Onset of the Summer Monsoon over the Southern Vietnam and its PredictabilityReport as inadecuate

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1 CRC - Centre de Recherches de Climatologie

Abstract : The summer monsoon onset over southern Vietnam is determined through a new criterion based on both in situ daily rainfall at 6 selected stations provided by the Institute of Meteorology and Hydrology, Vietnam, and the zonal component of the wind at 1000hPa from the National Center for Environmental Prediction-Department of Energy reanalysis 2 NCEP-DOE-II. Over the period 1979-2004, the summer monsoon onset mean date is on 12 May, with a standard deviation of 11.6 days. The temporal and spatial structures of the atmospheric conditions prevailing during the onset period are detailed. Clear changes are seen in the zonal wind strengthened over the Bay of Bengal and changed from negative to positive over South Vietnam and in convection deeper, in association with an intensification of the meridional gradients of sea level pressure at 1000hPa and of moist static energy at 2m over Southeast Asia. The predictability of onset dates is then assessed. Cross validated hindcasts based upon 4 predictors linked to robust signals in the atmospheric dynamics are then provided. They are highly significant when compared to observations 56% of common variance. Basically, late early onsets are preceded in March-April by higher lower sea level pressure over the East China Sea, stronger weaker southeasterly winds over southern Vietnam, decreasing increasing deep convection over the Bay of Bengal and the reverse situation over Indonesia 120°E-140°E, 0-10°S.

Author: Thanh H Pham - Bernard Fontaine - Nathalie Philippon -

Source: https://hal.archives-ouvertes.fr/


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