Interdecadal Variation of the Atmospheric Heat Source over the Tibetan Plateau and Surrounding Asian Monsoon Region: Impact on the Northern Hemisphere Summer Circulation

We use 71-yr (1948–2018) reanalysis data to investigate the interdecadal variation in the atmospheric heat source (Q₁) over the Tibetan Plateau and surrounding Asian monsoon region (AMTP) and its effect on the Northern Hemisphere summer circulation. The large-scale circulation driven by Q₁ over the AMTP is characterized by a center of convergent (divergent) or low (high) potential wind function in the lower (upper) troposphere. Q₁ over the AMTP shows a clear interdecadal variation (with positive–negative–positive phases) and these three phases correspond to the time periods 1948–1972, 1973–2005, and 2006–2018, respectively. The thermal circulation has a corresponding interdecadal variation as a response to the interdecadal variation in Q₁. An enhanced Q₁ leads to an increase in the conversion of the total potential energy to non-divergent wind kinetic energy via the divergent wind velocity. The maximum conversion occurs in the tropopause. The primary thermal forcing for Q₁ is produced by the intense, large volume precipitation of the summer monsoon. This induces a response in the large-scale circulation, leading to large-scale divergence patterns. The synergistic effects of Pacific Decadal Oscillation (PDO) and North Atlantic Multi-decadal Oscillation (AMO) influence Q₁ over the AMTP, which is ultimately responsible for the modulation of variations in the global divergent circulation. The global divergent circulation in summer is therefore essentially a direct thermodynamic circulation driven by the strong Q₁ over the AMTP.