- Meteorological Society of Japan
- 気象集誌. 第2輯 (ISSN:00261165)
- pp.2020-014, (Released:2019-12-08)
The East Asian summer monsoon (EASM) and the Australian winter monsoon (AWM) are two important components of the Asian-Australian monsoon system during boreal summer. The simultaneous variations of these two monsoons would have remarkable impacts on climate in the Asian-Australian region. Using the reanalysis datasets, we investigate the mechanisms of variation and impacts of East Asian-Australian Monsoons (EAAMs). The singular value decomposition (SVD) is performed of the June-July-August (JJA) mean anomalous zonal wind for AWM as left field and JJA mean anomalous meridional wind for EASM as the right field after both El Niño-Southern Oscillation (ENSO) and India Ocean Dipole (IOD) signals are filtered out. Our results demonstrate that AWM and EASM are closely related to each other as revealed by the first leading SVD mode. The anomalously strong (weak) EAAMs correspond to anomalously strong (weak) AWM and EASM to the south of 30°N. When EAAMs are anomalously strong, cold sea surface temperature anomaly (SSTA) appears in regions near northern and northeastern coasts of Australia whereas the warmer SSTA appears in the northwestern tropical Pacific and South China Sea. The colder SSTA is associated with the upwelling of cold water from below induced by equatorial easterly anomalies, reinforcing the anticyclonic circulation over Australia through the Matsuno/Gill-type response whereas warm SSTA appears in the northwestern tropical Pacific and South China Sea as a result of oceanic response to the intensified northwest Pacific subtropical anticyclonic circulation. The EASM couples with AWM via the anomalous easterlies near equator in the Maritime Continent (MC) region and the slanted vertical anomalous circulations. In the years with strong EAAMs, precipitation decreases in northern Australia and over areas from the western Pacific to Bohai Sea and Yellow Sea of China. Meanwhile, the western MC and the southeastern China experience more than normal precipitation.