Public sources of topographical data of Earth? I would like to find sources of topographical data for Earth's surface.

I've looked in GIS SE and Open Data SE but haven't found a good answer to this so I though I'd ask here in Earth Science.

Are there public sites where I can download free topographical data; tables of surface height above a reference surface?
Is it possible to download them in text or tabular form?

I'm looking for resolution of something of the order of 5 meters vertically an 10 horizontally, but there's no specific hard requirement.

This is an interesting and common question, so I'll try to give a good answer here, that I think is a good place, as well as GIS and Open Data SE.
First, regarding the format, you will never find data natively stored in text or tabular form, because the large data volume would lead to huge files very difficult to handle. Data is usually stored in binary files, common standards are .hgt and .tif. And there are many software and utilities that can export small subsets of the data into text, csv, or tabular formats.

I'll list here the global or near to global sources. All of them have advantages and disadvantages, and all have data gaps and artifacts, specially in areas with rough topography. So depending of your area of interest, one or the other can be better.

SRTM (Shuttle Radar Topographic Mission)

Resolution: 1 arc-sec (~30 m)
Data epoch: February 11$^{th}$ to 22$^{nd}$ 2000
Data type: Integer
Vertical reference: Orthometric (geoidal)

The most widely used standard, due to its quality, resolution, and coverage. It covers the whole globe between latitudes 60°N and 56°S.

In contrast to all other datasets, all the data was acquired in a 11-day mission, therefore, it have unmatched consistency, specially in areas with rapid terrain changes like glaciers, open pit mines, cities, etc.

The space shuttle was carrying two radars that created two independent terrain models, the coverage above corresponds to the SAR-C instrument that produced the data that is most widely used. The second instrument was the X-SAR, that had a narrower swath, and does not have global coverage.

There are multiple versions of these datasets:

SRTM v3

The latest official release is version 3. It comes in its original form, that includes data gaps and a gap-filled version, on which those gaps have been filled with data coming from multiple sources (but primarily ASTER GDEM).

The data can be accessed through multiple gateways, some of them are:

USGS EarthExplorer
NASA EarthData
LP DAAC Global Data Explorer
USGS data server (Version 2.1)

CGIAR SRTM

An independent post-processing of SRTM data.  Known also as SRTM v4.  It consists of a gap-filled version of SRTM using an advanced algorithm. It is only available at 3 arcsec resolution (90 meters) . It can be downloaded at the CGIAR SRTM Download manager

NASADEM

The SRTM data was reprocessed with cutting edge technology, improving accuracy and reducing data gaps. In contrast to other SRTM versions, it offers also a ellipsoidal version of the data (instead of geoidal), and the data comes in floating point values (instead of integers). NASADEM is expected to be the last official release of SRTM data. This DEM is still in the development phase but should be released at any time. A provisional version has been released and can be downloaded at the MEaSUREs data repository. More information on how to use this data can be found in my answer here.

This dataset should NOT be confused with the "NASA Shuttle Radar Topography Mission Global 1 arc second V003" (SRTMGL1). Which corresponds to the SRTM v3 data described above.

ViewFinderPanoramas

Some individuals like Jonathan de Ferranti, tackled the gargantuan task of doing a manual quality assessments of all the gaps of the SRTM and areas that have erroneous data. To then fix it using many sources, including many national mapping agencies from around the world. He produced a great version of SRTM with most errors fixed. Unfortunately, all this work was done before the worldwide release of full resolution SRTM data in 2014, therefore, for most of the world this data have only 3 arc-sec resolution (~90 m). And it can be downloaded at ViewFinderPanoramas.org.

SRTM X-SAR

Data from the second radar on board the Endevour space shuttle during the SRTM mission. It has slightly higher resolution (~20 m) but worst coverage, because the multiple swaths did not overlap, so for example, over North America the coverage looks like this:

This data can be downloaded from DLR Geoservice.

ASTER GDEM

Resolution: 1 arc-sec (~30 m)
Data epoch: 2000 to 2011
Data type: Integer
Vertical reference: Orthometric (geoidal)

With almost complete coverage between 83°N and 83°S, GDEM was produced from more 1.5 million stereo pair images by ASTER sensor. A joint project between JAXA and NASA on board of Terra satellite. This is the coverage of the latest release:

The current version is GDEM v3 (released on August 5 2019). This Release also includes the ASTER Water Body Dataset (ASTWBD), a valuable dataset to correct terrain models. GDEM v3 is available from:

NASA EarthData
Japan Space Systems

ALOS World 3D

Resolution: 5m (paid), 30 m (free)
Data epoch:  2006 to 2011
Data type: Integer
Vertical reference: Orthometric (geoidal)

Somehow the successor of ASTER, ALOS and its instrument PRISM, also offer stereo capability and higher resolution. And it was used to generate a new DEM with near global coverage:

The free 30 m resolution version of the data (with maximum resolution of 5 m), can be downloaded at JAXA AW3D30 DSM data page (need to sign up first). Current version is AW3D30 v2.2 (released in April 2019).

GSDEM30

The "Global Seamless DEM 30" is a 1-arcsec (~30 m) DEM that was constructed by merging unfilled SRTM, ALOS World 3D, and ASTER GDEM v2 datasets. By combining all these sources, it reduces data-gaps and significantly improves the quality of the data in regions where any of the base DEMs performs poorly. Data can be downloaded from the Wuhan University's SENDIMAGE servers. More details of the data merging process can be found in this paper.

TanDEM-X WorldDEM

Resolution: 12m (paid), 90 m (free)
Data epoch:  2010 to 2015
Data type: Floating point
Vertical reference: Ellipsoidal

The latest radar base global elevation model, created from two satellites orbiting in tandem formation (TanDEM-X), allowing high accuracy single-pass InSAR and DEM generation with truly global coverage. The free 90 meter resolution data can be downloaded from DLR Geoservice.

ArticDEM and REMA

Resolution: 2m
Data epoch:  2007 to 2018

This two projects turned the polar areas from being the ones with the worst available topographic data to the ones with the best data. By computing DEM's from millions of stereo image pairs from the high-resolution imaging satellites of DigitalGlobe. ArticDEM covers all latitudes north of 60°N:

And REMA covers all latitudes south of 60°S:

The data can be explored and downloaded from the ArcticDEM Exporer, and Antarctic REMA Explorer.


Why don't Antarctic waters have more upwellings, when Arctic waters are so rich in upwellings? Formation of ice and hence more dense saltwater sinking happens in both polar regions, creating downwellings. Meanwhile, only a few spots in Antarctica have upwellings

I refer to this image:

https://en.wikipedia.org/wiki/Upwelling#/media/File:Upwelling_image1.jpg

First, we might want to distinguish between the different types of upwelling:

Coastal upwelling: It is the best known form of upwelling. Winds in these systems flow parallel to the coast (with the coast to the left in the northern hemisphere or to the right in the southern hemisphere) and generate upwelling dynamics. Surface Ekman balance is setup (in deep enough waters) with water transport being to the right (left) of the wind in the northern (southern) hemisphere. The result is a deficit along the coast that requires a compensating flow in the deeper part of the water column bringing usually colder waters to the surface. If the wind blows in the opposite direction, then downwelling occurs.
The figure from the question refers to coastal upwelling (here in its original website with explaining caption). There is definitely more coastal upwelling in the northern hemisphere because of the abundance of shorelines as a greater amount of landmass is present in that hemisphere.

 Source Commons Wikipedia.

Equatorial upwelling: Winds from the east blow and converge along the equator as part of the Intertropical Convergence Zone (ITCZ). While the magnitude of the Coriolis acceleration is zero along the equator, Ekman transport takes place immediately north and south of the equator resulting in surface ocean divergence that requires a compensating flow of denser (nutrient-rich) water upwelled from below.

 Source

Southern Ocean upwelling: Strong westerly (eastward) winds dominate the atmospheric setting around Antarctica. The strong winds force the Antarctic Circumpolar Current, the strongest current in the ocean. The winds also result in an Ekman balance with northward flow in the upper part of the water column. To compensate that flow, some water flows up from greater depths. The magnitude of the Southern Ocean upwelling is still being studied, but some observations and models propose that it represents the main way for dense water from deeper areas to be reintroduced in the surface circulation. If that were the case, then it represents the largest upwelling system in the world. An alternative explanation proposes oceanic eddies as the main mechanism for dense water to reconnect with the surface circulation. Additionally, there is coastal upwelling over the Antarctic continental shelf driven by local winds that brings relatively warmer waters to the shelf contributing to local/regional ice melting.
 Source

The question also mentions downwelling associated with dense water formation. Deep water forms at high latitudes (typically north and south of 60°) in both the southern and northern hemispheres. As mentioned in the question, ice contains almost no salt, so when ice forms, a salty, sub-zero brine is left behind and sinks. In the Antarctic, as the saltier water moves down, it mixes with slightly warmer intermediate water. The mixture becomes Antarctic Bottom Water (AABW), which flows northwards along the bottom in all the main oceans. In the Arctic, the northward flowing branch of the Gulf Stream (salty and warm) joins the subpolar gyre and enters the Labrador Sea where as it cools, it starts to sink. The eastern branch of the Gulf Stream begins to sink in the Nordic Seas. The resulting water masses combine to form the dense North Atlantic Deep Water (NADW) that flows south at depth. Both the creation of AABW and NADW can be considered downwelling, as there is a net downward flow in the formation areas, but they are not related to wind-driven downwelling in the vicinity of coasts.


How much of Earth's land area has antipodal land area? Using the site antipodesmap one can quickly explore what the opposite point of the earth to any location would be. That is, the surface point connected to this point by a straight line through the centre of the earth.

It is easy to see that most land points have antipodes which lie somewhere in water, which made me wonder:

How much land area (as a fraction of total land area) has antipodal land area?

And how would I best find this out? Can somebody produce a map of those areas, e.g. highlight those areas on a world map?

