11.3

The Scatter in Tropical Average Precipitation Anomalies

Hui Su, University of California, Los Angeles, CA; and J. D. Neelin

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.

Session 11, Observed Seasonal/Interannual Variability (Room 608)
Thursday, 15 January 2004, 11:00 AM-3:00 PM, Room 608

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