Effects of the North Atlantic Subtropical High on summertime precipitation organization in the southeast United States
Effects of the North Atlantic Subtropical High on summertime precipitation organization in the southeast United States
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DOI：
10.1002/joc.6561
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发表时间：
2020-03
期刊：
影响因子：
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通讯作者：
Rosana Nieto Ferreira;T. Rickenbach
中科院分区：
文献类型：
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作者：
Rosana Nieto Ferreira;T. Rickenbach
本研究分析了北大西洋副热带高压（NASH）西脊的位置对美国东南部（SE US）降水组织日变化的影响。NASH的西侧，也被称为NASH西脊，在该地区夏季降水的变化中起着重要的作用。在这项研究中，NASH西脊的平均夏季位置被确定，并用于将2009-2012年期间的每个夏季日分为四个象限之一。计算了NASH西脊每个象限的天气尺度环流和中尺度降水和孤立降水特征（MPF和IPF）的合成。MPF贡献了大部分（约65%）的总夏季降水量，并占了大部分的四个NASH象限之间的差异。当IPF（MPF）降水最强（最弱）时，NASH-SW（NASH-NW）期间的域平均降水量最高（最低）。MPF降水最大值的区域性通常与低空急流和高空槽的位置有关。例如，在NASH-SW期间，当大平原低空急流向东移动时，美国东南部出现了正的MPF异常，这给美国东南部的对流带来了水分。相比之下，IPF降雨在美国东南部的分布更为均匀。最后，这项研究揭示了一个降水偶极子，它受NASH西部高压脊及其相关低空急流的位置控制。在偶极NASH-SE的一个极端，周期与增强MPF降水沿着海岸和近海几天的时间，并抑制MPF降水内陆。相反的模式发生在NASH-NW当MPF降水增强内陆和抑制沿着海岸和近海。
This study analyzes the effect of the location of the North Atlantic Subtropical High (NASH) western ridge on the daily variability of precipitation organization in the southeastern United States (SE US). The western side of the NASH, also known as the NASH western ridge, plays an important role in the variability of summertime precipitation in this region. In this study, the mean summertime position of the NASH western ridge was determined and used to classify each summer day during 2009–2012 into one of four quadrants. Composites of synoptic‐scale circulation and precipitation from mesoscale and isolated precipitation features (MPF and IPF) were calculated for each NASH western ridge quadrant. MPF contributed most (about 65%) of the total summertime precipitation and accounted for most of the differences between the four NASH quadrants. Domain‐averaged precipitation was highest (lowest) during NASH‐SW (NASH‐NW) when IPF (MPF) precipitation was strongest (weakest). The regionality of MPF precipitation maxima was generally associated with the location of low‐level jets and upper‐level troughs. For instance, positive MPF anomalies occurred across the SE US during NASH‐SW when the Great Plains low‐level jet turned eastward bringing moisture to fuel convection in the SE US. In contrast, IPF rain was distributed more uniformly across the SE US. Finally, this study revealed a dipole of precipitation that is controlled by the position of the NASH western ridge and its associated low‐level jets. In one extreme of the dipole NASH‐SE, periods are associated with enhanced MPF precipitation along the coast and offshore for days at a time, and suppressed MPF precipitation inland. The opposite pattern occurs during NASH‐NW when MPF precipitation is enhanced inland and suppressed along the coast and offshore.