A rough idea, using the Lambert Conformal image at the Cartopy projection list and Gimp:

The gold area should be the overlap.  So basically parts of South America with Indonesia and SE Asia... and Antarctica with the far northern islands of the northern hemisphere, plus a few smaller areas from islands like New Zealand and Hawaii and even smaller.

That assumes I did properly invert it.  To do so, I just vertically flipped the image, and offset it by 180 degrees.  Thinking that should be all that is needed.

So in the end it looks like it's not a lot of area at all.  Further exact statistics would take some GIS work (probably quicker than GIMP in the end!)  A central starting guess would be 8.5% (the 29% land cover squared), but particulars will make it a bit higher or lower.


What causes "hydrocarbons" to take the form of petroleum versus natural gas? "Hydrocarbons" are found in geological formations consisting of strata or layers of rocks. Specifically, they are formed from decomposed organic material (that contains carbon), that bonds with hydrogen, which is a component of water. (Somehow, the resulting oxygen is released).

Such hydrocarbons can take the form of either liquids (e.g. petroleum) or gas (natural gas). There are also "intermediate" products such as propane or butane that can easily take either liquid or gas form (at differing temperatures, but at temperature ranges that are normal for human existence).

What further factors cause hydrocarbons to take the form of petroleum, natural gas, or one of the others?

Oil and gas both form when organic matter is buried under anoxic conditions, such that it isn't oxidised and subsequently mineralised to the elemental components of the hydrocarbons.

What hydrocarbons are formed depends on both burial depth and temperature. Above approximately 1km below the surface no significant formation of oil takes place, and hydrocarbons are either mineralised or broken down to volatile products such as methane, propane, and butane.

The often so called 'oil window' is located below 1km, but above ~4km, and at temperatures between 40-50 °C and 150 °C. Under these conditions long hydrocarbon chains can form without being broken down to shorter, more volatile chains.

At larger depths or higher temperatures no (significant amount of) oil is formed, and all organic matter is transformed to natural gas.

An approximate graph after Nichols (2009).

Formation of these fossil fuels often takes place in shales (lithified clay) that are rich in organic matter, but as all sedimentary rocks this is a porous medium and thus liquids will tend to flow upwards to areas of lower pressure. To be preserved two other components are therefore necessary: a reservoir rock (often sandstone) and a sealing rock (numerous types of rock are suitable, including rock salt and certain igneous rocks), often in dome or fault structures.

Source: Nichols, Gary (2009) Sedimentology and Stratigraphy, p 293-295


Why is convective precipitation associated with heavy rains? Why is convective precipitation associated with heavy rains?

As per wikipedia's page on Atmospheric Convection: "Moist convection leads to thunderstorm development, which is often responsible for severe weather throughout the world".

Before we go any further it would be helpful to review this Q/A-Are clouds a gas, liquid, and/or solid?

The key to understanding this question is to realize that it is missing a comparison. Does convective precipitation produce heavier rains in comparison to some other form of precipitation ?

When we look at the different types of precipitation and the respective scales involved hopefully we can see why convective rains produce heavier rainfall.

So there are two forms of precipitation - convective and stratiform.

I am going to provide a definition of both types of precipitation based on the magnitude of the mean vertical velocity of an atmospheric volume. So the mean vertical velocity(obtained from observations) is the average vertical velocity over the atmospheric volume being studied(in this case the cloud(s) in question).

So stratiform precipitation is defined as

$ w << V_{ice,typical} $ and $w > 0$.  where w is the mean vertical velocity and $V_{ice,typical}$ is the terminal fall velocity of ice crystals and snow(typically in the range  1-3 m $s^{-1}$)

Convection precipitation is defined as

$ w \approx V_{ice,typical} $ and w is in the range  1-10 m $s^{-1}$ and sometimes exceeds the value of $V_{ice,typical}$

These definitions are due to Henry Houghton as shown from the reference - On Precipitation Mechanisms And Their Artificial Modification. Also stratiform precipitation occurs mostly from nimbostratus clouds and convective precipitation occurs from cumulonimbus clouds.

Now let us list the different types of instability in the atmosphere and the scales at which they evolve(any cloud has to form due to an instability in the atmosphere)

1) Conditional instability/Convective instability - (usually less than 10 km horizontally) and time scale - few minutes

2) Symmetric instability - ( 200 kms horizontally) and time scale - few hours

3) Baroclinic instability ( less than 2000 kms horizontally) and time scale - maximum 2-3 days.

Now let us match the speed of the vertical motions in the atmosphere with the scales at which a particular instability evolves. I am going to exclude symmetric instability  from this discussion.

Frontal systems(baroclinic instability), systems affected by topographic lifting and large scale horizontal convergence produce stratiform precipitation and continuous rain. In this case growth  occurs by deposition of vapor particles and aggregation of ice particles. Because of the slow updrafts we typically see continuous rainfall spread over a large distance and slowly varying over time.

Localized rain associated with either conditional instability or convective origin produce updrafts of several meters per second. There is not enough time for full growth of precipitation particles. Initial growth occurs just above the cloud base
and since the time for growth is very short and rain drops grow mainly by accretion of rain drops. Heavy rainfall realized over a short period is balanced by the smaller horizontal scale of the event. When convective rainfall is observed over a large horizontal area usually it is balanced by areas that have a) either no rain b) areas having stratiform precipitation.

References

Cloud Dynamics by Robert Houze, Chapter 6


Why is there a seasonal cycle to the amount of CO2 in the atmosphere? I'm doing some homework on the increase of $\mathrm{CO}_2$ in the atmosphere. On one of the graphs it shows the amount of $\mathrm{CO}_2$ peaks in May and has a low in November. Why is this? Shouldn't it just be constantly going up?

Overall, the measured amount of $\mathrm{CO}_2$ increases, but in a cyclic pattern, as can be seen in observations shown below:

Image source: NOAA: Trends in Atmospheric Carbon Dioxide (numerous observation data sets and graphs are available from that website)

The fluctuations are seasonal, which is explained in the web page Seasonal carbon dioxide range expanding as more is added to Earth's atmosphere (NSF, 2013) summarises the seasonality as being

  Levels of carbon dioxide in the atmosphere rise and fall each year as
  plants, through photosynthesis and respiration, take up the gas in
  spring and summer, and release it in fall and winter. Now the range of
  that cycle is expanding as more carbon dioxide is emitted from burning
  fossil fuels and other human activities.

Specifically, the effect is more pronounced in the northern hemisphere, with

  more carbon is accumulating in forests and other vegetation and soils in the Northern Hemisphere during the summer, and more carbon is being released in the fall and winter

Daily as well as seasonal variations were observed in northern Japan, reported in the article Diurnal and seasonal variations in atmospheric $\mathrm{CO}_2$ in Sapporo, Japan:
Anthropogenic sources and biogenic sinks (Miyaoka et al. 2007).


Why do certain areas on Earth have a higher or lower air pressure at sea level? For instance, looking at this map of world air pressure in January and this map of July, why do some land surfaces have a higher pressure during the winter?

I know that the tropics and Coriolis forces have something to do with the direction, and that wind flows from higher to lower pressure, but how can you guess what the pressure for an area will be for a certain season?

If I describe a certain surface area (water or land, cold or hot, high or low elevation) given a certain season (winter or summer), what generalizations can I make of the average air pressure during that season (high or low)?

By way of analogy consider a hot air balloon. The balloon encloses some air. As the air is heated, via massive gas burners, the air in the balloon becomes less dense compared to the air outside the balloon and eventually the less dense air in the balloon rises, lifting the balloon into the air.

Atmospheric air in contact with the Earth does the same thing. Air is differentially heated and cooled due to the effects of the Sun, clouds, cold air injected from polar regions and warm or hot air injected from equatorial regions. This affects the energy of the air and its density. Air density is also affected by moisture; very little over dry hot deserts and more over oceans, lakes, large water reservoirs and forests, due to transpiration from trees.

The temperature differentials result in relatively warmer and cooler spots within the air in contact with the Earth's surface and above it. Air in the relatively warmer spots rises. The height to which it rises will in part be affected by the amount of heat it contains when it starts to rise.

The surface of the Earth immediately below the column of rising air experiences less air pressure than neighboring regions, hence such regions have low air pressure. As the air rises it cools. Eventually, the air falls back down. The area of the Earth's surface below the falling column of air has a higher pressure relative to its neighboring areas, giving rise to high pressure systems.

The seasonal variation of the general locations of high and low pressure systems are due to the differences in the thermal energy of the air, which in turn is determined by the sources of heat and what might be inhibiting heating.

Edit: In Reply to Additional Questions in the Comment Section

If you look at the pictures you provided the links for in your question you'll see that during July there is a low pressure zone over North America in addition to the much deeper low pressure zone over north eastern Asia. Additionally, the north-east Asian low pressure zone extends into eastern Europe and north Africa. The high pressure zones, in the northern hemisphere are effectively “islands” over the Atlantic and Pacific Oceans centered around 30 to 40 degrees latitude. Apart from western Europe and parts of the eastern US coast, northern hemisphere landmasses are under low pressure.

When you look of the picture for January there is a continuous high pressure zone extending from North American to east Asia and into north Africa. There is even a high pressure zone over Greenland. The regions experiencing low pressure are the most of oceans and the equatorial zones – tropical and sub-tropic part of the Earth.

July in the northern hemisphere is the start of the summer and January is well into winter. By July, the landmasses have been accumulating heat from the Sun, since the end of winter, and warming the air above it causing the air to rise and the air pressure to be lower.

Conversely, by January, the landmasses have cooled so they are not heating the air above them. However, air from the northern equatorial region is rising and due to Hadley cells the air falls back down causing the high pressure zones.


How does moveout correction work in seismic reflection profiling? When you take a seismic reflection profile you take multiple shots and then stack them together around a common midpoint. Due to the extra distance travelled by the wide angle shots there is a moveout on time profile which you have to account for. Apparently, in order to apply the moveout correction you have to know (or guess) the velocity structure of the layers. I am confused as to why this is. Surely you know the extra distance travelled from the geometry of the shot you know the extra time because it is recorded in the arrivals so you should calculate the average layer velocity after lining up all the arrivals at the same time, not the other way around.

