Role of the Indochina Peninsula Narrow Mountains in Modulating the East Asian-Western North Pacific Summer Monsoon
Chi-Hua Wu1 and Huang-Hsiung Hsu1

1Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan



Unrealistic topographic effects are generally incorporated in the global climate simulations and may contribute significantly to model biases in the Asian monsoon region. By artificially implementing the Arakan Yoma and Annamese Cordillera-two south-north oriented high mountain ranges in the coasts of the Indochina Peninsula-in an 1° global climate model, we demonstrate that the proper representation of mesoscale topography over the Indochina Peninsula, is crucial for simulating realistically the seasonality of East Asian-western North Pacific (EAWNP) summer monsoon.

Presence of the Arakan Yoma and Annamese Cordillera helps simulate the vertical coupling of atmospheric circulation over the mountain regions. In late May, the existence of the Arakan Yoma enhances the vertically deep southwesterly flow originating from the trough over the Bay of Bengal. The ascending southwesterly flow converges with the midlatitude jet stream downstream in the southeast of the Tibetan Plateau and transports moisture across the Indochina Peninsula to East Asia. The existence of the Annamese Cordillera helps the northward lower-tropospheric moisture transport over the South China Sea into the Meiyu-Baiu system, and the leeside troughing effect of the mountains likely contributes to the enhancement of the subtropical high to the east. Moreover, the eastward propagation of wave energy from Central Asia to EAWNP suggests a dynamical connection between the midlatitude westerly perturbation and Meiyu-Baiu. Including the Annamese Cordillera also strengthens a Pacific-Japan (PJ) pattern-like perturbation in late July, by enhancing the cyclonic circulation (i.e. monsoon trough) in the lower-tropospheric western North Pacific. This suggests the contribution of the mountain effects to intrinsic variability of the summer monsoon in EAWNP.

Wu, C. H., and H. H. Hsu, 2016: Role of the Indochina Peninsula narrow mountains in modulating the East Asia-Western North Pacific summer monsoon. J. Climate, JCLI-D-15-0594. (Published online: 22 March, 2016)


Role of the Indochina Peninsula Narrow Mountains in Modulating the East Asian-Western North Pacific Summer Monsoon.png

Schematic diagram of the atmospheric response (200hPa, 500hPa, and 850hPa) to the mountains for (a) LATE MAY and (b) LATE JULY. Orange color denotes general feature in each period and blue color denotes mountain-induced changes. Abbreviations: H for high pressure and AC/C for anticyclonic/cyclonic circulation anomaly.