Tropical tropospheric warming

by Joe Archive on May 26, 2008

h2 id=”atl”a href=”http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo208.html”span style=”font-weight: normal;font-size:100%;” Warming maximum in the tropical upper troposphere deduced from thermal winds/spanspan style=”font-weight: normal;font-size:100%;” – Robert J. Allen amp; Steven C. Sherwood – Nature Geoscience (subscription required)/spanbr //a/h2br /br /The apparent lack of a tropical tropospheric warming signal in observations has been a problem with climate change predictions for some time. However, the direct temperature record has many problems – there have been many changes in the observation mechanisms: blockquotenon-climatic artifacts due to station relocations, observation time changes and radiosonde type or design changes… /blockquoteleading to difficulties in interpretation. Earlier studies have attempted to correct for these artifacts with uncertain amounts of success. Instead, Allen and Sherwood use the thermal wind balance relationship to back calculate spatial temperature gradients from the significantly more trustworthy wind fields.br /br /The “thermal wind” is a vertical shearing of the geostrophic wind arising from the pressure variations caused by horizontal temperature variations. The geostrophic wind is the wind that balances the Coriolis force with the pressure gradients. (See Wikipedia for a href=”http://en.wikipedia.org/wiki/Thermal_wind”thermal wind/abr /and a href=”http://en.wikipedia.org/wiki/Geostrophic_wind”geostrophic wind/a). These relationships are weak near the equator, where the Coriolis force vanishes, but they appear to hold for winds averaged over long timescales.br /br /This data gives a time series of spatial gradients in temperature, which can be integrated from a (collection of) “trustworthy” point(s) to give the temperature structure of the atmosphere. Allen and Sherwood cautiously report a warming trend in the upper tropical troposphere that is consistent with models showing climate change.

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