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

Abstract

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.