Changes in Great Plains Low‐Level Jet Structure and Associated Precipitation Over the 20th Century
Changes in Great Plains Low‐Level Jet Structure and Associated Precipitation Over the 20th Century
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DOI：
10.1029/2021jd035859
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发表时间：
2022-01
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影响因子：
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通讯作者：
C. Ferguson
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作者：
C. Ferguson
美国大平原暖季气候与该地区向南低空急流的频率和结构密不可分。在现今的气候中（1977-2009），在大平原的北方、中部和南部，低空急流分别出现在5 - 9月的26%、46%和62%的日子里，并且至少占同期这些地区降水量的26%、25%和36%。以前研究的一个缺点是未能将高层动力耦合或气旋诱导的急流与相对不耦合天气流的急流分开处理。区分喷流类型对于正确的机制诊断和将喷流相关的风、降水和温度变化归因于其本地陆地或远程海洋强迫至关重要。使用新的CERA-20 C客观动力学射流分类数据集，该研究首次定量评估了1901年至2010年NGP，CGP和SGP之间耦合和非耦合射流的变化。暖季喷气机频率的下降被精确地指向7月至9月的喷气机。在NGP和CGP中，两种急流类型的速度和高度都有显著的增加，同时CAPE和降水量也有所减少。NGP非耦合急流和CGP耦合急流降水分别减少了0.5和0.8 mm日-1，占1905-1937年和1977-2009年5 - 9月降水减少总量的41%-44%。一个动态的情况下，天气和当地土壤湿度的变化驱动相反的射流响应进行了讨论。
The U.S. Great Plains warm season climate is inextricably linked to the frequency and structure of the region's southerly low‐level jet. In the present‐day climate (1977–2009), low‐level jets are shown to occur on 26%, 46%, and 62% of May–September days in the northern (NGP), central (CGP) and southern (SGP) Great Plains, respectively, and account for at least 26%, 25%, and 36% of those region's precipitation during the same period. A shortcoming of previous research has been a failure to treat upper‐level dynamically coupled, or cyclone‐induced jets, separately from jets that are relatively uncoupled from synoptic flow. Differentiating between jet types is essential to proper mechanistic diagnosis and attribution of jet‐related wind, precipitation, and temperature changes to their local land or remote oceanic forcing. Using a new CERA‐20C objective dynamical jet classification dataset, this study achieves the first quantitative assessment of changes in coupled and uncoupled jets between 1901 and 2010 for NGP, CGP, and SGP. Declines in warm season jet frequency are pinpointed to July–September jets. In the NGP and CGP, both jet types have undergone significant increases in speed and height with concomitant decreases in CAPE and precipitation. NGP uncoupled jet and CGP coupled jet precipitation has decreased by 0.5 and 0.8 mm day−1, respectively, which accounts for 41%–44% of total May–September precipitation decreases between 1905–1937 and 1977–2009. A dynamic situation in which synoptic and local soil moisture changes drive opposite jet responses is discussed.