Thursday, July 12, 2007

How well can we model pressure broadening?

The mice clamored for actual examples of pressure broadened lines and how well they could be fit. This is a fairly specialized area, and papers appear in a very small number of journals, principally the Journal of Quantitative Spectroscopy and Radiative Transfer, the Journal of Molecular Spectroscopy, Molecular Physics and Applied Optics. Eli went and downloaded some papers from JQSRT about line broadening in CO2.

These are two examples from a diode laser spectrum of L. Joly, et al., "A complete study of CO2 line parameters around 4845 cm-1 for Lidar applications. JQSRT (2007), doi:10.1016/j.jqsrt.2007.06.003. The spectrum and the fit are shown in the top panels the residuals are shown in the bottom two panels for Voigt and Rautian profiles respectively. In this case the Rautian is better than the Voigt. In both cases the P12 line of the (201) <-- (000) transition is shown, on the left at 70 mbar, 292 K, on the right at 564 mbar, 291 K. Note the different scales on the frequency axes. The scale for the spectrum on the right is four times larger than for that on the left.











Next we can look at an example from V. Malathy Devia, D. Chris Benner, M.A.H. Smith, and C.P. Rinsland, "Nitrogen broadening and shift coefficients in the 4.2–4.5-m bands of CO2" JQSRT 76 (2003) 289–307 showing 20 calculated spectra (bottom panel) and the residuals between the calculated and observed spectra (upper panel). This includes self broadening and broadening due to N2. The cell has a mixture of 12C and 13C CO2. In this case Voigt profiles were used. The largest line is P(30) for the 12CO2 (001) <-- (020) band. There is also an R(28) line from 13CO2. The broadening depends on the rotational quantum number, the and the pressure. Details can be found in the paper and are included in HITRAN.

Wednesday, July 11, 2007

AlGorithms

There is a long history of Al Gore being right on many issues and being ridiculed for it. Such things are known as AlGorithms and are recited at night by good little girls and boys in the right households. Bob Somerby has been howling almost daily about this, visit his incomparable archives and read some of his many posts about the quintessential AlGorithm, the INTERNET story.

Previously we had discussed how a falsification in Byrnes review of "An Inconvenient Truth" provided the heavy artillery she used to attack Gore. Rather free form discussion broke out here, at Stoat and Deltoid. Big City Liberal has used the opportunity to post a pin up picture of Richard Tol who is the most serious of Byrnes' defenders.

Here we report on one of Kristen Byrnes' many AlGorithms.

Next, Al gets right to business showing some of the worlds receding glaciers. According to the national Snow and Ice Data Center, most glaciers around the world are receding. But when you look at scientific studies on individual glaciers you begin to understand that temperature is not always the cause and that all of the glaciers that Al mentions have been retreating for over 100 years.


There is then a paragraph about Kilimanjaro and one about the Grinnell Glacier. Kilimanjaro I leave to Ray Pierrehumbert who explains why Ms. Byrnes really should have RTFRs she provides before opining. But in both cases and in the case discussed below, a major part of the refutation is that CO2 mixing ratios and temperatures did not start increasing 100 years ago. The graphs in Eli's previous post show that CO2 concentrations started rising about 150 years ago, accelerating in the past 50 and one can say roughly the same about global surface temperature anomalies (yes we know that aerosols arrested the warming btw ~1940-70). Ms. Byrnes continues
Himalayas - Glaciers have been found to be in a state of general retreat since 1850 (Mayewski & Jeschke 1979). In this section he also claims that 40% of the worlds population gets half of their water from streams and rivers that are fed by glaciers. This is an easily confused claim. Rivers that are fed by the Himalayas get most of their run-off from the spring snowmelt. They also have many dams that ensure that water will be available during dry months.
Gore wrote in "An InconvenientTruth" (The tech squad finds it easier to quote from a book)
The Himalayan Glaciers on the Tibetan Plateau have been among the most affected by global warming. The Himalayas contain 100 times as much ice as the Alps and provide more than half of the drinking water for 40% of the world's population -- through seven Asian river systems that all originate on the same plateau.

