Study reveals decadal variation of relationship between East Asian summer monsoon and El Nino

November 9, 2017, Chinese Academy of Sciences
Study reveals decadal variation of relationship between EA summer monsoon and ENSO
Schematic representation of the Sea Surface Temperature (sst) anomalies over the Indian Ocean and the western tropical Pacific and western North Pacific anomalous anticyclone (WPAC) in the decaying summer of El Niño events. Credit: Institute of Atmospheric Physics

East Asian summer monsoon (EASM) is one of the most dominant climate systems in East Asia. The anomalous EASM can cause extreme high temperatures, floods or drought. And the 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 period of observational data, the related studies of decadal or multidecadal variation of ENSO and EASM have their own drawbacks. Therefore, model becomes an important tool. Using a coupled climate model with a 1000-year simulation, scientists from CAS Institute of Atmospheric Physics investigated the multidecadal variations of the EASM-ENSO interannual relationship. The EASM-ENSO interannual relationship is found to have experienced multidecadal variations.

During periods with a 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 the lower troposphere, and from the mid-latitudes to the south in the upper troposphere. The resulting 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 a weak ENSO-EASM relationship.

"The main reason for the multidecadal variations of ENSO-EASM 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.

Explore further: Scientists unravel effect of ENSO and Atlantic multidecadal oscillation on the East Asian winter monsoon

More information: Bo Liu et al, The multidecadal variations of the interannual relationship between the East Asian summer monsoon and ENSO in a coupled model, Climate Dynamics (2017). DOI: 10.1007/s00382-017-3976-3

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