美国东南部夏季冷锋活动频率、持续时间和地理范围的观测:1973-2020

T. Mitchell, P. Knapp, Jason T. Ortegren
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引用次数: 2

摘要

我们分析了1973-2020年美国东南部夏季(6 - 8月)冷锋活动的频率和持续时间,以总结和确定与冷锋、冷锋日数和多日冷锋事件相关的年和总小时数的时间趋势。利用来自34个ASOS网络站点的数据,我们将夏季冷锋定义为露点温度低于15.56°C(< 60°F)的事件。此外,我们还研究了500 hPa位势高度异常与冷锋频率/持续时间偏差为+/−1.0 SD的年份相关。冷锋活动范围呈现南北纬向梯度,在阿巴拉契亚山脉东侧表现为偏南纬向,在北纬30°以南可以忽略不计。冷锋活动在6月上半月最为突出。结果表明,在48年的研究期间,夏季冷锋活动的三个指标在区域尺度上都是稳定的,有几个站(3 - 5个)出现了显著的下降。区域尺度的稳定与美国东南部夏季最低、最高和平均气温的显著增加相一致。冷锋活动高于或低于平均水平的年份与支持美国东南部槽或脊的天气条件同时发生。我们的结论是,观测到的美国东南部变暖空洞的减弱是外部和/或内部强迫的结果,与夏季异常凉爽天气的减少无关。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Observations on the Frequency, Duration, and Geographical Extent of Summertime Cold-Front Activity in the Southeastern USA: 1973–2020
We analyzed summertime (June–August) cold-front activity via frequency and duration in the southeastern USA during 1973–2020 to summarize and identify the temporal trends of the annual and total number of hours associated with cold fronts, cold-front days, and multi-day cold-front events. Using data from 34 ASOS Network stations, we defined summertime cold fronts as events that lowered the dew point temperature below 15.56 °C (< 60 °F). Additionally, we examined 500 hPa geopotential height anomalies associated with years with cold front frequency/duration deviations of +/− 1.0 SD. The extent of the cold-front activity exhibited a north–south latitudinal gradient with a more southerly latitudinal expression on the east side of the Appalachian Mountains and was negligible south of the 30°N latitude. The cold-front activity was most prominent during the first half of June. Our results suggest that all three metrics of summertime cold-front activity were stable at a regional scale during the 48-year study period with a few (three–five) stations experiencing significant decreases. A regional-scale stability was coincident with significant increases in minimum, maximum, and average summertime temperatures in the southeastern USA. Years with either above-average or below-average cold-front activity were concurrent with synoptic conditions that supported either troughing or ridging in the southeastern USA. We conclude that the observed weakening in the southeastern USA warming hole is the result of external and/or internal forcings unrelated to reductions in anomalously cool summer weather.
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