The variability of the East Asian summer monsoon (EASM) on the interannual timescale is jointly affected by the thermal forcing from the ocean and land. How does the Tibetan Plateau (TP) thermal feedback regulate the response of the EASM to the global sea surface temperature anomaly (SSTA)? A new research published in Journal of Geophysical Research: Atmospheres led by the scientists from the Institute of Atmospheric Physics (IAP) at the Chinese Academy of Sciences and National University of Singapore (NUS) addressed this question.

"The EASM is known to have very different responses to the SSTA in developing and decaying years. Yet, there's almost no convincing explanation for such an asymmetric response," Prof. DUAN Anmin from the IAP, the corresponding author of the study, stated the motif of the study.

 
To investigate the underlying mechanism, the team used an atmospheric general circulation model called Finite-volume Atmospheric Model, developed by the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG) of the IAP to design and conduct the numerical experiments.

Their study revealed that the global SSTA during the four-year cycle has significant impacts on the anomaly of diabatic heating over the TP in summer. In the developing year summer, the diabatic heating weakens over the whole TP, leading to less rainfall over East Asia, an anomalous cyclone over the northwestern Pacific and an anticyclone in North China. In the decaying year summer, the SSTA induces an anomalous anticyclone in South China and an anomalous cyclone in North China. The TP heating shows an anomalous negative-positive pattern.

"Without the anomalous TP thermal forcing, in both developing and decaying years the EASM shows similar response patterns with an anomalous anticyclone over the northwestern Pacific, an anomalous cyclone in North China, and an enhanced main rainfall band." Prof. DUAN added.

Schematic diagram to summarize the responses of the low-level circulation to the global SSTA with/without the TP thermal feedback effect and the TP thermal feedback. (Image by LIU Senfeng)

DUAN along with collaborators from National University of Singapore concluded that the TP thermal feedback plays a key role in the asymmetric responses of the EASM to the global SSTA during the different stages, which causes less precipitation in developing years and an enhanced main rainfall band in decaying years.

Citation: Liu, S., Duan, A., & Wu, G. (2020). Asymmetrical response of the East Asian summer monsoon to the quadrennial oscillation of global sea surface temperature associated with the Tibetan Plateau thermal feedback. Journal of Geophysical Research: Atmospheres, 125, e2019JD032129. https://doi.org/10.1029/2019JD032129

Media contac: Ms. LIN Zheng, jennylin@mail.iap.ac.cn