Comments On “Oscilloscope – Britain’s Cold Snap Is Explained By The Arctic Oscillation” in the Economist

UPDATE: Feb 10 2010

The author of the article below has sent me a follow up which I have posted below with his permission. I appreciate his taking time time to follow up and clarify.

Dear Dr Pielke

I fear our article may not have been well expressed, because I think you have misinterpreted it. The point of the line “The atmosphere is not just about temperature, though. Wind patterns matter too” was not to deny the fundamental temperature/pressure/wind field link, but to say that while the temperature patterns associated with the negative phase of the oscillation might tend to decay ice, the wind patterns associated with the same phase might tend to preserve it. I’m sorry that wasn’t clear.

Best wishes

Oliver Morton
Energy and Environment Editor
The Economist

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The Economist has an interesting article in their January 11 2010 issue titled

Oscilloscope – Britain’s cold snap is explained by the Arctic oscillation

which (correctly) reports that the recent cold and snowy weather in the UK (and elsewhere) is a result of regional atmospheric circulation patterns. Excerpts from the article read

“IT IS an ill wind that blows no good, as people have been remarking to each other since at least the 16th century. In the case of the bitter easterlies that have brought Britain colder, snowier weather than has been seen for a couple of decades…”

“The atmosphere cannot make heat, or even hold that much of it. There is more heat stored in the top four metres of the oceans than in all the Earth’s atmosphere. 

So when the atmosphere cools down one part of the globe, it is a good rule of thumb that it is warming some other part. In the case of the current mid-latitude chill, it is the high latitudes that are seeing the warming. In Greenland and the Arctic Ocean, December was comparatively balmy. The air above Baffin Bay and the Davis Strait was 7ºC warmer than usual (though that still left it pretty cold).

This pole-centred roundel of warm-in-cold is symptomatic of what climatologists call the negative phase of the Arctic oscillation (AO). It is a mode of atmospheric circulation in which the stratosphere is unusually warm and westerly winds, which normally bring warmth from the oceans to northern Europe, are unusually weak.”

However, there is a significant misunderstanding that is presented in the article. It is written that

“The atmosphere is not just about temperature, though. Wind patterns matter too.”

The article is correct that wind patterns matter (as this is what transports the cold air from the higher latitudes and warm air from lower latitudes). However, the wind pattern is determined by the three-dimensional wind field.  This temperature field creates the three dimensional pressure field, and this pressure field produces the wind patterns. This is well understood in synoptic meteorology, as I have summarized in my lecture notes

Pielke Sr., R.A. 2002: Synoptic Weather Lab Notes. Colorado State University, Department of Atmospheric Science Class Report #1, Final Version, August 20, 2002.

The cold air in the troposphere at higher latitudes, for example, is why the winds in the middle and upper troposphere generally blow from west to east (i.e. the “westerly jet stream; also called the “polar jet”). This also explains why these winds are stronger in the winter than in the summer, since the higher latitudes are colder in the winter.  If you fly from New York to London, you typically arrive more quickly than when you fly from London to New York. The Arctic Oscillation which is the reason for the cold snowy period in the UK is a result of the spatial distribution of tropospheric temperatures.

Thus, despite the implication in the Economist article that wind patterns are distinct from the temperatures, they are intimately related to each other with the temperature field determining the wind patterns. This is why alterations in the spatial pattern of diabatic heating by human activity, such as we identified in our paper

Matsui, T., and R.A. Pielke Sr., 2006: Measurement-based estimation of the spatial gradient of aerosol radiative forcing. Geophys. Res. Letts., 33, L11813, doi:10.1029/2006GL025974.

is so important.  These alterations affect the wind field, and thus the weather than is experienced regionally. This is a much more important issue than changes in the global average surface temperature in terms of the effects on society and the environment.

 

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