The impact of El Niño-Southern Oscillation (ENSO) on the East Asian Monsoon (EAM) has been examined using a general circulation model (GCM). The observed monthly changes in sea surface temperature (SST) in the equatorial Pacific east of 172°E during 1950-99 were inserted as the lower boundary condition of the model. For all oceanic grid points lying outside of the region of SST prescription, the atmosphere was coupled to an oceanic mixed layer model. The typical evolution of the atmosphere-ocean system during ENSO was analyzed using composite charts. These patterns show that the key changes in the EAM sector are related to a prominent sea level pressure anomaly simulated over the South China Sea and subtropical northwestern Pacific. During warm ENSO events, the circulation anomalies associated with this anomalous anticyclone correspond to weaker winter monsoon flows along the East Asian coast, as well as above-normal precipitation over southern China. These signals move systematically eastward during the following spring and summer. Stationary wave modeling indicates that the atmospheric anomaly in the EAM region is essentially a Rossby-wave response to the ENSO-related diabatic heating pattern over the equatorial western Pacific. The wintertime atmospheric circulation anomalies over the western Pacific generate strong SST anomalies in the following spring. Further model diagnoses indicate that the feedback of these SST changes on the atmosphere leads to eastward propagation of the pressure anomaly in the EAM region, and to amplification of rainfall anomalies along the Meiyu-Baiu front. The atmospheric and oceanic changes in the EAM sector described in this chapter are discussed in the broader context of ENSO influences on the entire Asian-Australian monsoon system.
|Original language||English (US)|
|Number of pages||30|
|Journal||World Scientific Series on Asia-Pacific Weather and Climate|
|State||Published - 2019|
All Science Journal Classification (ASJC) codes
- Global and Planetary Change
- Atmospheric Science