SHORT-TERM COOLING OF OCEANS SUGGEST 'SPEED BUMP' IN WARMING

[mikegeukes]

[FONT=Verdana, Arial, Helvetica, sans-serif]SHORT-TERM COOLING OF OCEANS SUGGEST 'SPEED BUMP' IN WARMING[/FONT]
http://www.noaanews.noaa.gov/stories2006/s2704.htm

Mike​

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[MJ Poore]

This whole warming business is bizzare. We have had a freezing winter in the Southern Hemisphere this year, in contrast to the very hot summer taking place in the north. On Tuesday this week we observed a supercell that persisted for 6 hours ahead of a front, behind the supercell there was even light snow falling on the ground over 2000m. Sounds a bit like Nebraska or Iowa in early spring, actually its the high plains of Africa at 29'south. Go figure...

 

[David Wolfson]

Interesting report! This got me on a brief detour into statistics. Particularly, I wondered, how much energy do tropical cyclones transport from the oceans to the atmosphere, anyway? My thought was that, perhaps, we're semi-blind and feeling different parts of the global warming elephant.

According to Grey, based on older research, the average hurricane produces precipitation corresponding to the release of 5.2 x 10^19 J/day latent heat. Worldwide the yearly number of tropical cyclones has been steady at ~90, but research suggests that their energy release has increased by 70% over the last thirty years.

Basic rough calculation: 90 storms x 10 days duration x 5x10^19 = 4.5x10^22 J/year. 50% increase is 2.3x10^22 J/year.
Qualifiers: not all heat extracted from the ocean is released as near-field precipitation (increases energy); the average tropical cyclone energy release may not be representative of the average hurricane (increase or decrease -- hard to say, because a non-linear relationship with intensity, like earthquakes); ... and there are others, of course.

The report documents an ocean heat content net gain of about 1x10^22 J/year in 1993-2003 versus a loss of about 1x10^22 J/year in 2003-2005. The figures show a net gain of about 6x10^22 J over the 13 years -- or roughly 0.5x10^22 J/year.

Surprisingly (to me, anyway) the variability/natural increase in tropical cyclone energy extraction seems to be the same order of magnitude as the reported changes in global oceanic heat content.

My inference based on these statistics is that tropical cyclones are an important part in the ocean-atmosphere manifestation of global PBL energy change ("warming" or "cooling"). Exogenous atmospheric variables affecting tropical cyclone formation like El Nino, the MJO, Saharan dust, etc., are of sufficient magnitude as to allow multi-year coupled oscillations between ocean heat content and tropical cyclone extraction of that heat.

In otherwords, it's not inconceivable that last season's extraordinary performance might have extracted enough heat to suppress this season, irrespective of the longer-term increasing trend. Over the longer term, however, one can't keep the lid on the kettle. FWIW.