If someone can provide a detailed explanation of how common midpoint stacking and the moveout correction works that would be very helpful.

The offset is measured in meters, but the depth is still measured in time. The extra distance the wave have traveled to a longer offset is therefor also seen as an increased time in the CMP-gather (Common Mid Point) and the extra time depends on the seismic velocity of the layers.

If the velocities are high, the moveouts are short. The longer offset, the longer distance the wave have traveled through the layer and the larger moveout correction is needed before stacking. Sometimes we mute long moveouts as they tend to be distorted and noisy.

When we stack the traces in the CMP-gather, we need the reflectors to be at the same time and to do that, we perform NMO-correction (Normal MoveOut).

To find the right velocities to use for the NMO-correction, we can do a semblance analysis to get the NMO-velocity. That is to simply try possible velocities and see at what velocity the reflector in the CMP-gather is aligned horizontally and gives the highest peak when summed for all traces.

The figure shows a synthetic CMP-gather to the left. A semblance velocity scan is performed and the peaks are shown in the middle plot. The velocities are picked as shown in the graph and are used to NMO correct the CMP-gather as seen in the seismogram to the right. When this is stacked, the reflectors will add up and the noise will be suppressed. So in theory, we don't need the velocity beforehand to perform NMO-correction. The moveout can be used to calculate a NMO-velocity model.

The figure is from Madagascar development blog.

However, if we know the velocities, eg from borehole data or refraction studies, we don't need to rely on computing heavy semblance velocity scans and uncertain velocity picking. Data are rarely so neat as this synthetic example shown here. Also, it's impossible to derive the gradually increasing velocity in a formation without internal reflectors.

The velocity we use to do NMO-correction is not the same as the velocity of the layer, but rather the additional velocity to the average needed to correct the moveout. To finally estimate the actual velocity of the layer, we can use e.g. Dix equation to correct the velocities, but more accurate methods are usually used nowadays.

This is the basic application for stacking, but there is much more to it, you can read more e.g. here.


Axial Obliquity and Climate Change The Wikipedia page for Earth's Axial tilt says:

  Earth's obliquity oscillates between 22.1 and 24.5 degrees on a
  41,000-year cycle. It is currently 23.44 degrees and decreasing.

My Questions are:

What changes in climate pattern can be observed when obliquity is at the extremes?
How extreme can the climate get if the obliquity oscillates between 20 and 30 degrees?

What changes in climate pattern can be observed when obliquity is at
  the extremes?

While obliquity is easily googled, the specific effects globally aren't as easy to look up, so I'll give this one a shot.

For starters, the 41,000 year variation isn't precise.  It fluctuates some, having to do with the earth and other planets not being perfect spheres and not all orbiting in the same plane of elliptic, and the planets (Primarily Jupiter), tugging on each other.   The Moon stabilizes the Earth's obliquity somewhat, though that's often overstated.  More recent models have shown that the Earth's obliquity would be reasonably stable even without the moon and in the future, the Moon could fall into resonance that will destabilize the Earth's obliquity.  (I read that researching another question,  but don't have the article handy and that doesn't really apply to your question anyway).

The easy part to look up is that Obliquity is primarily a polar and seasonal effect.  Higher Obliquity (24.5% currently and the more extreme 30% proposed in your question) means colder winters and hotter summers in higher latitudes.  (higher latitude means both poles, just for clarity, high latitude = far from equator)

High obliquity means more extreme seasonality (hotter summers and colder winters in both hemispheres). This does not change the year-average energy reaching the Earth, but in terms of temperature the Northern hemisphere is more important because it contains more land: Land warms up faster than water and it also hosts the reflective ice-sheets that contribute to Earth's cooling. As a result, Ice ages (somewhat) coincide with cold Northern Summers.

So, the simplified answer is higher obliquity, hotter earth, lower obliquity, colder earth.

Source - Milankovich

Quote:

  The tilt is in the decreasing phase of its cycle, and will reach its
  minimum value around the year 11,800 CE ; the last maximum was reached
  in 8,700 BCE. This trend in forcing, by itself, tends to make winters
  warmer and summers colder (i.e. milder seasons), as well as cause an
  overall cooling trend.

and Source - NOAA Article

  less "tilt" means less severe seasons - cooler summers and milder
  winters. The earth wobbles in space so that its tilt changes between
  about 22 and 25 degrees on a cycle of about 41,000 years. It is the
  cool summers which are thought to allow snow and ice to last from year
  to year in high latitudes, eventually building up into massive ice
  sheets.

you asked:

  How extreme can the climate get if the obliquity oscillates between 20
  and 30 degrees?

With a 20 to 30 degree variation in tilt, figuring the same 41,000 year cycle, Ice would build up in the North as the cycle leaned towards 20 degrees and ice would melt in the North as the cycle leaned towards 30 degrees.  The "milder winter" that we might expect from a 20 degree tilt would be highly overcompensated for by the cooling effect of an ice sheet if there was an ice sheet, so, "milder at lower tilt", shouldn't be taken as strictly true but only true if there isn't an ice age coinciding with the lower tilt.

It's possible a 30 degree tilt, which would cycle upwards, 28 29, 30, 29, 28), that period of high tilt, lasting 10,000 years might be enough to melt Antarctica too, which for the most part hasn't melted in 15-25 million years or so.   Needless to say, with a tilt that high, we'd probably go through more extreme variation with the rise and fall of ice ages and rapidly changing sea level, and ice age cycles are already quite extreme in terms of sea level rise, flooding from glacial melt melt and other changes.   Anyone who was alive 12,000 - 8,000 years ago could verify that the changes were intense.  Fossil records show an increase in extinctions during periods of rapid climate change.

The last maximum tilt happened 8,700 BCE, so the moving towards the maximum coinciding quite well with the end of the last ice age and the minimum is going to happen about 11,800 CE (or 11,800 AD for anyone who went to school when I did), and that (might) coincide with the rising of the next ice age, but it's a bit more complicated than that, as we've figured out how to stop ice ages by burning lots of fossil fuels, and the other orbital factors would need to be considered as well.

That's the simplified answer anyway.  A more detailed answer would take into account the other orbital cycles (see Milankovich link above), the 100,000 year problem and the large permanent glaciers which survive the entire 41,000 year cycle, such as we currently have on Greenland and Antarctica and which affect albedo.  I might try to tie that in later, but that would get longer and at my level of understanding, a bit less certain.


Why does the color of this hillside rock vary? Below is a roadcut in central Marin County, California, in an area maps show to have Franciscan melange.  I assume this is graywacke, but as you can see it varies from gray on the sides to a buff color in the center.  Is the buff section due to some chert content, or did that section weather differently (and if so why)?  Thanks!

It's pretty hard to say anything about this kind of weathering without actually being there and having a closer look.

Usually, the simplest explanation for reddish or brownish colours in otherwise grey rocks is the presence of iron oxides. You can see that the brown area is on a fault or joint face. This leads me to think that maybe this was a conduit for groundwater that oxidised the rock. When the road cut (or whatever it is) was made, this part was exposed. Notice that you have some brown elsewhere - it could be that those are faults or joints cut perpendicular to the face, so that's why you only see a brown streak instead of a surface.


Can the shape and orientation of a large glacial rock deposit indicate glacial flow direction If a rock is tapered, does the tapered point indicate the glacier direction?

Yes, it can. There are large, elongated mounds of till carried by the glacier as it advanced and left behind as it retreated. These mounds are called drumlins. Their long axis points along the track of the now vanished glacier. They are wider, higher and steeper at the end which points toward the glacier's source and taper away gradually at the opposite end, which points away from the source. They vary in size, but are sometimes a few hundred yards in length and about 50 or 60 feet high. Most are smaller. Sometimes there is a group of them, called a drumlin field. Glaciers also leave behind mounds of debris transverse to their track called terminal moraines. A terminal moraine is formed where the end of the glacier was stationary for a while when it was retreating, and there may be several of them at intervals along the retreating glacier's track.


How are flying drones and unmanned vehicled used for exploring volcanoes? And what kind of vehicles and drones are used or are planned for now and for near future?

Here's a partial answer:

The Trail by Fire expedition 1.5 -- "We're a team of young volcanologists planning to measure the entire flux of gases emitted by volcanoes along the Nazca subduction zone." -- driving through South America has "a fleet of quadcopters with gas sensing and sampling capabilities, establishing a remote presence in the volcanic plumes we encounter along the Trail by Fire."

On their sponsors page they list the science payload for each of three Matrix quadcopters (more details about the mechanisms and some custom kit are on the page), which are used because of the difficulty and hazard of climbing to the vents along the mountain chain and sampling the plumes:

An Ocean Optics Flame UV-DOAS spectrometer for SO2 measurements
A multigas sensor built by INGV (Italy)
A gas collector to bring plume gas to the Delta Ray Spectrometer

There's also a bit of drone footage included in the videos on their blog page.

Note that their goal is specifically to understand the gases: "Our objective is to provide the first accurate and large-scale estimate of the flux of volatile species (H2O, H2, CO2, CO, SO2, H2S, HCl, HF, and more) emitted by volcanoes of the Nazca subduction zone."

(Disclaimer: I only know about this because one of the researchers worked for my institution during last year's initial expedition. A review of the literature may show more published uses of drones and UAVs beyond simply shooting video.)


Why in different places seems directions are changed? I'm living at place A I traveled to B and I seen like sun isn't set as in place A. Like directions are changed. Where east is in place B is north of A and south of A is   west of B. Because of sun wasn't set in B as usually as set in place A. Sun rises in north at place B and sets in south. I really confused with this phenomenon of nature. Is it mean we consider direction which region we living in? Is it all because of longitude and latitude? Why it'd be like this? May it because if sun travel by specific longitude and latitude and so we would confused in situation like this even sun is stable planet and just earth rotate?

