many times and when exactly the Bering Land Mass was free of water. Everything that I find is just pieces of information in different papers, one contradicting another. Is there any source that can be cited reliably in scientific literature with a timeline or something like a summary table?

Ok, I am answering to myself:
here are the papers, everything is in there

https://www.nature.com/nature/journal/v423/n6942/full/nature01690.html

https://www.nature.com/ngeo/journal/v3/n2/full/ngeo729.html


Is it possible to know what was the flow direction in a pegmatite dike? The following picture (Painted wall cliff in the Black Canyon of the Gunnison National Park, Colorado, USA) shows a pegmatite dike: is it possible to tell what was the flow direction? From thin (see below the printed 1 in the picture) to thick (2) or from thick to thin?

I am not sure those are pegmatites. They may simply be granitic dikes. But in either case, you would need to assess the regional geology to look for potential sources of this material, which would be a granitic type magma of younger age than the host rock. You could then map out the size, orientation, and frequency of these dikes to tie them back into their parent unit. Geochemical fingerprinting and age dating could help, too. But there is no way to look at that picture, or a given outcrop, and tell the direction. Remember that the geometry of the third dimension, the one in and out of the picture or outcrop, always needs to be kept in mind and is typically unknown.

I am pretty sure it was not top down, though!


Voronoi-like pattern in metal samples What is this pattern in the samples' surface called and how/why is it formed? I remember having seen a similar pattern in galvanized sheets.

Photos of metal samples from Wikimedia Commons (here and here):

As often in geology of any scale, the surface is only a manifestation of a 3-dimensional body.

It's typical for igneous rocks (e.g. granite see here) that the polished surface have the Voronoi-like-pattern. The minerals grow from a nucleus until they reach the next crystal and the melt is finished. Every point in the rock can be related back to its closest crystal nucleus, depending on the solidus conditions for the chemical composition.

Check this short animation.

You can see the same pattern in the microstructure of metals, e.g. ferrite and pearlite in steel e.g. here.


How much is Solar Radiation effected by Axial Tilt or Obliquity? I know that the Axial Tilt of Earth is about 23.4° - 23.5°. And I would like to know how much this change effects Solar Radiation for particular geo-location.

What is the Axial Tile change rate? How often or how fast does it change? How much precision do we need when we calculate Solar Radiation for Weather forecast?

What could be difference between 1920, 1939. 1945, 1950 or 2017 Axial Tilt and it's effect on Solar Radiation at particular geo-location?

Check out this matlab program that is presented in a paper by Kostadinov and Gilb, 2014. The paper is worth reading, and they have their full matlab code in the "supplement" link (top right corner under downloads).

The code launches a GUI. From it you can control the values of obliquity, eccentricity, precession, total solar irradiance, day of year, calendar start year and end year,  and latitude. Section 2.1 in the paper explains the coordinate system.

I don't think anyone could answer off the top of their heads the question "what is the difference between 1920, 1939, etc... of solar radiation at a particular geo-location". But with this program, you can mess around with the data and find out. So let us know what you discover! (ps, if you don't have Matlab, you can probably use this in octave which is free).

Here's a screenshot of the gui

And here's what some of the output looks like

Here's some alternatives to matlab:
1) nasa has online calculator that spits out raw text tables of insolation.
2) If you are savvy with fortran then you may like this fortran code.
3) The fortran code above also has an online interface
4) If you like python, then you may like this python code, climlab, where there are detailed instructions here on how to use the code and visualize the information.
5) If you like R, then try palinsol which has a little documentation here.


A circle shape in Madagascar I was seeing Madagascar on Google Maps and accidentally i saw a circle shape near Bebao. Coordinates are 17.4317443°E and 44.644248°S.

Please, to satisfy my curiosity, can you tell me why is this shape like a circle?

It is an extinct volcanic crater.
The location is not listed as one of the active volcanoes in Madagascar.

Simplified geologic map of Madagascar (reference) shows the crater to be mapped as basaltic / Gabbro lava,


Which mountains (or hills) are visible from both Boston and Rhode Island? In the description of the Norse exploration of America, there are two places mentioned, "Hop" and "Straumfjord", with some relationship to the same mountains.

E.g. The finding of Wineland the Good, p. 50:

  They concluded that the mountains of Hop, and those which they had now
  found, formed one chain, and this appeared to be so because they were
  about an equal distance removed from Streamfirth, in either direction.

According to the interpretation by Kåre Prytz these places are Boston, Massachusetts (Straumfjord) and Rhode Island (Hop), and the meaning of the text is that (1) the three locations (Boston, R.I., the mountains) form an equilateral triangle, and (2) the mountains are visible from both Boston and R.I.

Casual inspection of a map suggests this might well be accurate, but I am wondering if the exact peaks can be pinned down more specificly?

As Boston and Rhode Island are whole areas more than points, the question is easier to answer the other way around: From which mountain you can see Boston and Rhode Island?

To answer the question I'll use the SRTM Digital Elevation Model at 30 meters resolution, and pick the following five mountains or hills that seem good candidates:

Shown elevations are the ones derived from STRM data. From each of these points I've made a view shed analysis. And for easier comparison I've put them together in the following animation:

In these view shed analysis, the areas in read represent the one that would be visible from the corresponding mountain or hill. As you can see, Blue Hill and Moose hill are visible from some parts of Boston and Rhode Island. So that chain of hills (including Tower Hill) is definitely visible from many parts of both areas.

For the mountains further inland as Wachusett Mt. and Monadnock Mt., they don't seem to be visible from the coastal areas of Rhode Island.


Why did the Persian Gulf shrink during the influence of Ancient Mesopotamia? The Persian Gulf, today, looks like this.

But about 4,000 years ago, it looked like this.

This extended to the point where Ur, currently an inland city, was a coastal city. During this era, no other coastlines that I am aware of have had such a dramatic change. The research I've done has not yielded many results. I do believe that a while ago, I read something saying a flood of the Tigris and Euphrates rivers deposited sediment lower down. I was unable to find this again.
So my question is, what were the cause(s) of the change of coastline?

There has been lots of works trying to reconstruct the evolution of the Gulf shoreline through time. They do not agree on the exact same dates (see this review by Sissakian et al. 2020), but they generally agree that there was first a transgression (sea level rise) episode following the last ice age, then a regression (sea level drop). Reasons invoked to explain the regression are (not mutually exclusive):

Change in climate. The sea level peaked around the post-glacial climatic optimum. After that, the climate got cooler, which means more ice at the poles and less water in the seas.
Sediment filling of the Mesopotamian delta. The Euphrates and the Tigris carry a lot a sediments, which progressively accumulate in the lowlands, making the Gulf shoreline advance (seaward).
Neotectonics. There are evidence for anticline growth under the area, which could have contributed to its rise above sea level. This activity also changed river paths, which could have promoted point 2.


Would adding sulfur dioxide to the atmosphere have a global cooling effect? There is reasonable evidence to suggest that the Earth is warming. The most probable cause appears to be increased CO2 in the atmosphere, which has been reasoned about for quite some time.

There appear to have been some volcanic eruptions in the 1200s that lead to a mini-ice age. The cause appears to be increased sulfur dioxide (S02) in the atmosphere.

Could we engineer this?

My question is: Would adding sulfur dioxide to the atmosphere have a global cooling effect?

There have been a range of studies on the issue published in Atmospheric Chemistry and Physics and other scientific journals.

The short answer is "yes." The longer answer is "yes, but...."

In Climatic impacts of stratospheric geoengineering with sulfate, black carbon and titania injection, Jones, et. al. (2016) note:

  In this paper, we examine the potential climatic effects of
  geoengineering by sulfate, black carbon and titania injection against
  a baseline RCP8.5 scenario. We use the HadGEM2-CCS model to simulate
  scenarios in which the top-of-the-atmosphere radiative imbalance due
  to rising greenhouse gas concentrations is offset by sufficient
  aerosol injection throughout the 2020–2100 period. We find that the
  global-mean temperature is effectively maintained at historical levels
  for the entirety of the period for all three aerosol-injection
  scenarios, though there is a wide range of side-effects which are
  discussed in detail.

Those side-effects would vary with the size of the particles used and the method and location of atmospheric injection, but would include:

Impacts on human health from increased particulates.
Changes in surface albedo from particulate deposition.
Changes in the amount and location of precipitation across the globe.
Increased stratospheric warming.
Changes in stratospheric ozone levels.

There would be no amelioration for other climate impacts such as ocean acidification.

