Fang, Wei TingWei TingFangChang, Pao LiangPao LiangChangMING-JEN YANG2024-03-282024-03-282024-03-0100270644https://scholars.lib.ntu.edu.tw/handle/123456789/641574Intensification of Typhoon Chanthu (2021) along the eastern coast of Taiwan was accompanied by pronounced asymmetry in eyewall convection dominated by wavenumber-1 features, as observed by a dense radar network in Taiwan. The maximum wind speed at 3-km altitude, retrieved from radar observations, exhibited a rapid increase of approximately 18 m s-1 within an 11-h period during the intensification stage, followed by a significant decrease of approximately 19 m s-1 within 8 h during the weakening stage. Namely, Chanthu underwent both rapid intensification (RI) and rapid weakening (RW) within the 24-h analyzed period, posing challenges for intensity forecasts. During the intensifying stages, the region of maximum eyewall convection asymmetry underwent a sudden cyclonic rotation from the eastern to the northern semicircle immediately after the initiation of terrain-induced boundary inflow from the south of the typhoon, as observed by surface station data. This abrupt rotation of eyewall asymmetry exhibited better agreement with radar-derived vertical wind shear (VWS) than that derived from global reanalysis data. This finding suggests that the mesob-scale VWS is more representative for tropical cyclones than meso-α-scale VWS when the terrain-induced forcing predominates in the environmental conditions. Further examination of the radar-derived VWS indicated that the VWS profile pattern provided a more favorable environment for typhoon intensification. In summary, Chanthu's RI was influenced by the three factors: 1) terrain-induced boundary inflow from the south of the typhoon, observed by surface station data; 2) low-level flow pointing toward the upshear-left direction; and 3) weak upper-level VWS.Hurricanes/typhoons | Intensification | Radars/Radar observations | Shear structure/flows | Surface observations | Topographic effects[SDGs]SDG13[SDGs]SDG14journal article10.1175/MWR-D-23-0155.12-s2.0-85186589333https://api.elsevier.com/content/abstract/scopus_id/85186589333