How to get GHI data from MERRA-2? Help Requested

Does anyone know if MERRA2 contains hourly Global Horizontal Irradiance (GHI) data, or some other measurement which we can use to calculate GHI?, If so, could you please let me know how?

Background

I am attempting to use PVLib library in python to calculate the estimated solar generation of various solar farms across the world. PVLib can estimate GHI, Direct Normal Irradiance (DNI) and Diffuse Horizontal Irradiance (DHI), but I was hoping to bring in actual data.

Research and own findings

I've used MERRA-2 data previously to source hourly temperature and wind speeds. So I went looking here first for GHI data.

I looked though GES DISC directory for various MERRA2 reanalysis files. I found M2T1NXRAD (found here) and figured since it contains radiation data that it would contain GHI, but I didn't see anything which looked like GHI in the field list (found here). I did find "surface incident shortwave flux (SWGDN)", but I am not a meteorologist and don't know how this relates to GHI, or if it can even be converted to GHI?

Browsing the internet, it does look like there is some relation between SWGDN and GHI. I've seen many publications allude to it (such as here and here) but I wasn't able to figure out how they are calculating it.

an extract from the above article states

  MERRA-2 uses the Goddard Earth Observing System version 5
  (GEOS-5) atmospheric model and data assimilation system (DAS). The
  dataset offers two-dimensional diagnostics of surface fluxes, single
  level meteorology, vertical integrals and land states, generated at 1
  hourly, 3 hourly, daily and monthly intervals. This paper utilises the
  surface incident shortwave flux (SWGDN) from the single-level
  diagnostic tavgM_2d_rad_Nx data product averaged over a monthly
  interval (NASA 2017).

But it doesn't say how to convert SWGDN to GHI? if anyone knows how these two measures relate to one another, I would love an explanation!

Solved
After more investigation, and help from the PVLIB community, I learned that SWGDN is same as GHI.


Earthquakes and mountain height Tectonic plate motion is the main reason for earthquakes in Italy.

I suppose that a large motion produces higher mountain (as Monte Bianco, Monte Rosa or Adamello) and strong earthquakes.

But strong earthquakes are usually registered in the Apennines (not so high, with the exception of Gran Sasso) and the Julian Alps (not very high between Italy, Austria and Slovenia).

What is the reason of this counter-intuitive behavior?

Present earthquakes create new mountains, former earthquakes created old mountains.
Hence, the Alps are older than the Appenines. In the past surely the Alps had more earthquakes than now.


Derive Reference Potential Evapotranspiration from Potential Evapotranspiration I'm working on a project in Rajasthan, India involving modelling water supply and demand in a catchment. For this, I am working with WEAP which has modules for estimating groundwater recharge using a simple bucket model.

This model needs daily temperature and reference (potential) evapotranspiration values.
The reference evapotranspiration is calculated according to the modified Penman-Monteith equation as described in the FAO56-Paper.
As part of the project, I'd like to use climate models. One with a sufficient resolution is the HAR model, which has values for potential evapotranspiration. Is there a way to get from potential evapotranspiration to the reference evapotranspiration?

EDIT: I am not sure whether the model Potential Evapotranspiration values implicitly contain information about the surface, or if they are a spatially comparable, independent of the surface.
Since I am modeling the catchment disaggregated by landuse types with a uniform climate, I need a value that is independent of the surface properties and can be transferred to the landuse types via the surface coefficients as described in the FAO paper.

I agree that terminology about evapotranspiration is confusing especially when using the expression "potential evapotranspiration", as stated in the FAO-56 paper:

  The use of other denominations such as potential ET is strongly discouraged due to ambiguities in their definitions

Definition

So let's refer to the FAO terminology:

Reference evapotranspiration ($ET_0$) refers to the evapotranspiration observed on well watered grass  for given meteorological conditions (radiation, temperature, humidity, and wind speed).
Crop evapotranspiration under standard conditions ($ET_c$) refers to the evapotranspiration observed on well watered specific crop for given meteorological conditions. The relationship between $ET_c$ and $ET_0$ is given by:

$$
ET_c = K_C\times ET_0 \tag{1}
$$

Crop evapotranspiration under non-standard conditions ($ET_{c,adj}$) refers to the evapotranspiration observed on a specific crop under water and environmental stress for given meteorological conditions. The relationship to $ET_0$ is either defined using a stress coefficient $K_s$:
$$
ET_{c,adj} = K_s \times K_c \times ET_0 \tag{2}
$$
Or using an adjusted crop coefficient $K_{c,adj}$:
$$
ET_{c,adj} = K_{c,adj} \times ET_0 \tag{3}
$$

Confusions

Now, you may find different common usage for the terms potential or actual evapotranspiration that leads to your confusion.

Potential evapotranspiration is sometimes referred to $ET_0$ or $ET_c$ or even less strict definition such as atmospheric demand for water.

Actual evapotranspiration  is referred either to $ET_c$, $ET_{c,adj}$ or less strict definition such as the amount of water evaporated.

Pragmatism

Regarding your issue, pick one:

Read to find out what are the definitions involved in WEAP and HAR
Look at the data and find out if potential evapotranspiration refers to grass (definition 1) or to specific crop with a given coefficient (definition 2, eq.1)
Use the other HAR data (everything is available) to compute $ET_0$ using FAO-56 method.
Last but not least, do not bother that much as evapotranspiration is full of uncertainties and you could not proove which of $ET_0$, $ET_c$ or $ET_{c,adj}$ best represent your actual evapotranspiration. You are interested in the relative dynamics of $ET$, choose realistic ranges of landcover coefficient and calibration will do the mass balance.


During the "Ice Ages" or "Snowball Earth" times, where was all the energy? We often seem to accept the idea that there were periods of time in which the entire surface of Earth was frozen, for the most part. This implies that there were periods of time in which the entire surface was NOT frozen over. Thus, there must have been heat and energy present on the surface. How did all that energy move to cause an ice age? It seems absurd for all that energy to just radiate into space or move deep into the Earth.

I'm not quite sure if the question is asking about glacial, ice ages, or snowball Earth, and whether it's about the onset or end of a glacial period. I'll try to hit all three.
Ice Ages and Milankovitch Cycles
Ice ages are long spans of time that marked by periods of time during which ice reaches far from the poles, interspersed by periods during which the ice retreats (but never quite goes away). The periods of time during which ice covers a good sized fraction of the Earth are called glacials; the periods during which ice retreats to only cover areas in the far north and far south are called interglacials. We are living in ice age conditions, right now. There's still ice on Antarctica and Greenland. We are also in an interglacial period within that larger ice age. The current ice age began about 33 million years ago while the current interglacial began about 11,700 years ago.
The Milankovitch cycles determine whether the Earth is in a glacial or interglacial period. Conditions are right for ice to form and spread when precession puts northern hemisphere summer near aphelion and winter near perihelion and when both obliquity and eccentricity are low. The Earth currently satisfies the first of those conditions, but obliquity and eccentricity are a bit too high. That makes our northern hemisphere summers are a bit too warm, our winters a bit too cold.
The Milankovitch cycles] provides several answers to the question "where does the energy go?" Those times when conditions are ripe for glaciation have energy in the northern hemisphere spread more uniformly across the year than times not conducive to glaciation. Summers are milder, which means accumulated snow doesn't melt as much. Winters are milder, which means more snow falls.
Once ice does become ubiquitous, another answer to the "where does the energy go" question is into space. Ice and snow are white. Their presence reduces the amount of sunlight absorbed by the Earth.
The first paper listed below by Hays et al. is the seminal paper that brought the concept of Milankovitch cycles to the forefront. The second paper by Abe-Ouchi et al. dicusses a recent climate simulation that successfully recovers many salient features of the most recent glaciations. Most importantly, this paper appears to have solved the 100,000 year mystery and shows why deglaciation operates so quickly.

Hays, J. D., Imbrie, J., & Shackleton, N. J. (1976, December). "Variations in the Earth's orbit: Pacemaker of the ice ages." American Association for the Advancement of Science.
Abe-Ouchi, A., Saito, F., Kawamura, K., Raymo, M. E., Okuno, J. I., Takahashi, K., & Blatter, H. (2013). "Insolation-driven 100,000-year glacial cycles and hysteresis of ice-sheet volume." Nature, 500(7461), 190-193.
Icehouse Earth vs Greenhouse Earth
The Earth's climate appears to have been toggling between two climate extremes for much of the Earth's existence, one where things are cold and ice is likely to form and the other where ice is absent worldwide except maybe right at the poles. Dinosaurs roamed the arctic and Antarctica when the Earth was in one of its greenhouse phases. The Earth has been in a greenhouse phase for most of the Earth's existence.
Milankovitch cycles don't cause glaciation during greenhouse Earth periods. Ice ages happen when the Earth is in an icehouse phase. What appears to distinguish greenhouse and icehouse phases are the positions and orientations of the continents. Having a continent located over a pole helps cool the climate. Having continents oriented so they channel ocean circulation in a way that keeps the ocean cool also helps cool the climate.
The Earth transitioned from its hothouse mode to its icehouse mode 33 million years ago or so. That's right about when two key events happened in the ocean. Up until then, Antarctica was still connected to both Australia and South America. The separation from Tasmania formed the Tasmanian Gateway, while the separation from South America formed the Drake Passage. This marked the birth of the very cold Southern Ocean, it marked the buildup of ice on Antarctica, and it marked the end of the Eocene.

