Numerical Simulation of a Heavy Rainstorm in Northeast China Caused by the Residual Vortex of Typhoon 1909 (Lekima)

Abstract

From 14 to 17 August 2019, a heavy rainstorm occurred in Northeast China due to the combined influence of the residual vortex of typhoon 1909 (Lekima) and cold air intrusion. Based on the precipitation data of China Meteorological observation stations, surface and upper charts, HMW-8 satellite images, NCEP/NCAR 0.25° × 0.25° reanalysis data and WRF4.0 numerical prediction model are used to carry out numerical simulations. According to the weather situation and numerical simulation results, the cause of 1 h severe precipitation is thoroughly studied. Results show that: (1) According to the weather situation, the precipitation process can be divided into two stages. The first stage is from 1412 to 1612 August 2019, which is caused by the interaction between the residual vortex, the inverted trough of typhoon 1909 (Lekima) and the upper trough. The rain belt lies from northeast to southwest, and the rainfall center has typical meso-β-scale characteristics. At the second stage from 1612 to 1712 August 2019, the residual vortex of typhoon reaches Heilongjiang Province, at the same time, 500 hPa cold vortex falls to the south; (2) Based on the 1 h rainfall of automatic weather stations, it can be seen that there are three rainfall peaks from 00 UTC 14 to 12 UTC 17, which are 53.2 mm in the Middle East of Jilin Province, 38.2 mm in the south of 1610 Liaoning Province, and 21.3 mm in the east of 1707 Heilongjiang Province respectively. (3) Before the occurrence of 1 h heavy rainfall, the water vapor is concentrated in the middle and lower troposphere. The residual vortex trough of typhoon 1909 extends northward, converges with the southwest airflow at the edge of the subtropical high, and transports water vapor and energy to the northeast. The convective cloud clusters generated ahead of the trough move southeast, then merge into the mesoscale convective system in the inverted trough; (4) In the Bohai Bay and North Korea, there is a vortex-like zone composed of several convergence centers, and the convergence zone in typhoon-inverted trough meets with the trough in Central Jilin. There exist a rising area and a positive vorticity belt in the typhoon-inverted trough, and the center of heavy rain lies in front of the positive vorticity center. At the west of the inverted trough, there is a large center of positive vertical wind shear, and a small center in the east. The center of heavy rainfall is located on the line between the maximum and minimum centers, which is close to the right of the maximum center; (5) The high energy tongue is transported from the center of the typhoon to the northeast along the inverted trough of the typhoon, and the southwest airflow at the edge of the subtropical high. There is a zone titled downward from northwest to southeast that contains dry and cold air, where there is convective instability; (6) The strong precipitation area is located on the lee in the northwest of Changbai Mountain. There is a convergence area in the middle of the troposphere, and a strong divergence area in the upper troposphere, with remarkable topographic effect, and the west divergence column inclines on the east convergence column.