During the termination of the last glacial period the western U.S. experienced exceptionally wet conditions, driven by changes in location and strength of the mid-latitude winter storm track. The distribution of modern winter precipitation is frequently characterized by a north-south wet/dry dipole pattern, controlled by interaction of the storm track with ocean-atmosphere conditions over the Pacific and Atlantic Oceans. Here we show that a dipole pattern of similar geographic extent persisted and switched sign during millennial-scale abrupt climate changes of the last deglaciation, based on a new lake level reconstruction for pluvial Lake Chewaucan (northwestern U.S.), and a compilation of regional paleoclimate records. This suggests the dipole pattern is robust, and one mode may be favored for centuries, thereby creating persistent contrasting wet/dry conditions across the western U.S. The TraCE-21k climate model simulation shows an equatorward enhancement of winter storm track activity in the northeastern Pacific, favoring wet conditions in southwestern U.S. during the second half of Heinrich Stadial 1 (16.1–14.6 ka) and consistent with paleoclimate evidence. During the Bølling/Allerød (14.6–12.8 ka), the northeastern Pacific storm track contracted poleward, consistent with wetter conditions concentrated poleward toward the northwest U.S.
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机译:在上个冰川期结束期间,由于中纬度冬季风暴路径的位置和强度的变化,美国西部经历了异常潮湿的条件。现代冬季降水的分布通常以南北湿/干偶极子模式为特征,该模式由风暴轨迹与太平洋和大西洋上海洋大气条件的相互作用控制。在这里,我们显示了在最后一次冰消的千年尺度突变的气候变化过程中,相似的地理范围的偶极子模式持续存在并转换了符号,这是基于对冲积丘沃坎坎湖(美国西北部)进行的新的湖面重建以及区域古气候记录的汇编。这表明偶极子模式很健壮,一个世纪以来可能一直偏爱这种模式,从而在美国西部造成了持续的湿/干条件形成对比。TraCE-21k气候模型模拟表明,东北太平洋冬季风暴的活动在赤道上有所增强, Heinrich Stadial 1(16.1-14.6 ka)下半年有利于美国西南部的潮湿条件,并与古气候证据一致。在Bølling/Allerød(14.6–12.8 ka)期间,东北太平洋风暴路径向极收缩,这与潮湿的条件向美国西北部集中的极向一致。
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