Response of the Winter Moisture Circulation to the India-Burma Trough and Its Modulation by the South Asian Waveguide

Abstract:

The response of the winter moisture circulation to the daily evolution of the India-Burma Trough (IBT) is investigated based on the abnormal IBT cases during 1979-2014. The responded moisture circulation is characterized by zonally oriented wave trains along the South Asian waveguide from the northern Atlantic to the WNP. The abnormal moisture transported by the IBT is a part of such wave trains but persists longer and migrates further eastward than those in the upstream. As a strong IBT develops, the cyclonic moisture transport starts to build up over the Indian subcontinent–Indochina Peninsula, enhancing the moisture transport to South China gradually via the southern boundary. Such moisture transport shifts eastward abruptly after the peak of the IBT with the IBT-caused winter precipitation anomaly shifting from the west to the east over South China. Such moisture circulation response is the joint efforts of the synoptic, intraseasonal and interannual components which show similar wave-train structures, whereas slight differences still occur in the wavelength, propagation path, propagation and migration speeds. The synoptic moisture convergence is more intensive than other components along the waveguide except over Southeast Asia where all components are comparable. Investigation of the atmospheric circulation shows that the wave-train moisture circulation response is mainly attributed to the wind disturbance which is barotropic with the upper signals shifting slightly northward. The wave energy emitted from the Mediterranean Sea and its downward propagation is crucial for the IBT variation and the responded moisture circulation.