Even though sun always moves from east to west, latitude affects the north-south perception.
If you are in the north hemisphere, beyond the tropic of cancer, the sun will be most of the time in the south hemisphere (except close to dawn and dusk, where it might cross to the other hemisphere during summer). While if you're in the south hemisphere, beyond the tropic of capricorn, the sun will be at north.
Usually I use the sun to check where is the north in a map, but I must remember the north-south rule, otherwise I might choose the wrong direction to follow... that's why a bougth a cheap compass.

Since you're talking about two places that are in the tropical belt, most part of the year the sun will rise in the north-east, move later to the south and it will end in the north-west. But during the winter the sun probably will be always in the south hemisphere.

Probably the difference they are seeing between two close towns is due to different times of the year or due to a mountain that covers the exact sunset in the horizon in one place.


Heating and cooling a non-magnetic iron ore causes it to become magnetic? I'm a potter.  I find what I think are iron concretions in a deep red local clay.  I fired these iron concretions to cone 6 (about 2100F) and when I removed it from the kiln (room temp) they were then magnetic.  I tested for magnetism before and after firing just because I was curious.  What would cause this behavior?

Thanks for the help.

What's happening is called induced magnetism, detailed in a variety of places, including this paper by Kostadinova-Avramova and Kovacheva in Geophysical Journal International:

  It is well established that baked clays, when cooling from
  temperatures around 700 °C in a weak magnetic field, such as that of
  the Earth, acquire a thermoremanent magnetization (TRM) that is
  related to the direction and intensity of that field.

When materials are heated above their Curie temperature -- which varies based on the material -- they lose any permanent magnetic properties they had. As the material cools below its Curie temperature, its magnetic particles are influenced by the local magnetic field and the material develops a new, parallel magnetic structure in response.

So your ferrous clay could be picking up a magnetic field from the Earth, from a local electromagnetic field generated by your kiln or other electrical sources, or even a sufficiently strong local magnetic source.

This mechanism is sufficiently well understood that the field of paleomagnetism studies ancient fired clay objects and other materials of known dates to determine the strength of Earth's magnetic field in a given era and region.

History of Earth’s magnetic field exposed in Judean pottery explores one such application of the process:

  In a new study published in Proceedings of the National Academy of
  Sciences (PNAS), researchers from Tel Aviv University, Hebrew
  University of Jerusalem and University of California-San Diego cite
  data obtained from the analysis of 67 well-dated Judean jar handles.

  These heat-impacted ceramic pots, which bear royal stamp impressions
  from the eighth to second centuries BCE, show evidence of changes in
  the strength of the geomagnetic field over the years.

  “The period spanned by the jars allowed us to procure data on the
  Earth’s magnetic field during that time — the Iron Age through the
  Hellenistic Period in Judea,” said Erez Ben-Yosef of TAU’s Institute
  of Archaeology, the study’s lead investigator.


Math needed for Hydrology, specifically surface water hydrology I wanted to know what math is needed for hydrology, in particular surface water hydrology.

In my research online, of Master's programs (either in Hydrology or Environmental Science with a concentration in Hydrology), the undergraduate math pre-requisites differ greatly from program to program: some just required a year of calculus, others wanted or strongly recommended Calculus I, II, and III and yet other programs it was Calculus I, II, III, Linear Algebra, and Differential equations.

Does anyone have any suggestions or thoughts about how much math?!

Math is very important for hydrology. Especially for surface water problems, you require understanding of differential equations while open-water hydraulics like backwater calculations are complex. If you need a great deal of detail, these problems cannot be solved analytical, only numerical.

So I recommend a good mathematical basis to study surface water hydrology and hydraulics.


Why are the mountains predominately grey or dark brown? Observing many photos of mountains one can assume that most of the mountains are grey or brown. See also the mountain article at Wikipedia.

There are however several ways a mountain can form, which allow for exposure of various rocks, still mountains are mostly grey/brown.

Why is it so?
Why isn't there a single mountain out of Olivine, Pyrite, Tourmaline or, say, Autunite, or any other brightly coloured rock?

As Gary Kindel in his answer correctly said, mountains may consist of either magmatic, metamorphic or sedimentary rocks or all three together.

The greyish to brownish color is thus due to a mixture of all sorts of rocks and minerals that is covered by layers of eroded material of different grain sizes. This way, mountains appear to be of a single color when observed from a distance. This is similar to mixing a couple of watercolors together - the result will either be a greyish or a brown color. However, if we would magnify the watercolor mixture under a microscope, so that we see the individual pigments, we could tell that it isn't actually grey/brown. Same applies to the mountains. From a far, they appear to be grey/brown but when you get closer you can depict all sorts of colors.

The only exceptions to this are mountains, where the material is very well stratified, so that different colors can be seen from a distance.

To answer your second question: Please note that Olivine, Pyrite and Tourmaline are not rocks but minerals.

Olivine is mostly abundant in earth's mantle (check out Moho). The chance that a mountain is build solely by a material from the mantle is highly unlikely. What happened to the material that was on top? Secondly, Olivine is not stable at earth's surface according to the Goldich dissolution series. It alters into clay minerals and iron oxides that are easily eroded by e.g. rainwater. Thus, if there was a mountain made of olivine it would have surely been eroded by now.

Tourmaline is a mineral that forms in pegmatites and is thus far too rare to form an entire mountain. Especially since there is no process that individually picks Tourmalines from nature to build a mountain out of it.

Pyrite; there is still a great debate in the literature about the formation processes of Pyrite. But it is most likely a mineral that forms in a secondary process due to the intrusion of hydrothermal mineral-rich water. Thus, Pyrite is not concentrated in one area and is, like Tourmaline, far too rare to form a mountain.


Any idea what are these circular rock marks? During a family trip in the Israeli National Trail in the Pora Stream part (31.496871, 34.770928), I noticed these circular rock marks.

Any idea what are they?

It looks like onion skin weathering. It appears in places with large temperature differences between night and day and associated thermal expansion and contraction of rocks on daily basis. That creates weaker spherical zones, where cracks may form later. I have seen that several times in basalts but not limestones, though.


Why is it so important to gather data from inside tornadoes? Or, in other words, what kind of data can be gathered from inside tornadoes and how could it help in predicting them? Also, why isn't it possible to predict/estimate this kind of data from readings taken from outside the funnel (or is that what is currently done)?

Generally speaking, the types of data gathered outside a tornado can also be measured inside the tornado. Currently, forecasters try to estimate an area where tornadoes usually are. The forecasting time for tornadoes, or warn time, is about 13 minutes. There is still quite a bit we don't know about tornadoes, such as why some storms that look like they can produce a tornado, will not produce a tornado.

Currently, most data taken about tornadoes is taken outside of the tornado. Data from inside the tornado, while uncommon, can give improved estimates of wind speeds, and pressure changes, with a level of detail that is hard to get from the outside, looking in. The models we deal with are imperfect- there are too many sources of error and It generally doesn't help the current predictions, but research on that data may help future predictions.


How to Interpret this set of Latitude and Longitude? I have a house's coordinates that I know is in LA, Ventura, or Orange county, California and it says the latitude and longitude are

latitude    longitude
34144442    -118654084

These seem really big. How can I find the address this corresponds to?

It looks like your coordinates are written in decimal degrees but with the decimal points omitted.

34.144442 -118.654084 corresponds to 34°08'40.0"N 118°39'14.7"W.

Google maps shows this to be a location just outside LA.


The environments of particular deposits I came across this question in my text book:
"During a visit to a mountainous area, students noticed a high mountain consists of 3 different parts: The top of the mountain consists of fossiliferous limestone. The middle of the mountain consists of fine grained rocks. The foot of the mountain consists of thick layers of boulder, gravel and tree trunks.
Which of those parts belongs to a marine environment? And which belongs to an aerobic environment? And which belongs to a river environment?"
My attempt at a solution is this:

The top (fossiliferous limestone) -----> marine environment.
The middle (fine grained rocks) -----> aerobic environment.
The base (boulder, gravel and tree trunks -----> River environment.

I wanted to know if my answer was correct or not, because the answer to the question in the book was:

the top---> marine environment.
the middle---> river environment.
the base --> aerobic environment.

Could someone please clarify it for me?

Because the top layer is marine, you're being asked to think of the sequence being "coastal" in origin, where there is ocean, coastal plain, and inland mountains. In this scenario, two things are happening in tandem: the mountains are eroding and sea level is rising.

As the mountain erodes, boulders and cobbles (eroded from steep slopes) bury trees and form coarse conglomerates and source material for the coastal plain deposits, which are the middle unit of your sequence. As sea level rises due to local subsidence or a global sea level rise, the marine environment marches steadily inland depositing sands and then limestones.

Assuming no unconformities, yours is a textbook example of a continuous depositional sequence!


Are there any consequences to carbon capture and storage that also sequesters oxygen? A big argument for carbon capture and storage is true reversal; while switching to renewable energy and eliminating CO2 emissions is a must, it will not reverse the massive movement of carbon from underground hydrocarbons to the atmosphere and biosphere.

However, prevailing strategies are not exact reversals of burning fuels, either. Rather than converting CO2 to hydrocarbons to be buried, CO2 may be directly injected deep into the ground or converted to carbonates first. Would there be consequences for the biosphere if we do manage to bury 2-3 oxygen atoms for every carbon atom that will also be buried, that so far would have been released into the atmosphere?

EDIT: For the sake of argument, let's assume a hypothetical method of capture and storage that uses only renewable energy and that the buried matter does not leak back out. This question should not be construed as an endorsement of current carbon capture and storage technology.

No, I think there are not. At least not at the scale of the proposed projects. I say this just because $\text{CO}_2$ makes up only a 0.04% of the atmosphere, so even if you burn fossil fuels until you double the pre-industrial amount of CO$_2$ and then capture and bury it back (both the Carbon and Oxygen). You would only drop Oxygen levels from its current 20.95% to 20.91% or something like that, which is not very significant. In a closed space like your bedroom for instance, you would probably make a bigger change in the Oxygen level by just breathing inside for a few minutes.

Also, many chemical reactions that sequester Oxygen and are sensitive to its concentration (oxidation and combustion for example) would work towards keeping equilibrium: they will slow down if there is less Oxygen allowing the concentration to bounce back. Or they will accelerate if there is too much Oxygen, dropping the level back down.