Bijl, P. K., Bendle, J. A., Bohaty, S. M., Pross, J., Schouten, S., Tauxe, L., ... & Yamane, M. (2013). "Eocene cooling linked to early flow across the Tasmanian Gateway." Proceedings of the National Academy of Sciences, 110(24), 9645-9650.
Exon, N., Kennett, J., & Malone, M. Leg 189 Shipboard Scientific Party (2000). "The opening of the Tasmanian gateway drove global Cenozoic paleoclimatic and paleoceanographic changes: Results of Leg 189." JOIDES J, 26(2), 11-18.
Snowball Earth and the Faint Young Sun Paradox
Snowball Earth episodes were not your average ice age. Ice typically doesn't come near the tropics, even in the worst of ice ages. Snowball Earth means just that; the snow and ice encroached well into the tropics, possibly extending all the way to the equator.
The problem with snowball Earth isn't explaining where all the energy went. The real problem is explaining why the ancient Earth wasn't in a permanent snowball Earth condition, starting from shortly after the Earth radiated away the initial heat from the formation of the Earth.
The solar constant is not quite constant. While it doesn't change much at all from year to year, or even century to century, it changes a lot over the course of billions of years. Young G class stars produce considerably less energy than do middle aged G class stars, which in turn produce considerably less energy than do older G class stars. When our Sun was young, it produced only 75% or so as much energy than it does now.

Image source: http://en.wikipedia.org/wiki/File:Solar_evolution_(English).svg.
By all rights, the Earth should have been completely covered with ice. The young Sun did not produce enough energy to support open oceans. This obviously was not the case. There is plenty of geological evidence that the Earth had open oceans even when the Earth was quite young.
This 40 year old conundrum, first raised by Carl Sagan and George Mullen, is the faint young Sun paradox. There have been a number of proposed ways out of the paradox, but none of them quite line up with the geological evidence.
One obvious way out is that the Earth's early atmosphere was very different from our nitrogen-oxygen atmosphere and contained significantly more greenhouse gases. The amount of greenhouse gases needed to avert a permanent snowball Earth is highly debated, ranging from not much at all to extreme amounts. Another way out is a reduced albedo due to the significantly smaller early continents and lack of life. The young Earth would have been mostly ocean, and ocean water is rather dark (unless it's covered with ice). Lack of life means no biogenic cloud condensation nuclei, which means fewer clouds.

Goldblatt, C., & Zahnle, K. J. (2011). "Faint young Sun paradox remains." Nature, 474(7349), E1-E1.
Kienert, H., Feulner, G., & Petoukhov, V. (2012). "Faint young Sun problem more severe due to ice‐albedo feedback and higher rotation rate of the early Earth." Geophysical Research Letters, 39(23).
Rosing, M. T., Bird, D. K., Sleep, N. H., & Bjerrum, C. J. (2010). "No climate paradox under the faint early Sun." Nature, 464(7289), 744-747.


What physical measurement / elevation is used to define Earth's radius? Earth's radius is usually given as 6378137 meters (equatorial radius), its flattening is defined as 1/298.257223 (WGS84), and thus its polar radius is calculated as 6356752 meters.

However, the average depth of the Earth's oceans is 3688 meters (i.e. 3688 meters below mean sea level), and the average height of all land above the oceans is 840 meters.

Assuming 71% oceans and 29% dry land, this gives

$0.71 \times (-3688~{\rm m}) ~+~ 0.29 \times 840~{\rm m} ~=~ -2374.8~{\rm m}$. In other words, 2374.8 meters below (current) mean sea level would be the "billiard-ball" Earth if all the oceans were drained1.

So, my question is:

What is the defining elevation of how the Earth's radius is measured? Is it the billiard-ball elevation, current mean sea level, or something else?

1 Of course, this ignores the oblateness caused by the flattening and all the undulations described by the geoid.

Originally, the concept of a reference ellipsoid was an ellipsoid that best approximated mean sea level. This concept predates satellite-based geodesy by hundreds of years. There are now better ellipsoids in terms of providing a better fit to mean sea level than the WGS84 ellipsoid. Yet the WGS84 ellipsoid is used worldwide (including the ridiculously over-precise flattening value).

The WGS84 reference ellipsoid is now just that, a reference ellipsoid (that is, it's the ellipsoid used as a reference by GPS and related systems). In 1993 the WGS84 governing committee voted, with one exception, to retain the 1984 defining values, despite improvements to those defining values. The one exception: The flattening in the original definition of WGS84 was a calculated value, based on the Earth's second dynamic form factor as determined from satellite orbits ($\bar C_{2,0}$ in WGS84, $J_2$ in GRS80). This calculated value became a defining value in 1993. The reason for keeping those older values was GPS. It's better to have a reference ellipsoid that is constant over time than it is to have an ever improving best fit ellipsoid.

Besides, not all of the changes in the best fit ellipsoid represent a reduction in measurement errors. The best fit ellipsoid truly does change over time as the Earth continues to recover from the last glaciation and as the Earth's rotation rate slows down. There are very few applications where a best fit ellipsoid truly is needed while there are many applications where a constant reference ellipsoid is the "best fit".


How do rivers last so long in dry weather? I got caught in a downpour while climbing a mountain and was amazed to see, as I climbed down, the tiny trickles of water combine to form mini-streams, the dry rocks I had climbed up now hosted sizable waterfalls, and the path which I had followed to the mountain had become a small river.

But it got me wondering about my question, which  is the reverse of this. Why, after a long period of dry weather, are many rivers still flowing? I live near a river and it seems that it takes over a week of dry weather before there's any noticeable drop in its level. How does it not simply run out of water?
Is it simply that it takes very a long time for the water at its source and the sources of all its tributaries to reach the point I'm observing from?

It seems there's a constant supply of water when I would have expected the network of rivers to start draining, and the drying up starting from the source the moment the rain stopped.

The rivers are generally fed by water that percolated into the ground, it takes longer for that water to work its way down to the stream so the streams and rivers keep flowing long after the initial rain. https://water.usgs.gov/edu/rivers-contain-groundwater.html


Can up-welling water at oceanic fronts be physically felt? If you were swimming/floating within a body of water experiencing upwelling due to sea-surface thermal fronts, would you be able to physically feel the water that is being up-welled or is it on a different scale not sensed by humans?

There is a sea-surface thermal front at the northwest tip of Scotland. On the western side is water from the Gulf Stream Drift - cool, but sufficiently comfortable to swim in. On the north side is Arctic water which is horribly cold and which nobody in their right mind would swim in. I write from personal experience!


Will the definition of the second be changed? (Please excuse my English)
A well known fact about Earth's rotation(around its axis) is that the rotation is slow down due to the tidal friction. And because of it, the length of Day is slowly increasing.
Originally, the definition of Second(time) was derived from the day length and Earth's rotation. The original definition of the second was 1 day / 24 / 60 / 60 = 1 day / 86400. However, the modern definition of the second is derived from the atom's oscillation period, for precise time keeping, independent of Earth's rotation, because of irregularity of Earth's rotation. Thus, compared to the original definition, the modern definition of the second has rigidly fixed value.
My question is : Someday in future, the length of a day will be longer than 86400 atomic seconds. Then what should future human do?
Changing the definition of the second will lead to incredibly complex situations. Also changing the definition of the day will cause tremendous complex situation.

Someday in future, the length of a day will be longer than 86400 atomic seconds. Then what should future human do?

Having a time standard that works well with the ever improving capabilities of physics and having a time standard that stays in sync with the Earth's rotation are at odds with one another. One solution is to continue to do what we do now.
The length of a day is already longer than 86400 atomic seconds. Every once in a while a leap second is added to keep time as measured by the rotation of the Earth in sync with time as measured by an atomic clock. To date, 37 leap seconds have been added since 1972. This concept will continue to work, at least for the next few to several hundred years. Eventually the Earth's rotation rate will have slowed to such an extent that the leap second trick will no longer work.

Will the definition of the second be changed?

Almost certainly.
Scientists will eventually find something that is even better than is the unperturbed ground-state hyperfine transition frequency of the cesium-133 atom as a timekeeping device. That science advances is what science does. It has already been proposed to use pulsars rather than atomic clocks as a more precise timekeeping drive. One thing is certain: The second will not be redefined to be 1/86400 of a day.


MERRA-2 Reanalysis data V and U wind are missing values over land at 1000 hPa pressure level I need 6-hour MERRA-2 reanalysis data to do some research.
I downloaded the data from this website:
https://disc.gsfc.nasa.gov/datasets/M2I6NPANA_5.12.4/summary?keywords=merra

When I used ncview to check this data, I found that V and U wind are missing values over land at 1000 hPa pressure level.

Have you ever seem this problem before?
Thank you so much.

TL;DR: It is not a problem, it is a feature.

As it was pointed in the comments, 1000 hPa over land (and sometimes over ocean) is below the surface. MERRA is just fair enough not to put any values where they do not exist. Other reanalyses use some procedure to fill the gaps and make fields without holes. The procedure is reanalysis specific, and, can ususlly be found in corresponding technical manual. The gap-filled fields have little physical meaning anyway.

If the gaps do not make sense for you, 1000-hPa wind is, probably, not the field you need. E.g. if you are after near-surface wind, 10-m wind is more appropriate quantity.


Do "water-worlds" not have plate tectonics? Water-worlds are becoming increasingly important in the exoplanet/astrobiology community. If plate tectonics create land masses, then can we say that a water-world (a planet with a global ocean and no land) does not have plate tectonics?

Many astrobiologists say that plate tectonics may be a prerequisite for life to form on a given planet. Therefore, if the assumption that water-worlds do not have plate tectonics is true, then can we also say that these water-worlds cannot harbor life?

can we say that a water-world does not have plate tectonics?

No we can't. Take for example Earth, add in a lot of water to cover all of the continents and you get a water-world with active plate tectonics. The driver for plate tectonics is not whether water exist or not on the surface, but rather the internal heat a planet contains.

Or, the plates of plate tectonics could actually be water ice, as is hypothesised for Jupiter's moon Europa. You have to remember that currently our sample size is one. There is only one planet where we know for sure that there are active plate tectonics, and that is Earth. Ruling out plate tectonics on other planets just because we don't know how it will look like or how it will work is not correct.

That said, water plays an important role in plate tectonics on Earth. Be it modifying the composition of the crust, changing the strength and ductility of the rocks, or some other process.

  then can we also say that these water-worlds cannot harbor life?

No. Again, our sample size is one. There is only one planet we know with life and that is our Earth. Who knows what may be out there? For starters, we don't even know what fired up life here on Earth in the first place. It could be volcanos or hydrothermal vents in the ocean around hot spots, which are (almost) independent of tectonic activity.

