Role of submonthly disturbance and 40-50 day ISO on the extreme rainfall event associated with Typhoon Morakot (2009) in Southern Taiwan

摘要

Typhoon Morakot that made landfall on Taiwan during 7-9 August 2009 caused record-breaking rainfall in Southern Taiwan and nearly 700 deaths from mudslides. It was the most severe natural disaster in Southern Taiwan caused by a typhoon in 50 years. Different from typical typhoon cases, characterized by an isolated vortex, Typhoon Morakot was embedded in a large-scale convection region with monsoon circulation of different time scales in the tropical western North Pacific. Morakot's landing on Taiwan occurred concurrently with the arrival of a largescale cyclonic circulation in a submonthly wave pattern (10-30-day) during the cyclonic phase of the 40-50-day intraseasonal oscillation. It is suggested that the abundant moisture supply from the southwesterly embedded in the multiscale large-scale circulation and the topographic lifting effect of steep terrain resulted in the record-breaking raintall in Southern Taiwan.