Dolomite in deep-water environment Is it possible that dolomitization occur in deep-water environment?
If it possible, how?

For dolomitization to occur, either by primary precipitation or by diagenesis, requires a highly magnesian environment and alkaline conditions. The most favourable environment for this to occur is by deeply circulating seawater into the upper mantle which underplates oceanic crust. I don't mean the hydrothermal circulation around spreading centres (which is acidic), but the relatively mild temperatures of submarine groundwater. In the occasional cases where this upper mantle is obducted onto land as ophiolites you will find magnesite predominating, with minor huntite, and dolomite of various early and late-stage paragenesis. The process of serpentinization releases aqueous magnesium, and reaches pHs as high as 12. Moreover, the associated dolomitization starts in the marine environment, and continues after the ophiolite becomes land. For example, you can go to the Semail ophiolite in Oman and find primary and secondary dolomite precipitating - along with occasional metastable huntite and hydroxycarbonates.


How does 10mm/yr of plate subduction provide enough material to create eruptions? If the convergent boundary is only consuming 10mm of oceanic crust per year, it "seems" like that would provide insufficient material to cause the level of eruption generally observed. I am making the assumption that it is the consumed oceanic crust that is ejected from the volcano as molten lava. It is probably more complex than that.

Yes, the situation is much more complex than you make out - the generation of melt is typically caused by partial melting of the mantle wedge located beneath the volcanic arc. This process is mainly affected by the trench geometry (flat or steeply dipping slab), the local geotherm, and volatile content (water, gases etc.) of the slab or subducted material.
You're neglecting the total volume of the plate being subducted, as there is an along-trench length of the plate, as well as the thickness of the slab.

When it comes to amount of melt generated, the localisation and upwelling of melt from the mantle wedge isn't fully understood - so it is hard to determine how many volcanic centres will be fed from the material.


Water and explosive volcanoes in the Pacific ring of fire Most volcanoes in the Pacific Ring of Fire have an explosive nature. This is due to high concentrations of water in their magma. Obviously, this magma comes from several kilometres below the earth's crust. How is it possible for magma to contain water at such depths?

How is it possible for magma to contain water at such depths?

This can happen precisely because the magma is at such depths. Think of CO2 in soda or coke. When the drink is closed and pressurised, the CO2 is dissolved in the liquid. This means it's part of one physical phase. There is one "thing" that contains the liquid and the CO2 together: the CO2 is not a gas! Only when you open  the bottle, the CO2 can escape being dissolved in the liquid, and separates from the liquid as a distinct gas phase.

The same thing happens in magmas. While the magmas are pressurised at depths they have water dissolved in them. Note that this water is not separate liquid water or vapour flowing around the magma. It is inside the magma in one physical entity. Think of dissolving salt in water - you can't see salt grains but it's there. Anyway, once the magma rises it loses pressure. This causes the water to separate out from the magma into a distinct vapour phase that rises and expands rapidly, causing the explosive eruption.


The effect of the 2019-2020 bushfires/wildfires in Australia What was the total damage of the 2019-2020 bushfires/wildfires in Australia?

The total area burned was 12.6 million hectares, or 126,000 square kilometers. This is equivalent to:

The US state of North Carolina (125,920 sq km)
The US state of New York (122,057 sq km)
The US state of Mississippi (121,531 sq km)
North Korea (120, 408 sq km)
96% of Greece (130,647 sq km)
52% of the United Kingdom (241,930)
36% of Germany (348,672 sq km)
22% of France (549,970 sq km)
45% of Ecuador (276,841 sq km)
10% of South Africa (1,214,470 sq km)
20% of Australia’s forests
Nearly twice the size of the 2019 fires in Siberia
5.5 times the size of the 2019 Amazon fires
6 times the size of the 2018 California fires

The amount of carbon dioxide emitted was 434 million tonnes. This equated to over three-quarters of the 532 million tonnes Australian industry emitted in 2018-19. Air quality during the fires was up to 20 times higher than hazardous levels.
The smoke encircled the Earth and discolored the snow on the alpine regions of New Zealand leaving it caramel colored.
The number of people affected by smoke for the fires was 11.3 million, or 57 percent of the population of Australia.
The estimated number of animal killed by the fires is 3 billion (revised on 28 July 2020, from 1 billion animals, when updated information was available). The breakdown by animal type is:

143 million mammals
2.46 billion reptiles
180 million birds
51 million frogs

28 July 2020
Substantial summary of the fires in Wikipedia.


From where do asteroids get water from? We all know that the water on Earth came from asteroids that collided on the Earth. But how does water form in the asteroids?

hydrogen is the most common element in the universe, Oxygen is the third most common element in the universe, hydrogen + oxygen + heat/energy = water. Water is literally the most common compound in the universe.


How viscous is the Earth's mantle? I'm posting here to get some more expert information based on this question.

If the Earth were to stop rotating, removing the centrifugal force causing the equatorial bulge, how long would it take for the mantle and crust to return to hydrostatic equilibrium?  That is, immediatly, thousands of years, or millions of years?

Never mind that changing the rotation in reality would involve forces and timescales that would not really provide this condition. if matter were arranged in such a shape, how long (orders of magnitude) would it take to settle?

The mantle viscosity is likely to be non-linear, e.g., it could be as low as $10^{18} \textrm{Pa}\cdot\rm s$ (over shorter time scales) or as high as $10^{21} \textrm{Pa}\cdot\rm s$ (over longer time scales). In any case the values reported in the literature are somewhere between $10^{18}-10^{21} \textrm{Pa}\cdot\rm s$ and these are based on studies from earthquakes, glacial rebound etc. So you can calculate the relaxation time(s) using these two end member values.

E.g., if you assume the average i.e., $10^{19.5} \textrm{Pa}\cdot\rm s$ then we get a relaxation time of $10^{19.5}/150\cdot10^9$ (viscosity/mu) which is $2.1082\cdot10^8$ seconds or ~$6.6$ years.


How vertically deep do lava conduits go? I'll preface this with the truth and hope it doesn't disqualify the question but rather give context: after reading Journey to the Center of the Earth by Jules Verne, I am amazed at the prospect of venturing into volcanic conduits to explore the interior of the Earth. How deep do lava conduits go, why don't they go deeper, and what kinds of formations or environments exist at their terminus?

I am not new to Earth science but am pretty new to in-depth geology (pun intended) and volcanology. From what I can tell, the type of lava cave which goes the deepest is referred to as a lava tube. Apparently these tubes can be fairly long (e.g. a tube from Mauna Loa goes 50km before terminating[?] at the ocean!) but not very deep (Wikipedia on lava tubes lists a mere 15m!) Why do these tubes not go far deeper?

The deepest conduit from surface to inner Earth is apparently the Kola Superdeep Borehole which terminates at ~12km deep upon reaching higher-than-expected temperatures. I think of magma - liquefied hot rock erupting out of volcanoes - as coming from even deeper than that depth. Therefore, why doesn't lava tubes or other volcanic conduit continue to such deep depths? Do they, but it is too difficult to explore? Do they during eruptions, but soon after cool and fill with solidified rock or eventually collapse and thereby fill with rock?

As noted I'm new but interested to the subject, so any info to help me understand the processes and environment involved in this interface between inner Earth and the surface would be much appreciated.

As mentioned in the comments, lave caves and tubes are surface features. You get a lava tube when there's a lava flow and the external part in contact with air (or water) cools down and solidifies while the interior is still flowing. National Geographic made an excellent feature on it, all with diagrams and photos and stuff.

Why do these tubes not go far deeper?

Because lavas are liquid, and they flow downwards. If there's a hole that goes deep, the lava will fill it. It's possible to explosively eject lava out of a hole (as commonly happens), but these are violent events that will cause the collapse of the conduits, forming breccia pipes, with collapsed calderas.

I think of magma - liquefied hot rock erupting out of volcanoes - as coming from even deeper than that depth
...terminating at the threshold of the asthenosphere?

Let me clear a common misconception here: there is no magma ocean in the interior of the Earth. There is no large reservoir of magma in the deep earth, and volcanoes are not just holes through which this (non existent) magma is coming out. Both the crust and the mantle are essentially solid rock. The asthenosphere is solid rock.
Melting is an uncommon occurrence in the Earth's crust and mantle. It needs exceptional circumstances to happen, which mostly happen above subduction zones (i.e. the Pacific Ring of Fire) or above hotspots (East Africa, Hawaii, Yellowstone). The erupting magma can come from anywhere that's as shallow as less than a kilometre below the surface (which can be above sealevel if you're on a high volcano) to several tens of kilometres. Very rarely these magmas come directly from asthenospheric depths. These magma chambers can have complex plumbing systems beneath them and all sorts of morphologies of feeders.


How to calculate hourly rainfall projections? If the National Weather Service website shows increasing probability of precipitation (POP) over a 6 hour period (e.g. 10% rising gradually to 60%), what is the POP in this time interval if the confidence percentage is unknown?

The Probability Of Precipitation or POP is the exceedance probability over a given area for a given duration. The exceedance amount is generally taken as 0.25 mm, but may be any specified value. Again, the time $t$ must be specified, and is usually 3, 6, 12 or 24 hours.

Strictly speaking, the POP is meaningless unless the area under consideration is also specified, although in public weather forecasts this is seldom indicated. Individual storm cells generally have a footprint only a few kilometers wide, so obviously, the larger the area the higher the probability of precipitation, but the lower the average rainfall.

As for the confidence, this is a function of rainfall record duration and continuity, and raingauge network density.


calculate UV index in vertical plane Due to extensive damage to my face because of an accident, I am currently undergoing skin therapy (laser/IPL/medication), that makes my skin extremely sensitive to UV radiation. So I need to stay out of the sun, at the very least between 11:00 and 16:00, need to reapply sun screen every two hours, and generally be careful with exposure. Since that makes me hyper aware to the sun, perceived warmth, UV index and all that, it made me reasearch the subject.

