The responses of East Asian Summer monsoon to the North Atlantic Meridional Overturning Circulation in an enhanced freshwater input simulation

• Published in: Chinese science bulletin Vol. 54; no. 24; pp. 4724 - 4732
• Main Authors: Yu, Lei, Gao, YongQi, Wang, HuiJun, Guo, Dong, Li, ShuangLin
• Format: Journal Article
• Language: English
• Published: Heidelberg SP Science in China Press 01.12.2009
• Subjects: Atmospheric Science; Brackish; Chemistry/Food Science; Earth Sciences; Engineering; Freshwater; Humanities and Social Sciences; Life Sciences; Marine; multidisciplinary; Physics; Science; Science (multidisciplinary); 东亚夏季风; 北大西洋; 沃克环流; AN, North Atlantic; North America; IS, Tropical Pacific; Hadley Circulation; Walker Circulation; freshwater; East Asian Summer Monson; AMOC
• ISSN: 1001-6538; 2095-9273; 1861-9541; 2095-9281
• DOI: 10.1007/s11434-009-0720-3

We investigated the response of the East Asian Summer Monsoon （EASM） to a weakened Atlantic Meridional Overturning Circulation （AMOC） and its mechanism in an enhanced freshwater input experiment （FW） by using a fully-coupled climate model. The response was a weakened EASM and the mechanisms can be explained as follows. The simulated weakened AMOC resulted in a drop in sea surface temperature （SST） in the North Atlantic （NA） and, correspondingly, an anomalous high sea level pressure （SLP） over the North American regions, which in turn increased the northeast surface winds across the equator in the eastern tropical Pacific （ETP）. The anomalous northeast winds then induced further upwelling in the ETP and stronger air/sea heat exchange, therefore leading to an anomalous cooling of the eastern tropical sea surface. As a result, the climatologic Hadley Circulation （HC） was weakened due to an anomalous stronger sinking of air in the ETP north of the equator, whereas the Walker Circulation （WC） in the western tropical Pacific （WTP） north of the equator was strengthened with an eastward-shifted upwelling branch. This feature was in agreement with the anomalous convergent winds in the WTP, and led to a weakened EASM and less East Asian summer precipitation （EASP）. Furthermore, comparison with previous freshwater experiments indicates that the strength of EASP could be influenced by the magnitude of the added freshwater.