关键词: 台风, 降水, 辐合, 温度, 露点

Abstract:  Based on NCEP/NCAR reanalysis data and observation data from radar, sounding station and ground-encrypted observations, the reason why the precipitation center of the northward NO.10 typhoon “Ambi” moved from its right front side to left front side and the precipitation intensity increased significantly  were analyzed. The results are as follows: (1) The 500 hPa western Pacific subtropical high ridge line on 24 July 2018 extended abnormally northward, and the southerly air flow on its west side provided favorable circulation conditions for the typhoon moving northward. At the same time, the stability of the upper warm ridge prevented the eastward movement of the west trough, and enabled the “Ambi” to maintain a complete warm core structure when it moved northward to 40°N. (2) At 08:00 BST on July 24, the southwest jet on 200 hPa strengthened, the divergence and the ascending motion both enhanced on the right side of southwest jet entrance area, and the latent heat of condensation released, which further strengthened the low-altitude convergence and the ascending motion on the north side of “Ambi” and promoted the precipitation enhancement. (3) At 08:00 BST on July 24, the northeastern wind speed on 925 hPa in the northwestern part of the “Ambi” reduced to 4 m·s-1, while the easterly jet in the northestern part of the “Ambi” increased to 25 m·s-1, which caused the convergence center moving westward and the precipitation center moving westward. (4) The water vapor transport mainly concentrated below 850 hPa. The net inflow of water vapor transport was mainly from input of zonal wind from the eastern boundary of the precipitation area. Compared with 20:00 BST on July 23, net input of water vapor in the latitudinal direction increased by 3 times at 08:00 BST on 24. (5) On night of  July 23, “Ambi” carring warm and humid airflow moved northward, and temperature and dew point in the northwest side of the typhoon center gradually declined due to radiation cooling and weak cold air infiltration, but temperature and dew point on the southeast side were still high, which caused northwest-southeast temperature and dew point gradient. The corresponding mesoscale rain belt made the precipitation center move to the left front of the moving path.

Key words: typhoon, precipitation, convergence, temperature, dewpoint