  It is therefore important to note that the safest possible solution to
  avoiding the sort of climate change instantiated by, e.g., Fig. 6a of
  this report is to effectively mitigate greenhouse-gas emissions.

Other issues not addressed by this physics-based paper include:

The requirement for any geoengineering scheme to be maintained for decades or centuries.
The need for a substantial industrial base to manufacture and distribute the particulates involved.
The (presumed) need for an international body to manage the process and address political concerns such as the costs and benefits of the   geoengineering; such as if the process was going to increase or reduce rainfall to a particular region.


Mud bricks with shale I have recently bought a medium sized plot of wood/scrub land. Half of this plot was once used to dump shale from coal mines, which means I have a lot of shale.

I have been wondering/looking for possible uses for the stuff. One thought I've had is to make "mud bricks" however I can't find any mention of whether it is possible or not. I know the traditional method uses loamy soil but would it work with shale?

I don't have a kiln or any way of baking the bricks, so would be reliant on the sun. I was thinking maybe adding water and maybe some loam?

Aside: there are no suitable tags for my question and I do not have the reputation to add any, I'm thinking I could be on the wrong site for this question, if I am, please advise me of a more suitable one.

Your idea has merit. Shale is classified by geologists as being a mudstone. It is composed of silt and clay sized minerals.

According to this geology website, shales can be crushed to produce a clay and then mixed with water. These days, items that were once made from natural clay, such as terracotta pots and tiles for roofs, are now made from crushed shale.

Extra Information

One thing to be mindful of is that clays expand when wet and contract when dry. Anything you make from it, such as bricks, that isn't baked or protected from water by a sealed coating will expand and contract according to it moisture content.

Another application which you may want to consider is to supply crushed shale as a garden mulch or other such landscaping product.


Why doesn't the sun reach its highest point overhead at exactly 12:00 noon? Many sources state that 12:00 noon is the high-point or mid-point of the sun's path across the sky.

However, for where I am, this is obviously wrong. In my own town the high point of the sun occurs at about 13:30 in the summer (because of DST), and 12:30 in the winter, but clearly not 12:00 noon.

Why, at different longitudes, is the high-point of the sun not at 12:00?

Thank you in advance.

It's not a question of latitude but longitude and time zones.

Prior to the advent of railway transportation the time set on clocks varied from towns within close proximity because the clocks were set to noon when the Sun was at its highest in the sky. This was more apparent for towns east and west of each other (ie different longitudes).

When railway transportation was developed there was a need to standardize times so that train timetables could be developed and arrival and departure times would be accurate and consistent

This precipitated the development of time zones. Each time zone is approximately 15 degrees of longitude wide, but there are differences because of national/regional priorities. China which has a similar longitudinal extent as the contiguous states of the US has only one time zone, whereas there are four in the contiguous states of US.

Within a band of longitude the time is the same. In the time zones immediately east and west, the time is one hour more (east) and one hour less (west) - ignoring difference due to daily savings.

The reason for time zone being approximately 15 degrees of longitude wide is the rate of spin of the Earth is 15 degrees/hour (360 degrees every 24 hours).

You state that in your town, noon is either 12:30 or 13:30, depending on daylight saving time. The reason for noon occurring at half past the hour is due to the boundaries of the time zone where you live. Where I live, noon is approximately at quarter past the hour.


Does a green or yellow sky actually indicate a tornado? It seems to be a fairly widely held belief that if the sky is green or yellow, a tornado may be developing/approaching. But is there any truth to it? Could the color of the sky actually be associated with the hail that usually accompanies a tornado?

You know, there hasn't been too much research into this... but there has been some. For the most part, it's been proven that a green sky most likely means that a thunderstorm is coming. According to a researcher:

  Green is significant, but not proof that a tornado is on the way. A
  green cloud “will only occur if the cloud is very deep, which
  generally only occurs in thunderstorm clouds,” Bachmeier says. “Those
  are the kind of storms that may produce hail and tornadoes.” Green
  does indicate that the cloud is extremely tall, and since
  thunderclouds are the tallest clouds, green is a warning sign that
  large hail or a tornado may be present.

In addition, a Scientific American article was run on this:

  Over the past 15 years, a small group of scientists have weathered the elements working on green thunderstorms as a pet project, publishing a handful of articles in meteorological journals. All point to the existence of green skies with severe thunderstorms but no direct connection to tornadoes or hail can be made.

They then go on to state:

  Threatening green skies during a thunderstorm also proved entirely
  independent of the type of severe weather that came with it. Gallagher
  measured hailstorms where the dominant wavelength of light was green
  as well as hailstorms where it was the typical gray-blue color of
  thunderstorms. Tornado-producing storms proved similarly divorced from
  any particular sky color, other than dark.

We do know that green skies are a sign of thunderstorms, though:

  The moisture particles are so small that they can bend the light and
  alter its appearance to the observer. These water droplets absorb red
  light, making the scattered light appear blue. If this blue scattered
  light is set against an environment heavy in red light—during sunset
  for instance—and a dark gray thunderstorm cloud, the net effect can
  make the sky appear faintly green.

So to sum all of this up: we know that thunderstorms sometimes create a green sky. However, there is no evidence to prove that a green sky is a sure sign of a tornado or hail. It is however a warning sign, as it shows that a thunderstorm is most likely coming, and it could be a strong storm.


Relative dating of granite pluton In selecting a sample for age-dating of a granite pluton, which site is a better site to collect a sample from, the centre, top or side? Why was this site a better choice? Which dating method would you recommend and why?

I know that it is better to get a sample from the middle but I'm stuck answering the last two questions.

Any help would be appreciated!

What exactly are you trying to measure? some of the great North American and Andean batholiths have cooling histories of at least 20 million years, and maybe more than 50 million years. It is perhaps inappropriate to think of the crystallization process as having a single date. Phenocrysts near the top of the pluton are cooler, but may sink to deeper levels where they are partially resorbed or mantled in multiple cycles, giving rise to zoned phenocrysts. It can be a very long process. Generally, late stage pegmatites, which have been enriched in volatiles that depress the melting temperature, will indicate the youngest age of crystallization. Deeper levels of the magma chamber will be older, but really one needs to study the specific field relations, including extent of metamorphic aureole to decide upon the most appropriate younger or older samples. The middle will most probably give a reasonable average date. Remember, what you are measuring is the time of that the mineral cools through its 'closure temperature', which will be slightly to significantly younger than its time of crystallization.

As to the method of isotopic dating, K-Ar is generally OK but the relative error bounds get worryingly large for dates < a million years. Ar-Ar is more precise but more expensive. It's also an excellent method, as is Rb-Sr, especially for really old precambrian plutons - provided the sample is fresh. Any weathering or diagenesis messes up the method.


Is the ocean guaranteed to warm in a warming climate, regardless of whether it absorbs LW radiation? More specifically, I've seen some discussion of this article:

http://www.realclimate.org/index.php/archives/2006/09/why-greenhouse-gases-heat-the-ocean/

which claims that the observed ocean warming is explained by the ocean skin absorbing long-wavelength radiation. What I am asking is: is this mechanism necessary for ocean warming to occur? My naive understanding was that our increasing the magnitude of the greenhouse effect meant that there was less radiation escapting to space, and therefore the average temperature of the entire ocean+earth+atmosphere system will increase until it reaches a new equilibrium, where outgoing radiation again equals incoming. Is this correct? And if it is, does it not imply that the ocean must also get warmer, simply because it is a thermally coupled part of the entire warming system? I had someone tell me that the a warming atmosphere could not warm the ocean beyond an infinitesimal amount, because the atmosphere has a much lower heat capacity. But it seems to me that the constraint on the final equibilibrium temperature means that all components must warm, no matter how inefficient the means of energy transfer between them - as long as there is some means for energy transfer, increasing the overall temperature must increase each of the components. Am I right, or have I misunderstood?

My naive understanding was that our increasing the magnitude of the
  greenhouse effect meant that there was less radiation escapting to
  space

That's 100% correct.   If we assume constant solar input, there's only two ways the Earth's surface temperature can change.   Albedo and Thermal radiation.   Greenhouse gas driven climate change means exactly what you said - less heat radiates off Earth into space.    Most of this heat goes into the Ocean.

  And if it is, does it not imply that the ocean must also get warmer,
  simply because it is a thermally coupled part of the entire warming
  system? I had someone tell me that the a warming atmosphere could not
  warm the ocean beyond an infinitesimal amount, because the atmosphere
  has a much lower heat capacity.

Your friend is half right, and half wrong.   Air has a bit over 1/4th the heat capacity compared to water and it's about 800 times less dense, so he's correct, but it's not that simple.

