East Asian summer monsoon (EASM) is one of the most dominant climate systems in East Asia. The anomalous EASM can cause the extreme high temperature, flood or drought. And El Niño-Southern Oscillation (ENSO), the dominating mode in the tropical Pacific, is the most important factor affecting EASM. Understanding the processes for interannual to interdecadal variability of EASM-ENSO relationship is crucial.
Owing to the limited available time of the observational data, the related studies of decadal or multidecadal variation of ENSO and EASM have their own drawbacks. Therefore, climate model becomes an important tool. Using a coupled climate model with a 1000-year simulation, scientists from CAS Institute of Atmospheric Physics investigate the multidecadal variations of the EASM-ENSO interannual relationship. The EASM-ENSO interannual relationship is found to have experienced multidecadal variations. During the periods with significant ENSO-EASM relationship, the ENSO-related circulation anomalies show a Pacific-Japan (PJ)-like pattern with significant wave-activity flux propagating from the tropics to the north in lower troposphere and from the mid-latitudes to the south in upper troposphere. The resultant ENSO-related precipitation anomalies are more (less) than normal over the East Asia (Western North Pacific) in the decaying summers of El Niño events. In contrast, the circulation and precipitation anomalies are weak over East Asia-western North Pacific during the periods with weak ENSO-EASM relationship.
"The main reason caused the multidecadal variations of ENSO-EASM relationship is the amplitude discrepancy of SST anomalies over the Indo-western Pacific Ocean", says HUANG Gang, the corresponding author of the study, " and the discrepancy in turn leads to the intensity difference of the western North Pacific anomalous anticyclone and related climate anomalies over the East Asia-Western North Pacific." The study is published in Climate Dynamics.