Global atmospheric sensitivity to tropical SST anomalies throughout the Indo-Pacific basin

The sensitivity of the global atmospheric response to sea surface temperature (SST) anomalies throughout the tropical Indian and Pacific Ocean basins is investigated using the NCEP MRF9 general circulation model (GCM). Model responses in January are first determined for a uniform array of 42 localized SST anomaly patches over the domain. Results from the individual forcing experiments are then linearly combined using a statistically based smoothing procedure to produce sensitivity maps for many target quantities of interest, including the geopotential height response over the Pacific - North American (PNA) region and regional precipitation responses over North America, South America, Africa, Australia, and Indonesia. Perhaps the most striking result from this analysis is that many important targets for seasonal forecasting, including the PNA response, are most sensitive to SST anomalies in the Nino-4 region (5degreesN-5degreesS, 150degreesW-160degreesE) of the central tropical Pacific, with lesser and sometimes opposite sensitivities to SST anomalies in the Nino-3 region (5degreesN-5degreesS, 90degrees-150degreesW) of the eastern tropical Pacific. However, certain important targets, such as Indonesian rainfall, are most sensitive to SST anomalies outside both the Nino-4 and - 3 regions. These results are also relevant in assessing atmospheric sensitivity to changes in tropical SSTs on decadal to centennial scales associated with natural as well as anthropogenic forcing. In this context it is interesting to note the surprising result that warm SST anomalies in one-third of the Indo-Pacific domain lead to a decrease of global mean precipitation.