On a personal note, we've all seen how astronomy advanced from "are there any other planets out there?" to actually discovering hundreds of them. What was once the exception is now the rule. Who knows, life might actually exist on just about every solar system out there.


Predicting rainfall with governing equations Which model is a good starting point for predicting precipitation (rain) for 24 hours in advance? I looked at Kalnay's Atmospheric modeling, data assimilation and predictability, and Holton's An Introduction to Dynamic Meteorology as well as various other sources. These are great references but I could not figure out which part I could use to compute what I needed. It seems there are governing equations which are solved numerically, the output is used for a prediction. I am knowledgeable on numerically solving ODEs, PDEs, and am familiar with Matlab, Python, but there aren't any references that I could find providing clear formula -> data -> code -> output.

The most talked about model with clear solution is the Barotropic Vorticity Equation, which, I believe, models wind and pressure. This model was proposed by Charney, Fjortoft and von Neumann during the 50s, and solved with a computer, the results are recreated by Peter Lynch on 2008 (Matlab code available). Could this model be used for rainfall prediction?

If one has to dig in the basic equations, which part of the governing equations should I focus on? Any pointers, references with running code is most welcome.

The Barotropic vorticity equation is insufficient to model rain. Part of this is due to the word 'Barotropic,' which indicates a lack of thermal gradient. The other reason is that while vorticity is a useful quantity, it lacks explicit information on the atmospheric state.

The primitive equations are a system of partial differential equations that are used by most numerical weather prediction models to model various quantities. Rainfall rate is a parameterized variable, a diagnosed formula (or formulas) based on atmospheric state, based on research. Sometimes the results of the research can give wildly different answers given the same data, which is a weakness of parameterizations. The idea is to model the Reynolds-averaged primitive equations and intermittently invoke the parameterizations (including turbulence, radiation, cloud cover, and so on).

Here is a good book that discusses parameterization schemes in general.


What causes the 'calm before the storm'? The old adage "The calm before the storm" certainly has an observational scientific meaning to it -- something that many (including myself) have experienced -- that on a hot summer's day, when a change in the weather starts rolling in, humidity rises, but it becomes very calm with little to no wind, before the storm begins.

(This of course is not the only phenomenon associated with a change in weather).

What confluence of meteorological factors results in the 'calm before the storm'?

Quoting from Is there really a "calm before the storm"? at howstuffworks.com this sometimes happens ("Other storms skip the calm and proudly announce their presence by instantly unleashing bad weather").

  As warm, moist air is pulled into a storm system, it leaves a
  low-pressure vacuum in its wake. The air travels up through the storm
  cloud and helps to fuel it. The updrafts in the storm, however,
  quickly carry the air upward, and when it reaches the top of the cloud
  mass, this warm moist air gets spit out at the top. This air is sent
  rolling out over the big, anvil-shaped head of the thunderclouds or
  the roiling arms of hurricanes. From there, the air descends -- drawn
  back toward lower altitudes by the very vacuum its departure created
  in the first place.

That descending air becomes warmer and drier which is relatively stable, and once it blankets a region, it stabilizes that air in turn. This causes the calm before a storm.

Follow the link so see a more extended explanation with graphics.


Why is colored seismic inversion called 'colored'? One of the seismic inversion algorithms is called 'colored' inversion. It is performed in the frequency domain and the point is in building an operator that directly transforms a seismic trace into reflectivity trace. The question is - what means 'colored' and why was the specified technique named this way?

Colored inversion is designed to approximately match the average spectrum of inverted seismic data with the average spectrum observed impedance (Lancaster and Whitcombe, 2000). The earth’s reflectivity can be considered fractal, and the resulting amplitude spectrum favors high frequencies (spectral blueing). If there was no preferred frequency, then you would have a "white spectrum", but as there are some frequencies with more energy, then it is called "colored".

Figure 4 from Lancaster and Whitcombe: Acoustic impedance from 4 sites in the North Sea


How was the Earth's core made? All I've heard until now is that when the Earth was very hot and slimy, the relatively heavier elements went down to the center of the Earth to form the core. But lately I've come up a contradiction or something. They say the gravity of the very center of the Earth is 0 because you'd get pulled from all the other directions. Then how did the heavier elements go down all the way to the bottom which shouldn't be the place that had strongest gravity?

When the Earth was newly formed by collisions with asteroids, comets, planetesimals and other debris of the early solar system 4.6 billion years ago, the planet was incandescent and the mantle hotter and more fluid than it is today. Just as you have heard, the heavy metals sank toward the centre.

And just as you say, there is a tiny place at the very centre where almost all the mass of the Earth and therefore almost all the gravity is outside this central point. Imagine this central point to be a cannonball. There is no enormous mass at its centre, pulling it down, and the gravitational field of the mass above it is pulling it outward and upward, so why doesn't it migrate back toward the surface?

You need to remember that only the imaginary cannonball is in this exclusive central position. For any substance close to it but not at the absolute centre, there will be more mass to one side of it than the other, so there will be a gravitational force pulling it toward that direction, in other words, toward the centre of mass.

The other thing to remember is that on top of the imaginary cannonball, in all directions, is a column of molten material reaching nearly 4,000 miles right up to the surface, and this column has enormous weight and pressure. Because of this pressure there is a substantial region where the iron-nickel core is solid. How did infalling heavy metals reach the centre if there is a solid mass there? Well,it wasn't always solid, and there was a stage when it was liquid. The gravity-free zone at the Earth's centre is purely theoretical and doesn't allow the centre to behave as though it were in zero gravity.


How to estimate dispersion in stratified flows Consider a 2-dimensional domain with the typical x-z coordinates. Given an arbitrarily stratified flow, how can we estimate the depth varying horizontal dispersion of passive particles induced by the flow?

At the moment, I am seeding the domain with passive particles throughout the entire horizontal and vertical extent of the domain. Regarding the initial particle location, I employ a structured Gaussian distribution in the horizontal direction and a linear distribution in the vertical direction. Then, given the temporally variable Eulerian velocity field, I integrate all particle trajectories with a Lagrangian particle tracking code for the desired length of time.

To measure dispersion, first I calculate the Standard Deviation (sd) of the horizontal distance between the particles in the initial time ($sd(\Delta x_i)$) and the final time ($sd(\Delta x_f)$) and normalize it by its maximum absolute in the initial and final stage, respectively.

$$\overline{sd_1} = \frac{sd(\Delta x_i)}{max(abs(sd(\Delta x_i)))}$$
$$\overline{sd_2} = \frac{sd(\Delta x_f)}{max(abs(sd(\Delta x_f)))}$$

Given that, I use the difference between $sd_1$ and $sd_2$ as my depth variable dispersion measure.

Is there a better/more official way of doing it (taking into account that I want to use Lagrangian particle tracking methods).

There are lots of studies considering Lagrangian dispersion. One critical aspect is the addition of random displacement to the deterministic particle track in order to consider subgrid-scale processes. Your measure of dispersion seems acceptable except for the fact that it might be dependent on the resolution of your flow field. In order to compare your dispersion with other areas or times, you might need to scale it by the horizontal diffusivity of the flow. Some studies that could be helpful are Mariano et al. (2002), Proehl et al. (2005), Lynch & Smith (2010).


Effects of global warming on drought in India Is there an intuitive explanation for non-specialists why India is projected to experience a decrease in drought (= increase in PDSI) due to global warming, unlike most areas at the same latitude(s), at least according to these maps by
 Dai (2010)?

Since you asked for an intuitive explanation, my thoughts would be that due to predicted increasing sea and global temperatures, the models used might be predicting a corresponding increase in monsoonal moisture or duration.

From Climate of India :

  In India a tropical wet and dry climate is more common. Noticeably
  drier than areas with a tropical monsoon climate, it prevails over
  most of inland peninsular India except for a semi arid rain shadow
  east of the Western Ghats.

An article on
 the National Geographic site discusses the relationship between the ocean air temperature and the monsoons in India:

  The summer monsoon is associated with heavy rainfall. It usually
  happens between April and September. As winter ends, warm, moist air
  from the southwest Indian Ocean blows toward countries like India, Sri
  Lanka, Bangladesh, and Myanmar. The summer monsoon brings a humid
  climate and torrential rainfall to these areas.

So in a region which is warmer, both air and ocean temperature, this monsoon effect is apparently predicted to be altered accordingly, resulting in either a higher precipitation, or longer duration to the wet cycle, to effectively make this region wetter than it is today. Without knowing more about how the models were derived, this is just speculation however.


How are natural specimens, such as ‘Moqui Marbles’, distinguished from man-made artifacts? If a particular type of rock specimen is found throughout Earth and is made entirely of natural minerals, but the individual specimens differ minutely from another in size and shape and look to be manufactured by intelligence, does science have to conclude it’s just a rock because the composition is entirely from earth minerals? Or is it because these specimens are also found on Mars? If only Earth had them, would science say that they are ancient artifacts from a past civilization?

Here are photos of Moqui Marbles from Earth, and similar formations on Mars. I've held some that are hollow and some that were filled. They even have a negative pole effect on each other as though intended to keep a distance from the next one.

Like Michael, I find your question a little unclear, but the crux of it seems to be this:

  ... does science have to conclude [that a specimen is] just a rock because the composition is entirely from earth minerals?

The answer is an emphatic no. There are lots of non-rocks out there, many of them manufactured by the (alleged) intelligence known as Homo sapiens. There is certainly no rule in geology that you have to exclude this possibility from consideration when identifying a rock, no matter what its composition. After all, we’re perfectly capable of manufacturing artefacts from earth minerals. In fact, when identifying a specimen, you have to consider the possibility that it's a product of intelligence: many enthusiastic amateurs have ended up collecting bits of brick, rubble, salt-lick, industrial slag and so forth by failing to do this :-).

One factor you mention in your question is the property

  look to be manufactured by intelligence

This, it turns out, is often a less useful diagnostic than you might expect. Lots of manufactured specimens don't look particularly manufactured, especially after a bit of erosion and weathering. Conversely, lots of naturally occurring objects look remarkably regular and intricate.

