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The A-train

A little behind schedule, I finally found time to read the article in the July 2010 edition of Physics TodayTouring the atmosphere aboard the A-Train” by Tristan S. L’Ecuyer and Jonathan H. Jiang. I think this article is a worth-while read, telling a fascinating story about how new satellite missions lead to greater understanding of our climate system.

PhysicsYoday, July 2010, Figure 1

The so-called ‘A-train’ consists of an array of satellites that follow in close succession, as shown in the figure above, each in a Sun-synchronous orbit, 705 km above the ground. The clever thing about this is that they all carry different instruments with minimal interference between different types of instruments, and together they provide a platform for many diverse types remote sensing, and hence complement each other in terms of looking at different physical aspects.

Among the results from the A-Train, according to L’Ecuyer and Jiang, is that a 16% decrease in the summer-time cloudcover over the Arctic played a significant role the well-known September 2007 Arctic sea-ice minimum. This comes in addition to the anomalous winds, and was news to me. But it makes sense: less cloudiness has resulted in greater absorption of short-wave radiation (sunlight) at the surface, providing increased heat for ice melting.

Another important topic that the data from the A-train can elucidate is the relationship between clouds and aerosols. According to L’Ecuyer and Jiang, high concentrations of aerosols cause clouds, that are made of liquid drops, to rain less frequently, grow deeper, have smaller cloud drops, and appear brighter from above.

The data from the A-train has also provided more insight into the question about how areosols affect ice clouds, suggesting that polluted ice clouds generally contain smaller particles and produce less precipitation than ice clouds embedded in cleaner air.

Some of these dependencies between aerosols and clouds have been predicted by researchers previously, and these are now confirmed by the remote sensing data from the ‘A-train’. For instance, this type of predictions are inserted into so-called ‘cloud parameterisation’ of the global climate models that try to include so-called ‘indirect aerosol effects’, and have some effect on climate simulations. This demonstrates real value of both the data and theory.

26 Responses to “The A-train”

  1. 1
    Mark Schaffer says:

    Hi Rasmus,
    Please note that in the last sentence of the first paragraph that “interms” needs to be separated. Otherwise thanks for a another factual post that is the opposite of what the so called ‘skeptics’ do!
    Take care,
    Mark Schaffer

    [Response: Fixed, thanks.]

  2. 2
    Kurt Erlenbach says:

    I find the very enlightening discussion of the A-Train in the Physics Today article somewhat at odds with the comment from Robert Bindschadler quoted in Sunday’s NYT article, “We are slowly going blind in space.” Are our space-based capabilities getting better, worse, or just different?

  3. 3

    Very interesting–for me, particularly the bit about the 2007 melt, as I’ve seen denialists frame it as a purely “wind-driven event” (and one, of course, with no context whatever!)

    But the cloud/aerosol stuff is probably more central to improving our understanding of relevant physical processes, I suppose.

  4. 4
    davey says:

    It might be worth mentioning that data from the A-Train can be accessed from the NASA A-Train Data Depot.

  5. 5
    Timothy Chase says:

    One of the A-train is the Aqua satellite. It has fifteen sensors, one of which is the “AIRS” Atmospheric InfraRed Sounder. Impressive machine.

    Designed to improve weather forecasting (e.g., it is able to measure temperature with a 1°C accuracy for each kilometer of tropospheric atmospheric column) it is also responsible for high accuracy imaging of carbon dioxide. To within 2 ppm. And the physical principles that it employs in seeing carbon dioxide are the same as those through which carbon dioxide participates in the greenhouse effect — so in essence when you look at one of the images not only are you seeing carbon dioxide but you are seeing it in action as it participates in the greenhouse effect.

    For those who are interested, I have put together a webpage that describes the AIRS instrument in some depth here:

    The webpage includes some of the images and a bit more. The website is still at the early stages, though.

  6. 6
    Fred Magyar says:

    Re: Sea level rise caused by melting glaciers:

    Congressman John Shimkus, who has publicly stated during a congressional session said that we don’t need to worry about Anthropogenic Climate change destroying the earth because, God has promised not to do that any more has also recently suggested that, “God May Sink Florida, but that that’s OK with him.”

