Discrepancies between observed and ocean general circulation model-simulated anomalies in recent SSTs of the tropical Indian Ocean caused by apparent trends in atmospheric reanalysis data

摘要

We investigated the discrepancy between observed and ocean general circulation model (OGCM)-simulated anomalies in recent sea surface temperatures (SSTs) of the tropical Indian Ocean. Observed SSTs show a warming beginning in the late 1990s, whereas simulated SSTs show a cooling over the same period. Examination of surface heat fluxes in the OGCM showed that the simulated SST cooling was caused primarily by a decreasing trend in the reanalyzed solar radiation used as the surface boundary condition. In the atmospheric reanalysis, the decrease in solar radiation was attributed to an increase in cloud cover, deduced from precipitation data, and in part responding to observed local warming of the Indian Ocean SSTs prescribed as the lower boundary condition. Observation-based estimates of precipitation, however, show no significant increasing trend, so no increase in cloud cover is indicated. Caution is needed when atmospheric reanalysis data are used for surface boundary conditions for OGCMs.