Within the next half-century, that 40% of the world's people may well face a very serious drinking water shortage, unless the world acts boldly and quickly to mitigate global warming.
The seven rivers are the Indus, Ganges, Brahmaputra, Salween, Mekong, Yangtze and Yellow. Geographers can argue about where the plateau starts and ends, how many people use the river water, what percentage comes from melt, and other details, but we read in the IPCC WG II Summary for Policymakers says:
Glacier melt in the Himalayas is projected to increase flooding, and rock avalanches from destabilised slopes, and to affect water resources within the next two to three decades. This will be followed by decreased river flows as the glaciers recede. * N [10.2, 10.4]
The full report is not yet available (there is a story there, as the meeting that lead to the SPM for WG II was particularly contentious with the US and China demanding many changes to soften the impact.). From a draft of the Technical Summary we read that scientists are highly confident that global warming will make water shortages a major issue for Asia in the next 100 years especially because of rapid melting of glaciers.

The Himalayan glaciers will melt even more rapidly then they currently are (which is fast enough, see below) because of increasing temperatures. At first there will be increased flooding and avalanches which will interfere with water supplies as the glacial water floods down onto the plains. Once the glaciers are all or mostly gone the river flow will seriously decrease.

McClatchy News Service reports the IPCC has said that
"Glaciers in the Himalayas are receding faster than in any other part of the world and, if the present rate continues, the likelihood of them disappearing by the year 2035 and perhaps sooner is very high if the Earth keeps getting warmer at the current rate," the report said. The total area of glaciers in the Himalayas likely will shrink from 193,051 square miles to 38,600 square miles by that year, the report said.
in Geography News from January of this year
Glaciers of the Himalaya Mountain Range are an enormous reservoir of fresh water and their meltwater is an important resource for much of India, Bangladesh, Pakistan, Nepal, Bhutan, China and Burma. A team of Indian scientists lead by Anil V. Kulkarni of the Indian Space Research Organization, studied surface area coverage for nearly 500 glaciers in the Chenab, Parabati, and Baspa basins using satellite data collected between 1962 and 2001.

They documented that most of these glaciers have retreated significantly. In 1962 a total of 2077 square kilometers was covered by glaciers and in 2001 that area was reduced to 1628 square kilometers. This represents a deglaciation of over twenty percent over a forty year period.
They also learned the the number of glaciers actually increased in this area. The increase in count was caused by fragmentation. Climate change was blamed for the decrease in sustainability for these Himalayan glaciers.
The paper itself concludes:
The observations made in this investigation suggest that small glaciers and ice fields are significantly affected due to global warming from the middle of the last century. In addition, larger glaciers are being fragmented into smaller glaciers. In future, if additional global warming takes place, the processes of glacial fragmentation and retreat will increase, which will have a profound effect on availability of water resources in the Himalayan region.
The threat is so large that India and China, sort of the Michael Mann and Steve McIntyre of countries, have agreed to cooperatively map the glacier melt on the Tibetan Plateau, an area both of them consider to be of the highest strategic importance, often close to outsiders for security reasons, have fought wars over and frequently use to engage in small and larger armed battles.

*The map is from www.globalwarmingart.com.

Monday, July 09, 2007

Ponder the Maunder

Tony at Deltoid points to a web site put together by a young lady, Kristen Byrnes, in Portland as a refutation of the IPCC AR4.

I'm disappointed no one talked about "Ponder the Maunder", the extra credit assignment of a 15-year-old student that rips one in the global warming scam. It just goes without saying that a school project is far more trustworthy than anything coming out of the IPCC. James Hansen is paid lots of money!
Richard Tol is a great fan thinking her more accurate than the Stern Report and Inconvenient Truth.
If a 15-yr-old can punch tiny holes, then all credibility is gone. Anyone who does not want to believe Al Gore's message, just has to point to Kristen Byrnes and say "ha ha, he cannot even hold his own against a school kid". Debate over.
Ms Byrnes is now using her new found popularity to establish the Kristen Byrnes Science Foundation. This being the case, google first lead Eli to the Kristen Byrnes Science Foundation review of an Inconvenient Truth, as good a place to start as any. A key point in Ms. Byrnes' argument is that
Al then shows global temperatures for the past 100 years using a graph similar to the one below. “In any given year it might look like it’s going down but the overall trend is extremely clear” I’ve added the green line, which is CO2. What Al does not show you is that most of the warming started before the CO2 increase. He also fails to mention the cool period between 1944 and 1976 does not correlate with greenhouse theory; the globe should have been warming at that time
Each of the large divisions on the right of Ms. Byrnes' graph would correspond to about 20 ppm CO2. Now that green line looked awfully familiar to the bunnies, a flat line with a little bump to the left and a sharp rise to the right, so we started looking for graphs of CO2 concentrations as a function of time, and we found this one in a pretty good presentation by Steven Schwartz (PS it is also in the TAR, but not nearly as prettified.)The shape of the CO2 mixing ratio that Ms. Byrnes added is the same, the only problem is that her curve starts in 1880, using the data from 800. A millenia among friends is not a big deal, but if you look at the curve immediately above you see that the CO2 mixing ratio actually started to rise ~ 1800 not at 1940 as in Ms. Byrnes' addition, which she specifically says she added by herself.