    Well, since I happen to actually live within walking distance of the South East Flordian sea shore, I’ve take it upon myself to resort to another high ranking deity, namely, Akash Bhairab, The Hindu sky god, who apparently can be easily appeased just by sacrificing a couple of goats. BTW, that was actually done just a few years ago by Indian officials to resolve some technical problems in their aircraft and it seemed to have worked well…

    I’m hoping that since Akash Bhairab’s jurisdiction is the sky, (close enough to atmospheric science for gubmint voodoo, in my book) I’ve decided to acquire a couple of goats to sacrifice, as a substitute for the very high flood and wind insurance premiums that I am currently paying.

    I was wondering if any of you highly paid climate scientists might have any suggestion on which particular breed of goat would be most effective and if there might be any way to get a government grant for the purposes of studying the effectiveness of goat sacrifices with regards mitigation of the deleterious effects of anthropogenically induced climate change.

    Any help would be greatly appreciated.
    Heh, captch ‘Logic makham’, you bet!

    [Response: If I find any highly paid climate scientists, I will send ’em your way!–eric]

  7. 7
    Leonard Evens says:

    Kurt Erlenbach said

    I find the very enlightening discussion of the A-Train in the Physics Today article somewhat at odds with the comment from Robert Bindschadler quoted in Sunday’s NYT article, “We are slowly going blind in space.” Are our space-based capabilities getting better, worse, or just different?

    I don’t see any contradiction. The Physics Today article refers to things as they are today. The NY Times article referred to the prospects for the future. Satellites don’t stay up forever, and we will need more and better satellites in the future to be able to follow what is happening. Given the nation’s current political struture, it seems unlikely that the necessary funding will be available. The NY Times article explained why that might be the case.

  8. 8
    jorgepeine says:

    I am wondering, how the CERN project CLOUD will affect physical understanding of cloud formation.

    [Response: We’re generally not holding our breath. See some of our former commentaries, e.g. here.–eric]

  9. 9

    PARASOL has already de-orbited, Aqua is 8 years old, and there aren’t any real replacements planned. Glory will launch next year, but is targeted at aerosols.
    There are plenty of additional key satellites that are aging and desperately need replacements, such as LandSat 7, or passed on already, such as QuikSCAT and IceSat, or never made it to space, like the Orbiting Carbon Observatory.
    Also, the delay and eventual cancellation/restart of NPOESS is yet another hit.

  10. 10

    Whoops, nevermind, the French just moved PARASOL to a new orbit, it’s not been de-orbited.

  11. 11
  12. 12
    richard french says:

    re #9. An overview of the status of all the various satellite missions or other projects (both current and planned) designed to support climate science would be a worthwhile endeavor. Does such a report exist?

  13. 13
  14. 14
    Chris O'Dell says:

    @12, also the NASA Decadal Survey has a lot of suggestions for future missions. Many of them are pie-in-the-sky, but some like IceSat-2 and SMAP should definitely happen.

    Also, here is an image of what the A-train should look like in 2 years with the addition of GCOM-W1 (2012) and OCO-2 (2013).

  15. 15
    ZHF1987 says:

    , also the NASA Decadal Survey has a lot of suggestions for future missions. Many of them are pie-in-the-sky, but some like IceSat-2 and SMAP should definitely happen.

  16. 16
    Tom Dayton says:

    Be sure to bookmark JPL’s Eyes on the Earth 3D. Click on the satellite names along the top; Aqua is one of them. When you click Aqua, then on the right side of the resulting window click “Show Data Map,” and pick “Carbon Dioxide” to see the Earth superimposed with CO2 levels from the past 31 days.

  17. 17
    richard french says:

    Thanks for the links. The JPL site has a lot of information, but it seems to be organized around the tool (the individual satellite), not the problem (unanswered question in climate science).

    Is there something available that is organized in terms of the unanswered questions in the field–What programs are underway (not just NASA, and not just USA) or planned to try to address the unanswered questions?