I live in The Netherlands and the meteorology institute published real time UV measurements (as UV index) at https://www.rivm.nl/Onderwerpen/Z/Zonkracht
However the UV index is defined as the amount energy that is radiated on the flat surface of the earth. As we humans generally have more vertical surfaces, especially sensitive surfaces like the face, would it not make more sense to not just measure in the horizontal plane? Especially during the evening and the morning the sun is at a low angle, so the (relative) energy on a vertical plane would be a lot higher than the above graph suggests.

I made a small program that parses this image, and recalculates the UV index for the vertical plain (divide the UV index by the tangent of (90 degrees minus current zenith angle). This would be the output (blue line is vertical UV index):

According to Ultraviolet Radiation, Human Health, and the Urban Forest it would seem at least the general shape you obtained is correct:

Here they tracked the irradiance at noon over different months of the year not hours of the day, but the basic change is the same: high to low to high Solar Zenith Angle when irradiating a vertical surface leads to an irradiance graph with 2 "shoulders" on both sides of the maximum solar elevation point. The irradiance is lower at the central point because the direct rays are parallel to the target surface and the only contribution are the scattered and reflected rays from the environment and the rest of the sky, and then as the SZA progresses more and more toward 90 degrees (or elevation toward 0 degrees) the increasing atmospheric absorbance comes into play and reduces the irradiation long before the rays become exactly perpendicular to the target surface.
But if the goal of the UV Index was to provide safety data for the general public, I would say it should've been measured assuming the absolute worst-case scenario of some unprotected skin being exposed to exactly perpendicular solar rays at any hour of the day (this is possible because our bodies have complex surfaces and it's always possible to have at least a little skin that's perpendicular to almost any ray direction in all of 3D space). So they should've used a detector that is rotated to face the sun at all hours of the day, and the resulting graph I suspect would not look like the official daily UV Index graph but also not like the "2 shoulders" one we have here. It would probably look more like the "IND", "SYR" and "INL" variants in the image above: a sort of "Gaussian with a wider top".
LE: Here we go, it should look like the Direct Normal Irradiance curve, with no cosine correction for horizontal receiving surfaces: https://www.researchgate.net/figure/Direct-normal-irradiance-vs-solar-time-at-Izana-Tenerife-Kaashidhoo-Maldives-and_fig1_236314638


Flooding lakes in geography Came across the following problem on a question sheet. At its maximum level following deglaciation, approx 11,000 years ago, Lake Melville flooded the Sebaskachu River valley to an elevation of 135m above sea level. However the upper reaches of the Mulligan River and its tributaries were not flooded by Lake Melville. The tributaries of the Sebaskachu River above 135m elevation were not flooded also. What differences in river geomorphology exist between the higher river systems and the Sebaskachu River below 135m?

I know river morphology isused to describe the shapes of river channels and how they change in shape and direction over time. It is a function of a number of processes and environmental conditions, including the composition and erodibility of the bed and banks.Erosion comes from the power and consistency of the current, and can effect the formation of the river's path

I've never heard of the 'Mulligan river', and neither, apparently has Google Earth, (apart from the Australian Mulligan). However, there are some obvious features of the Sebaskatchu River on Google Earth that one might note. As background, 11,000 years ago the Earth was just beginning to emerge from the last ice age, so ice cover was very much greater, and sea level was very much lower, so I assume that the +135 metre lake level to which you refer is relative to today's sea level, consisting of a temporary glacially dammed lake level. These ancient lake shore lines are a common feature of glaciated terrain, as may be seen in Alaska, Scotland, Norway and New Zealand.

All lakes are relatively short-lived in geological terms, being effectively sediment traps. Sediment accumulation in the lower Sebaskatchu river basin has been intense, and has all but filled the entire lower basin. This is most obvious from the extreme river meandering, which occurs only wherever there is a high sediment load combined with a low hydraulic gradient.  There are two phases of sediment fill - a general fill over a large area, and a specific small lake fill which you can see about 6 km (as the crow flies) from the river mouth, and for about 8 km further upstream.

You may note that none of the lower basin drainage is guided by the bedrock, whereas the upper basin, presumably above your threshold of +135m, is of a different style, This upper drainage is partly guided by the underlying rock structure, i.e. along strike, and partly by a cross-cutting component. The latter is most likely 'superimposed drainage', which has cut down through ice and glacial drift into the bedrock.


Has a scientific consensus been reached concerning the formation of the Grand Canyon? new student of Oceanography here!

I'm studying Earth Science right now, and I found conflicting reporting re: the formation of the Grand Canyon; whether it was formed singularly by the Colorado River over millions of years, or if it was formed by other processes with the river only filling into it relatively recently.

Is there a consensus yet in geology with regard to the Grand Canyon's geologic history? If so, could you share resources that help explain it?

Thank you so much!

I'm studying Earth Science right now, and I found conflicting reporting re: the formation of the Grand Canyon; whether it was formed singularly by the Colorado River over millions of years, or if it was formed by other processes with the river only filling into it relatively recently.

Yes, it was formed by other processes with the river only excavating into it relatively recently.
The Grand Canyon National Park Service describe the events involved in the formation of the Grand Canyon widely. The sequence of events was as follows:

Emplacement of an igneous and metamorphic body.
Sedimentation over the igneous and metamorphic body.
Uptlift of the complex by tectonic forces forming Colorado Plateau.
Excavation of the Plateau by Colorado River.

Read full explanation at Grand Canyon National Park website.


Strange circular structures found on a photo from Mars rover Curiosity at Dingo Gap What are all these gaps / circular structures found on a photo taken by Mars rover Curiosity at Dingo Gap? Have a look at the image I made to see what gaps I mean.

(I know the quick paint job looks terrible)

As you can see on the image I marked the area green where I found all these strange gaps. On the left I placed a zoomed view of the gaps, where I highlighted one.

You can find the original picture on nasa.gov. Here is the accompanying article

There are no circles, it is an image artifact. Here is another picture from Dingo Gap that shows nothing at the exact same position.

Your mind is a well-trained pattern-matching machine that makes up patterns even when they are not actually there.
In other words don't jump to conclusions. You are claiming that there are actual structures, which is one step too 'far'.

(Credit: Emily Lakdawallah blog post)


Why do the Siberian methane craters have smooth vertical walls? I expect most of you have heard of this by now.

All the news is about whether or not they were formed by the release of methane, but it is also mysterious to me why this crater has jagged edges but smooth vertical walls. It almost looks like it has been drilled.

I'm not a geologist but I would expect it to be rough all the way down. Can someone explain why it isn't?

Permafrost is defined as

  a ground, or medium, (including rocks, soils and organic matter) with a mean annual temperature less than 0 °C for at least 2 consecutive years.

The smooth appearance of the walls can be explained by understanding how permafrost works. Permafrost is characterized by an active layer, which is a layer normally at the surface which freeze yearly during winter and thaw during summer - this layer at Yamal can be 1-2 m deep depending on the local ground characteristics (snow depth, albedo, slope, air temperature, thermal conductivity, runoff etc).  The ground in the area is ice-rich.

Then let's assume this crater was caused by a methane bubble escaping/exploding and walls could be rough immediately following the event. By deduction, there should not be an active layer found on the walls following the explosion, as it is the first time this ground (walls) were exposed to air. During the middle of the summer, above 0°C air enters the hole due to convection. The ground is ice-rich (can be porous or invisible ice but still ice-rich) and active-layer start to form on the wall.

Due to the near vertical orientation of the walls, saturated soil (or active layer in formation) cannot stand because as soon as it thaw to a depth exceeding its equilibrium limit, it fall at the bottom of the crater due to gravitational forces, exposing a new frozen surface (and the cycle continue until equilibrium can take a few years). Thawing sediments in ice-rich soils can reach saturation quickly, further adding to the weight and accelerating the time of the fall. Rugged and unequal surface are typically the first elements to thaw and fall.

I took this picture about an hundred km from the featured crater.

This display a very ice-rich section of the Yamal Peninsula littoral in the course of erosion. This coastal section has been eroding for decades at least. At the top the active layer is light brown, and look dry (1 m deep). Just under this top-layer, the ice is poly-genetic: ice wedge ice-rich soil and massive ice can be seen as well. The active layer cannot stand on the side for the reasons I exposed in the previous paragraph (gravity).

Side-note, the jagged edges were not initiated by anything related to a pingo. It takes decades, up to many centuries for a pingo to develop until its natural collapse. When it happen, a depression can form at its center - which could lead to a lake, but these are not overnight processes. Also, contours of the pingo mound would not appear as jagged edges if this was a pingo - the remains would appear pretty old and vegetated, alike the surrounding countryside.


What is the difference between Water Holding Capacity, Field Capacity and TAWC? I am reading the paper Characterization of yield reduction in Ethiopia using a GIS-based crop water balance model by Gabriel B. Senay and James Verdin, and it says on page 3:

  Soil water content (SW) is estimated through a simple mass
  balance equation where the total volume is defined by the water
  holding capacity (WHC) of the soil. SW is the amount of soil
  water present at a given time step. The value of SW varies from
  a minimum of 0 to a maximum equal to WHC (in mm)

What is the WHC here? Is it the Field capacity or Field Capacity - Wilting Point?

Okay Water Holding Capacity(WHC) is how much water the soil has in it at total saturation, if you filled every soil pore space completely with water.

Field Capacity(FC), if I remember correctly from first year, is shorthand for the water that stays in the soil after surface runoff and groundflow has ceased; the sub-saturation "ground state" of the moist soil if you will.

Soil Water(SW) would appear based on the excerpt provided to be referring to the percentage of WHC present at time of measurement.

You've also asked about Total Available Water Capacity(TAWC) which is the water that can be accessed by plants, this is the water stored in macro, as opposed to micro, pores in the soil (it's more complex than that but we always worked it as a two grade problem; pores big enough for plant roots and pores too small for them). Usually to quantify this figure WHC, or FC depending on what's of interest, is multipled by the percentage of plant accessible pore spaces in the soil, this gives the volume of water plants can access before they start to wilt.

