Interannual covariability of summer monsoon precipitation in Yunnan, China, and diabatic heating anomalies over the Arabian Sea-Bay of Bengal

摘要

Covariability of summer monsoon precipitation in Yunnan and diabatic heating anomalies over the Arabian Sea-Bay of Bengal (AS-BOB) is analyzed using ERA-Interim monthly reanalysis data and monthly mean precipitation data from 124 stations across Yunnan, China. Singular value decomposition analysis indicates a seesaw pattern associated with the diabatic heating over the AS-BOB and summer monsoon precipitation in Yunnan over interannual timescales. When the diabatic heating over the AS-BOB is weaker (stronger) than the climatology during the summer monsoon season, more (less) summer monsoon precipitation generally occurs in Yunnan. A significant correlation between the diabatic heating over the AS-BOB and summer monsoon precipitation in Yunnan begins in late spring-early summer and persists throughout the summer. The AS-BOB diabatic heating in late spring-early summer may thus have a prediction potential for summer monsoon precipitation in Yunnan. The anomalous low-level winds associated with the diabatic heating anomalies over the AS-BOB influence the Indian summer monsoon trough, the vertical motion in Yunnan, and then the summer monsoon precipitation. Numerical experiments based on a linear baroclinic model confirm the key physical process revealed in the observational diagnosis. These experiments also indicate that the diabatic heating over the AS-BOB has a greater impact on summer monsoon precipitation in Yunnan than does diabatic heating around Yunnan on the atmospheric circulation over the AS-BOB. The diabatic heating anomalies over the AS-BOB contributed to the severe summer droughts in Yunnan in 2010, 2011, and 2013 by influencing the circulation.