Thursday, 15 January 2004: 11:30 AM
The Scatter in Tropical Average Precipitation Anomalies
Room 608
Tropical mean precipitation anomalies appear quite scattered
in relation to tropical average sea surface temperature (SST) anomalies
, based on examination of a number of observational datasets and
atmospheric general circulation model (GCM) results. For a given warm
SST anomaly, the tropical average precipitation anomalies can be of either
sign due to the near-cancellation of positive against negative
values. No simple relation is found between and . On the other hand,
tropical average tropospheric temperature anomalies are approximately
linearly related to SST forcing. The scatter of versus and
challenges the prevailing view that tropical tropospheric
temperature anomalies are proportional to tropical convective heating
anomalies (i.e. precipitation anomalies), while the latter are governed
by SST forcing. A simple analytical model shows that convective heating
anomalies are more strongly influenced by dry static energy transports
into or out of the tropics and by nonlinearities within the tropics
than are the tropospheric temperature anomalies. Convection plays an
important role in transporting upward the effects of boundary forcing
to constrain the tropospheric temperature, but the amount of convective
heating is subject to complex balances with various cooling mechanisms.
Thus the tropical average convective heating anomalies are
only weakly related to SST anomalies, allowing mid-latitude transports
to create large scatter.
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