Sunlight - somewhat counter-intuitively, isn't great at warming oceans because the photons from sunlight are energetic enough to evaporate water molecules into gas molecules.  Oceans have low albedo which means they absorb most of the energy from the sunlight, but much of that heat is lost in evaporation by visible light photons.   While that has nothing to do with your question, it's worth pointing out that sunlight isn't as good at warming oceans as one might think.   (If anyone has one of those solar mirror ovens, I'd be curious to see how well they work on pure water . . . just out of curiosity, evaporation loss vs rate of warming).

The back-radiation from the atmosphere is comparatively much less total solar energy, but oceans are good at absorbing and storing thermal back-radiation reflected back off the greenhouse gas rich atmosphere into the ocean.   This is a tiny amount of the total heat Earth gets from sunlight, and the increase of this radiation due to greenhouse gas is a fraction of one percent of solar energy, but it adds up.

One way to explain this is that 85 degree air will warm 80 degree water. That's a thermodynamic law.  It just takes a while and because the heat capacity and density of water is much greater, it takes about 4 liters of air to give 1 degree back to warm 1 cc of water 1 degree.  But despite the inefficiency, warmer air still transfers heat into colder water.  It takes many decades, perhaps centuries, for the oceans to catch up to the warming air, but air, however inefficiently, does warm the oceans.

The quirk in this, is that the oceans, despite warming much more slowly than the air, are still absorbing over 90% of the trapped heat added by the increase in greenhouse gas.   It's a matter of scale.  Oceans warm slowly because they're enormous and always circulating and it takes much more energy to war them, but they also absorb most of the heat, for the same reason, they're very good at holding heat.  Slow to heat up, but also, slow to cool down.  That's why bodies of water often feel warm when you go swimming at night.

I should probably add something about increased evaporation in higher air temperature, which effectively cools the oceans and surface air, but also increases the greenhouse effect with an increase in water vapor, but running those numbers is a bit over my pay-grade.   The greater efect is the one mentioned above.


If the Oceans Were Deeper Back home, the average depths of the world's oceans--and the Mediterranean Sea--are as follows:

Atlantic--3926 meters

Pacific--4028 meters

Indian--3963 meters

Arctic--1205 meters

Southern--4500 meters

Mediterranean--1500 meters

In this alternate Earth, the average depths are as follows:

Atlantic--4679 meters

Pacific--6896 meters

Indian--3295 meters

Arctic--3460 meters

Southern--2735 meters

Mediterranean--3767 meters

How would these changes in depth affect the world's climate and ocean currents?

Might not be the answer you're looking for but the most obvious effect would be a sinking of land and a spreading out of the oceans.   Granite, basalt, glaciers and oceans are in a sense, balanced like weights on a scale by their enormous mass and the gravity of Earth.   By replacing a mile or so of basalt rock with water at the bottom of the oceans the weight would be unbalanced and the continents would sink, similar to how some land is currently rebounding from the last ice age.  The net effect over time would be a few hundred meters of sea level rise if the oceans were to become that much deeper.

But I suspect that's not what you were looking for in your question.   You probably wanted to know about weather or oceanic temperature effects.   That's a little harder.   I can give a sort of answer.

Larger oceans would mean more dissolved atmospheric gas.  I had no luck finding good estimates as to how much atmosphere is dissolved in the deep oceans overall, I was able to do a very crude calculation using this website and estimates that there's about 50 times as much CO2 in the Oceans as there is in the atmosphere.   Now, my estimate is hugely crude, but there may be an entire Earth's atmosphere, both Oxygen and Nitrogen trapped in the oceans.   The deep oceans hold a fair bit of Oxygen and Nitrogen so by making the oceans bigger, the effect might be a thinner atmosphere.   10% thinner?   20%?   5%  I couldn't guess the amount, but something somewhere in that range seems probable.

Regarding deep ocean currents, it's difficult (perhaps impossible) to say how currents might change.  In general, ocean currents, while not simple, seem to follow fairly simple patterns.   My guess is that the amount of depth you've added isn't enough to change that, though if you were to make oceans significantly deeper, you might get a few layers of circulation, not the three, sometimes four layers we currently have.  (see pictures).

Source of pictures

Larger, deeper oceans would also provide a greater heat sink that would take longer to warm up or cool down with the rise and fall of glacial periods.   It's possible that there would be no glacial periods with these changes, but predictions get kind of speculative there.

That's all I can think of.  I invite corrections and additions.


Percentage of power plants with carbon capture and sequestration (CCS) technology? Does anyone know roughly what percentage of fossil fuel power plants around the world are equipped with carbon capture and sequestration (CCS) technology?

If you accept GE's estimate of the number of global fossil fuel power plants ( 17,500 ) and compare it to the number of CCS projects out there ( 22 ), you get roughly 0.1 %.

The Global CCS Institute released its 2014 annual report;

  The world’s first large-scale carbon capture and storage (CCS) project in the power
  sector commenced operation in October 2014 at the Boundary Dam power station
  in Saskatchewan, Canada. Two additional large-scale CCS projects in the power
  sector – at the Kemper County Energy Facility in Mississippi and the Petra Nova
  Carbon Capture Project in Texas – are planned to come into operation in 2015 and
  2016 respectively. Construction is also underway on the world’s first large-scale CCS
  project in the iron and steel sector, the Abu Dhabi CCS Project in the United Arab
  Emirates (UAE). These four projects are among the 22 large-scale CCS projects in
  operation or construction around the world – double the number at the beginning of
  the decade.


Climate consequences of very large asteroids striking the Deep Ocean For every asteroid or meteorite that hits dry land, two hit the sea. If a Manicouagan-sized asteroid struck the deep ocean (but not above a trench),how would the H2O vapour, chlorine, iodine bromine and other elements affect the climate, and for how long? Also, if it had thousands of feet of water to penetrate, would it leave a large crater on the sea bed? For sure it would create massive tsunamis, so is there any evidence for these in the geological record? The Manicouagan crater is far from being the largest on Earth, but is only slightly smaller than the Chicxulub example. It was caused by an asteroid 5km in diameter traveling at 25km per second, though friction with the atmosphere probably reduced this slightly before it struck the ground.

Manicouagan, however, is just an example, we are talking here about a hypothetical asteroid of this size striking the deep ocean. Don't be misled by the word hypothetical; given the number of large impacts which have happened on land there must have been some which landed in deep ocean. How deep? Let's call it 6,000 feet, which is nowhere near a record depth.

A 5km impactor would make a very, very global mess.

Here's a discussion of tsunami formation from asteroid impacts. It presents numbers for impactor size up to 2km, and posits a rule-of-thumb that indicates a 5km impactor would generate a coherent wave (one that doesn't dissipate much over great distances) as long as it impacts in water less than 20-30km deep -- in other words, in any ocean on Earth. The tsunamis would propagate right around the globe.

Here's a discussion of more general effects from larger impactors. Fireball radiation from a 5km impactor would ignite flammables within a 600km radius, and the secondary radiation from returning ejecta would cause a firestorm across a 5000km radius. Earthquakes and hurricanes would take care of whatever the tsunamis couldn't reach. The skies would be completely dark for months (once the glowing stuff finished landing).

About our best hope would be for a polar impact, where global atmospheric circulation patterns might spare the opposite hemisphere the worst effects.


Optimal vertical coordinate for complex topography There are plenty of choices in models in so far as choice of vertical coordinate is concerned for meteorological models.

Five that I know of:

The sigma coordinate system - Hybrid coordinate system(used by ECMWF);
Terrain following pressure as vertical coordinate that is used by WRF WRF Vertical Coordinate;
The system used in CM1 which is Cartesian coordinate (that leads to metric terms);
Step-mountain coordinate used in the Eta model, which was NCEP's operational regional model (NAM) from 1993 to 2006.
Gal-Chen and Somerville vertical coordinate Gal-Chen Somerville vertical coordinate

How applicable are these different vertical coordinate systems in complex topography, especially in mountainous areas?
Is there a case that one can make for a different type of vertical coordinate or can these existing vertical coordinate systems adequately reproduce meteorological measurements and observed phenomena?

Phrased differently: What sort of vertical coordinate leads to ease of implementation as well as adequate portrayal of weather events (lee troughs, pressure gradient force, etc) in mountains.

Please ignore whether such a coordinate system has currently been implemented by any model, but specify what an "ideal" vertical coordinate should be for complex topography.

