[A-AS14] Extreme Events: Observations and Modeling

[AAS14-08] The Synoptically-Influenced Extreme Precipitation Systems over Asian-Australian Monsoon Region from TRMM PR Measurements

*Wei-Ting Chen¹, Hong-Wen Jian¹, Peng-Ren Chen¹, Chien-Ming Wu¹, Kristen L. Rasmussen² (1.National Taiwan University, 2.Colorado State University)

Keywords:Extreme rainfall systems, Synoptic-scale flow, TRMM

This study investigates the synoptic-scale flows associated with the extreme rainfall systems over the Asian-Australian monsoon region. Based on statistics of the 17-year Precipitation Radar observations from Tropical Rainfall Measurement Mission, a total of 916 extreme systems with both the horizontal size scale and maximum rainfall intensity exceeding the 99.9^th percentiles of the tropical rainfall systems were identified over this region. The annual number of occurrences of these systems showed an increasing trend of + 0.76 year^-1. The synoptic wind pattern and rainfall coverage distribution surrounding each system are classified into four major types: Vortex, Coastal, Coastal with Vortex, and None of the above, and each account for 44%, 29%, 7%, and 20%, respectively. Despite the different types of synoptic environment, these extremes show a similar internal structure, with broad stratiform and wide convective core rain. The occurrence of coastal-related types shows significant seasonal variations with high frequency at the Bay of Bengal in boreal summer and at the west side of Borneo and Sumatra in boreal winter. Besides, coastal-related types occur more frequently during late night to early morning (01-09 LT), and more likely with lightning flashes. High-frequency regions of both high total column water vapor and low-level vertical wind shear is consistent with the distribution of coastal-related extreme in the warm season. Our results highlight the critical role of the strength and direction of synoptic flows to the generation of extreme rainfall systems near the coastal areas. With the enhancement of the low-level vertical wind shear and moisture by the synoptic flow, the coastal convections triggered diurnally can have a higher chance to organize into meso-scale convective systems and hence higher probability to produce extreme rainfall.