Guest Post by Willis Eschenbach
I got to thinking about the effect of thunderstorms on the surface air temperature. So I figured I’d wander once more through the TAO buoy dataset. The data is available here. I swear, every time I perambulate through that data I get surprised, and I learn things, and this was no exception.
I decided to look at the relationship between sea surface temperature (SST), surface air temperature (SAT), and rainfall. Figure 1 is a graph showing all three of those variables from one of the TAO buoys.
Figure 1. Hourly data from the TAO buoy at 0°N, 156°E (in the Pacific warm pool north of the Solomon Islands). This shows both rainy and dry hours. Black line shows a 1:1 slope, where a 1° rise in SST is equalled by a 1° rise in SAT. Both color and size indicate rain amount. N = 9,067 observations
So … just what are we seeing here? And what might I learn from it?
I went into this to see how much thunderstorms affect surface air temperature and sea surface temperature. Now, I was surprised by the shape of this graph. The first thing I concluded is that we’re seeing two different regimes here. One is what is happening during the thunderstorms, and the other is what’s happening during the dry hours.
I also note the well-known SST limitation of just over 30°C. Only 0.4% of the sea surface temperature measurements in the total dataset are over 31°C (N = 62,507).
Next, it’s clear that thunderstorms are temperature limited. To investigate that, I looked at solely the hours which had measurable rain. Figure 2 shows just those records.
Figure 2. Rainy hours only of the hourly data from the TAO buoy at 0°N, 156°E (in the Pacific warm pool north of the Solomon Islands). Black line shows a 1:1 slope, where a 1° rise in SST is equalled by a 1° rise in SAT. Both the color and size indicate rain amount. N = 422 observations
As you can see, the thunderstorms have a clear minimum temperature. They are unable to persist with a temperature of much less than about 29.5°C. It’s also clear that the greater the rain, the greater the depression of the air temperature and the sea surface temperature. And as you’d expect, the depression in air temperature from the thunderstorm is larger than the depression in SST. Air temperatures drop up to maybe 3°C, from 28° or 29° down to 25° to 26°, whereas sea temperatures only drop up to about 1°C, from say 30.5° down to 29.5°C.
Finally, here are the records of only the dry times, the times without an active thunderstorm overhead. Figure 3 shows those hours when no rain is falling.
Figure 3. Dry hours only of the hourly data from the TAO buoy at 0°N, 156°E (in the Pacific warm pool north of the Solomon Islands). Black line shows a 1:1 slope, where a 1° rise in SST is equalled by a 1° rise in SAT. N = 8,645 observations
Note that both the SAT and the SST move in parallel much of the time (black line). I would say that the residual observations in the lower central area represent the colder air and colder ocean temperatures that remain after a thunderstorm when it has stopped raining.
CONCLUSIONS:
• Thunderstorms cause the coldest air temperatures in the record, well below the temperatures when there is no thunderstorm activity.
• Thunderstorms drive air temperatures down by up to 3°C or so, and sea surface temperatures down by up to 1°C or so.
• This ability to drive the surface temperature well below the normal temperature is the sign that the thunderstorms function as a governor, rather than as a feedback.
At least that’s how I interpret the graphs, YMMV of course. Dang TAO data … always turning up new stuff to puzzle my cranium …
My regards to you all,
w.
cd says:
March 28, 2013 at 5:53 pm
Philip
It seems you got it one:
http://cimss.ssec.wisc.edu/wxwise/class/thndstr.html
Thanks for the link. It helps explain how thunderstorms can persist after sunset when there is no solar heating. A continuos supply of moist air drives the thunderstorm process into the night time. As I have previously noted, close to the equator (within 100km – Singapore, Riau Islands), thunderstorms occur at all hours of the day and night with no noticeable afternoon peak.
It would appear that thunderstorms are driven primarily by humidity close to the equator and solar heating further away from the equator, eg in the region of the Solomon Islands.