On the left, objects manufactured by intelligence (slag from the Knight Smelter in Utah). On the right, a naturally occurring specimen of dodecahedral pyrite from Elba, Italy. So a subjective, purely visual judgement that something ‘looks manufactured’ or ‘doesn't look manufactured’ can be very misleading.

Your question also asks specifically about the ‘Moqui marbles’ of the Navajo Sandstone:

  If Earth only had them would science say they are ancient artifacts from a past civilization?

The answer here is, again, a firm no. This is easy to check because, of course, the ‘Moqui marbles’ had been observed long before Opportunity landed on Mars in 2004, and at that time scientists did not regard them as ancient artifacts from a past civilization. For example, Chan et al. (2000) described them like this:

  Small concretions of secondary iron oxide deposits are exclusively hematite-cemented sandstone. These concretions form all kinds of shapes from millimeters to centimeters in diameter, and cut across primary bedding structure. Some concretions are solid spherical balls around unknown nuclei; others are spherical rinds with plain red-stained, host rock interiors (lacking black-colored hematite cement on the inside). Concretions also exhibit forms that appear to have coalesced or joined (similar to two glued marbles), or exhibit a variety of other odd shapes (buttons, disks, irregular knobby forms to spiked-looking balls).

As you see, the authors identify these objects as concretions. (Also note that, although you claim that they're only "minutely" different in size and shape, the description here mentions a great deal of variation in both those properties.) Concretion is an extensively studied geological phenomenon which occurs across the globe. There’s no need to invoke an ‘intelligent manufacturer’ to explain it, whether or not concretions are found on other planets.

Chan, M. A., Parry, W. T., & Bowman, J. R. (2000). Diagenetic hematite and manganese oxides and fault-related fluid flow in Jurassic sandstones, southeastern Utah. AAPG bulletin, 84(9), 1281-1310.


Looking for a reference for identifing stream regimes(Intermittent, Perennial) I'm a hydrologist with a good background in GIS. I'm looking for a reference (Methodology, Technical guide) for identification of temporary, intermittent and perennial streams. I google and only found this reference for North Carolina.Is there any standard reference guide for such an identification?

I'm not sure if this is a standard per se, but I found it useful.  These definitions are from a 1923 publication of the United States Department of the Interior entitled Outline of Ground-Water Hydrology.  Here is the link to the PDF and the specific definitions below can be found on pages 57-58.  Hope this helps.

Perennial:

  A perennial stream, or stretch of a stream, is one which flows
  continuously. Perennial streams are generally fed in part by springs,
  and their upper surfaces generally stand lower than the water table in
  the localities through which they flow.

Intermittent streams are divided into spring-fed intermittent streams and surface-fed intermittent streams.

  A spring-fed intermittent stream, or stretch of a stream, is one that
  flows only at certain times when it receives water from springs. The
  intermittent character of streams of this type is generally due to
  fluctuations of the water table whereby the stream channels stand a
  part of the time below and a part of the time above the water table.
  This is the ordinary type of intermittent stream.

  A surface-fed intermittent stream, or stretch of a stream, is one that
  flows during protracted periods when it receives water from some
  surface source, generally the gradual and long-continued melting of
  snow in a mountainous or other cold tributary area. The term may be
  arbitrarily restricted to streams or stretches of streams that flow
  continuously during periods of at least one month.

Ephemeral:

  An ephemeral stream, or stretch of a stream, is one that flows only in
  direct response to precipitation. It receives no water from springs
  and no long-continued supply from melting snow or other surface
  source. Its stream channel is at all times above the water table. The
  term may be arbitrarily restricted to streams or stretches of streams
  that do not flow continuously during periods of as much as one month.


Why does upwards lightning use only one path but downward lightning uses multiple paths? My question pops-up from this question "Why does lightning strike from the ground-up" which I consider partially unanswered.
Why do I consider it partially unanswered?
Because only one answer tried to explain why the difference of the several to one paths occur in this phenomenon.

PS: there is another question that arises also
Why does lightning strike from the ground up at this particular location in Earth and has it happened before (at the exact same location)?

Upwards stroke happens when the stepped leader and the traveling spark have already connected. This path then becomes much more conductive than any other paths where the connection hasn't happened yet—because the latter ones have gaps of non-ionized air inside them. This highly conductive path shunts all the remaining stepped leaders, lets the charges quickly cancel out, and thus basically stops propagation of the leaders.


Precipitation and Elevation Does precipitation increase or decrease as elevation increases? Because I heard that in the mountains they get more precipitation due to the orographic effect and how the mountains drain the moisture from the clouds but in 8th grade my science teacher told me that precipitation actually decreases as elevation increases so I’m just confused?

What usually happens is that moisture laden air is blown toward mountains and forced to climb higher. As it rises, it tends to  become colder and less dense, so can hold less moisture. The surplus moisture is often precipitated in the hills or mountains, so when the air passes beyond the mountains there is much less rainfall. This is known as rain shadow. Here in Hereford UK we have plenty of rain, but not nearly as much as some places in the Welsh hills which lie 20 miles to the west of us, so I think we benefit a little from rain shadow. It was my experience in Borneo that there was more rain in the hills than at lower altitudes, but whether this holds true for the summit if Mount Kinabalu, which is over 12,000 feet high, I am not so sure. Probably not. More likely the rain is precipitated on the lower slopes.


Any historical examples of destructive climate warming? Summation: Local cooling climate changes, since the last ice age seem relatively common and all seem to cause significant harm to human population. But I can't find instances of the reverse, warming climate changes that caused harm. If anything, the correlation seems reversed, warming climate change brings benefits. (Note: Droughts to not indicate warming.)

Are there any known or suspected historical i.e. Holocene climatic warming associated with negative impacts on human populations?

Details:

This one caught me by surprise. I had assumed episodes of destructive warming would be common and well documented.

I am reading
The Great Famine: Northern Europe in the Early Fourteenth Century by Medieval scholar William Chester Jordan. The book regards a massive famine that hit Western/Northern Europe 1315-1322. Until recently, the Great Famine was overshadowed by the "Great Mortality" pandemic episode of the Black Death which struck 1346–53. Computerization of period sources in the last 20 years has allowed researchers to correlate much wider patterns than in the past and the event is now know to have been much wider in area and of longer duration than realized.

Besides the scale, what makes the Great Famine possibly unique is that it was caused by three or more years of continuous rain i.e. it rained roughly 9 out of every 10 days, Spring, Summer and Fall.

The rain essentially drowned the seedlings in spring, the roots in summer, then rotted crops in the fields towards fall. In addition, the extraordinary wet conditions caused a "murine" an outbreak of diseases in almost all domestic animals but particularly cattle e.g. Hoofed animals often had their hooves (which are just giant toenails) so constantly immersed that eventually they just sloughed off. Other's died of water born illnesses.

I was intrigued by the event because I assumed before reading the book that the catastrophe must have been a localized example of the "The Big Sog" outcome predicted by some climate models in which the increase in world temperatures leads to significantly higher humidity world wide which causes incessant rain. I knew that the effected years fell into the Medieval Climate Anomaly which definitely represented a sustained warming in Europe and likely most of the Northern Hemisphere.

However, the chronicles, various accounting records and climate proxies all show a dramatic cooling, with brutal winters of intense cold, deep snows and ice packs forming on the Northern shores Europe. The overall climate/weather-patterns had shown a general but widely oscillating cooling pattern since the late-1200s. After the 1320s, Europe (at least) slipped into "The Little Ice Age".

It was this cooling that allowed the Black Death to spread by altering the way in which the Y. Pestis bacteria clump inside the fleas that carry it. The same dynamic of cooling, rain, harsh winters and plague outbreak, occurred in 542 in the Mediterranean world during when several years of cooling probably caused by a volcanic eruption, reduced harvest, drove nomads southward and nearly destroyed the Byzantine and Sasanian empires.

During the Medieval Anomaly it appears that the climate of MesoAmerica, North America west of the Sierras grew dryer with years and possibly decades of drought conditions. However, the overall temperatures seemed to have cooled.

Drought conditions can cause higher peak daytime temperatures because of the loss of cloud cover, but these peaks are offset by nighttime lows by the same mechanism, just as occurs in deserts. The actual heat content of the atmosphere, its enthalpy, which drives weather and climate, actually decreases because most of the heat is held in the atmospheric humidity and the biomass. It's easy to see how cooling can cause droughts.

I'm looking for the kind of increase in enthalpy predicted for world wide by current climate models.

If such events are unknown, that would be a separate question.

To answer the question

  Are there any known or suspected historical i.e. Holocene climatic warming associated with negative impacts on human populations?

One recent (actual) example that come to mind is the sea level rising. Here we see that since the early satellite measurements in 1993, sea level rise was about 8 cm. On the same page, less reliable gauges indicated a coastal sea level rise of 20 cm between 1870 and the late 1990.

Some Islands are particularly vulnerable to sea level changes, in regard with fresh water supplies, soils and shore degradation following storms and strong high tides, etc. Marshall Island (~2 m), Maldives (~1 m) are examples of emplacements with very low mean ground level. It is really a question of time before these places become unlivable.

While these are small islands, other populous places are quite vulnerable to similar situations such as Bangladesh.


Why does haze and poor visibility present in stable air? Haze is not considered to be a cloud or mist, and it also is not fog.

What is the ultimate reason that haze and general poor visibility ranges prevail in stable atmospheric conditions?

Is the cause concentration of pollutants, some other effect caused by the presence of moisture/humidity, a combination of both, or something else completely?

Traditionally, haze has been regarded as,

  an atmospheric phenomenon in which dust, smoke, and other dry particulates obscure the clarity of the sky...

  Sources for haze particles include farming (ploughing in dry weather), traffic, industry, and wildfires...

  Whereas haze often is thought of as a phenomenon of dry air, mist formation is a phenomenon of humid air. However, haze particles may act as condensation nuclei for the subsequent formation of mist droplets; such forms of haze are known as "wet haze" ...

