Mechanisms for Springtime Onset of Isolated Precipitation across the Southeastern United States
Mechanisms for Springtime Onset of Isolated Precipitation across the Southeastern United States
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DOI：
10.3390/atmos12020213
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发表时间：
2021-02
期刊：
影响因子：
2.9
通讯作者：
R. Ferreira;T. Rickenbach
中科院分区：
文献类型：
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作者：
R. Ferreira;T. Rickenbach
这项研究使用了四年的基于雷达的降水组织和再分析数据集来研究导致美国东南部孤立风暴(美国东南部)春季降水突然开始的机制。尽管美国东南部地区全年降水量相对恒定，但以前的研究表明，在孤立降水特征(IPF)中存在一个“隐藏的”夏季最大值，其年周期类似于亚热带季风气候。在美国东南部，IPF降雨在5月份突然增加，并持续到8月底至10月初的某个时候。这项研究表明，美国东南部地区IPF季节的开始是由缓慢的热力学过程和快速的动力触发因素共同作用的结果，如下所示。首先，在IPF发生前几周，墨西哥湾对流可用势能(CAPE)出现了逐渐的季节性积聚。然后，在爆发前的一到两候中，对流层上层急流向北移动，有利于美国东南部存在缓慢移动的锋面系统。急流位置的这种极地转移反过来允许北大西洋副热带高压西脊在美国东南部上空建立，与从墨西哥湾向极地输送的高角空气一起导致美国东南部建立IPF降水的暖季制度。
This study uses four-year radar-based precipitation organization and reanalysis datasets to study the mechanisms that lead to the abrupt springtime onset of precipitation associated with isolated storms in the Southeast United States (SE US). Although the SE US receives relatively constant precipitation year-round, previous work demonstrated a “hidden” summertime maximum in isolated precipitation features (IPF) whose annual cycle resembles that of monsoon climates in the subtropics. In the SE US, IPF rain abruptly ramps up in May and lasts until sometime between late August and early October. This study suggests that the onset of the IPF season in the SE US is brought about by a combination of slow thermodynamic processes and fast dynamic triggers, as follows. First, in the weeks prior to IPF onset, a gradual seasonal build-up of convective available potential energy (CAPE) occurs in the Gulf of Mexico. Then, in one-to-two pentads prior to onset, the upper-tropospheric jet stream shifts northward, favoring the presence of slow-moving frontal systems in the SE US. This poleward shift in the jet stream location in turn allows the establishment of the North Atlantic subtropical high western ridge over the SE US which, with associated poleward transport of high CAPE air from the Gulf of Mexico, leads to the establishment of the warm-season regime of IPF precipitation in the SE US.