It is worth spending a minute or two with the actual CO2 rise. The first part of the rise comes from land use changes, particularly the settlement of the American west, and parts of South America and Australia. Industrialization only starts to bite about 1850-1900, a point that is often lost.

Finally we can look at the relationship between CO2 mixing ratio and global surface temperature anomaly in a figure from the Pew Center on Climate Change



So unfortunately we are left with a number of questions about the source of this error, upon which the edifice is built and is this astroturf?

For a discussion of Ms. Byrnes' cherry picking on the slopes of Kilimanjaro, there can be no better read than Ray Pierrehumbert's discussion of tropical glacier retreat.

UPDATE: Hans Erren rightly points out that Eli, lazy Rabett that he is, has copied graphs showing the concentration of CO2 to compare with global temperature anomalies rather than the CO2 forcing which is proportional to the logarithm of the concentration. Bad bunny. Steven Schwartz's presentation linked above has the appropriate information

Sunday, July 08, 2007

High Pressure Limit. . . .

This is a continuation of playing with Eli's new chewy carrot colored Spectral Calculator toy the mice left in the burrow. A couple of days ago, the Rabetts looked at the effect of pressure, and before that temperature on CO2 bending mode absorption spectrum. Eli remarked on the fact that the peak of the pressure broadened absorption stays at about the same level for a constant volume mixing ratio above 50 mbar total pressure. This means that the peak of the absorption stays the same while the line gets wider, for example at 100 mbar and 1000 mbar total pressure and 380 ppm volume mixing ratio











The mice had a nice chatter about this. Eli wants to use this as a jumping off point.

There are three relevant line widths. The natural line width, which is a measure of the vibrationally excited state radiative lifetime and the associated uncertainty spread in the energy level. For vibrational lines these are sub MHz.

Since spectroscopy goes back and forth between MHz (very high resolution, microwave spectroscopy) and cm-1 (IR, visible, UV spectroscopy) we need an equivalence. Simply divide 1 MHz by the speed of light in cm/sec, 3 x 10^10 finding that 1 MHz is equivalent to 3.3 x 10^-5 cm-1.

The shape of the natural (isolated/no collisions) line is Lorentzian (from Wolfrum Mathworld).
















where the Gamma (the thing like the hangman uses) is the full line width at half maximum (FWHM).

The second linewidth that we have to worry about is the Doppler width. Doppler broadening is a shift in frequency when something (the molecule) is moving towards you (increase) or away from you (decrease). For emission or absorption of light the shift will be wo(1+v/c) where wo is the frequency of absorption/emission in the rest frame, v the speed along the direction the photon moves in and c the speed of light. When you average over all possible directions of molecular motion, this turns out to be Gaussian













We can estimate the Doppler linewidth. The translational energy of the molecule is Et= 3/2 kT, where k is Boltzmann's constant, 1.38 x 10^-23 kg-m^2 /K-s^2. This yields Et= 6.2 x 10^-21 J, but we also know that Et= 1/2 m v^2, so v = sqrt(2Et/m) where m is in kg. The mass of one CO2 (C= 12 g/mole, O=16 g/mole. If you want to do this to four significant figures you don't have the one tru back of the envelope koan) molecule is 0.044 kg / 6.02 x 10^23 molecules/mole and we get that the velocity is ~ 400 m/s.

The speed of light is 3 x 10 ^8 m/s so v/c is 1 x 10^-6. For a 600 cm-1 transition (CO2 bend) this is about 1 x 10^-3 cm-1 or 30 MHz. The Doppler width varies directly with the frequency of the transition, so a transition at 6000 cm-1 would have a Doppler width that is ~300 MHz at room temperature.

Finally the line shape associated with collisional line broadening is also Lorentzian. The natural and collision broadened line shapes can be simply combined by setting the line width equal to the sum of the radiative and collisional terms. The collisional term is proportional to the total pressure in the binary collision limit (atmospheric, unless you deep down in Jupiter). The higher the pressure, the more collisions. Remember this.