  In meteorological literature, the word haze is generally used to denote visibility-reducing aerosols of the wet type. Such aerosols commonly arise from complex chemical reactions that occur as sulfur dioxide gases emitted during combustion are converted into small droplets of sulfuric acid. The reactions are enhanced in the presence of sunlight, high relative humidity, and stagnant air flow. A small component of wet-haze aerosols appear to be derived from compounds released by trees, such as terpenes. For all these reasons, wet haze tends to be primarily a warm-season phenomenon.

A haze can also be considered an atmospheric colloid, where,

  one substance of microscopically dispersed insoluble or soluble particles is suspended throughout another substance.

Examples of atmospheric colloids include: fog, mist, clouds, condensation, smoke and atmospheric particulate matter.

The forces behind the suspension of haze particles includes: electrostatic interactions, Brownian motion, van der Waal forces, and entropic forces. The effect of these forces on the light (low mass) particles within a haze counter gravity to keep the particles suspended in air.


Define components of mineral assemblage? Given the a mineral assemblage with the minerals $$cp (\ce{CuFeS_2}), bn (\ce{Cu_5FeS_4}), cc (\ce{Cu_2S}), mt (\ce{Fe_3O_4}), py(\ce{FeS_2})$$
where cp, bn, mt are in contact, and py, cp, bn, cc are in contact.  What are the components?

I was told #components=#constituents-#reactions -#constraints but I don't know how to define constituents or constraints.  I'm not sure what the number of reactions is either.  I was trying to define constituents based on oxidation states of the metals (assuming S and O are always -2), and I got $$\ce{Cu^{+1}, Fe^{+4}, Fe^{+3}, Fe^{+2}}$$ where the $$\ce{Fe^{+3}} : cp (\ce{CuFeS_2}), bn (\ce{Cu_5FeS_4})$$ and the  $$\ce{Fe^{+4}}: py(\ce{FeS_2})$$
and $$\ce{Fe^{+3}, Fe^{+2}}: mt (\ce{Fe_3O_4})$$

As for the number of reactions, I'm confused because only one of the minerals has oxygen (so can't be part of a reaction with one of the others to produce another), and I was having a hard time balancing reactions between the others.

Can anyone give me any advice on how to figure out what the components are, and in general how I should define components, constituents, and reactions based on assemblages of minerals?

This question is based on a problem from Walther "Essentials of Geochemistry"
here is a [Link] to the question.

Just to clarify based on the given answers, the components are cc, cp, py, and mt?  Since bn is the only one that can be formed from a reactions of the others?

Let's start by understanding what a component is. The components of a system are the minimum amount of chemical 'species' required to describe a system. What does that mean? Let's take a familiar example. Periclase, forsterite, enstatite and quartz. That's MgO, Mg2SiO4, MgSiO3 and SiO2. So we can say we have 4 components, each of those formulas I just noted. But that's not the minimum number. We can get a smaller number. So we can say, for example that our components are Mg, Si and O. We can create all of the mineral formulas from those 3 components. But wait - we can go even lower! If we choose our components to be only MgO and SiO2, we have 2 components that can still describe our entire system. We can combine 2MgO+1SiO2 to describe forsterite and 1MgO+1SiO2 to describe enstatite. Basically, the components have to be independent. If there is one component that can be described by others, then it is not actually a component.

So let's go to your problem. First of all, I would say that your assumption that the oxidation state of Cu is +1 and that of S is -2 is not entirely correct. In pyrite, S is actually -1 and Fe is +2 (Fe4+ does not exist). As an aside, the oxidation state of Cu (and others) in sulfides is a can of worms: those are not ionic compounds but rather a mixture of metallic and covalent compounds where oxidation state does not mean much, especially in the more complex cases such as bornite and chalcopyrite.

That said, if you look carefully and try to balance your reactions (try to make one mineral using the others), you can see that bn = cp + 2cc, so bn is not a component. Can you still reduce the amount of components? No. Fe3O4 must be there, and there is no way you can make CuFeS2 from Cu2S and FeS2. You might think about using the components S-Fe-Cu-O, but that would actually be incorrect because for that to happen S has to be the same valence, which obviously is not (compare Cu2S2- and FeS1-2).


Regarding velocity of P/S-waves I feel like I am missing something blindingly simple, but I am curious about something.

We are given the velocity of a P-wave as $v_{p} = \sqrt{(K+\frac{4}{3}μ)/ρ}$.  So I am to understand conceptually that as density increases, the velocity of the P-wave also increases.  However looking at the equation would indicate a lower velocity with increased density.  Is it just a matter of the bulk and shear modulus' increasing at a more rapid rate than density as you travel through lower depths?

That is not a silly question! And your intuition is correct: As you bury and compact a sedimentary rock, its porosity will decrease, so its density increases. But we also see that its velocity tends to increase. This appears contrary to what that equation shows.

However, as you bury the rock and decrease its porosity, you are simultaneously increasing the rock's effective stiffness (bulk and shear moduli). And yes, this effect overwhelms the density effect so the outcome is a faster P-wave velocity. So even though the derivation of this equation from continuum mechanics tells us that stiffness and density are independent parameters, they seldom are in nature. Most geological scenarios where density would increase, also raise the effective stiffness of the rock.

But here is an example where this is not the case. Imagine you have sandstone between two shales. The sandstone has some porosity and it is completely filled with brine. If that exact same sandstone (i.e. holding everything else constant) is now filled with gas instead of brine, its Bulk modulus will go down by a lot and Density will also go down but by less. However, according to Gassmann's equations, the Shear modulus will stay constant. So the P-wave velocity goes down because the Bulk modulus effect overwhelms the Density effect and the Shear modulus doesn't change. But now consider the S-wave velocity whose equation is $v_s = \sqrt{μ/ρ}$. In this case there is no Bulk modulus to overwhelm the density and so the S-wave velocity will actually go up by a small amount when the rock is saturated with gas. This is purely a density effect.

This effect is commonly observed in hydrocarbon exploration where they have drilled a well into a sandstone that is full of water, but then go up dip and find something like an anticline where the same sandstone is now full of gas.


What are the benefits of using conservative temperature in oceanography? The new standard for ocean temperature is the "conservative temperature". It is based on a hypothetical adiabatic and isohaline change in pressure to the sea surface. Conservative temperature was adopted as the standard by the oceanographic community as part of the Thermodynamic Equation Of Seawater - 2010 (www.teos-10.org). The previous standard (EOS-80) was Potential Temperature.

What are the differences between potential and conservative temperatures? What are the benefits of using conservative temperature? Where should I expect the biggest departures between the two temperatures and why?

The TEOS-10 manual, page 26, says that the potential temperature is the temperature that a parcel of fluid conserving its Gibbs energy and absolute salinity would have if brought to the surface, or from an integral of the adiabatic lapse rate. The conservative temperature is not a true temperature, but a multiple of the enthalpy. It's really an energy that's been scaled to have units of temperature. The scale factor is the heat capacity of water in a standard state, since it's taken to be constant. In the potential temperature, the heat capacity is allowed to vary during ascent.

This distinction crops up a lot in meteorology, where the moist static enthalpy is conserved under adiabatic ascent, whereas other measures of temperature aren't conserved. I think the reason for the change is similar to why we would use enthalpy in meteorology, too. Suppose that the adiabatic changes in pressure and temperature also change the equilibrium coefficients of some reaction, say $\ce{CO2 + H2O -> H+ + HCO3-}$. This would change the absolute salinity, since it's splitting apart a water molecule into ions. The actual ascent can be adiabatic - there's no mixing with the surrounding water - but it's no longer isohaline. The enthalpy will still be conserved, though. This is why I think your questions (here's the other one) are related: using a mass-based salinity fits in much better with a thermodynamically-consistent formulation of the Equation of State, and using the enthalpy over the potential temperature is part of this complex salinity-temperature-entropy relationship.

The manual mentions that near the surface, the differences between potential and conserved temperature should be really small. The heat capacity chosen to scale the enthalpy is similar to that for surface water. You'd get the largest differences at depth and where the composition of seawater is much different (like with absolute salinity). The difference here is whether that composition is expected to change with temperature and pressure.


The relation between the magnitude and duration of earthquake I am asking this question in reference to the recent earthquake that struck Nepal last month. I read that the magnitude 7.8 richter scale earhtquake would have caused more damage had it lasted for longer time. In case of Nepal it lasted for nearly 30 seconds. I also read that that magnitude scale was not able to release all the energy that has been stored in the form of strain in the plate.

So what I wanted to ask is that if that earthquake had lasted for more time, would it have released more energy? Similarly does an earthquake of magnitude, say 6, would release energy just as equal to 7.8 if it lasted for more time?

It is helpful to start with the USGS definition of magnitude, which can be seen as:

  based on measurement of the maximum motion recorded by a seismograph.

According to the Seismology Research Centre page Earthquake Size and the USGS FAQ page What was the duration of the earthquake? Why don't you report the duration of each earthquake? How does the duration affect the magnitude?, the duration and magnitude are generally related, specifically given that an earthquake is the movement (motion) of an area of a fault, rather than a single point -

  So the larger the area of the fault that ruptures, the longer the duration of the earthquake. And larger magnitude earthquakes have larger fault areas.

In the case of the recent Nepalese earthquake, if the fault movement area was larger, then this potentially could have resulted in a larger magnitude, longer duration earthquake.

However, a major reason for the uncertainty (why the USGS page refers to the relationship as a 'general' relationship) is due to the geology of the affected area, from the USGS:

  The duration of shaking at a point on the ground depends on how long the earthquake took to occur and how the waves move through the ground to that point. If there are a lot of reflections and resonances near the point (for instance in a sedimentary valley) the shaking will last longer. In an area without resonances (for instance on a hard block of rock) it will last a shorter time.


What are these Pebbles Found these Pebbles at a lake edge where a Serpentinite belt runs through, there are lots of serpentine pebbles along this lake in Co. Sligo Ireland.

The larger pebble is 1 5/8'' a Yellowish white color underneath and translucent, and has a tiny pitted surface The smaller pebble is opaque.

