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A reanalysis of the relationship between strong westerlies and precipitation in the Great Plains and Midwest regions of North America

机译：北美大平原和中西部地区强西风与降水关系的再分析

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A conceptual model relating expanded or strengthened mid-latitude summer westerlies with summer precipitation patterns has been used to explain past drought events in the Great Plains and Midwest of North America, including drought between 1200 and 1400 AD. However, this relationship was originally described using 20 years of instrumental data from the mid 20{th} century, and has not been verified with modern datasets. We reinvestigated the relationship between July westerlies and precipitation in the United States using instrumental records of the last 55 years. We also investigated whether changes in summer zonal flow patterns associated with precipitation anomalies represent a shift in the latitude of peak westerly winds or an increase in wind speed, or a combination of both. Finally, we briefly compare the pattern of precipitation anomalies to paleoclimatic records of drought between 1200 and 1400 AD. Results confirm that strong westerlies are associated with a band of decreased precipitation extending from the northern Rockies into the Midwest. Changes in summer westerlies associated with these patterns are characterized by a strengthening of mean westerly winds, with only a slight southward shift of peak winds over the Atlantic. Changes in the strength of the westerlies over both the Pacific and Atlantic appear to be important to precipitation deficits in the Midwest. Proxy-climate records from 1200 to 1400 AD indicate widespread drought in the Great Plains and Midwest, consistent with thehypothesis of stronger westerlies at this time. However, drought conditions also extended to other regions of North America, indicating a more detailed understanding of the potential causes and synoptic climatology is needed.
机译：将扩大或加强的中纬度夏季西风与夏季降水模式联系在一起的概念模型已被用来解释北美大平原和中西部过去的干旱事件，包括公元1200至1400年的干旱。但是，这种关系最初是使用20世纪中期20年来的仪器数据来描述的，尚未得到现代数据集的验证。我们使用过去55年的仪器记录重新调查了7月西风与美国降水之间的关系。我们还研究了与降水异常相关的夏季纬向流型的变化是否代表西风峰纬度的变化或风速的增加，还是两者的结合。最后，我们简要比较了降水距平的模式与公元1200年至1400年之间的干旱的古气候记录。结果证实，强西风与从北落基山脉到中西部的降水减少带有关。与这些模式有关的夏季西风的变化特征是平均西风增强，大西洋上空的峰值风仅向南轻微移动。太平洋和大西洋西风强度的变化似乎对中西部的降水不足很重要。从公元1200年到1400年的代理气候记录表明，大平原和中西部地区普遍干旱，这与当时强西风的假说相符。但是，干旱条件也扩展到了北美其他地区，这表明需要更详细地了解潜在原因和天气气候。

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