09 August 2010
Question place
Time to hang out the shingle for questions. As always, response time will be variable, including that I may not be able to answer. If so, maybe a reader can. And maybe we can have some discussion about the question and how we might go about finding the answer.
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12 comments:
I've been wondering about moulins (the holes in the ice) in Greenland, how deep are they and how the lapse rate effect might affect these. Have any direct measurements of the temperature profile of a deep moulin been done?
Are there any good tabletop experiments that demonstrate the warming effects of CO2?
A recent paper suggests that many of the common demonstration experiments are actually picking up differences in convective or other non-radiative properties (http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000078000005000536000001&idtype=cvips&gifs=yes&ref=no) and the paper also shows some nice calculations of what the theoretical effect should be... which is a couple percent boost to whatever change from ambient you'd expect from your IR source... which _should_ be detectable.
(the small effect is understandable when you think about the fact that doubling CO2 gets you 4 w/m2: that means that a multiple-kilometer column of CO2 gets you a couple christmas tree lightbulbs worth of warming at the surface - which, when added up over the surface of the earth is large, but for a single experiment in a single, tens of centimeter tall flask, is kind of not so large)
-M
Oale:
You and I will have to take a look at scholar.google.com (something I heartily recommend to all) to see about whether there have been any direct measurements.
You raise an interesting idea. To back up for others: In Greenland, one of the things we've started observing is massive moulin formation. As Oale mentions, they are holes in the ice. They form when meltwater on the surface of the ice sheet pools to great enough size/depth/area that it chews through the ice. You then get a massive waterfall and drainage. Plus, this water can get all the way to the base of the ice sheet -- and provide lubrication for it to flow faster towards the sea. A nice, brief, video of moulin drainage is at http://www.youtube.com/watch?v=d6rkHs9DiW0.
The lapse rate is the business that the atmosphere cools as you go higher in the atmosphere. Conversely, then, it warms as you go lower -- say because you have opened a moulin and the atmosphere can now reach to the base of the ice sheet rather than the surface.
I don't know if there are any direct measurements, hence the suggestion of scholar.google.com. But a couple of thoughts. One is that the thicknesses involved are 1-4 km (0.5 to 2.5 miles). Since clouds aren't forming (as far as I know, which isn't terribly far) in the moulin, the lapse rate would probably be the dry adiabatic -- 10 C per km. But before we have visions of +40 C air at the base of the ice sheet, we have to think about the fact that having colder air below warmer air is stable. At the bottom of the ice sheet, we're surrounded by ice, so would quickly cool right back to the freezing point. Since the moulins are narrow, there probably isn't much circulation to drive air into or out of the moulin. So, while there's probably an effect from the lapse rate, at least on the initial opening of the moulin, it probably doesn't persist long. We just go back to near-freezing air all the way down.
But ... I'm saying that based on what seems intuitively reasonable to me. My intuition in this area is probably worth mentioning (so I do), but the research literature is a better place to look for the solid answer. The video I link to above was shot by Jason Box, who is a scientist studying Greenland, another key term to use in looking.
Do you know of any climate link to the earth's nutation? I've seen papers discussing atmospheric excitation, and relating the angular momentum of the atmosphere to the wobbles, but they described that as a stochastic process. Could there be any climate effects as well?
anonymous-m:
I don't know, yet, of any good tabletop demonstrations. That raises a question I'll take up in a post for tomorrow. As you mention in the cite, many of the experiments that have been done are influenced by other effects.