The white one is milky quartz, the yellowish/brownish one could be some variation of quartz or quartzite, too.

Further information about quartz and milky quartz can be found here


Are plastics a carbon sink and how much carbon is released to the atmosphere making them? If we were to make some technical jump to renewable fuel and renewable energy, would making plastics from oil release green house gasses, how much, and would plastic function as a carbon sink?

Sorry if this is a basic question I don’t know much about earth science.

The idea of a carbon sink is a bit misunderstood here. The idea of a carbon sink is a reduction of carbon that comes from the atmosphere. It must “fix” carbon that is already in the air. Trees are a carbon sink, for the most part, because their mass is made of of carbon obtained from
The atmosphere. Unless the plastic formation process you are thinking of is vastly different that any industrialized ones, they are taking carbon from oil essentially. Since the carbon from the oil
Has not yet been released into the atmosphere, it would not qualify as a sink.


Why is mass fraction always abbreviated wt% and not ma%? In most geology papers, major elements chemical analyses are expressed as mass fraction of oxides, i.e. SiO$_2$ 64.2 wt%, K$_2$O 4.3 wt%, etc. The mass fraction unit is always abbreviated as "wt%". Even my bible when it comes to igneous rocks classification/terminology (Le Maitre et al. 2002) uses it.

What bothers me is that "wt" refers to the weight, which is a force, not a mass. I know it is common usage to use "weight" to refer to the mass of an object, but when writing science shouldn't we be more accurate and use the proper words? Molar and volume fractions are abbreviated mol% and vol%, respectively. Isn't it time for the "ma%" or "mas%" revolution? If I write "mas%" in a paper, will the reviewers/editors accept it?

This is because of historical inertia.

Yes, you are correct that "mass" is technically more correct than "weight". However, because these are percentages, it does not matter. There are no units. A rock that has 50 weight% SiO2 also has 50 mass% SiO2, regardless of the planet (i.e. g) you are in.

Regarding using "ma%" - I have never seen it and it would be confusing, especially since "ma" will probably be interpreted as the unit "milliannum" which is weird. Using "mass%" would be better, but "wt%" is only 3 characters compared to 5 so there's the issue of laziness. I have seen papers using "mass%" and that's fine, and I wouldn't object to such usage if I were to review a paper.

That said, geologist often weigh rocks. Yes, the numbers are mass. But the action itself is "weigh". Go figure.


Did temperature for the US state of Illinois reach an all-time record low 1/31/2019? The State Climatologist Office for Illinois says the all time low temperature of Illinois was -36 °F, with a report of -37 °F in 2009 being disqualified.

This morning, the station Sinnissippi Point reported:

  6:00 AM -37.6 °F
  6:15 AM -37.8 °F
  6:30 AM -38.3 °F
  6:45 AM -38.5 °F
  7:00 AM -38.4 °F
  7:15 AM -38.9 °F
  7:30 AM -38.7 °F
  7:45 AM -39 °F
  8:00 AM -37.7 °F

Galena was slightly lower reporting:

  6:48 AM -39 °F
  6:53 AM -39 °F
  6:59 AM -39.2 °F
  7:04 AM -39 °F
  7:09 AM -39.2 °F
  7:14 AM -39 °F
  7:19 AM -39 °F

and other stations (such as North Fork Plum River: -36.8 °F; Hawkeye Observatory: 37.4 °F) are reporting temperatures near -37 °F.

Was a new record set this day? Or is there some reason to disqualify or consider unofficial today's reports.

The record is unlikely to change, at least based on the particular measurements provided in the initial question.

According to the Illinois State Climatologist Office at the link you provided, the -37°F temperature record was discarded for lack of quality assurance: "However, that observation came from a small airport station designed for aviation purposes and was not part of the climate network in Illinois. As a result, the data were not always archived and no quality control procedures were applied to the data."

From the URLs in your question, the recent weather observations you refer to exist within Weather Underground's network of personal weather stations. In other words, they are often relatively inexpensive sensors that are owned and maintained by private individuals, and their measurements will not have the accuracy required to be included in the official temperature records for the state. The actual temperature at the Sinnissippi Point station may or may not have been colder than Illinois' verified lowest temperature, but without additional info (e.g. knowledge of specific instruments/sites and operator, as implied in the answer by @DavePhD) the official record will not change based on that measurement.


Frost in trees in the middle of summer (of 536) It was so cold that frost formed inside trees in the middle of summer.
Traces of this have been found in Russia, among other places. It is very rare for trees to freeze internally during the summer.

The long, harsh Fimbul winter is not a myth
How would this freezing leave a "trace"?

Frost leaves a record by damaging the cell structure, creating a "frost ring". Hadd et al discuss data on frost rings in N. American trees.
There is specific discussion of the Fimbul event (in AD 536) in this paper by Helama et al. 2019 (unfortunately with a pay wall). There is also discussion that there may have been a similar event in 1627 BC.
If the data is good enough, it may be possible to get an estimate of the time of year at which the damage occurred by looking at the structure of the damaged cells and seeing how it fits with what is known about the annual cycle of cell growth. This requires more detailed analysis than the widely used approach of measuring ring thickness to estimate annual mean (or growing season mean) temperature.
There is more recent information on ultra-cold summers in the Northern hemisphere, the "year without winter".


Is it possible to see Auroras from the equatorial region? I thought Auroras are only visible in the North Pole and South Pole, but recently, I found out that Auroras can be seen in areas of the world closer to the equator.

An example is that in the year 1909, a great storm of Auroras were seen in Japan and other countries.

This made me wonder: could an Aurora be seen in equatorial regions, too?

Quoting from the Wikipedia article on the Solar Storm of 1859;

  On September 1–2, 1859, the largest recorded geomagnetic storm occurred. Aurorae were seen around the world, those in the northern hemisphere even as far south as the Caribbean; those over the Rocky Mountains were so bright that their glow awoke gold miners, who began preparing breakfast because they thought it was morning.[2] People who happened to be awake in the northeastern US could read a newspaper by the aurora's light.[4] The aurora was visible as far from the poles as Cuba and Hawaii.

So, it didn't quite make it to the equator, but it came very close.  There is no physical reason why you can't get aurora at the equator, but it takes a lot of very energetic particles being ejected by the sun over a brief period.

However, as I mentioned in my comment, a solar storm of that magnitude would wipe out most of the Earth's electric grids.  Even the telegraph systems of the 1800's couldn't survive.  Another quote from the Wikipedia article;

  Telegraph systems all over Europe and North America failed, in some cases giving telegraph operators electric shocks.[6] Telegraph pylons threw sparks.[7] Some telegraph systems continued to send and receive messages despite having been disconnected from their power supplies.[8]


What is the difference between subvolcanic rocks and plutonic rocks? I'm studying Plutonic (Intrusive) rocks and I really don't understand the difference between Plutonic Rocks that form in Sills and Dikes from the so called  subvolcanic rocks, also known as a hypabyssal rocks. Aren't they the same? Why?

Main difference between a subvolcanic verses a  plutonic is depth at which the rock solidified at from its molten state.  Plutonic implies a depth greater than subvolcanic by definition but I am sure there is some overlap between shallow end of plutonic and subvolcanic.  Depth of emplacement for plutonic would mostly be much greater than 2 km.

Plutonic is an igneous rock formed by solidification at considerable depth beneath the earth's surface.

Subvolcanic rock, also known as a hypabyssal rock, is an intrusive igneous rock that is emplaced at medium to shallow depths (<2 km) within the crust.


Why isn't the acceleration of an object in Earth's gravity related to the object's mass? Why isn't the acceleration of an object in Earth's gravity related to the object's mass?

Please, try to explain this effect without physical formulas, but using only logical formulation.

This is clearly related to Newton's 2nd law, but since you have asked about the phenomenon rather than the formulas, a Physics SE user explained much better than I can possibly can:

  (..) the gravitational force is different on different masses. Half
  the mass only has half the weight, so it is also only pulled in half
  as much by gravity.

  What gravity does is to pull in every single "particle" equally. If
  there are double as many "particles", then the pull in each is still
  the same and each accelerates the same amount.


Movements of the tectonic plates - collison between Indian Plate & Eurasian Plate I am a high school student, my question is about the collision between the Indian Plate and the Eurasian Plate. When this happens what happens to the area of the Asian continent. Does it increase or decrease? Also, south Asia gets Monsoon rains, is this an effect of this collision?

As the continental crust is too buoyant (light) to be subducted, when two continents collide they smash against each other creating a mountain range, in this case the Himalayas.
This process happen trough thrusting and folding of the plates, leading to something called lithospheric shortening. Which basically means that the plates (lithosphere is the stuff of which plates are made of) gets shorter. In other words: the area of the colliding continents gets smaller. And the missing area is used to build up the mountains by thrusting and folding, a process that is nicely illustrated by the following animated GIF that I put together from a video by the Department of Earth Sciences of UC Santa Barbara.

In this question, this process is also discussed.

In regard  of the Monsoon, it is not a direct consequence of this collision. But it is due to the fact that Eurasia is a big continent close to the equatorial Indian ocean. Now, as this collision helped to put together Eurasia and bring it closer to the equatorial Indian ocean in the area associated with the Monsoon, you can argue that played a significant role in creating the Monsoons as we know them.


Looking for evidence against some points raised in Ivar Giaever's speech on climate change I just listened to Ivar Giaever's speech on the climate change, and he raised following points which seem significant to me:

Temperature differences y/y are very small compared to natural
variation during the year, and the trend we see could be statistical
illusion, especially that the scientists who developed the method
were looking to demonstrate exactly that sort of trend.
The correlation between CO2 emissions and measured
temperature changes is not perfect.

Can anyone provide evidence to mute those points?

