Insight into the Role of Lower-Layer Vertical Wind Shear in Tropical Cyclone Intensification over the Western North Pacific |
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| Authors: | SHU Shoujuan WANG Yuan and BAI Lina |
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| Institution: | 1. Key Laboratory of Mesoscale Severe Weather/Ministry of Education, and School of Atmospheric Sciences, Nanjing University, Nanjing 210093
2. Key Laboratory of Mesoscale Severe Weather/Ministry of Education, and School of Atmospheric Sciences, Nanjing University, Nanjing 210093;Shanghai Typhoon Institute, China Meteorological Administration, Shanghai 200030 |
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| Abstract: | Vertical wind shear fundamentally influences changes in tropical cyclone (TC) intensity. The effects of vertical wind shear on tropical cyclogenesis and evolution in the western North Pacific basin are not well understood. We present a new statistical study of all named TCs in this region during the period 2000–2006 using a second-generation partial least squares (PLS) regression technique. The results show that the lower-layer (between 850 hPa and 10 m above the sea surface) wind shear is more important than the commonly analyzed deep-layer shear (between 200 and 850 hPa) for changes in TC intensity during the TC intensification period. This relationship is particularly strong for westerly low-level shear. Downdrafts induced by the lower-layer shear bring low θ e air into the boundary layer from above, significantly reducing values of θ e in the TC inflow layer and weakening the TC. Large values of deep-layer shear over the ocean to the east of the Philippine Islands inhibit TC formation, while large values of lower-layer shear over the central and western North Pacific inhibit TC intensification. The critical value of deep-layer shear for TC formation is approximately 10 m s?1, and the critical value of lower-layer shear for TC intensification is approximately ±1.5 m s?1. |
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| Keywords: | vertical wind shear tropical cyclone intensification western North Pacific |
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