Combining the Gaussian Doppler broadening with the Lorentzian radiative and collisional terms is trickier. The solution was first found by Armstrong, and is called the Voigt line profile. However, it should be clear that if the collisional broadening is >> than the Doppler broadening (0.001 cm-1 @ 300 K for the CO2 bend) and the Doppler broadening is >> the natural line width, we can neglect the foofaw and treat the line profile as a Lorentzian whose width is aP where a is a constant for broadening of CO2 lines by air (there is some dependence on rotational state, some non-linear component, but remember this is back of the envelope)

The integral of the Lorentzian profile across all frequencies is unity (1). The total absorption of the line whether broadened or not will be Abs = A PCO2 L where A is the line absorption, PCO2 the partial pressure of CO2 and L the path length. PCO2 = VMR P where P is the total pressure and VMR is the volume mixing ratio.

At line center (substitute x = xo) into the Lorentzian formula the magnitude of the maximum is
The maximum absorption is Abs x L(xo). Substituting for Abs and Gamma we get

Max Abs = 2 A VMR P/pi aP = 2 A VMR/pi a

where pi should be the Greek pi. The absence of Greek letters is annoying. A is the integrated line absorbance for unit pressure, a the linear line broadening coefficient and VMR the volume mixing ratio.

If you go to very low pressures, the Doppler broadening approaches the pressure broadening and this approximation no longer works, but for tropospheric and stratospheric pressures it is fine.

Friday, July 06, 2007

Pinatas!!

Not only excellent wine but Australia has got to be the home of the world's best Pinatas. Jennifer Marohasy brings word of the Lavoisier Group 2007 Meeting to Rehabilitate Carbon Dioxide. Even better, they have posted the presentations!! Have a whack!

Thursday, July 05, 2007

Throwing in the towel

One of the things that you learn is that no one every gives up in public, but it is pretty easy to see when the game is over, people are thinking about picking up their marbles and leaving town. Stoat points to a new article to be published in the Proceedings of the Royal Academy showing that Svensmark and others of the solar driven have no clothes, all indicators of solar activity having fallen while the global temperature rises. Pete DeCarlo has the Nature comment on this. What stands out is the towel being thrown into the ring.

On other timescales however, Sun-climate links may remain worthy of study. "Climate change is a cocktail of many effects," says Jasper Kirkby, a physicist at CERN, the European particle physics laboratory near Geneva Switzerland, who is leading an experiment aimed a simulating the effect of cosmic rays on clouds. "Past climate changes have clearly been associated with solar activity. Even if this is not the case now, it is still important to understand how solar variability affects climate"
UPDATE: The Sloan and Wolfendale paper trashing Marsh and Svensmark, referenced by Tim Lambert is available at the Arxiv. The PRA article is yet to come

NOAA The Fish and Wildlife Service muzzles the polar bears

Michael Tobis has spotted (Michael also points out that it was not NOAA) another case in which NOAA the Fish and Wildlife Service is muzzling its scientists, restricting travel by and limiting what they can say to the administration position. Michael is quite subtle about it.

Scientists representing the Soviet Union traveling overseas were enjoined from mentioning certain technical topics that might reflect negatively on soviet socialism, and were required to refer any questions about those polar bears to their accompanying commisar.
Go read the underlying documents, which among other things say
The Service traveler, Mrs. Hohn, will be participating in an Arctic Council's Senior Arctic Official meeting as a member of the U.S. Delegation, and as the U.S. National Representativte to the Conservation Arctic Flora and Fauna Working Group. This trip will include Mrs. Hohn stopping in Trondheim on the way to Tromso, to confer with the Norwegian CAFF National Representative on the narrower questions of which chapter or chapters of the Circumpolar Biodiversity Monitoring Plan Norway may be able to provide lead or co-lead authors for. There will be no discussion of polar bears, sea ice, or climate change at this meeting. Mrs. Hohn understands the administration's position on climate change, polar bears, and sea ice and will not be speaking on or responding to these issues.

Pressure broadening

Eli has been a happy hare with the new chewy carrot colored Spectral Calculator toy the mice left in the burrow. He is digging out the effects of increasing CO2 concentrations on the greenhouse effect from the spectroscopic point of view. Recent posts on Real Climate by Spencer Weart and Ray Pierrehumbert touched this off, and, of course Motl's folly aggravated the lab bunnies beyond the breaking point. Yesterday Eli looked at the effect of temperature on the CO2 bending mode absorption spectrum. Today we are under pressure. If you don't know much about pressure, you could do a very lot worse than looking at our mob blogging friend Tamino's Introduction to the Gas Laws and his post on Pressure and Height, how pressure varies with altitude.

