NUMERICAL SIMULATION STUDY OF THE INNER-CORE STRUCTURES AND THE MECHANISM FOR INSHORE STRENGTHENING OF SOUTH CHINA SEA TYPHOON VONGFONG (0214) DURING LANDFALL |
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Authors: | LI Jiang-nan HUANG Xiao-dong WANG Gang FONG Soi-kun and LI Wei-biao |
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Institution: | 1. School of Environmental Science and Engineering,Sun Yat-sen University,Guangzhou 510275 China 2. Jiangmen Meteorological Bureau,Jiangmen 529020 China 3. Macao Geophysical and Meteorological Bureau,Macao China |
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Abstract: | An explicit simulation with a fine mesh at intervals of 6 km is used to explore the inner-core
structures of Vongfong (0214). The dynamic mechanism for the inshore strengthening of Vongfong is
examined. It is found as follows. (1) The radius of maximum wind of the axisymmetric structures of the
typhoon decreased with height during its mature stage. When Vongfong was inshore, the strongest
low-layer inflow located in front of it and the outflow was to the rear of it, which was just reversed from
the Atlantic hurricanes and other Pacific typhoons. (2) The dynamic and thermodynamic fields were highly
asymmetric in structure. Convection was stronger in the northwest quadrant of the typhoon than in the
southeast; the strongest convective cloud bands were consistent with the maximum wind region. During its
strengthening stage, it was cold west of and warm east of the eye in the lower layer but warm in the west
and cold in the east of the mid-upper layer. During its mature stage, a warm-core structure was evident in
the lower and middle-upper layer. (3) The interactions between a mid-latitude cold low in the
middle-upper troposphere and the typhoon were responsible for the latter to strengthen inshore. Firstly, the
outer circulation of the cold low entered the typhoon from the middle troposphere when an outer cold
airflow from the cold low flowed into the northwest quadrant of the typhoon so that geopotentially instable
energy increased and convection developed. Secondly, the downdraft in the cold low was just the
corresponding branch of the secondary circulation of the typhoon system; when the cold low weakened
while moving south, the typhoon strengthened inshore. Due to the CISK mechanism, these two phenomena
might be realized. |
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Keywords: | dynamic meteorology typhoons numerical simulation structure |
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