第九届青年地学论坛

The movement of tropical cyclone (TC) Khanun (2017) was studied by the analysis of the data from the Weather Research and Forecasting (WRF) model simulation. The comparison in motion of the TC between observation and simulation generally shows the best agreement at 500 hPa. The simulated motion is induced by the ventilation flow of both environmental vector (Ve) and asymmetric rotational vector (Vψa) averaged over the area with the radius of 200 km from the center. The results reveal that during the intensification period of Khanun, Ve barely changes, while the intensity and direction of Vψa exhibits significant changes as Khanun moves from southwestward to the northwestward. The moving direction switch is consistent with the rotation of ventilation flow vector of Vψa as shown in the streamfunction analysis. The results show that the cyclonic circulation center rotates counterclockwisely from the northeast in the slow intensification period to the north in the rapid intensification period and wanders in the rapid intensification period. The calculation of asymmetric rotational kinetic energy (Kψa) reveals that the rapid counterclockwise rotation results from the conversion from environmental kinetic energy (Ke) to Kψa through the interaction between Vψa and environmental tangential wind. During the rapid intensification period, the slightly counterclockwise rotation from the north results from the conversion from Ke to Kψa through the interaction between Vψa and asymmetric rotational tangential wind. The slightly clockwise rotation back to the north later is caused by the conversion from symmetric rotational kinetic energy (Kψs) to Kψa induced by the advection of symmetric rotational tangential wind by environmental radial wind.