Ivar's graph is mischievous in trying to imply that there should be an exact correlation. The global air temperature is not a good parameter to chart against CO2 emissions because the increasing heat doesn't just warm up the air. Most of the heat goes into warming the upper layers of the oceans, but it is not a linear relationship. The ratio of air and ocean warming varies massively with the state of ocean current, in which El Nino is just the largest of several ocean oscillations. If, instead of graphing the global air temperature, he graphed the global heat absorbtion, he would have arrived at a much more uniform relationship to greenhouse gas emissions.
Ivar is an engineer and a physicist, not a climate scientist, and his inability (or unwillingness) to look at the holistic picture makes me doubt his climate change credentials.


What is meant by Global-warming Potential (GWP)? I was under the impression GWP (global-warming potential) is the measure of a gas' impact on global warming, in comparison with CO2.

E.g. methane has a GWP of 86 over 20 years - Wikipedia

Comparing paper and ceramic cups for GWP, this article (page 24) shows GWP in kilograms. Does this make sense to show GWP in kg? Can anyone explain why?

Rather than using the GWP as a ratio, they are expressing the GWP as compared to a release of $\ce{CO2}$ with equivalent radiative effects.  To use their numbers use the mass they give you and a GWP ratio of 1 for that mass (as if it were carbon dioxide).  From what I've seen for chemical industry sales and marketing literature it is fairly common that they express GWP this way in units of "$\ce{CO2}$ equivalent".

In other words, they are saying whatever their product is made of and its production methods have the same radiative forcing as $x$ kg of $\ce{CO2}$.


How is geological time divided into units? Earth's history is divided into eons, which are divided into eras, which are divided into periods etc. Consecutive time units differ in their geology and/or fossil species. But what events are the basis for dividing time into discrete bands?

Roughly speaking (forgive the approximation), the Hadean is the time before life, the Archean is the subsequent time before eukaryotes, the Proterozoic is the subsequent time before complex multicellular animals, and the Phanerozoic is the time since then. Yes, I know that the actual definitions are in terms of either what can be seen in the rocks or a certain number of Mya; and yes, I know the Ediacaran biota technically lived in the late Proterozoic; but, if I've understood correctly, the reason we separate these four parts of Earth's history is because of such distinctions. We can similarly divide the Phanerozoic into three eras based on the P-T and K-Pg mass extinctions. (However, the other three of the Big Five extinction events define the start of new periods rather than eras.)

Is there a more thorough list than this of the qualitative events and processes in Earth's history that motivate the specific ways we've defined eons, eras and periods? I realise there may be some arbitrariness in it, e.g. the fact that some mass extinctions "only" start a new period instead of a new era. However, I'll be satisfied with a summary of the key moments on which these divisions are based.

The divisions in the geologic time scale have evolved over time.
Its origins can be traced back to Nicolaus Steno in 1669 described two basic geologic principles.

The first stated that sedimentary rocks are laid down in a horizontal manner.
The second stated that younger rock units were deposited on top of older rock units.

Work by James Hutton, Charles Lyell and William Smith helped define "principle of uniformitarianism". This work led to definitions in the Mesozoic and Paleozoic eons in Europe and Great Britain.

The Mesozoic and Paleozoic eons helped define the extinction events reflected in the fossil record. It was these correlations that led to the discovery of the extinction events and not the other way around.

Radiometric dating based on the work of Clair Patterson added absolute ages to the time scale.

Over time, the process of grouping together or splitting apart rock units  has grown more sophisticated as better dating techniques have been introduced and more data from mapped rock outcrops have been collected analysed.

References:

http://www.ucmp.berkeley.edu/exhibit/histgeoscale.html

http://www.sepmstrata.org/page.aspx?pageid=22

http://evolution.berkeley.edu/history/radiometric2.shtml


Obtaining hourly weather data, including direct and diffuse insolation I really need some reliable measured hourly weather data for a few sites across the world. It needs to include solar diffuse and direct values or their equivalents.

I've tried the usual sources: Met Office, Weather Underground and Weather Analytics but none of them provide what I need. They are either not hourly, don't contain solar radiation, or have difficult licence/ access restrictions. This is for some research to determine if there's any relation between position of sun, temperature, relative humidity, wind speed and direction. So I'd need a couple of years data for a couple of locations. Aggregate data isn't much use I'm afraid.

If reanalysis data (ERA, ECMWF, CSFRR) is too aggregate for you, try looking for the datasets used to calibrate photovoltaics models (PVGIS, PVWATTS and the like) - they include both direct and diffuse insolation.

Also, follow the citation trail for papers that describe the calibration of the PV models, and the reanalysis models - some of the datasets you are seeking will be somewhere in that trail.

Barry Carter has pointed you at the NOAA ISD-Lite dataset, and I'd like to extend that pointer to the whole Integrated Surface Data from NOAA, which is enormous: 20,000 global stations. Because it's an amalgamation of many different sources, they don't all share the same metadata, but this pdf lists the breadth of the metadata: the insolation variables are on pages 64-77.


Iron-nickel phase in pallasite meteorites I have recently been learning and researching about meteorite types and classification. Pallasites are mainly composed of a 'solid-solution' of olivine crystals and an iron-nickel alloy. My question is: what is the phase of the iron-nickel alloy, in a body-centered cubic crystal structure (alpha-iron, and hexahedrites) or face-centered cubic?

First, a correction. A solid solution is between different compositions in the same phase. For example, olivine is a solid solution of forsterite (Mg2SiO4) and fayalite (Fe2SiO4).
There are two common iron–nickel alloys found in meteorites (pallasites and others): kamacite and taenite. They are commonly intergrown into lamallae called "Widmanstätten pattern". It looks like this:

Kamacite has up to about 10% nickel, whereas taenite can get up to ~60% nickel, but commonly found up to 30%.
Kamacite has the space group Im3m, making it hexoctahedral body-centered. Taenite has the space group Fm3m, making it hexoctahedral face-centered.


What effect does climate change have on the Earth's rotation? I recently read a blog entry from a leap-second expert explaining that in near term (i.e. last 3 years) the Earth has been spinning ever so slightly faster, delaying the need to insert a leap-second (that accounts for the Earth spinning at a different speed than once per 24 * 60 * 60 seconds).
That got me wondering what effect Climate Change might have had on the spin of the Earth over the last century, and into the next.
I reasoned that melting ice caps would bring mass closer to the centre, lowering the moment of inertia and speeding up the spin (which was a silly thought - see comments).
But then I reasoned that warming oceans would lower the density of water, pushing the mass away.
Then I realised I had no idea what effect of the changing atmosphere might have.
I came away knowing I had a very poor understanding of the problem.
What predictions do the scientific models make about the effect of climate change on the previous rate of gradual slowing of the Earth's spin?
[Note: This is an idle curiosity question from a non-expert. Please tailor your answering efforts appropriately.]

The only answer I can come up with is related to isostasy.
1 - Poles melt, so there's more water in the oceans.
2 - As there's more water in the oceans, there's more weight on the oceanic crusts, so they bend, making deeper some parts of the oceans.
3 - The parts of the ocean that are deeper are in the centre of the oceans, far from continental crust. It should be mainly the Pacific Ocean, Indic and Atlantic, but not near Antarctica, as this area is continental crust (lighter) and will be also unloaded from ice.
4 - As a result, the shape of the Earth crust becomes a bit longer in N-S direction.
5 - As the mass of the Earth is closer to the rotation axis, it accelerates the spin.
Lithospheric density is approximately 2.5 times that of water, so amount of water in the ocean isn't as important as crust flexion.


Is there a reliable way to identify regions with negatively-correlated winds? When examining the potential for large-scale electricity grids, and when identifying the lowest-cost ways to generate clean electricity, a recurring theme is of spreading wind generation across a wide-enough area that it evens out.

One way to bring down costs a lot, is to combine on the same grid, regions where the wind over a period of weeks to years, are negatively correlated: that is to say, it helps if we can easily identify pairs of regions where low winds in one region tend to happen at the same time as high winds in the other.

At a scale of days, sufficiently distant regions are uncorrelated. At a scale of weeks to years, a set of correlations of reanalysis data (e.g. ECMWF or CFSR) suggests that there are pairs of regions which do exhibit negatively correlated wind, either seasonally or annually.

Is there a reliable way to identify such combinations of regions?

My suggestion would be to do a Principal Component Analysis (PCA) or Empirical Orthogonal Functions (EOF) analysis on the wind data. The result of the analysis would be a set of modes of variability. You would be looking for modes that show areas that are large in magnitude but out of phase. As for the time scale, you need to check the eigenvectors and eigenvalues of the analysis to determine the scale of temporal variability.

You can find appropriate code in many places, for instance here.


Why do winter temperatures account for most of the increase in global temperature? If you examine the detailed temperature records that form the basis for our understanding of global warming, there are some strange anomalies (at least from a naive point of view where warming affects everywhere equally).
For example, by far the largest temperature increases are confined to winter months in the northern hemisphere. As one commentator has it:

Winter months in the Northern Hemisphere are responsible for most of the observed land warming in CRUTEM4.  The summer months (June, July, August, September) essentially show no warming at all from 1850 to 1990. Overall,  NH winters have warmed about twice as much as  NH summers.
...The same exercise for the southern hemisphere shows very little difference where of course the seasonal months  are inverted.

Is there a sensible explanation of this effect? Is it reproduced, for example, in climate models?

Energy balance in the winter is highly dependent on the total amount of area covered by snow or ice.   Snow increases the albedo of the Earth which directs the short-wave radiation from the Sun back to space, stopping it from being absorbed by the Earth.  Winters with minimal snow/ice cover effectively allow more solar radiation to be absorbed by the Earth.   Depending on the winter, the amount of snow cover can be quite different from year to year, which can cause great variability in temperature.   In contrast, summer months generally have more stable temperatures because snow cover is less dynamic during those months, and there is roughly the same total solar radiation absorbed from year to year.


How significant is a 5-10 mb drop in pressure over a 20 minute period? I would be interested in seeing how significant a 5-10 mb drop in pressure would be at the surface, and 80 m in the air. The temporal scale would be 20 minutes. If the pressure starts to steadily increase after the drop in pressure, would this hint that the instruments are measuring data incorrectly, or is there something else at play?

On the synoptic scale (thinking along the lines of cyclones, weather fronts etc.), then that's a pretty significant drop in that amount of time.