On the other hand, things may not be as dire for creating an experiment as you seem to think. While the atmosphere is indeed pretty deep -- we can take it at 10 km -- this doesn't amount to a lot of CO2, in terms of distance. The amount of CO2 above a sea level location is about 4 meters (13 feet) and standard temperature and pressure. That's the translation of 400 ppm. Preindustrial CO2 would have been about 2.8 meters (about 9 feet).
anonymous2:
This connects to the 'other project' I mentioned in the atmospheric cycles post. I'm looking in to this myself, and will have something to post soon. For now, sea ice is the only thing I know of that has a response to the wobbling of the earth's rotation axis. See if you can get hold of the full text for Oscillatory Behavior in Arctic ice concentrations. The Chandler wobble, an about 14 month wobble in the earth's rotation axis, shows up in the time series. This is an example of something showing up as being statistically significant, but, since there was no reason for it to be there, no further work has been done. I might have that reason. (cue stirring music for a later triumphal entrance :-)
There is a paper here which mentions nutation in connection with climate. It seems it is related to a lunar cycle, so any effect will be lost in lunar tides.
References:
Sorry, don't have it but it can be found by a search for nutation and climate with Google Scholar
Cheers, Alastair.
Alastair:
um ... D'oh!
Now that you mention it, I've seen several (well, a few) papers on the nutation due to the 'Lunar node'. Most have been oceanography papers, looking at temperatures at depth (200-1000 meters), and typically at high latitude (like your paper being Alaskan).
So, such papers definitely exist. I can't say they've taken the field by storm. But they're out there waiting for ... something.
Hi,
Why does the specific humidity at around the altitude of the tropopause apparently correlate with solar activity levels?
Thanks!
http://tallbloke.files.wordpress.com/2010/08/shumidity-ssn96.png
Roger: hard to read exactly what you were plotting.
One rule of thumb I use in considering correlations is to ask how many things I might might tried to correlate. For humidity, for instance, you could have tried a couple of dozen pressure levels, plus a number of temperature levels (300 K potential temperature, ...), plus assorted features (tropopause, stratopause, middle of ozone layer, ...). As the number of candidates rises (even if you didn't compute them -- I'm not saying that you were cherry-picking), the chances of finding a correlation even between random series increases.
so one thing to do is to start computing the correlations for those other pressure levels. if it shows up in many levels, the chances of it being chance dive. on the other hand, if they're all small, it could be a signal that the governing process is one tied to a particular height level. thence more research while you try to find mechanisms and signs in other variables (humidity is unlikely to be the only parameter affected in any geophysically-driven connection between sun and earth).
for your further work:
* there's a paper by Labitzke and van Loon from the mid 1990s, looking at solar effects on the quasi-biennial oscillation. they should be a good source of ideas on how to proceed, and might have some answers.
* it'll be good to compute the quantitative correlations. eyeball values can be shockingly inaccurate.
* it'll be even better to run the time series through a time series analysis package. I like the freely-available AnalySeries from http://www.lsce.cnrs-gif.fr/
(it's a mac program; I'm sure counterparts exist for windows.) In particular, look at the coherence as a function of period. (and at whether the coherence is statistically significant).
the briefer answer to why there's an apparent correlation:
a) I dunno
b) do some more looking to see if the appearance is solid
c) write it up for a scientific journal (seriously) if it holds up.
Great reply, thankyou.
Apologies for the pooorly annotated graph, it took me a while to figure out the NCEP axis labels, and I didn't find time to make it clearer.
The troposphere/stratosphere boundary is a particularly special interface in Earths climate system. When tropospheric temperature rises, stratospheric temperature falls, and vise versa.
That is why I think the solar effect at that level is indicative of an important point of balance in the Earth's equilibrium seeking climate system.
I will pursue this further in the ways you suggest.
rog:
believe me, I understand about recalcitrant graphics software. It was while going out for a run to relax from graphics that I broke my wrist.
I'm with you on why you want to look at that level. just some encouragement to look farther afield so that you don't get bitten, as so very many have for over a century, by the fact that chance does routinely (about 5% for 95% confidence levels) produce what looks like a good correlation. solar correlations have been particularly prone to this.
as you make progress, and maybe get to the point of having a full document to present, I'll note my interest, and offer you a spot for guest post on the topic. One thing I want to do here is show students what science -- the live activity that interests me -- looks like.
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