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.
[snip . . OT . . mod]
Anyone who has spent a lot of time on the ocean, e.g. Windsurfing will tell you the same. You experience a sudden drop in air temperature with the onset of a storm. Sea temperature is more difficult to asses quantatively.
Thnx Willis.
Am I interpreting the last graph correctly, i.e. SSTs seem to be mostly about 1.5DegC warmer than SATs?
Willis: Some of the rain probably evaporates as it falls, perhaps cooling the air the 3 degC and the surface of the ocean (with a much greater heat capacity) much less. The air may remain cooler than the ocean for several/many hours after the rain ends, possibly accounting for the dry hours which lie well below the line in FIgure 3.
Didn’t know the buoys recorded precip. It does tend to back up your thermostat theory.
More interesting finds Willis. Nice digging.
“thunderstorms function as a governor, rather than as a feedback.”
You may or may not be right about this but in order to have any meaningful discussion or for that conclusion to mean anything and be useful you need to define what you mean by both terms.
As I pointed out in your last thread on this, a governor works by feedback (both +ve and -ve) . So when is a governor not a feedback?
You have quite a firm opinion on this and you’re bright fella so I’m inclined to think you may be right but with a clear definition I’m not sure what you may be right about.
I think your governor implies it must control the lower as well a putting an upper bound. I’m not sure I can see how that would happen or where the data demonstrates this.
Perhaps you could expand.
Thanks for the post.
“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.”
Should it be 24,5 degrees C?
The sun heats the sea, and the air is warmed by convection (and conduction) from the sea water.
Thus, the water is in average warmer tha the air. A large portion of the energy from the sun is removed from the water as phase transformation -liquid water turns into water vapour – rises, condenses into clouds, releasing that energy some 1000 m height. The cool(er) water forms droplets and fall back as colder rain into the sea. The air is due to lower heat capacity more cooled than the sea water. And the next day, it all starts again, or seen from above, moves 15 degrees/hour westwards.
“As you can see, the thunderstorms have a clear minimum temperature. ”
Your claim is not supported by your graphs. There’s a huge orange blob in the area where most measurements are and it’s not clear what are relative volumes of events per unit of graph area. Make a histogram and then claim something like that.
“Thunderstorms cause the coldest air temperatures in the record, well below the temperatures when there is no thunderstorm activity.”
I don’t see any such thing on your graphs. Coldest non-storm air temperature on your graph is about 24C, coldest storm temperature is about 24C as well. If you are talking about average, then again get rid of that orange blob and make a histogram.
“Thunderstorms drive air temperatures down by up to 3°C or so, and sea surface temperatures down by up to 1°C or so.”
It’s clear that something like that happens, the underlying physical principle is called evaporation which depends on surface area which is clearly larger during thunderstorm when the sea surface is extended by wind and rain drops have enormous surface area just as they are.
However your numbers are again not substantiated by your graphs. My guess is no significant influence on water temperature and maybe about 2C on air.
“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.”
I wonder where did this come from. I don’t see how any such claim can be derived from your data.
Sorry, a typo:
“Coldest non-storm air temperature on your graph is about 28C, coldest storm temperature is about 28C as well.” should have been 24C for both.
[Fixed. -w.]
Greg,
By no means would I pretend to speak for Willis, but in basic terms I suspect he is referring to a governor in the sense of an engine governor, i.e. a rev limiter. In this sense a governor is not a feedback, it is simply a threshold.
Put another way, when excess atmospheric heat builds in the tropics, thunderstorms are created, which remove the heat by evaporation and convection, etc. When it is cooler nothing happens. Governors in the sense I have for them do not have lower bounds.
It may be informative to redo the rainy hours plot and join the dots. Scatter plots can be useful but throwing away the time information in a time series often loses key information.
Trond A says:
March 28, 2013 at 2:17 am
It’s an SST, I’ve changed the text to clarify that.
Thanks,
w.
Kasuha says:
March 28, 2013 at 2:29 am
Huh? Take a look at Figure 2, where I’ve removed the “huge orange blob”. You want a histogram? Sure:
Guess what. It doesn’t show anything more than Figure 2 shows.
Well, since you needed a histogram to see what was obvious above, I suppose the same could be true now … but no, Kasuha, I’m not going to do that one. If you can’t see how much the storms are cooling the air by looking at the graphs above, you’ll never get it.
Thanks for your guess, Kasuha. However, since you’ve proven that you couldn’t read Figure 2 without an accompanying histogram, I fear that your guess is not of great interest to me.
