Statistical Relationships between Two Types of Heavy Rainfall and Low-Level Jets in South China
Statistical Relationships between Two Types of Heavy Rainfall and Low-Level Jets in South China
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华南两类暴雨与低空急流的统计关系
DOI：
10.1175/jcli-d-21-0121.1
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发表时间：
2021-08
影响因子：
4.9
通讯作者：
Yu Du
中科院分区：
文献类型：
--
作者：
Xiaoqing Li;Yu Du
摘要 华南地区夏季梅雨期间，暖区暴雨和锋面暴雨两种类型的强降雨同时存在，且表现出不同的机制和特点。它们都与两种类型的低空急流 (LLJ) 表现出密切的关系：边界层急流 (BLJ) 和天气系统相关的低空急流 (SLLJ)，但方式不同。本研究的目的是利用TRMM降雨数据和ERA5再分析来阐明华南两类强降雨与低空急流之间的统计关系。一般来说，暖区强降雨主要发生在沿海地区和清晨，主要是夜间BLJ与陆风相互作用造成的。相比之下，锋面强降雨主要集中在内陆地区，并受到不同地点不同昼夜强迫的调节。统计分析表明，76%（62%）的暖区（锋面）强降雨事件与低空急流有关。强降雨时，北部湾、南海北部和锋面南侧的低空风常增强，分别对应海洋上空约950 hPa的南风BLJ和陆地约850~700 hPa的西南低风急流。此外，BLJ 与两种类型的强降雨及其出口区域最常发生的降雨有关，而 SLLJ 与锋面强降雨的关系更为密切。 SLLJ 轴的左侧（入口）有利于锋面（暖区）强降雨的产生。区域降雨分布受低空急流的结构和位置影响。
AbstractTwo types of heavy rainfall, namely warm-sector and frontal heavy rainfall, coexist in South China during the presummer rainy season and manifest as varying mechanisms and features. They both exhibit close relationships with two types of low-level jets (LLJs): the boundary layer jet (BLJ) and synoptic-system-related low-level jet (SLLJ), but in different ways. The motivation of the present study is to elucidate the statistical relations between the two types of heavy rainfall and LLJs over South China using TRMM rainfall data and ERA5 reanalysis. Generally, warm-sector heavy rainfall mainly occurs over coastal areas and during the early morning, which is primarily caused by the interaction between the nocturnal BLJ and land breeze. In contrast, frontal heavy rainfall is mostly concentrated in inland regions and modulated by distinct diurnal forcings at different locations. Statistical analysis indicates that 76% (62%) of the warm-sector (frontal) heavy rainfall events are associated with LLJs. In the presence of heavy rainfall, low-level winds are often strengthened over Beibu Gulf, northern South China Sea, and the south side of fronts, corresponding to two branches of southerly BLJs at ~950 hPa over the ocean and the southwesterly SLLJs at ~850–700 hPa on land, respectively. Furthermore, BLJs are shown to be linked to both types of heavy rainfall and with the most frequent occurrences of rainfall in their exit region, whereas SLLJs are more closely associated with frontal heavy rainfall. The left side (entrance) of the SLLJ axis is favorable for frontal (warm-sector) heavy rainfall production. The regional rainfall distributions are affected by the structures and locations of LLJs.