Effects of vertical wind shear on intensity and rainfall asymmetries of strong Tropical Storm Bilis (2006)

• DOI: 10.1007/s00376-009-9030-6
• Publication Date: 2010-04-19T23:12:17Z
• Authors: Jinhua Yu; Zhemin Tan; Yuqing Wang
• Keywords: Eye; Rainband; Intensity

The effects of environmental vertical wind shear (VWS) on the intensity and rainfall asymmetries in Tropical Storm (TS) Bilis (2006) have been analyzed based on TRMM/TMI-estimated surface rainfall data, QuikSCAT wind fields, 850- and 200-hPa winds of the NCEP-NCAR reanalysis, precipitation data at 5-min intervals from automatic weather stations over mainland China, and the best track data of TS Bilis (2006). The results show that the simultaneous and 6-hour-lagged correlation coefficients between VWS and storm intensity (the minimum central sea level pressure) are 0.59145 and 0.57438 (P < 0.01), respectively. The averaged VWS was found to be about 11 m s−1 and thus suppressed the intensification of Bilis (2006). Distribution of precipitation in Bilis (2006) was highly asymmetric. The azimuthally-averaged rainfall rate in the partial eyewall, however, was smaller than that in a major outer rainband. As the storm intensified, the major rainband showed an unusual outward propagation. The VWS had a great impact on the asymmetric distribution of precipitation. Consistent with previous modeling studies, heavy rainfall generally occurred downshear to downshear-left of the VWS vector both near and outside the eyewall, showing a strong wavenumber-one asymmetry, which was amplified as the VWS increased.