This is a big question, but there are benefits and difficulties with all representations, and the efficacy of any coordinate will also depend upon other numerical choices such as the calculation of horizontal pressure gradients [Zängl 2012].  There are broadly two categories: terrain following layers and Cartesian systems such as step terrain and cut cell grids.

Terrain following layers are typically implemented using a coordinate transformation such that the computational domain is rectangular.  There are essentially two choices to make here.  First, the vertical coordinate may be geometric height, pressure, or entropy (potential temperature), or some other monotonic function.  Second, the decay function controls how the influence of the terrain on computational surfaces decays with height: this might be a linear decay (called Basic Terrain Following (BTF) or 'sigma' coordinates [Gal-Chen & Somerville 1975]), or something more elaborate such as Smooth LEvel VErtical (SLEVE) [Schär et al 2002] or Smoothed Terrain Following (STF) [Klemp 2011].

One of the motivations for smoothing coordinate surfaces is to make horizontal pressure gradient calculations more accurate: in areas of steep terrain metric terms in the coordinate transformation can increase errors [Dempsey & Davis 1998].  This is also one of the motivations for step terrain and cut cell grids, since the grid is orthogonal everywhere except in the cells next to the ground.

Another issue with representing terrain is that cells can become very thin (over steep slopes with terrain following layers) or very small (in a cut cell or partial-step grid) which constrains the timestep for explicit numeric methods due to the CFL criteria [Klein 2009].  There are several methods that can overcome this 'small cell problem' [Jebens et al 2011, Yamazaki & Satomura 2010, Steppeler et al. 2002]

This is by no means an exhaustive answer but I hope it gives you some understanding of the issues involved with vertical coordinates.  Additionally, I gave a presentation in 2015 on this topic, the slides are available online.  Another useful review article on nonhydrostatic models, including terrain representation and vertical coordinates, is presented in Steppeler et al 2003.

References

Dempsey, D. and C. Davis, 1998: Error analyses and test of pressure gradient force schemes in nonhydrostatic, mesoscale model. 12th Conf. on Numerical Weather Prediction, Phoenix, AZ. Amer. Meteor. Soc., 236–239
Gal-Chen, T. and R. C. Somerville, 1975: On the Use of a Coordinate Transformation for the Solution of the Navier-Stokes Equations. J. Comp. Phys., 17, 209–228
Jebens, S., O. Knoth and R. Weiner, 2011: Partially implicit peer methods for the compressible Euler equations. J. Comp. Phys., 230, 4955–4974.
Schär, C., D. Leuenberger, O. Fuhrer, D. Lüthi and C. Girard, 2002: A new terrain-following vertical coordinate formulation for atmospheric prediction models. Mon. Wea. Rev., 130, 2459–2480
Steppeler, J., H.-W. Bitzer, M. Minotte and L. Bonaventura, 2002: Nonhydrostatic Atmospheric Modeling using a z-Coordinate Representation. Mon. Wea. Rev., 130, 2143–2149
Steppeler, J., R. Hess, U. Schättler and L. Bonaventura, 2003: Review of numerical methods for nonhydrostatic weather prediction models. Meteorology and Atmospheric Physics, 82, 287–301
Yamazaki, H. and T. Satomura, 2010: Nonhydrostatic Atmospheric Modeling Using a Combined Cartesian Grid. Mon. Wea. Rev., 138, 3932–3945
Zängl, G., 2012: Extending the numerical stability limit of terrain-following coordinate models over steep slopes. Mon. Wea. Rev., 140, 3722–3733


How strong is the correlation between the dew point of a town and the seawater temperature next to that town? For example, the towns that has the highest dew point are usually next to the Red Sea and the Persian Gulf where the seawater temperature exceeds 30 degrees in summer.

It depends upon location, latitude, sea surface temperature and seasonality, dominant wind direction (offshore / onshore) and what dew point you are measuring - diurnal mean / min / max, mean weekly / monthly/ annual?

I don't recall anyone ever having asked this question, and I suspect that the answer will be vague and inconclusive. Test a hundred different coastal towns and you will get a hundred different answers. Also, it is time consuming, so do your own research. Numerous databases, which include coastal meteorology sites, will yield dew point data. Sea surface temperatures may not be so easy. I can only speak for Australia where the Bureau of Meteorology has SSTs available on-line. Prepare the two data sets with corresponding dates on an Excel spreadsheet - be careful to maintain exact date correspondence (errors can occur from missing data, systematic errors, transcription errors, and 'February 29th'). Then run the command "=PEARSON" to find the Pearson moment correlation. You could even publish your findings.


Building massive seawall around endangered Islands like Mauritius to save from climate change Would it be possible to build a massive seawall, say maybe even made from metal that could rise as the sea level rises to prevent being erased?

I am not considering costs here, nor beauty, only if such a wall would be able to resist the force of the entire ocean trying to get into the "empty" pool.

Is it feasible?
What kind of material would be required? How high could one go?
In the event of a leak, "terrorist" assault, what kind of disasters and how quickly would the Island become "erased"

You can give an example approximation on the size of the Island.

Just theoretical.

This is more of an engineering question. For some situations it may be possible to build such a wall around some islands. Such a sea wall would be a cofferdam, which have been used for small scale temporary projects.

Complicating factors would be:

The height of the sea wall and how much water would need to be held back.
The depth of to the sea floor. If the island is the tip of a seamount with steep sides and a large depth to the sea floor then a sea wall would be impossible.
The depth into the sea bed that the wall would need to be anchored into, or the wall would need to sink into, for the wall to be stable.
The wall would have to be able to withstand typhoons/cyclones/hurricanes,  small tsunamis and seismic events.

A metal wall would not be a long term solution due to corrosion of the metal. The most suitable material would be rock or concrete. Such a wall would need to be very wide. However, over time, even such a wall would need to be replaced/repaired due to sea erosion and battering.

Securing the wall against leaks would be critical and such a system may require solar power pumps to continuously move excess water out of the enclosure.


Why does San Francisco see so much more fog than Seattle? Having learned that fog often forms when wet air hits cold land, I’m now wondering why San Francisco sees so much more fog than Seattle does.

They’re both Marine West Coast, with moist, westerly Pacific Ocean winds, and both have water on both their east and west sides.

As njuffa alludes to there is a current just offshore from the California coast. This is a deep, cold ocean current. As it hits the continental shelf off the coast it is deflected upwards towards the ocean's surface. But here's where it gets different: a thermal low that forms in the Central Valley of California during the summer draws in the air from the Pacific through the delta and bay waters. As that air meets the cold upwelling water that was deflected upward by the continental shelf, it draws moisture from it. That cold water also cools the air which then forms fog and gets drawn into San Francisco. As that moist air gets drawn further inland, it warms sufficiently for the fog to return to vapor. This actually cools the Central Valley to where this onshore breeze (we call it the delta breeze) gets shut off, the valley warms again, and the whole cycle repeats. Of course, other weather factors (position of the Eastern Pacific High, for instance) can override this process, but it is pretty much the standard summertime pattern. If you need citations, I'm not sure I can provide them, as this is something I learned in a physical geography class in college many years ago. I've also seen some other explanations that are just plain wrong.


Why do tropical cyclones get more attention than extratropical cyclones? For tropical cyclones we have carefully tracked every instance of them, and naming them as soon as they have reached a certain intensity... flying aircraft in to measure conditions... compiling databases... creating models... and putting great emphasis on improving predictions.

However, it seems like for extratropical cyclones we do less. People only recently started to name extratropical cyclones... there doesn't seem to be a database of them... and they're just not portrayed as being as concerning when you hear about them on the news, even though they can have comparable wind speeds and minimum pressure to many tropical cyclones.

Why is there this difference?

Extratropical cyclones are relatively well understood. They often follow the Norwegian Cyclone model, which was developed in the 1910's and 1920's. Because of their spatial extent, extratropical cyclones are often less intense than their tropical counterparts. Since they are so much larger and live longer over land, it is easy to get data about an extratropical cyclone.

Tropical cyclones, on the other hand, have faster winds and affect people in a more dramatic fashion. If an extratropical cyclone is announced in winter, a grocery store may run out of bread. If a tropical cyclone is announced, there may not be a clerk available to restock the shelves. Tropical cyclones often don't live very long over land and are smaller, so it is hard to get data about them. Because they are smaller and the wind speed change over distance is so much greater in extratropical cyclones than tropical cyclones, errors in the forecast tend to have more of a dramatic effect on tropical cyclones.

To summarize:

Extratropical cyclones are often less intense.
We have an abundance of data on extratropical cyclones.
The theory behind the development of extratropical cyclones is longstanding and generally well established.
Tropical cyclones are much more dramatic and concentrated.
Forecast errors impact tropical cyclones more severely than extratropical cyclones (i.e. less predictable).