Please note I'm mostly working from my memory of an entry level class I took nearly a decade ago so this may not be perfect, but it it does check against the research material I quickly skimmed while writing.


Do divergent tectonic plates destroy mountains? Tectonic plates meeting (convergent plates) form mountains. But if those plates change direction (which I am just assuming they can over time, I have no idea if it's true) and start pulling apart (divergent plates), will the mountains automatically crumble away as the plates split, or can some mountains become part of one or the other plate, like clay sticking to your hands when you remove them?

Feel free to explain any prerequisite knowledge you feel I lack. This might be an important question to me.

Quite the opposite. Divergent boundaries can cause mountain (well, actually volcano) building, because upwelling magma is part of the rifting process.

First and most importantly, the Mid-Ocean Ridge can be considered the longest, most massive mountain range in the world.

It's more obvious, of course,
 on continental rifts like the East African Rift. Mt. Kilimanjaro, a product of rift volcanism, is the highest mountain in Africa.

Another famous locale of volcanism at a divergent boundary is Iceland, although a hot spot may play a role there.

Source: USGS (via usu.edu)

But BUT BUT it seems you want to know what happens to existing mountains. Some others have answered that only erosion destroys mountains, and that's mostly right, but only because it's a matter of timing.

It's often difficult for us humans to comprehend just how big geological time scales are. Most of the time, a mountain range created by a continental collision is eroded away completely by the time the next rift comes along.

This was the case along the eastern seaboard of the United States. The mountains created by the collosion of Africa and North America in the Carboniferous (the Alleghenian Orogeny) were almost completely gone by the Triassic, when the Atlantic Ocean began to form from a rift along about the same line.

However, we have an example that might result in a qualified "yes" to your question, a little closer to the present. This is the way the Yellowstone Hotspot moved across what would become the northwestern United States.  One of the things that caused geologists to recognize the Yellowstone Caldera was the 80km gap it melted in a mountain range it passed under, separating the Gallatin Range in the north from the Red Range in the south.

The hotspot's track might just be the genesis of a new rift that breaks North America apart, given enough time and the right stresses.

(Source: USGS)


Paleontology science fair ideas? My daughter, age 8, wants to do her science fair project in paleontology. For the fair, we need to come up with a question that can lead to a hypothesis, then apply the scientific method to test this hypothesis. The wall we are hitting is that we don't know what kinds of tests paleontologists use in their work. Can anyone offer suggestions of where we can start to come up with our question, and what sort of tests would be useful in the process? I do not want the project spelled out for us, just a place to start so that we can learn along the way. Thanks.

I just wanted to address the comment about science fair participation. We are homeschoolers. When I refer to us as we concerning my daughter's project, it is not because I am going to be doing her work for her, but because I am a part of the process. Also, I find that in homeschooling, I learn a lot, too. The work and ideas will be hers. Thank you for your concern.

Further information: She is interested in prehistoric sharks. We have joined the Dallas (TX) Paleontology Society and will be going out to hunt fossils with them soon (and will continue well after the science fair). We traveled to UTA to talk to a micropaleontologist and learn about his work, and get ideas. He offered use of a high powered microscope (with enough notice), so that is a resource available to us. We have met Roger Farrish, who wrote a book of prehistoric sharks and rays of Texas. He is a resource. Homeschooling is more adventure than not. I keep asking, everywhere I can, for input from others int he paleo- fields as my background is in cultural anthropology, and culinary. We do appreciate your help.

Palaeontologists use lots of methods to investigate past life.

Like most sciences these day, palaeontology is a growing field. More scientists are applying more methods in more sophisticated ways. The literature — what we 'know' — grows and grows. So palaeontologists use hundreds of different methods and tools today; indeed there's a whole journal dedicated to the subject!

But like a lot of other geological disciplines, it's more or less impossible to test a hypothesis rigorously, because there are no actual dinosaurs, they died out ages ago, and so we cannot know everything about them. So we have to get creative.

For example, a palaeontologist interested in how dinosaurs or early insects walked might...

Make detailed drawings of some fossils of the organism.
Use X-ray tomography to see through a specimen and look at a fossil in 3D.
Make a 3D computer model to look at how the animal might have walked.
Examine museum collections to look for evidence of a hypothesized gait, eg in field photos or in casts from actual outcrops — perhaps there's a track out there somewhere!
Look at the chromosomes of similar modern animals to determine lineages and 'shared DNA', and compare walking styles.
Build or 3D-print an actual model and see if it actually does what the scientist thinks.
Dress up like a dinosaur or dragonfly and walk around on a beach or mudflat to study the footprints. (I'm sort of but not really joking.)

(Google around dinosaur locomotion for more!)

I realize you can't do all of this sort of thing for a science fair, but hopefully it illustrates that, when it comes to hypothesizing about the past, we have to come at problems from a few different angles, using high and low technology.

Hope this helps a bit, good luck with the project!!


Where can I get hourly ambient temperature for each county in United States? Need temperature for 24 hours for each county of United States. Average values is ok, seasonal granularity welcome. I've been looking at nClimDiv datasets

You can get this from the Integrated Surface Dataset (ISD).

First get a list of all weather stations from ftp://ftp.ncdc.noaa.gov/pub/data/noaa/isd-history.txt:

stations = pandas.read_fwf("ftp://ftp.ncdc.noaa.gov/pub/data/noaa/isd-history.txt",
                           skiprows=20, parse_dates=["BEGIN", "END"],
                           skip_blank_lines=True,
                           dtype={"WBAN": "O"})

Then select the ones in the USA:

stations_us = stations[stations["CTRY"]=="US"]

That give us 7326 stations.  Although the state of each station is described, the county is not.  To get the county you will need to combine the lat/lon for each station with a county database.  That is a bit beyond the scope of Earth Science SE, but maybe you can get help at GIS SE.  The station ID is a combination of two fields:

ids = stations_us["USAF"] + stations_us["WBAN"]

We can then download the measurements for a particular year from AWS S3:

meas = pandas.read_csv(f"s3://noaa-global-hourly-pds/2020/{ids.iloc[200]:s}.csv", parse_dates=["DATE"])

And extract temperatures:

temps = meas.TMP.str.extract(r"([+-]\d{4}),([012345679ACIMPRU])")[0].astype("f4")/10

Let's get the valid ones (there's a 9999 fill value) and plot:

valid = temps<999
meas[valid].set_index(meas.DATE[valid])["temps"].plot()

Enjoy!

For a description of the fields, see the ISD Format Document at https://www.ncei.noaa.gov/data/global-hourly/doc/isd-format-document.pdf .


What potential geoengineering technologies could help a country "achieve its Paris (agreement) targets"? CNN's China to expand weather modification program to cover area larger than India ends with the following sentence:

"While China has not yet shown signs of 'unilaterally' deploying geoengineering projects on the ground, the scale of its weather modification and other massive engineering projects, including mega-dam projects (such as the Three Gorges), suggests China is willing to deploy large-scale geoengineering schemes to tackle the impacts of climate change and achieve its Paris targets."

and the scope of my question is limited to the Earth Science aspects of geoengineering projects that could "..tackle the impacts of climate change and achieve... Paris (agreement) targets".
To my knowledge the Paris Agreement primarily focuses on the reduction of greenhouse gas emission itself, so I would think that geoengineering solutions might involve removing gases already emitted in the form of new biomass or as gas in geological sequestration sites, or by producing energy with a technology having a lower greenhouse emission rate.

Is that so? If so, what are specific examples?
Since the same article discusses both cloud seeding for precipitation induction and the dispersal of reflective particles to reduce global warming earlier, could there be some atmospheric dispersal technology that could help a country "...achieve its Paris targets"?

I think the third paragraph of the article hints at what might be the thinking.

In the next five years, the total area covered by artificial rain or snowfall will reach 5.5 million sq km, while over 580,000 sq km (224,000 sq miles) will be covered by hail suppression technologies. The statement added that the program will help with disaster relief, agricultural production, emergency responses to forest and grassland fires, and dealing with unusually high temperatures or droughts.

Firstly, rain will absorb some CO2 by creating small amounts of carbonic acid (H2CO3). Agricultural production would remove some CO2. Reduction of CO2 production via the possible prevention of grass & forest fires. This would also be aided by the supposed reduction of temperatures and droughts. With sufficient rain to ensure the Three Gorges Dam is always full, potentially consistently reliable hydroelectricity could be achieved, thus reducing the amount of CO2 producing energy sources used for energy production.
Finally, hail suppression technologies were mentioned. By eliminating hail one eliminates the potential for damaging hail to occur thus reducing the need to manufacture building products to repair buildings damaged by hail. It also prevents crop damage by hail thus eliminating the need to plant replacement crops.


What causes this white coloration of the ground in Gilf-Kebir? It seems, these white blotches are reflective enough that they caused oversaturation of a spot of image taken from a satellite at the L1 lagrangian point (click to open at max resolution, the purple spot is squat in the middle of the picture).

Clear quartz crystals has been found nearby ( link ), but could it be this? Can quartz so clear and reflective appear in such abundance? Or is it some other cause?

(I thought it might be frost, which shows up on the desert in the mornings, but the photo taken from L1 places the point at peak of the summer with the Sun precisely in zenith above it; I doubt any frozen water could withstand that. Also, Wikimapia has some photos taken nearby with what looks like frost, but the daytime is obviously different).

The white areas appear to be formed on the edge of elevated parts of the landscape and in low-lying flat areas. You can see this if you use Google Earth and looking at the elevation profiles along paths you sketch across the landscape. They don't appear to form at a particular elevation or other pattern that would indicate they are bedrock outcrops.

I think the most likely possibility is that they are caliche deposits (calcium-carbonate cemented sediments), formed as water ran off of higher elevations, mobilizing calcium and evaporating to cause calcite saturation. They could be halite but I would expect more extensive deposits in the broader drainage areas if they were salt. They could have formed under wetter climate conditions. If you look at 23 degrees 14.053' North, 24 degrees 25.22' East, you can see deposits being covered by sand dunes.


