2023年6月一次北部湾低压极端暴雨过程天气气候特征OA

The weather and climate characteristics of the persistent extreme rainstorm process of a depression in the Beibu Gulf from 7 to 10 June 2023 were studied using daily reanalysis data.The results show that:(1)the subtropical high was abnormally north-westerly and in a stable position during the pre-and period of the persistent extreme rainstorm.The tropical convergence zone along the Bay of Bengal-South China Sea-Philippines was active,and a low-pressure system was generated in the western part of the South China Sea and moved into the Beibu Gulf.(2)The intra-seasonal oscillation(MJO)was in the 2nd and 3rd phases,influenced by its eastward transmission,and the position of the trough-ridge formed by the mid-and high-latitude circulation was favourable for cold air to move southward to affect Guangxi.There was a northeast low-vortex maintaining near the northeastern China at 500 hPa,and the strong northerly wind behind this vortex guided the cold air to the south,which was blocked by the north-westerly subtropical high,causing a small cold-air infiltration to affect Guangxi to the south.(3)The trans-equatorial airflow in the Indian Ocean and the southwesterly monsoon were strong at 850 hPa in the lower layers,but their activities were skewed to the south,and the southwesterly jets of the Indian Ocean-Central South Peninsula-South China Sea was blocked by Typhoon Guchol and shifted into southerly winds,which led to the cyclonic convergence of the airflow around the Beibu Gulf.There is a weak northeasterly wind in northwestern Guangxi,which enhanced the cyclonic convergence of the airflow around Beibu Gulf.(4)The southern part of Guangxi and the Beibu Gulf area were located to the right of the 200 hPa East Asian subtropical high-level jet stream and to the left of the 850 hPa southwesterly jet streams,with high-level divergence and low-level convergence,and abundant water vapour conditions in the 1 000～300 hPa water vapour flux convergence zone.Overall,the above collaborative effect of the mid-and low-latitude weather systems provided a favourable and stable large-scale circulation background,as well as adequate thermal and dynamical conditions for this persistent extreme rainstorm.