How much carbon is sequestered out of the atmosphere through marine snow? Marine snow in the deep ocean is a continuous shower of mostly organic detritus falling from the upper layers of the water column.  How much carbon is sequestered in this process? How does it compare with the amount of carbon sequestered through plants?

I'm also curious: what percent of this carbon sequestration comes from plankton and what percent from fish? Do seabirds reduce this carbon sequestration? What about marine mammals?

This probably doesn't answer your question but might help the thought process:

The part of the carbon cycle you are inquiring about is referred to as the biological carbon pump.
Phytoplankton total net primary productivity is estimated to be ca. 45 to 50x1015g of (fixed) Carbon per year (Falkowski et al. 1998). In comparison land plants are producing an estimated 50 to 60x1015g of (fixed) Carbon per year (Field et al. 1998), hence a roughly 50-50% situation.

Of course not all of it is being buried: some is being recycled by heterotrophs and some decomposed (and thus released).

As far as the zooplankton and zoonekton (fishes, marine mammals, swimming molluscs and arthropods,...) are concerned, although I do not have numbers to back this claim, I would assume their impact on the carbon cycle to be (necessarily) smaller than that of the phytoplankton (since the carbon they are exporting comes, ultimately, from recycling the phytoplankton).

Source:
Falkowski, P. G., Barber, R. T., Smetacek, V., 1998. Biogeochemical Controls and Feedbacks on Ocean Primary Production. Science, 281: 200-207.
Field, C. B., Behrenfield, M. J., Randerson, J. T., Falkowski, P., 1998. Primary Production of the Biosphere: Integrating Terrestrial and Oceanic Components. Science, 281: 237-240.


How to recharge ground water directly from river water I am not sure if I am asking it on a correct platform or not.
A rainy river passes through my village. We suffer both in summer and in rainy seasons due to this. Could anyone explain how to recharge the ground water with river water. What would be the cost?

What you are asking about is called "Managed Aquifer Recharge" It has been successfully employed in some situations but depends greatly on the geology of the area. The aquifer needs to be relatively shallow with permeable sediments between it and the surface. If the sediments are not permeable (e.g. clay rich or solid rock) The water won't flow down to the aquifer in a reasonable time.

As one comment pointed out the water can be diverted into an artificial lake to drain slowly into the sediments. It also may be possible to form a lake by placing a dam on the river.


Is the Younger Dryas associated with an extinction event? It's often said that, while warming and cooling have happened before, what is unusual about the current anthropogenic warming is that it's happening so fast, relative to previous warming phases$^1$. This is considered to be likely to contribute to mass species extinction, as some species will not be able to migrate or adapt fast enough.

However, the warming at the end of the Younger Dryas seems to have also happened quite fast. Is this period associated with any known extinction event?

  $^1$: "It is thus clear that the current rate of global climate change is much more rapid and very unusual in the context of past changes." - IPCC AR4 FAQ 6.2

Some authors thinks that the extinction of the Pleistocene megafauna (large mammals such as mammoths, etc.) was contemporaneous with the Younger Dryas (Firestone et al. 2007; Faith & Surovell 2009), while some thinks that it predates it by a couple thousand years (Gill et al. 2009).

Whether or not it was contemporaneous with the Younger Dryas, it constitutes a rather modest extinction event compared to the Big Five (i. e. the five bigger mass extinctions of the Phanerozoic: End Ordovician, Late Devonian, Permian/Triassic boundary, Triassic/Jurassic boundary and Cretaceous/Paleogene boundary, see this previous answer of mine for more details on that), with nonetheless a noteworthy impact (e. g. Johnson 2009) on the remaining ecosystem. The current/future mass extinction is however often considered to be at a comparable scale with these previous five (see for instance Barnovsky et al. 2011), but climate change is not the only one to blame: active destruction of ecosystems, mainly through anthropization, is one major factor as well.

References:
Barnovsky et al., 2011. Has the Earth’s sixth mass extinction
already arrived? Nature, 471: 51-57.
Faith & Surovell, 2009. Synchronous extinction of North America’s
Pleistocene mammals. PNAS, 106(49): 20641-20645.
Firestone et al., 2007. Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling. PNAS, 104(41): 16016-16021.
Gill et al., 2009. Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America. Science, 326: 1100-1104.
Johnson, 2009. Ecological consequences of Late Quaternary extinctions of megafauna Proc. Roy. Soc. B, 276 (1667): 2509-2519.


Circum polar regions in Interglacial periods Is it true, that circumpolar regions around North pole, were not submerged in water and had a habitable genial climate, until  the last Iceage, or glacial period?

I understand following comment as part of your question:

  Was that climate and terrain habitable by prehistoric humans?

I also assume that by "interglacial periods" you don't mean the last and current one, the Holocene. The next latest one is Eemian. The wikipedia sais on the sea level during that period:

  Sea level at peak was probably 4 to 6m (13 to 20 feet) higher than
  today...

  A 2007 study found evidence that the Greenland ice core site Dye 3 was
  glaciated during the Eemian,[7] which implies that Greenland could
  have contributed at most 2 m (6.6 ft) to sea level rise.[8][9]
  Scandinavia was an island due to the inundation of vast areas of
  northern Europe and the West Siberian Plain.

So there regions were submerged either under ice or sea and definitely not habitable.

And what before? I didn't find as thorough data through a brief google search, but supposing that Homo Heidelbergensis was the first "prehistoric human" species, we have some 600 ky of history, with several interglatials. Continental drift is marginal during this period (few kilometers IS marginal), so no continent could have been near the North Pole during any period of that time. During interglacials, the temperature was about the same as now, +/- 2 °C, and so the sea level was similar to current level. Even if some parts of Lomonosov ridge (just under North Pole) were above sea, they wouldn't be habitable for the humans of that time, at least due to ice. Paleolithic Eskymos in that areas are extremely unlikely.


What is the area with the largest velocity vertical shear in the ocean? While there are areas with really strong tidal currents in the ocean, these currents tend to be primarily barotropic. My question relates to the largest vertical difference in velocity and it is likely to be baroclinic in nature. What is the location with the largest shear? What is the magnitude of that shear?

Areas associated with velocity shear at a stratified interface are notably strong in the region of the Equatorial Undercurrent, straits (ex: strait of Gibraltar, the Bosphorus) and regions of the thermocline where internal waves are strong (South China Sea).
These areas are typically associated with strong turbulence as a direct result of the strong velocity shear and shear instabilities that trigger Kelvin–Helmholtz billows (if the Richardson number is less than 1/4 for a sufficient amount of time) and subsequent hydrostatically unstable configurations and mixing.
Examples of magnitude of shear:

Maximum in Equatorial Undercurrent: $du/dz \approx 0.02$ s$^{-1}$
At the base of the mixed layer but above the core of the Equatorial Undercurrent the shear is the largest. See plot from Peters et al (1988) https://i.imgur.com/YbmAtV2.png

East of the Carmarinal Sill in the strait of Gibraltar: $du/dz \approx 0.024$ s$^{-1}$
In the Mediterranian, water flows westward into the Gulf of Cadiz as an undercurrent through the strait of Gibraltar, as these waters make a sharp turn northward, they may give rise to sub-surface eddies or "Meddies" when encountering canyons and underwater bathymetric features off the west coast of Portugal.

Very large amplitude internal waves in the South China Sea: $du/dz \approx 0.05$ s$^{-1}$
In the South China Sea very large amplitude internal solitary waves are ubiquitous features propagating on the thermocline with inherently large shear across the interface. See plot from Lien et al (2014)  https://i.imgur.com/qhQBI9g.png

References:
Ren-Chieh Lien, Frank Henyey, Barry Ma, and Yiing Jang Yang, 2014: Large-Amplitude Internal Solitary Waves Observed in the Northern South China Sea: Properties and Energetics. J. Phys. Oceanogr., 44, 1095–1115.
Fernando, Harindra JS. "Turbulent mixing in stratified fluids." Annual Review of Fluid Mechanics 23.1 (1991): 455-493.
Thorpe, Steve A. The turbulent ocean. Cambridge University Press, 2005.
Peters, H., M. C. Gregg, and J. M. Toole. "On the parameterization of equatorial turbulence." Journal of Geophysical Research: Oceans (1978–2012) 93.C2 (1988): 1199-1218.