I’d like to ask once again; have I interpreted these graphs correctly, i.e. SSTs are always warmer than SATs
Baa Humbug says:
March 29, 2013 at 1:12 am
“I’d like to ask once again; have I interpreted these graphs correctly, i.e. SSTs are always warmer than SATs”
That is definately true in the Western Pacific around Samoa. That is the driving force for the formation of thunder clouds. Evaporation makes the air lighter. The lighter air strives to maintain a wet adiabatic laps rate and rapidly rises in the center of the cloud like a flue. Think about the terminal velocity of golf ball size hail. That updraft air is constantly being replaced by cold downdrafts on the outsides of the thundercloud. As you move toward the poles where much less energy is being absord from the sun, SATs become warmer than SSTs and you don’t have thunderclouds. That should give you an idea of how this “temperature control” mechanism works.
Willis Eschenbach says:March 28, 2013 at 10:07 am
Steve Keohane says:March 28, 2013 at 5:10 am
Willis, I don’t see this supported by the graph(s)
It’s also clear that the greater the rain, the greater the depression of the air temperature and the sea surface temperature.
[…]
Since the small ones are (by and large) up near the black line, and the large ones are (again by and large) lower down, this means that the greater the rain, the greater the depression of the air temperature.
w.
Thanks for your response Willis. Sorry to be so pig-headed, but while I agree with everything you say, I can’t believe the graph shows the depression of air temperature. I could say it shows the average temperature. I could say it indicates the average air temperature is proportionately cooler during heavier rain. I don’t see how it supports a change in temperature from prior to and after it rained.
Brad says:
March 28, 2013 at 5:44 am
Again, Willis finda a correlation and calls it a conclusion. What great science. This would never pass peer review.
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First, I read no conclusion ….. only theory with supporting data.
Honestly Brad, What does passing peer review have to do with anything? Since climategate I generally ignore it when someone says, “Here’s proof I’m correct cause it’s peer reviewed.”
Doesn’t passing peer review mean very little and depend entirely on the submitter and reviewer?
At least that’s what I read in the climategate emails, didn’t you?
This is real science. Here’s Willis’ data, his process and his reasoning in front of you. Try to get Mikey and the Team to do this even with a FOIA demand. Cold theory laid bare for you to push forward or destroy. Your choice.
Here’s your chance to review real science instead of just repeating talking points.
Now, prove Willis’ science wrong.
thanks w.
cn
I believe the non-rain part of the steeper part of your fork is “close to rain”. It is the hours when there are clouds before and after rain. The flatter part of fork are sunny hours. The only assumption needed is that air warms up faster than water?
I’d like to ask once again; have I interpreted these graphs correctly, i.e. SSTs are always warmer than SATs
The graphs do show that on average this is true throughout the day for this location. I wouldn’t expect this to be the case outside the afternoon thunderstorm/monsoon zone. Where I live in a mediteranean climate (no afternoon thunderstorms) summer afternoon air temperatures exceed SSTs by a large amount.
And globally, average SSTs are about 1.5C warmer than surface air temperatures. And as fhhaynie notes, this is an important characteristic of the Earth’s climate.
Hi Willis: Good stuff, both your scientific observations and your life essays. In your Figure 3 you attribute the goat-beard hanging from the 1:1 line as cooling after a rain. How about filtering the data to remove measurements 2, 5, 10 hours after a rain event. If it is rain induced cooling you might expect to see the goat-beard progressively trimmed with increasing time after a rain. If the goat-beard persists during intervals with no recent rain events it could be attributed to gust-fronts/downdrafts distal to the rain event. You might also expect SST not to lower as much. Cheers, Mark
Mark Beeunas says:
March 29, 2013 at 10:25 pm
I did that, Mark, and found exactly what you predicted. When I removed the data from one, two, and three hours after a rain, the “goat beard” got progressively shorter. So the beard is from the cooling after the rain. It was a pain to do it, it was late, and I didn’t snap screenshots, but that’s the outcome.
All the best,
w.
Steve Keohane says:
March 29, 2013 at 4:51 am
Not sure I can help with that, Steve. It is clear that most of the time, SST and air temperature run in parallel. However, when there is rain, the air temperature is much lower. You say this doesn’t show “the depression of air temperature”, so I’m totally at a loss about how you understand the whole system.
How do lower air temperatures not indicate a depression of air temperature?
And how does a depression of air temperature from rain not indicate that the succeeding temperatures will be cooler than if the rain had not occurred?
Perhaps you should get the TAO data and work through it yourself, Steve. I fear I can’t explain it much better or differently than I have.
All the best,
w.