Tropical teleconnection and local response to SST anomalies during the 1997-1998 El Nino

The quasi-equilibrium tropical circulation model (QTCM) is used to examine the response to various sea surface temperature (SST) anomalies in the tropical oceans during the 1997-1998 El Nino. Both local and remote responses are noted. The negative precipitation anomalies to the north and south of the El Nino - Southern Oscillation (ENSO) enhanced precipitation region are largely a response to the warm SST anomalies in the central and eastern Pacific. However, in the western Pacific and maritime continent, reduction of rainfall is mainly caused by local cold SST anomalies. In the winter of the 1997-1998 El Nino, strong warm SST anomalies in the Indian Ocean contributed to the local enhanced rainfall. They affect precipitation anomalies in central, eastern, and southern Africa. The drought in northern South America is clearly a remote response to ENSO warm SST anomalies in the Pacific, while the SST anomalies in the Atlantic also impact the drought. The tropical Pacific cold SST anomalies surrounding the ENSO warm anomalies appear not to be caused by surface flux changes associated with atmospheric teleconnection (in simulations with specified SST in the ENSO warm region and a mixed-layer ocean model elsewhere). Atmospheric circulation tends to spread the warm anomalies, but ocean dynamics appears also to be important for both cold and warm SST anomalies outside the equatorial upwelling region. In both the regional specified SST experiments and mixed-layer experiments, relative subsidence tends to occur within convective zones, and it is generally localized. On the other hand, tropospheric temperature and wind anomalies spread much farther. The typical spatial scale of the remote response in temperature and wind fields tends to be larger than the dominant scale of the precipitation response. The remote response in precipitation anomalies does not appear to be related to temperature and wind anomalies in a simple manner.