How to convert Relative humidity (%) or Specific humidity (kg/kg) to Air humidity (mb)? The model I use needs the data of Air humidity and unit is 'mb' (there is no other explanations about this variable), but now I only have two datasets and there are Relative humidity (%) or Specific humidity (kg/kg).
(Specific humidity: This parameter is the mass of water vapour per kilogram of moist air. The total mass of moist air is the sum of the dry air, water vapour, cloud liquid, cloud ice, rain and falling snow)
So how can I convert RH or SH to the humidity with unit 'mb'?

I guess what you need is water vapour pressure - that is one way of expressing humidity as the partial pressure of water vapour - in mb or hPa (they are equal).
According to World Meteorological Organization (WMO No.8 Guide to Instruments and Methods of Observation, Vol 1 Measurement of Meteorological Variables, ANNEX 4.B. FORMULAE FOR THE COMPUTATION OF MEASURES OF HUMIDITY), saturation vapour pressure - ews(t) - in hPa may be derived by the following formula, where t is temperature in degrees Celsius:
ews(t) = 6.112 exp [17.62 t/(243.12 + t)]

in hPa and degrees C, for liquid pure water (–45 °C to 60 °C)

This is the saturation water vapour pressure - a kind of "maximum" water vapour that can normally exist at a certain temperature t.
To know what the actual water vapour pressure - ew(t) - is, you must multiply it by the relative humidity (Rh) (and divide by 100 if Rh is in percentage):
ew(t) = ews(t) * Rh(%) / 100
So,
ew(t) = 6.112 exp [17.62 t/(243.12 + t)] * Rh(%) / 100
This is your "humidity" in mb, if you use Celsius for t.


What do the derivative or the integral of amplitude of a seismogram mean? I'm doing a project in which I'm analyzing earthquake seismogram waves. I used a program to graph the exact amplitudes and how they changed over the course of a single earthquake. For the project I need to incorporate calculus, so I was wondering, what does finding the derivative of amplitude do? And what does finding the integral get you?

The integral is the area under the entire wavelength, but I was wondering if it was equivalent to energy released, or some sort of geology/physics thing I didn't understand. Thank you.

This is a very simple answer, and it depends on the what the seismometer is measuring. I'm assuming you mean the time derviative/intdegral  $\frac\partial{\partial{}t}$ or  $\int{dt}$

Most seismometers measure displacement over time or velocity over time (series). So taking the time derivative will give you the spectral velocity or the spectral acceleration respectively when you take their derivatives.

When you take the integral of displacement, you calculate the total area displaced over time, and when you take the integral of velocity, you calculated the displacement.

It's all physics 101 really!


Why does winter get colder after the solstice? Intuitively, it makes perfect sense to think that the coldest day of the year would be the day that gets the least sunshine, the winter solstice.  In the northern hemisphere, this occurs a few days before Christmas.  But as anyone who lives in places that gets snow can tell you, the most bitter parts of winter are in January and February, not December.

Why does it get so much colder when sunlight (and the warmth it should be bringing with it) is increasing?

Primarily because of inertia.  This phenomenon is called seasonal lag.

It is true that the December solstice is the moment that the northern hemisphere gets the lowest total amount of insolation.  Conversely, the June solstice corresponds to the moment of maximum insolation.  The oceans, and to a lesser degree the land, absorb a lot of heat.  Due to the large heat capacity of water and the large amounts of water, the seasonal lag can be considerable.  In general, mid-latitude areas near large bodies of water have the largest seasonal lag, to the extent that the warmest month of the year in most of western Europe is August.

It is illustrated very well by this Warmest day of the Year map that NOAA NCDC (now NCEI) produced for the contiguous United States:

As expected, areas with a humid climate, such as southern Texas and nearby areas, tend to have the warmest day of the year in August.  The west coast is even more extreme, with some places having the warmest day in September.  Conversely, desert areas in the southwest (southern Arizona, New Mexico, western Texas) have the warmest day of the year in June.  For the Big Bend area in Texas, it's even in the first half of June, which must have entirely different reasons (probably related to dynamics) because a negative seasonal lag doesn't make much sense.
 There is a corresponding map for coldest day of the year:

(Source: NCEI)

The detailed structure is somewhat different, which has to due with local climate and circulation, but the overall trend related to humidity and proximity to ocean shows up in both.  We can also see the mountains, which I would guess to be a snow albedo feedback effect (ever notice how nights get colder when the ground is snow-covered?).  At NCEI you will also find similar maps for the rest of the USA.


Would a global cooling event disable solar energy usage? Imagine that we've improved the level quality, affordability, and ease of use of photo-voltaic solar, and it's use is widely distributed in the USA.  We've improved the grid for power distribution, we increase wind, hydro, geothermal sources for 24-hour generation and create a storage network to the point where fossil fuel generation is only needed for, say, 20% of our energy needs, and peak/backup needs.

Everyone is happy, bliss abounds.

Would such a system be vulnerable to a natural disaster?  If there was another Krakatoa event, with an equivalent amount of ash thrown into the atmosphere, how much, percentage-wise, of a reduction in solar intensity would we see, and for how long?

I am not sure about the size of Krakatoa eruption but the eruption of Mt. Pinatubo in Indonesia around 12th June 1991 is considered as the largest eruption in the past 100 years. Global average of decrease in solar radiation after 4 months of eruption was about 2.7 +/- 1 W/m^2. Global average surface reaching solar radiation is about 198 W/m^2. In other words, Mt. Pinatubo eruption caused about 1.3% decrease.

The number 2.7 W/m^2 is a global average, so the decrease might have been more in tropical regions and less at high latitudes. It took about three years for stratospheric aerosol amount to return to the background level.

Reference:

Minnis et al., 1993, "Radiative climate forcing by the Mt. Pinatubo eruption", Science, vol. 259, 1411-1415, doi: 10.1126/science.259.5100.1411
Kremser et al., 2016, "Stratospheric aerosol - observations, processes and impact on climate, Review of Geophysics, vol. 54, 278-335, doi:10.1002/2015rg000511


Why does El Niño only exist in the Pacific Ocean and not the Atlantic/Indian Oceans? El Niño is associated with the weakening of the ‘normal’ pressure/temperature gradients between the western and eastern Pacific Oceans.

My question is this: why does it only exist in the Pacific Ocean?

Could it be that the Atlantic is always in an ‘El Niño’ state too, given that the pressure/temperature gradients in the Atlantic aren't as steep as those of the Pacific to begin with?

First, to describe El Niño as a Pacific Ocean event seems overly simplistic. The effects of El Niño are felt worldwide as can be seemed by a principal component (EOF) analysis (e.g., Alexander et al., 2002). Also, using the term "El Niño" to describe the entire oscillation (ENSO, El Niño Southern oscillation) can lead to confusions as the term "El Niño" corresponds to one of the phases of the oscillation.

The size of the Pacific Ocean and the lack of equatorial constraints makes it a prime candidate for large oceanic fluctuations such as ENSO. The large distance between the western and eastern sides of the basin allows for a more dynamic equilibrium with the presence of large scale waves (Kelvin and Rossby; e.g., Kirtman, 1997). This equilibrium can be altered by external (atmospheric) forcing resulting in the different modes of oscillation of ENSO.

Apart from that, there are a number of significant modes of oscillations (see http://www.esrl.noaa.gov/psd/data/climateindices/list/ for a very good list) that occur in basins outside the Pacific ocean. A good example is the North Atlantic Oscillation (NAO; Hurrel [1985, Science]; http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.shtml) that affects not only the North Atlantic but also the climate of Europe and North America.

Other examples of modes of climate variability include the Pacific Decadal Oscillation (PDO; Zhang et al., 1997), the Atlantic Multidecadal Oscillation (AMO; Schlesinger & Ramankutty, 1994), or the Arctic Oscillation (AO; Thompson & Wallace, 1998).


Climate change review for a scientist I am a Ph.D student in Computer Science and Statistical Genetics. I recently became very interested in climate change, for obvious reasons. I would like to use my solid scientific and statistical background in order to get a good grasp of the models that climate scientists use to generate the dire predictions of global warming, which quickly seem to become reality, and to understand the possible outcomes and their probabilities.

Is there a good reference or review, book or paper(s), that could provide a clear, thorough introduction to the field for people like me, who have no background in climate studies but are interested in the technical details?

EnergyNumbers suggestion is good, but you can only go so far in reading about it second hand. I suggest that you pick a grid cell of interest, then go to the World Bank's climate change knowledge portal.

Climate Change Knowledge Portal

This gives a good cross section of 16 CMIP-5 AOGCM outputs. Check out the variation, and accuracy of the hindcasts vs evidence-based field instrumental data for the same location. Then you will get a good feel for the strengths and weaknesses of the modelling. Also, remember that water-related parameters are much less accurate to forecast than temperature-related parameters.