However, you could consider it this way. Without thunderstorms, the air and sea temperatures generally run in parallel. When one goes up a degree, so does the other one. This is indicated by the black line.
Since during the thunderstorms the air temperatures are up to 3° below the black line, my claim is most assuredly substantiated by the graphs. Note that I was not indicating the AVERAGE as you appear to be doing. I was indicating the RANGE (up to 3°C), which the graph clearly shows.
The claim that thunderstorms act as a governor is derived from a whole host of data, and I have written about it often. This is merely one more piece of evidence for that claim.
Regarding the nature of the evidence, think about whether simple linear negative feedback, the only kind discussed by the IPCC, can push a system below its starting point.
w.
Thunderstorms are also extra shiny white on top and are very good at reflecting sunshine back to cosmos. They usually develop when moist are are warmed quickly by the Sun(IR from the surface).
I would argue that it’s(moist air over sea/equator) a positive feedback increasing temperature quickly and a negative feed when the temperature approaches 30 deg C.
A climate cruise control or thermostat?
Peter says: “Put another way, when excess atmospheric heat builds in the tropics, thunderstorms are created, which remove the heat by evaporation and convection, etc. When it is cooler nothing happens. ”
What you have just described is a feedback, which is why all this needs some clear definitions to be meaningful. Hopefully Willis can provide a clear definition of what he means by governor and feedback. This is about the third article he’s written on this without defining what he means by governor and what he means by “a feedback”.
Greg says:
March 28, 2013 at 2:10 am
Interesting point, thank, Greg. Yeah, I have a post half written on this question.
The IPCC only discusses simple linear feedback .One basic difference between a governor and simple linear feedback is the following:
With simple linear feedback, the size of the feedback is proportional to the size of the input.
With a governor, the size and the sign of the feedback is proportional to the difference between the current value of some system variable (temperature, rpm, etc.) and the desired value for that variable.
There is a second difference;
With simple linear negative feedback, a system can never be driven past its starting point. To do so, the feedback factor would have to be less than -1 … and that is unstable.
With a governor, the system can be driven past its starting point. For example, when thermostat turns the air conditioner on in a house, it stays on until the heat drops past the starting point. To control a lagged system like a house or the climate, where things take time to heat up or cool down, such “overshoot” is necessary.
Now, let’s consider the thunderstorms. They are not a function of the size of the input (forcing). Instead they are a function of the temperature. In addition, they can drive the temperatures down below the starting point. For both of these reasons, I say they are functioning as a governor (e.g. a thermostat), rather than a simple linear feedback.
I will edit the text in the head post to make it clear what kind of feedback I’m discussing.
All the best,
w.
it is all about Latent Heat. Only a difficult concept for climatologists.
Can you plot the hour just after the rain occurred? Doing so would confirm “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.” — John M Reynolds
All of the excellent articles on this website lead me to the inescapable conclusion that whilst we know a fair bit about the climate of our planet, we still know painfully little or at least enough to know that we can’t make definitive policy decisions on what we do know. The little we know is dangerous in the hands of those who would seek to exploit it. We are in the realm of a religion where interpretation is everything. Is this how science works?, Are you a heretic long before you become a visionary?. Someone needs to explain because I’m paying taxes that the mafia would be proud of.
Frank says:
March 28, 2013 at 12:41 am
That was my speculation. I figure I can quantify it. My schemo fantastico is to find a bunch of isolated hours of rain (no rain in the hours before or after).
Then I can compare the SSTs and the air temps before, during, and after the thunderstorm … all it takes is time. Well, plus then I have to actually do it …
w.
The other thing a thunderstorm cell does, is it scrubs humidity from the air around it, acting as a condenser to aggregate moisture and concentrate it. This changes the heat capacity of the local atmospheric environment in the vicintiy of the cells. This is not so apparent in large mesocale systems but is readily evident on land (at least) when individual cells and super cells go to work.
I was surpised to learn that we have Top-Of-Atmosphere buoys – then read it again ;(
I’ve always maintained (whether right or wrong) that the loss temperature is the mechanism for creating thunderstorms with heat energy converted into electrical energy (lightening) and that lightening is not due to the rather naïve “rubbing together of raindrops” etc.
For example lightening can also occur above volcanoes where the air is cooled as it rises without any rainfall. So this theory would seem at odds with Willis’s thunderstorm controlling mechanism if I have understood him correctly although lightening is a manifestation of dissipating the heat energy in my book.