Calculating a cloud cover index based on comparison of horizontal and tilted irradiance from pyranometers I have data from 2 pyranometers, one in the horizontal plane and one in a tilted plane. The relevance of the tilting relates to their useage in solar-power plants whereby the tilt is in the same plane as the solar generators.

We can apply simple trigonometry to convert the horizontal data to a theoretical value in the tilted plane. On some days we notice a very good correlation between the measured data in the tilted plane compred to the theoretical value calculated from measured data in the horizontal plane. On other days the correlation is not so clear and the degree of correlation can differ greatly.

Hypothesis : I imagine that the difference in correlation that we notice is due to the effects of cloud cover.

Question : Is there an established method to calculate this cloud cover from our two datasets ?

Not being an expert in the subject, I agree with your hypothesis. But, I think that what you are measuring with the difference in the readings is the anisotropy of the illumination. In very cloudy skies, the amount of light from all directions in the sky is the same (that's why you can't tell where is the Sun). In a extreme case, like the condition refereed as whiteout (dense fog over snow) a pyranometer on any direction would measure the same value.

However, I don't think that can be used to calculate cloud cover in the common sense, as the anisotropy will be very high even if there is a small gap in the clouds that let the Sun light through, so your conversion into cloud cover would only work when the cloud cover is homogeneous, and would fail when it is patchy.

I would think that you have better chances to estimate clod cover if you have one pyranometer shielded from direct sunlight , so you can measure how much energy is coming from the sky. However, you would only know the cloud cover in that area, and still with many posible source of error.

Measuring cloud cover is a difficult problem. Naked‐eye observation of sky cloud cover has widely resisted automation. Some successful approaches use analysis of images like in Whole sky cameras or more sophisticated whole sky imagers.

However, there are methods developed to estimate cloud cover based on standard AWS data. Like APCADA, that uses longwave downward radiation, temperature, and relative humidity measurements. It is described in the paper "Automatic cloud amount detection by surface longwave downward radiation measurements", that reports that:

  APCADA estimates. Results show that about 86% of all cases agree
  within ±1‐octa cloud amount difference for sites with moderate
  climate, 82% for sites with arctic climate, and 78% for the site with
  tropical climate.

I would think that for the direction technology have taken, the most affordable options will go in the direction of having a camera taking pictures of the sky (in infrared if you can), and having and algorithm to analyze it and evaluate cloud cover. I found this paper that talks about that. It looks like the Red/Blue ratio is a good indicator to classify an image pixel as cloud or cloudless.


Effect on poles when Earth is not tilted Say a Mars size object hits the Earth in such a way that it knocks the Earth in a straight 0 degree angle, and let's assume that we somehow do not go extinct.

What would happen to the poles in this scenario, in terms of temperature and volume of ice?

My guess is since now there is no longer a tilt, the poles would receive the same amount of solar input, which would increase the ice caps of both poles.As there is no incentive to melt the caps, maybe this would even cool the planet.

If we ignore the giant impact (which would have enormous effects), and just look at the effect of the Earth having a 0 degree axial tilt, the most immediately apparent effect is that the seasons would be reduced almost to nothing and the very small seasons that remain would be planet wide, not alternating between the 2 hemispheres.

The Earth is currently closest to the sun in the first week of January and furthest in the first week of July.  Source, so it's pretty obvious that being closer to the sun doesn't create summer.  The axial tilt is what causes the seasons, but the change in distance to the sun still has some effect.

There's a little  over 3% variation in distance, see source, yielding a bit over 9% variation in energy received between the Earth's perihelion and aphelion, but that doesn't mean a 9% change in temperature.  It's much smaller than that due to the Earth's oceans, atmosphere and to a lesser extent, surface are all heat sinks that take a long time to warm up or cool down.   The seasonal difference in temperature would be much less than that.   Maybe a few degrees, perhaps 5-10 degree difference between summer and winter, probably less than the change between night and day.

No tilt also means, you lose the 6 months of sunlight, 6 months of darkness that we currently get near the poles and the sun wouldn't be higher in the sky in summer than in winter.    At the poles, you'd effectively get sunset, 24 hours a day, 365 days a year but over most of the Earth you'd have 12 hours (and a few minutes) of sunlight and nearly 12 hours of, not darkness, cause you'd still have twilight and dawn, but over the most of the planet, it would be 12 hour days pretty much.

The poles would receive less solar energy and could be colder and there wouldn't be a spring thaw or summer growth.  Plant Growth would be pretty consistent all year around.

The equator would have more peak sun and could be hotter.  With our current tilt, the pole to equator solar energy ratio is 0.4 to 1.  Source.  With no tilt, it would be 0 to 1.  The poles could see an increase in permanent ice.

But, despite that increase in ice, you'd get a decrease in solar-ice-reflection, so that could mean a warmer earth, even with more ice on both poles.   The equatorial region could be hotter.

Circulation is hugely complex, so that's a great big wild-card.   Seasonal driven ocean and air currents would be greatly reduced but temperature driven currents should increase, though the reduction of temperature variation is difficult to predict.  You still get night to day temperature variation, but the overall effect on wind and ocean currents is too hard for me to predict.

Hyper-physics says the tilt is essential to life (linked above).  I'm not sure that's true, but no seasons and potentially reduced circulation due to more consistent temperatures could have a pretty big effect.   The potentially worst outcome could be a significant still water in the oceans which could create large dead zones.  That's by no means a certainty, but it's possible.

Article on the effects of the ocean conveyor belt stopping, if interested.

If I missed anything, comments are welcome.


Haze in Arizona / Grand Canyon that gets more apparent around noon - smog or something else? I just came back from the Grand Canyon, and it's awesome.

However, my friend and I did notice something - it seems that there's some kind of haze in the far horizon that seems worse as the sun rises to noon.

One interesting bit is that a polarizer can clean it up when we take photos, so that suggests it's reflected light.

Regardless, I'm curious, is that just pollution blown into the area? or some other atmospheric feature that I didn't know about

Most of the haze I've seen in AZ is blown dust. If it's windy and hazy, it's probably dust. There is little moisture/humidity to create haze. Pollution is also a possibility. It would have to travel from somewhere else as there isn't a lot of civilization in that area.


What type of fossil or stone is this found at beach of the Black Sea? I need some help identifying this stone or fossil. I found it at beach of the Black Sea. The Stone or fossil approx 14 cm x 12 cm x 9 cm (5.5 x 4.7 x 3.5 inches).
Photos below (60x microscope)

Its not a fossil, it is just a septarian concretion. They come in a wide array of shapes and sizes but the crack pattern and crack fill is a dead giveaway.


Preservation of clay items I have a general question which may sound naive: archeologists eg in Ancient Greece take a lot of information from preserved pottery they found. What physical attributes of ceramic items made of clay make them so likely to be preserved?

Its chemically stable oxide, thus non-combustible, does not rot, and fairly hard.

Clay ceramics (just ceramic covers a huge swath of materials) are very non-reactive, and fairly hard, both are exactly what you want for preservation. The clay used in these ceramics is what is left when you chemically remove everything else from rock, it is usually the most stable components, mostly oxides. Earthenware clay in particular is often iron rich which makes it even stronger. once refired the clay transforms into a solid mass, essentially a man made rock.

When you look at what destroys artifacts most don't apply or apply the least to clay ceramics.

Rot/decomposition: not an option for clays nothing organics to rot
Combustion. again not an option for clays, they are already oxides, under the right condition heat can actually make them tougher.
Erosion, this still destroys clay ceramics just like anything else but clay is fairly resistant. It is fairly hard and strong, some stones and metals are more resistant, and these are likewise more likely to be preserved.
Corrosion, clay ceramics ar mostly chemically inert oxides, already in their lowest energy state, so they won't corrode or dissolve when exposed to water, so they survive better than most metallic metals, or ionic compounds.
Theft vs rarity, ceramics generally were not valuable enough to be stolen unlike gold or gemstones or even plain stone, which would survive as well if not better. They were also common enough that that were basically all over a human habitation. If you had a human civilization you usually had hundreds of millions of ceramics. In the case of bricks the homes themselves might be made of it. So they were abundant enough that there was a good chance some would end up in the right conditions to be preserved.

there is one other feature that applies to clay tablets. When a library full of books burns down the books are destroyed, when a library full of clay tablets burns down they clay actually gets tougher much of the time.


Will model resolution have an effect on model spin-up time? In terms of uncoupled AGCM studies, I've seen people use periods within a decade (say, 5 years) as spin-up time, but I also see some people take tens of year as spin-up in some recent studies. So I'm thinking if it's related to the model resolution in different simulations. So does GCM spin-up time affected by the resolution they use? For example if the same model is run in different resolution, would the spin-up time be any different? Thanks!

Without spin-up time, our initial conditions would be blank or generic.

I guess the simple answer is "NO" spin-up time is not really affected by the resolution, unless the model resolution changes are so great that it takes much longer for diffusion / advection between cells to flush out. Though that wouldn't explain a 5 year change in spin up time unless you made drastic changes to a model with very large time steps. Increased model resolution could theoretically increase the necessary spin-up time by a small amount, if the changes in resolution were very large and the time steps used were coarse.   However, in a reputable research setting the spin up time is chosen based on how long (in model time) it takes for things to get to an acceptable initial condition, and changes in resolution are usually not so extreme.

Complexities in the model can increase desirable spin-up time if they have long time-horizons before an acceptable initial condition is achieved.  The spin-up time you choose for your model will influence the degree to which the initial conditions actually represent a realistic distribution of numerics across all parameters, assuming the model is adequately developed.


What does slat and elat (slon, elon) in latitude and longitude values mean? I have data from the national storm prediction center that is marked with values of :
elat
slat
elon
slon

`slat        slon        elat        elon
`31.6671    -90.9352    31.6998     -90.8813

What do those values mean?
What does the "s" & "e" prefix stand for?

This might be product specific, but if it's anything like my MODIS experience this refers to start and end latitude and longitude. Are you looking at a small region on the Mississippi/Louisiana border?