  18. 18
    Vendicar Decarian says:

    53% – Majority of Republicans No Longer See Evidence of Global Warming

    A 53%-majority of Republicans say there is no solid evidence the earth is warming. Among Tea Party Republicans, fully 70% say there is no evidence. Disbelief in global warming in the GOP is a recent occurrence. Just a few years ago, in 2007, a 62%-majority of Republicans said there is solid evidence of global warming, while less than a third (31%) said there is no solid evidence. Currently, just 38% of Republicans say there is solid evidence the earth is warming, and only 16% say that warming is caused by human activity. In 2007, three-in-ten Republicans said global warming was the result of human activity. Also, by nearly a two-to-one margin, Republicans say scientists do not agree that the earth is getting warmer because of human activity. Few Republicans see global warming as a very serious problem (14%) or in need of immediate government action (24%)

  19. 19
    Edward Greisch says:

    Sorry for off topic, but
    is relevant to RC in general. “New work reinforces the notion that fear is not your friend if you’re a communicator seeking action on climate.”

  20. 20
    Wouarnud says:


    A more complete reference is the CEOS and its famous handbook:

    All the missions, all the sensors, all the projects.


  21. 21
    Susan Anderson says:

    “Weather Satellite Work Begins”

    OT, Edward Greisch, thanks for the heads up on DotEarth. Unfortunately the deniers dominate big time. Following article needs help as well (comments just beginning, so we have a chance).

  22. 22
    Fred Magyar says:

    Vendicar Decarian @ 18,

    Among Tea Party Republicans, fully 70% say there is no evidence.

    Does the poll, perchance, collect data on what percentage of those people have also submitted to full frontal lobotomies recently. Sigh!

  23. 23
    ge0050 says:

    I’ve seen a lot of graphs showing global atmospheric CO2 versus global average temperature, trying to prove the pro and con side of AGW.

    Why do we not see graphs of human produced CO2 (ACO2) versus temperature? What I talking about here is total human produced CO2, say going back to 1870, not just the amount remaining in the atmosphere.

    The reason I ask is that if AGW is correlated with ACO2, then we should see a stronger correlation between total human produced CO2 as compared to total atmospheric CO2.

    This would be strong evidence that AGW from ACO2 is correct. However, is the correlation is weaker, then it would tend to show AGW from ACO2 is not correct.

    This seems to be a very simply test. Why not post it? This is my challenge to the pro and con AGW groups. Show that ACO2 is more/less strongly correlated with AGW than total atmospheric CO2.

    [Response: Actually, you would expect the *forcing* from anthropogenic factors to correlate more with temperatures, and it does. – gavin]

  24. 24

    #23 ge0050

    In addition to the wonderful page Gavin gave you, you might also be interested in seeing a picture of the attribution so you can see how the natural and human signals look and how the temperature is following one path, and not the other.

    Plus this page:

    Which gives you an idea of how you can view the general assessments. It’s just food for thought to give you an idea about how the human effect change can be seen as pretty much 100% human caused. Of course remember that natural variation is still occurring, so the change due to human cause is separate from natural changes.

    Economics: Balancing Economies
    October Leading Edge: The Cuccinelli ‘Witch Hunt”

    Fee & Dividend: Our best chanceLearn the IssueSign the Petition
    A Climate Minute: Natural CycleGreenhouse EffectClimate Science HistoryArctic Ice Melt

  25. 25
    Hank Roberts says:

    > ge0050
    > why do we not see
    Maybe you’ve been looking in the wrong places? You want pictures; I know Spencer Weart’s history (first link under Science in the sidebar at Realclimate) so I did an image search, like this:

    That search, just scanning the first page of hits, finds this excellent summary that answers your question, with the picture you wanted:

    See also
    Brief excerpt follows:
    “The complacent view that CO2 from human activity could never become a problem was overturned during the 1950s by a series of costly observations. This was a consequence of the Second World War and the Cold War …. Among the first products were new data for the absorption of infrared radiation, a topic of more interest to weapons engineers than meteorologists.

    … scientists could now track the movements of carbon with a new tool — the radioactive isotope carbon-14. This isotope is created by cosmic rays in the upper atmosphere and then decays over millennia. The carbon in ancient coal and oil is so old that it entirely lacks the radioactive isotope….”

  26. 26
    Steve says:

    Maybe satellites will give us all we need for sniffing out methane seeps in permafrost regions, but if not here’s an idea for some grad student to explore:

    Sort of like XBT sampling using equipment mounted on commercial vessels, maybe someone could generate useful data mounting gps-equipped methane sensors on the fleet of trucks plying the permafrost regions of the north country. Have fun, Steve El, USA