Searching for common wave vocabulary What do you call the leading waves and activity leading before a large wave?

Here is what I found if useful for others -

Oceanic Wave Clarification

Wave position in space (x,y) and in time (t) are different concepts

Ocean waves in time are a vertical oscillation generated most often from surface winds creating a circulation (eddy). There are no 'leading waves' to a 'big wave' rather simply a continual progression in size.

Ocean waves in space are generated from the simple motion of the wind. As the depth decreases the energy density of the wave increases, increasing the wave amplitude

Illustration (1)

Common Vocabulary (if useful)

Reference

(1) Quora - >When do waves stop forming in the ocean?
(2) Hyperphysics - Ocean Waves


Can a tornado burn itself out? I know that hurricanes can basically "burn" themselves out of energy if they get too strong, but can the same thing happen with a tornado?

Neither hurricanes nor tornadoes burn out because they get "too strong". Their strength is dependent on how supportive the atmospheric conditions are. If a hurricane stays in the same place for too long, moves over land, or moves over colder water, it will weaken. Likewise, a tornado will weaken if its parent storm moves into less favorable conditions and weakens.

All storms operate at "maximum strength" - they always are using all the energy that is available to them.


What are the differences between an LES-SGS model and a RANS based turbulence model? I'm kind of new to the Large Eddy Simulation (LES) modeling world and I wondered what is the difference between an LES subgrid scale model like the Smagorinsky–Lilly model and a one-equation Reynolds-Averaged Navier-Stokes (RANS) based model like the Spalart-Allmaras. They are both based on the Boussinesq eddy viscosity ($\mu$) hypothesis and both
using a one-equation approach for modelling $\mu$. However, no one is using the Smagorinsky–Lilly model for RAS or the Spalart-Allmaras for LES.

What is the difference between these two models and what kind of physical processes are they applied to?

The biggest difference between LES and RANS is that, contrary to LES, RANS assumes that $\overline{u'_i} = 0$ (see the Reynolds-averaged Navier–Stokes equations). In LES the filter is spatially based and acts to reduce the amplitude of the scales of motion, whereas in RANS the time filter removes ALL scales of motion with timescales less than the filter width.

I would recommend reading Fröhlich, Jochen, and Dominic von Terzi. "Hybrid LES/RANS methods for the simulation of turbulent flows." Progress in Aerospace Sciences 44.5 (2008): 349-377.

From that paper, specifically the section 'Structural similarity of LES and RANS equations', you can see that the equations being solved are essentially the same for LES and RANS, however, the physics are different. The main difference being that in RANS the unclosed term is a function of the turbulent kinetic energy and the turbulent dissipation rate whereas in LES the closure term is dependent on the length scale of the numerical grid. So in RANS the results are independent of the grid resolution!

  A model qualifies as an LES model if it explicitly involves in one or
  the other way the step size of the computational grid. RANS models, in
  contrast, only depend on physical quantities, including geometric
  features like the wall distance.

As far as typical processes, this figure summarizes it pretty well. DNS resolves all scales of motion, all the way down to the Kolmogorov scale. LES is next up and resolves most of the scales, with the smallest eddies being modeled. RANS is on the other end of the spectrum from DNS, where only the large-scale eddies are resolved and the remaining scales are modeled.

The figure above is from André Bakker's lectures: http://www.bakker.org/dartmouth06/engs150/10-rans.pdf

DNS: Very small scale flow (ex:turbulent boundary layers). Currently computationally intractable for most problems.

LES: Aims to solve the computational cost that DNS poses and reveals the eddies hidden behind the mean in RANS. Good for coastal scale scale 2D simulations and possibly lab-scale 3D simulations with a highly optimized parallel code.

RANS: It is the least computationally expensive method that is used for turbulent modeling, but it is really not very good when certain phenomena cannot be averaged, such as instabilities. Acoustic waves are also incorrectly modeled because they are inherently unsteady processes which can't be averaged, so typically modelers will crank up the turbulent and numerical viscosity to remove acoustic waves from the system.

This shows the main difference between LES and RANS.


Satellite image displaying as panchromatic I have a 4 band image (Blue, Green, Red and Near Infrared). If I display my image with only the green band in the RGB channel, the image displayed is panchromatic.

Why is that?

An RGB image can not be rendered if you only supply information for one color channel. This is because three channels are needed: Red, Green and Blue. Different software will deal with this invalid input in different ways: Some might set the remaining channels as black (i.e. filling with zero values). In that case the resulting image will be monocromatic. In shades of green in your example.

Other software might fill the missing channels with the same information supplied for the available one. In that case the result is a gray scale version of the band supplied.

In a general case, the rendered image will only display varying colors if two or more channels contain different information (i.e. different bands).

As mentioned in the comments, it is important to note that the difference between monocromatic and pancromatic. The former is a general term used to describe images formed by shades of a single color. While the latter is a specific term used in multispectral sensors to denote a band with a wider spectral response, and that usually have also higher spatial resolution.


When it is said that air moves from warm object to a cold object, how is it possible that air moves from high pressure area to low pressure area? By air moving from high pressure area to low pressure area means that it's moving from colder area to a warmer area,  are they both not contradictory? I might have understood something in a wrong way, pls help.

You are correct that air generally moves along the surface from high pressure towards low pressure (not directly, but deflected due to the coriolis effect).

However, this does not imply that it is moving from a colder area to a warmer area. And, there is nothing contradictory in a cool air mass moving horizontally to displace a warm air mass.

Extratropical cyclones (a kind of low pressure system found in mid latitudes) are actually related to the movement of a cold front and a warm front, as part of a frontal wave. They drive cold and warm air masses to move.

Your claim that "air moves from warm object to a cold object" might be the root of your misunderstanding. That claim isn't true. It is true that heat will move from a warmer object to a cooler object through conduction and radiation. But that is not related to whether the air itself will move. A local effect called a "sea breeze" demonstrates the opposite scenario. A hot beach creates a warm, rising column of air (and a local area of low pressure), bringing in cooler air from the ocean to replace it.

You have conflated the transfer of heat with the movement of air and air masses.


Looking for global cloud cover animations or videos I am looking for a video of global cloud cover. Something like an animated version of this image:

(Originally presented at http://naturalearth.springercarto.com/ne3_data/8192/clouds/africa_clouds_8k.jpg)

Any ideas of where to find such video?

Thanks a lot

Bernie

That kind of "moving clouds animation" is a very common one, as it is used routinely to aid in weather forecasting. However, it is not very common to see it in a whole-world geographic projection as the example you show, I'll elaborate later on why that's the case.

Traditionally, a common source of "cloud animations", have been NOAA's geostationary GOES satellites, in operation since 1975, with 17 satellites launched so far and more to come.

If you are looking for visually compelling animations, the latest GOES-16 satellite is capable of producing color images of the Earth's disk every 15 minutes at a resolution of 0.5 km per pixels (at the equator). They look like this:

And you can access images and animations pretty much right after acquisition, here is an example of the 24 hours before I posted this (reduced to a 20% of the size due to Stack Exchange upload size limits):

You can see updated animations at any time on the GOES-East Image viewer.
More traditional, B&W images (infrared band) can be found in the NOAA GOES page, or many other weather data sources. Also, beside GOES satellites there are many other geostationary weather satellites that cover different parts of the globe.

The reason images like the one you posted are rare (whole-Earth images), is because these kind of images are either taken from:

Geostationary orbits, that can't see polar areas and suffer of a strong degradation of the ground resolution per pixel at higher latitudes, or
Polar sun-synchronous orbits, like MODIS or Suomi, that allow whole-world composites but using images from multiple passes. Therefore, the full image is composed of images acquired at different times, leading to an ambiguity in the image's time and an impossibility to produce a seamless image, due to the de displacements of the clouds between the different passes.

Worldview is a great source of such multi-temporal composites, and as an example, here is a preview of yesterday's cloud cover by Suomi:

Worldview also allows to produce animations of the cloud cover spanning several months at one day interval. You just have to click on the video icon in the lower left and select the dates interval.

The GOES-East Image viewer stores images of the last four days (with some gaps some times), if you bulk-download them you can create longer animations. As an example, I just did a one of the last four days that you can see here (I do recommend to enable HD resolution).

Another interesting one, that also allow for animated display is the EPIC camera on DSCOVR satellite. Despite that the time resolution is a bit too low for looking at the clouds evolution, its unique perspective from the L1 point (42 times further than geostationary orbits) allow a full view of the illuminated side of the Earth. In addition from the animation in the link above, this video is also worth checking.