A bomb or explosive cycogenesis in meteorological terms is defined as a drop of at least 24mb in 24 hours, so your observation easily fits this description of being a significant rapid pressure change. There's a list of similar events here.

You ask what the significance would be at the surface, and only 80m up, which makes me think you might be talking about smaller scales (perhaps?), in which case @naught101 is right in suspecting small scale eddies from buildings could be causing the surprising readings. 80m isn't really going change the significance of an observation that much on synoptic/meso -scales.

Sources:

http://glossary.ametsoc.org/wiki/Bomb

Synoptic-Dynamic Climatology of the "Bomb"


How long to melt all the polar ice? The answers to this question say that the sea level will rise 66m if all the polar ice, etc, melts.

How long will this take?

Transporting incredible amounts of heat energy to the poles and injecting it into the ice, a good insulator, so that it melts must be very, very slow. The Netherlands, London, and all the rest will be long gone for other reasons, I imagine, long before it could be completed.

I am looking for an order of magnitude minimum under which it is provably impossible for the ice to all melt any faster.  Wild and crazy assumptions are welcome, so long as they err on the side of making the ice melt faster than it would in reality - that way the estimate will always be a minimum.

The question is requesting an answer that has no practical application. So rather than improving on some hypothetical calculation, I will describe the problem and hopefully make the difficulty providing a real answer to a time frame clear.

First: "polar ice" Antarctica is located in a polar position and consists of a multi-km thick ice sheet. The Arctic is covered by sea ice except for smaller glaciers and Greenland, which is not located in a polar position equal to Antarctica. One has to remember that Antarctica is circulation-wise isolated from the rest of the planet by circumpolar circulation, both in th esea and atmosphere, a situation not met in the Arctic. Hence the term polar ice is very fuzzy and should be avoided. It is better to speak about the objects directly.

Second: an ice sheet such as Greenland and Antarctica is not a stagnant sheet of ice, it has its own dynamics and which can change over time depending on forcing and change in forcing.. Greenland is largely land based but with outlet glaciers that terminate in the sea. Although mass loss through these have seen an increase in loss, much of the Greenland mass gain and loss is through surface mass balance (snow accumulation minus ablation, melt). Antarctica is a different beast since East Antarctica is largely land based while West Antarctica is to a large extent sitting on ground below (in places several km) below sea level. Te latter situation is more unstable since the ice could disintegrate by calving (loss through ice berg formation), a process which is potentially much quicker than surface melt (of which there is currently very little in Antarctica). So one part of Antarctica is much more unstable than the other.

Now, several other processes are at play. Ocean currents are sen to produce massive amounts of submarine melt on both Greenland outlet glaciers as well as on the sea-terminating edges of Antarctica. In places, circulation models estimate up to equal loses by calving an submarine melt. This occurs at the same time as there is hardly any surface melt to speak of. So calculating mass loss by surface melt is clearly a lost cause when calving and submarine melt dominate.

Finally, in this still simplified picture, the dynamic response of the ice sheets to changes in forcing is not well understood. This means we do not know how unstable East Antarctica really is. That Antarctica will totally disappear seems very unlikely any time soon and time frames of 10^3-10^4 years is a minimum. Greenland, not being a polar ice sheet is more sensitive in that as it loses mass it is also on average lower in altitude, experiencing more melt. There appears to be a point of no return for Greenland, under which elevation the ice sheet would not be able to recuperate unless the climate cooled significantly. Again the time to melt off the ice is long.

despite the seemingly slow increase in sea level, much infra structure  in the coastal environments is threatened by only dm to m changes in ea level so the 66.1 m quoted from IPCC is not something that will happen in a life time but that does not mean the rates are not already problematic.

As a PS, I will add some relevant references once I am back home in case someone misses them at the moment.


Is there any information on the height of waves near New Zealand resulting from today's M 8.1 Kermadec Islands earthquake? The video in this tweet shows the small wave produced at Tokomaru Bay in New Zealand following the  M 8.1 - Kermadec Islands, New Zealand 2021-03-04 19:28:31 (UTC) event. These are so far the only thing I've seen in terms of "data" on waves produced by the quake.
Warnings went out and people did rapidly evacuate low elevation coastal areas as a precaution.
Question: Are there any potential measurements of any transient sea-level changes via buoys or perhaps even satellite (e.g. radar, laser), either likely very small ones out at sea or larger ones nearby the coast where the height would be amplified?
Or is all information going to be basically anecdotal?
The data doesn't necessarily have to be available yet, I'm just curious about what measurement capability exists.

Norfolk Island experienced a tsunami wave 64 cm tall. In Australia the tsunami wave was 10 cm at Tweed Heads and 9 cm at Port Kembla. In Vanuatu the height was 32 cm and in Fiji 13 cm  and 8 cm in Tonga.
Australian Burea of Meteorology report
TSUNAMI DETAILS:
The following sea level gauges have observed a tsunami, heights refer to wave
amplitudes (positive wave values):
Name                  Country       Lat     Lon      Height (m)  Time (UTC)
East Cape             NEW ZEALAND   37.50S  178.17E  0.15        04 MAR 2210
Nuku'Alofa            TONGA         21.10S  175.20W  0.06        04 MAR 2115
Suva Viti Levu        FIJI          18.10S  178.42E  0.13        04 MAR 2200
Rarotonga Wharf       COOK ISLAND   21.20S  159.79W  0.08        04 MAR 2200
Kaingaroa Chatham Is  PACIFIC OCEA  43.70S  176.27W  0.22        04 MAR 2320
Norfolk Island.       AUSTRALIA     29.10S  167.95E  0.64        04 MAR 2245
Port Villa            VANUATU       17.80S  168.31E  0.32        04 MAR 2320
Ouinne                NEW CALEDONI  22.00S  166.83E  0.2         04 MAR 2320
Tubuai                FRENCH POLYN  23.30S  149.48W  0.06        04 MAR 2305
Port Kembla           AUSTRALIA     34.50S  151.00E  0.15        05 MAR 0205
Mare                  NEW CALEDONI                   0.15        04 MAR 2330
North Cape            NEW ZEALAND                    0.15        04 MAR 2130
Great Barrier Island  NEW ZEALAND                    0.20        04 MAR 2240

See also [1], [2] & [3]


How old is Earth's groundwater? In my house, we drink the groundwater that we get from our well. It is 40 meters deep. The question is, how old is the water that we drink today? Is it from the rain 100 years ago?

Another issue is, today much pesticide is used. Someday they will diffuse down to the underground 40 meter. How long will it take?

The age of groundwater can vary over a large span. The moment a drop of rain enters the ground it becomes groundwater and when it reaches the groundwater table, the water starts to flow towards a lower hydrostatic level, usually towards the sea, a river or a lake. If you have a well, you'll pump up water to lower the hydrostatic level near the well, so that local groundwater will flow towards the well instead of the ocean.

The velocity of the flow depends on a number of parameters. Naturally, the distance from the recharge area, the hydrostatic pressure, that is the elevation difference over the flow, and finally but not least important, the permeability of the soil and rocks it flows through. If the ground consists of e.g. porous sand, gravel from outwash planes or very fractured rocks the water will flow fast towards a lower level, but if the ground in impermeable, eg. shale or igneous rocks without cracks, the flow will be much slower.

If you have sandy ground, and shallow groundwater table, the pesticides will reach the groundwater table in very short time (maybe days?), if the aquifer is covered by clay, it might take millennia. It also depends on the unsaturated zone and the mosture above the groundwater table.

So, unfortunately, it's impossible to answer your question(s) without more information. Shallow groundwater is typically from zero to a couple of hundred years old. Some thousand years are not uncommon and for deep aquifer (that have little hydrostatic pressure reason to flow towards an ocean). It can be millions or even billion years old.

The age of groundwater can be detected by Carbon-14 decay or by measuring known contamination, eg. CFCs, depending on the age range.

If you are worried about contamination of you your well, apart from analyse the water, I'd make some sketches of the groundwater flow, e.g. map nearby rivers (river surface = groundwater surface) and the hydrostatic level (well water surface) in your well to find out what direction the water and contamination flow. If the contamination is between you and a river, the best guess would be that the contamination flows away from you, but if you pump up alot of water, the gradient of the groundwater table might change and the contaminations flow toward your well instead of the river.


What percent of the Earth's core is uranium? What percent of the Earth's core is uranium?  And how much of the heat at the core is from radioactive decay rather than other forces?

Good question! Geochemists and geophysicists agree to disagree, sometimes quite strongly. There are also disagreements within each group as well as between the two groups.
It's not just uranium. There are four isotopes whose half-lives are long enough that they can be primordial and whose half-lives are not so long that they don't produce much heat. These four isotopes are

Uranium 235, with a half-life of 0.703 billion years,
Potassium 40, with a half-life of 1.277 billion years,
Uranium 238, with a half-life of 4.468 billion years, and
Thorium 232, with a half-life of 14.056 billion years.

The consensus view amongst geochemists is that there is very little, if any, of any of these isotopes in the Earth's core. Potassium, thorium, and uranium are chemically active. They readily oxidize. In fact, they readily combine chemically with lots other elements -- but not iron. They are strongly lithophilic elements. Moreover, all three are "incompatible" elements. In a partial melt, they have a strong affinity to stay in the molten state. This means that relative to solar system abundances, all three of these elements should be strongly enhanced in the Earth's crust, slightly depleted in the Earth's mantle, and strongly depleted in the Earth's core.
Geophysicists look at the amount of heat needed to drive the Earth's magnetic field, and at the recent results from neutrino observations. From their perspective, the amount of residual heat from the Earth's formation is not near enough to drive the geomagneto. The growth of the Earth's inner core creates some heat, but not near enough to sustain the geodynamo. Geophysicists want a good amount of heat flux across the core mantle boundary to sustain the geodynamo, and to them the only viable source is radioactivity. Recent geoneutrino experiments appear to rule out uranium or thorium in the Earth's core, but not potassium 40. The neutrinos generated from the decay of potassium 40 are not detectable using current technology.