Characteristics and Preliminary Causes of Tropical Cyclone Extreme Rainfall Events over Hainan Island

摘要

The characteristics of tropical cyclone (TC) extreme rainfall events over Hainan Island from 1969 to 2014 are analyzed from the viewpoint of the TC maximum daily rainfall (TMDR) using daily station precipitation data from the Meteorological Information Center of the China Meteorological Administration,TC best-track data from the Shanghai Typhoon Institute,and NCEP/NCAR reanalysis data.The frequencies of the TMDR reaching 50,100 and 250 mm show a decreasing trend [-0.7 (10 yr)-1],a weak decreasing trend [-0.2 (10 yr)-1] and a weak increasing trend [0.1 (10 yr)-1],respectively.For seasonal variations,the TMDR of all intensity grades mainly occurs from July to October,with the frequencies of TMDR ≥ 50 mm and ≥ 100 mm peaking in September and the frequency of TMDR ≥ 250 mm [TC extreme rainstorm (TCER) events] peaking in August and September.The western region (Changjiang) of the Island is always the rainfall center,independent of the intensity or frequencies of different intensity grades.The causes of TCERs are also explored and the results show that topography plays a key role in the characteristics of the rainfall events.TCERs are easily induced on the windward slopes of Wuzhi Mountain,with the coordination of TC tracks and TC wind structure.A slower speed of movement,a stronger TC intensity and a farther westward track are all conducive to extreme rainfall events.A weaker northwestern Pacific subtropical high is likely to make the 500-hPa steering flow weaker and results in slower TC movement,whereas a stronger South China Sea summer monsoon can carry a higher moisture flux.These two environmental factors are both favorable for TCERs.