Interdecadal Variation and Its Mechanisms of Summer Low Cloud Cover Over the Tibetan Plateau Lake Group

Abstract

This study explores the long-term change and associated mechanisms of low cloud cover (LCC) over the Tibetan Plateau lake group (TPLG). The LCC over the TPLG in the summer of 1979–2020 exhibited a sudden shift of increased interdecadal variation in 1995. The abnormal increases in evaporation and whole-layer specific humidity, and the abnormal convergence of 400 hpa water vapor flux, led to an increase in water vapor over the TPLG, which increased the LCC. The water vapor budget shows that the increase is the most significant along the southern boundary. The cyclonic circulation anomaly in the southwest of the TPLG can transport water vapor to the region. The southerly wind and upward wind anomalies in the south favored water vapor transport through the climbing effect. The water vapor budget at the eastern boundary of the TPLG had the highest correlation coefficient with LCC on the interdecadal scale. The anticyclonic circulation anomaly over Lake Baikal inhibited the outflow of water vapor across the eastern boundary. The anticyclonic circulation was associated with the Rossby wave train. The interdecadal warming of sea surface temperatures in the North Atlantic and Mediterranean-Black Seas played roles in the maintenance of the Rossby waves. The Rossby wave train propagated upward and eastward from the low layer to 200 hpa in the positive anomaly area of the Rossby wave source. The positive anomaly centers of the Rossby wave source were over the North Atlantic, the area around the Black Sea, and the southeastern region of Lake Baikal.