关键词: 持续性暴雨, 大气低频振荡, 准双周振荡, 广东省

Abstract:

From August 27 to September 1, 2018, there was persistent heavy rainfall in Guangdong, which was one of the top ten weather events in Guangdong Province during 2018. We analyzed this rainstorm process by using the ECWMF global reanalysis ERA-Interim data, encrypted data from the Guangdong Province automatic observation station, China's surface annual value dataset (1981—2010), and daily and long-term mean average long-wave radiation data from the NOAA along with wavelet analysis, band-pass filtering, and regression analysis methods. We discuss the impact of atmospheric oscillation at low latitudes on the process of this continuous rainstorm in order to provide reference for forecasting this type of rainfall event. The results showed that the rainstorm lasted for a long time and affected a large area. The main weather system that affected the rainstorm was monsoon depression, accompanied by a shear line and low-level jet. Tropical low pressure named 92W on August 25 made landfall in Fujian after a westward shift, and then formed a monsoon low pressure. Due to the sub-high block, the warm and humid airflow brought by the southwest monsoon could not move northwards; hence, the monsoon low pressure was maintained and continued to develop, gaining long-term control of most of the southern coast whilst moving slowly westwards. The mid-level of the troposphere strengthened and extended to the northern part of the South China Sea. The southwest rapids intensified, the low pressure center appeared to the northeast—southwest—turning trough, the water vapor flow reached its maximum, and the coastal areas experienced a wide range of extreme precipitation. After the monsoon low pressure moved westwards and weakened, together with the northwest high pressure of the South China Sea, extreme precipitation peaked along the coast of Guangdong. The precipitation across Guangdong from July to September 2018 had a significant 6-13 days oscillation feature, which was mainly affected by convective oscillation in the west Pacific Ocean and the tropical north Indian Ocean. After convection formed in the west Pacific region, it continued to spread northwestwards and reached the coastal areas of southern China. The airflow from the tropical north Indian Ocean reached the coastal areas of south China via the Bay of Bengal and the Indo-Chinese Peninsula, thus forming a vertical circulation with a low frequency oscillation, which was conducive to water vapor transport and convective development in the coastal areas of south China. The combination of the two was more conducive to the occurrence of continuous heavy rainfall in Guangdong.

Key words: persistent heavy rainfall, atmospheric low-frequency oscillations, quasi-biweekly oscillation, Guangdong province