P(z) = Po exp (-g u z/ kT)

where z is the altitude, g the gravitational constant acceleration due to gravity, u the average mass per molecule, T the temperature and k Boltzmann's constant. As Tamino points out, what we call the scale height is the altitude at which guz/ kT = 1 and the pressure is exp(-1) or 36% of the pressure at sea level, Po. This altitude is ~8.5 km.

We will use the Spectral Calculator to look at this. First, let us look at the 300 K CO2 absorption spectrum (mice wanting to play along should fire up Spectral Calculator and follow the instruction in the preceding post on Temperature
We want to select a couple of lines from this, so after setting all the parameters as before (CO2 gas, the O(16)C(12)O(16) isotopomer, 10 cm cell length, 296K, 100 mbar total pressure, 0.000380 volume mixing ratio CO2) go to the observer page and set the upper and lower wavelength ranges as 680 and 684 cm-1. You will then see this spectrumIf we now increase the total pressure to 1000 mbar (~one atm), keeping the mixing ratio constant the result isand looking carefully (you might have to click on each graph to bring up full screen images) we see that the transmission at each of the peaks in both spectra is ~93% (7% of the incident light is absorbed).

Wait a minute. The volume mixing ratio in both spectra is 380 ppm. The total pressure in the first case was 100 mbar. The total pressure in the second case was 1000 mbar, ten times greater. That means that the amount of CO2 is ten times greater. We can, of course, keep the amount of CO2 constant by decreasing the mixing ratio in the second case to 38 ppm.Transmission at the line centers is not 99.3%!. If we carefully integrated under each peak in this spectrum and the one taken at 100 mbar the integrated amount of absorbed light would be the same, just that the peaks are wider and shorter at 1000 mbar. Total absorption does not increase due to pressure broadening (within limits, see below), but it is spread to a wider range of frequencies /wavelengths.

Finally a bit of ear waving about the origin of the pressure broadening. An isolated molecule's energy levels are shifted slightly when another atom or molecule nears and their electric fields interact. This changes the wavelengths at which molecules can absorb or emit. At low pressures only a relatively few molecules will collide at any instant, and pressure broadening occurs in the so called binary collision limit.

One can order the strength of electric interactions as ion > dipole > neutral. As a general rule, broadening by an ion is much longer range and stronger than broadening by a neutral. Broadening by a molecule with a permanent dipole moment stronger than broadening by one without. O2, because it has a magnetic moment in the ground state (two unpaired electrons) will be more effective as a broadener than nitrogen.

Having simplified all this, Eli will now point to the brier patch where there are lots and lots of nettles to sting you. First, as the molecules pass near to each other, the interaction will mix nearby quantum states. Transitions can borrow strength from each other and the absorption coefficients in each line can change. Second, collisions are of finite duration and range, which has the effect of decreasing intensity in the wings and increasing that at line center. Third, if absorption is observed for a relatively long path length (km) and for a molecule with a relatively high mixing ratio (CO2, H2O) absorption due to broadening can be significant 30 cm-1 or more away from the line center.

Now THAT would be a post.

Wednesday, July 04, 2007

Temperature

The anonymice gave Eli a new Spectral Calculator toy for the Fourth of July, and he wants to use this to talk about CO2 absorption and emission in the atmosphere and how it is affected by pressure, temperature and composition. Today temperature. Tomorrow pressure. and the day after composition. These are prequels to Ray Pierrehumbert and Spencer Weart's Real Climate posts on CO2 concentrations and greenhouse warming. The Spectral Calculator allows a simpler graphical presentation (Eli hopes).

