[Climate dynamics] Modulation of the Indian Ocean SST on the Interannual Variability of Heat Source over the Tibetan Plateau in Late Spring

Previous studies have indicated that, as a capacitor of ENSO signals, the Indian Ocean Basin Mode (IOBM) can maintain the boreal winter ENSO signals to spring and summer in the next year, and further modulate the Asian summer monsoon. Meanwhile, the so-called 'sensible heat pump' over the Tibetan Plateau (TP) is also considered to be a key factor that dominates the Asian summer monsoon. Combining these two aspects, a clearer understanding of the Asian monsoon requires us to investigate the relationship between the adjacent plateau heat source and the remote large-scale SST forcing in the Indian Ocean.

Considering the very different background circulation in different stages of ASM onset, traditionally seasonal mean viewpoint on this topic may obscure some important information. Here, by choosing month by month study, we found that, with seasonal evolution from winter to summer and the westerly jet move northward, the surface wind changes its direction after the summer monsoon onset over the Bay of Bengal, and the TP surface sensible heating is closely related to the IOBM signal in May, which is totally different from the case in February-April.

Results from both data diagnosis and numerical simulation suggest that, due to the intensified local Hadley cell during the IOBM warm-phase years, the cloud amount, radiation flux and precipitation over the plateau receive significant influence, inducing the significantly intensified in situ surface heat source. This work provides further insight of the intrinsic connection between the remote oceanic forcing and the TP heat source, with emphasis on the land-air-sea interaction of the nature of monsoon and earth climate system.

Figure 1. IOBM-induced circulation behave like a reinforced local Hadley Circulation which arise from the southwestern tropical Indian Ocean, and descend at Bay of Bangle and Southeastern Tibetan Plateau (Red vector).

Figure 2 Indian Ocean Basin Mode (IOBM, bottom left) induces a local Hadley circulation (top panel) which arises from the southwestern tropical Indian Ocean, and descend at Bay of Bangle and Southeastern Tibetan Plateau (bottom right), suppressing local precipitation and cloud volume and further enhancing the surface sensible heat.

Citation:

Zhao, Y., Duan, A. & Wu, G. Interannual Variability of Late-spring Circulation and Diabatic Heating over the Tibetan Plateau Associated with Indian Ocean Forcing. Adv. Atmos. Sci. (2018) 35: 927. https://doi.org/10.1007/s00376-018-7217-4

Contact: ZHAO Yu, zhaoyu@lasg.iap.ac.cn