You can also find animations created using models instead of real data. That approach allows seamless global coverage at an arbitrarily high temporal resolution. A nice example is the one year long animation (at one hour time steps) of cloud cover and precipitation created from the NCAR's CESM model.


Luis Alvarez's K-T Impactor Calculation I am trying to perform the calculation that Luis Alvarez used to establish the size of the K-T impactor. I used the following information:

Assume that the clay layer with iridium was uniformly distributed around Earth by the impact.
On average, the layer had a concentration of iridium of 10 parts per billion (ppb) by weight.
On average, the layer was 4 cm thick.
The density of the layer was 2.5 g/cm3.
Assume the meteor was spherical, with a density of 6.0 g/cm3, and an iridium content of 0.5 parts per million (ppm) by weight.
The radius of Earth is 6378 km.

What is the diameter of the meteorite? The answer isn't exactly 10 km, as stated. By how much would you have to change the assumed thickness of the iridium layer to arrive at an asteroid diameter of exactly 10 km?

My attempt:

$m_{layer} = \pi(2.5 g/cm^3)((6378 \cdot 10^5)^4 - (6378 \cdot 10^5 - 4)^4) = 3.26 \cdot 10^{28} g$

$m_{iridiuminlayer} = (3.26 \cdot 10^{28})(10^{-8}) = 3.26\cdot 10^{20} g$

Here is where I get stuck. It seems there is not sufficient information to calculate the radius of the meteor, as D = m/V, and we are given density and a mass ratio. I tried doing the second portion, in which you assume the diameter of the asteroid is 10 km, calculating the mass of the meteor, the iridium in the meteor, and the average iridium distribution over Earth's surface. I would be able to solve the rest of the question if I knew how to calculate the Volume/mass of the meteor. Please help!

The volume of a sphere is $\small\sf{\frac4 3\pi R^3}$, where $\small\sf{R}$ is the radius.

The volume of Earth with the 4 cm deep iridium rich layer is,

$\small\sf{V_{Ei} = \frac 4 3\pi (6.378\cdot10^6)^3}$ $\small\sf{m^3}$ = $\small\sf{1.086 \ 781 \cdot 10^{21}}$ $\small\sf{m^3}$

The volume of the 4 cm deep iridium rich layer is,

$\small\sf{V_i = \frac 4 3\pi (6.378\cdot10^6)^3} -\frac 4 3\pi (6.378\cdot10^6 - 0.04)^3 $ $\small\sf{m^3}$ = $\small\sf{2.044 \cdot 10^{13}}$ $\small\sf{m^3}$

Now, density is mass divided by volume, $\small\sf{\rho = m/v}$, thus the mass of the iridium rich layer is,

$\small\sf{m_i = 2.5 \cdot 2.044 \cdot 10^{13} = 5.110 \cdot 10^{13}}$ tonnes

The proportion of iridium in the layer is 10 ppb, therefore the mass of iridium within the layer is,

$\small\sf{5.110 \cdot 10^{13} \cdot 10 \cdot 10^{-9}} = 511 \ 000$ tonnes

Now, the proportion of iridium in the meteor was 0.5 ppm, therefore the mass of the meteor was,

$\small\sf{511 \ 000 / (0.5 \cdot 10^{-6}) = 1.0220 \cdot 10^{12}}$ tonnes

The density of the meteor was  $\small\sf{6.0 \ g/cm^3}$, which is the same as $\small\sf{6.0 \ t/m^3}$, therefore, the volume of the meteor was,
$\small\sf{1.0220 \cdot 10^{12}/6.0} = 1.703 \ 333 \cdot 10^{11} m^3$

Using this and the equation for the volume of a sphere, the radius of the meteor was,

$\small\sf{\sqrt[3](\frac 3{4\pi} \cdot 1.703 \ 333 \cdot 10^{11})} = 3438.774 \ m$

and the diameter of the meteor was 6877.5 m or 6.878 km

Not the 10 km you wanted.

To get the thickness you want for a 10 km diameter meteor, do the calculation in reverse.

For diameter of 10 000 m, the volume of a spherical meteor would have been,

$\small\sf{\frac 4 3 \cdot \pi \cdot 5000^3} = 523.598 \ 776 \cdot 10^9 \ m^3$

With a density of $\small\sf{6 \ t/m^3}$, the mass of meteor would have been,

$\small\sf{6(523.598 \ 776 \cdot 10^9)} = 3.141 \ 592 \ 6 \cdot 10^{12} t$

with a metal grade of 0.5 ppm of iridium, the mass of iridium in the meteor would have been,

$\small\sf{3.141 \ 592 \ 6 \cdot 10^{12} \cdot 0.5 \cdot 10^{-6} = 1 \ 570 \ 796 \ t}$

The metal grade of iridium in the layer on the Earth is 10 ppb, therefore the mass of the iridium layer is,

$\small\sf{(1 \ 570 \ 796)/ (10 \cdot 10^{-9}) = 1.570 \ 796\ 327 \cdot 10 ^{14} \ t}$

With a density of $\small\sf{2.5\  t/m^3}$, the volume of the layer is,
$\small\sf{(1.570 \ 796\ 327 \cdot 10 ^{14})/2.5 = 6.283 \ 185 \cdot 10^{13} \ m^3}$

From the previous calculation, the volume of layer is,

$\small\sf{6.283 \ 185 \cdot 10^{13} = \frac 4 3\pi (6.378\cdot10^6)^3} -\frac 4 3\pi (6.378\cdot10^6 - x)^3 $ $\small\sf{m^3}$ = $\small\sf{2.044 \cdot 10^{13}}$ $\small\sf{m^3}$

Solving for $\small\sf{x}$, which is the thickness of the layer, gives $\small\sf{x} = 0.123\ m\ or\ 12.3\ cm$


Would you see a correlation between detrital zircon age and grain shape? If one was to quantify the shape (particularly roundness) of detrital zircon grains, would there be a correlation between the age of the detrital zircon grains and their shape? For example, if the grain is an Archaean one, would it be much more rounded than a grain that is Devonian?

My thought is that you would not see any correlation because grain roundness has to do with how long it has been in the sedimentary system rather than its crystallisation age. That is, if one sampled a modern sediment in which a 650 Ma zircon grain from a 650 Ma granite has only recently been eroded from its granite source then one would expect this zircon to be euhedral (and this is not taking into account magmatic effects like resorption which would affect its shape!). But a 650 Ma zircon in the same sediment may have been eroded from a different Neoproterozoic granite during the Cambrian, in which case one would expect that it has been rounded by multiple cycles of sedimentation. Therefore no correlation could be made between the shape of the zircon grains and their crystallization age.


Why is the Yarkant River braided in the Pamir mountains? The formation section in the braided river Wikipedia says that very erodible soil causes braided rivers. Intuitively, a rising mountain range like the Pamirs would not be easily erodible.

The Yarkant changes so abruptly, I'm curious what special geological feature is at these straight/meandering-to-braided junctions.

  The critical factor that determines whether a stream will meander or braid is bank erodibility. A stream with cohesive banks that are resistant to erosion will form narrow, deep, meandering channels, whereas a stream with highly erodible banks will form wide, shallow channels, inhibiting helical flow and resulting in the formation of braided channels.

Braid 1

Here's near the edge of the Pamir range.

Braid 2

Here's another braided section in the Pamirs, far upstream.

A source

There appears to be a glacier at a source of the Yarkant in Central Karakoram Park. If glaciers present/past explain braiding, why is it intermittent?

Minimal braiding in the Rockies

Mountainous braided rivers seem rare/mild elsewhere, like here in the Rockies in Missoula.

Braiding will occur in any river where two conditions are met: 1) a very high sediment load must be available, as is usually the case in a peri-glacial or post-glacial environment, and 2) there is an abrupt change from high energy rivers (steep hydraulic gradient) to low energy deposition with flat space on either side of the river. Go for a hike in any glacial or post-glacial mountains and you will see that rock hardness has little to do with sediment availability - there is always more sediment than the river can mobilize at any one time, even in extreme floods. The classic example is the Canterbury Plains on the east side of South Island New Zealand. Braiding is an inherently unstable and transient river configuration.
Meandering is the river's minimum energy configuration. It is another chaotic process, achieved through helicoidal flow and superelevation on the convex side of a bend. It will occur anywhere the river is laterally unconstrained, and where the rotational kinetic energy, perpendicular to the direction of flow, is a significant fraction of the forward kinetic energy.