A diagnosis of the extreme rainfall associated with the typhoon Morakot in southern Taiwan: Roles of submonthly disturbance and 40-50-day ISO

Typhoon Morakot struck Taiwan from 7-9 August 2009, causing 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 TWNP (tropical western North Pacific). Morakot's landing on Taiwan occurred concurrently with the arrival of a large-scale cyclonic circulation in a submonthly wave pattern (10-30-day) during the cyclonic phase of the 40-50-day ISO (intraseasonal oscillation). It is suggested that the multiscale interaction between the typhoon and large-scale circulation and the topographic effect of the steep terrain in Southern Taiwan were the key factors leading to this extreme event.