Start by going to the Spectral Calculator

  1. Click on the observer tab
  2. Set the Lower Limit to 620 cm-1
  3. Set the Upper Limit to 720 cm-1
  4. Click on calculate. You have now set the spectrum window to match the CO2 low frequency bending mode spectrum, the mode that is responsible for CO2's greenhouse activity. Don't worry about what appears. Is is the absorption spectrum of water vapor in this window.
  5. Click on the Gas Cells tab
  6. Select CO2 from the Gas drop down menu
  7. Set the Isotopologue to 1 O(16)C(12)O(16). All but a few percent of the CO2 in the atmosphere is in this form, but we are doing this to simplify what follows. You can fool around later by selecting All isotopologues, or one of the rarer ones.
  8. Set the VMR (volume mixing ratio) to 0.000380. This matches the current 380 ppm CO2 atmospheric concentration.
  9. Set the Pressure to 100 mbar. We want to isolate the effect of changing temperature and keep the total pressure relatively low. Remember that the CO2 pressure is the product of the VMR and the Total Pressure
  10. Set the Length to 200 cm. This was chosen so the software serves graphs covering the full scale.
  11. Set the temperature to 200 K (we will change this later) 200 K is about as cold as it gets in the troposphere, during Antarctic winter.
  12. Click on calculate. You should see the following spectrum:
You should click on this to see a larger, clearer picture

The hump on the right is called the R branch and corresponds to a transition where the rotational quantum number in the excited vibrational level is one greater than that in the ground state. The hump on the left is called the P branch for which the rotational quantum number is one less in the excited vibrational level, and the sharp peak in the middle is the Q branch, where the rotational quantum numbers are the same in the upper and lower vibrational levels. This transition is from the ground state, with vibrational quantum number v"=0 to the first vibrational state, with vibrational quantum number v'=1. Call this a (1,0) transition.

The rotational levels in the R and P branch closest to the center Q branch originate in states with the lowest rotational numbers, those furthest away, to the far right-R branch, or the far left-P branch start from the highest rotational quantum numbers. You can count the lines in theP branch starting from the Q branch head, and the number of the line is the same as the rotational quantum number. The first R branch line is hidden under the Q branch

If you look carefully between the lines in the P and R branches you see a little bit of "noise". These are really absorptions from v"=1 to v'=2. This would be the (2,1) band. We can see this if we raise the temperature to 330K (as hot or a bit hotter than it gets on Earth)The rotational lines of the (1,0) transition for larger values of rotational quantum number (those to the far right in the R branch and the far left in the P branch) are bigger because as the temperature increases, the concentration in the higher rotational levels increases as (2J+1) exp(-B"J(J+1)/kT). J is the rotational quantum number in the ground state, B" is a molecular constant, k Boltzmann's constant and T the temperature. The intensity of the absorption depends on how many molecules are in each rotational level of the ground vibrational state. Count carefully the lines in the P branch. The maximum absorption (minimum transmission) at 200K is J=7, while for 330K it is at J=10. Second we see that the intensity of the (2,1) band increases.

You can play with increasing the temperature even further. Also go back to the observer page and narrow the bandwidth (to perhaps 620 - 680 cm-1) to see lines in the (2,1) band more clearly. Set the temperature very low, say 100K and see that many fewer lines appear and how they are as a group closer to the center.

Higher temperatures increase the population of higher energy/quantum number rotational levels. These levels absorb IR light further away from the center of the band. If you increase the path length from 200 cm, to 2000 cm the lines in the center of the band are saturated, but those on the outside are not.
If you keep the path length constant at 200 cm but increase the mixing ratio by an order of magnitude, the same thing happens.
In this way, even though increasing the CO2 concentration will not increase the absorption of light at the center of the band, it will at the wings.

Mice bearing gifts
(Anyhow this is not an endorsement of anonymouse.de which is a free anonymizer.)

In the comments to Motl's folly, SCM (To be known henceforth as Some Cool Mouse if he or she does not object. Eli is a nerd bunny, with very strange cool standards:) points to a great toy, spectracalc.com. This is a set of calculators for spectra, atmospheric profiles and much more put up by GATS Inc.

  • Even the free version gives you access (click on Spectral Databases) to HITRAN, with graphical output.
  • The Spectral Calculator on the free version appears to be currently limited to 100 cm^-1, chunks which makes it awkward for some uses.
  • The Atmosphere Browser gives you fingertip access to atmospheric compositions, pressure and temperature for various standard configurations.
  • The Solar Calculator tells you sunrise, sunset and the position of the sun anytime, anywhere (on Earth). Perhaps of interest to the weather obsessed at Capital Weather and elsewhere
  • And finally, the generic unit converter
They are selling subscriptions for more functionality, such as access to GEISA and HiTEMP data bases, ability to model larger spectral regions, etc. GATS is a contractor to various agencies (NASA) for remote sensing.

Ms. Rabett calls, the roasting carrots ARE burning on the barbecue. Later tonight Eli will run through a calculation using these toys showing the effects of pressure, temperature and composition on CO2 spectra.