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

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 large‐scale 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 rainfall in Southern Taiwan.