低纬准双周振荡对2018年8月广东持续性特大暴雨过程的影响

2018-08-27—09-01广东发生了一次持续性特大暴雨过程，被列为广东省2018年十大天气事件之一。文章综合利用欧洲中期天气预报中心（ECMWF）全球再分析资料ERA-Interim、广东省加密自动站观测资料、中国地面累年值日值数据集(1981—2010年）、NOAA日平均和长期平均向外长波辐射数据，采用小波分析、带通滤波、回归分析等方法，对此次暴雨过程进行分析，主要探讨低纬大气准双周振荡对此次持续性暴雨过程的影响。结果表明：此次暴雨持续时间长、影响范围大，影响此次暴雨天气过程的主要天气系统为季风低压，并伴随有切变线和低空急流；季风低压减弱西移后，与南海西北部高压共同作用，广东沿海极端降水达到最强。2018年7—9月广东省降水和向外长波辐射OLR有显著的6~13 d振荡特征，同时受低纬西北太平洋对流振荡和热带北印度洋对流振荡的影响。低频振荡自西太平洋地区，向西北方向传播，引起了华南沿海的低频对流与环流的发展；来自热带北印度洋上的气流经由孟加拉湾、中南半岛到达华南沿海地区，形成了低频振荡的垂直环流圈，有利于水汽输送及对流发展。两者叠加，影响了此次持续性暴雨的发生发展。

Influence of Low-Latitude Quasi-Biweekly Oscillation on a Persistent Heavy Rainfall Event in August 2018 in Guangdong Province

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.