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Regional and general

机译：区域和一般

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Persistent weather regimes characterized by anomalous temperature or precipitation are often associated with persistent anomalies (PAs) in the tropospheric geopotential height field. To identify PAs throughout the annual cycle, an earlier definition is modified to apply a seasonally varying magnitude threshold, based on a smoothed, daily varying climatological average of daily 500-hPa geopotential height variability. The modified index can be applied to a wide variety of analysis, reanalysis, or model-forecast gridded data. Here, the modified PA index is used to identify positive and negative Northern Hemisphere PAs in all seasons and to compute trends in PA frequency, strength, location, and duration, in the ECMWF ERA-Interim reanalysis dataset (1979-2016). Height data are detrended and anomalies are weighted with an inverse sine-of-latitude function. In addition to maxima in PA frequency identified previously (North Pacific, North Atlantic, and Russia), an additional summertime maximum appears in the Arctic; this feature has not been analyzed extensively. A composite of summertime positive Arctic PA events reveals an equivalent barotropic structure, similar to that documented for midlatitude PAs. Arctic PA frequency is greatest in summer; it exhibits no trend in frequency over the 38-yr ERA-Interim analysis period. In fact, no discernable trends in PA frequency, strength, or duration are evident in the analysis period for the primary PA regions, although there is a suggestion of a northward shift in positive PA activity in the North Pacific.
机译：持久的天气制度以异常温度或沉淀为特征，通常与对流层地球态高度场中的持续异常（PAS）相关。为了在整个年度周期中识别PA，修改了早期的定义，以基于每日500-HPA地球态高度可变性的平滑，日常不同的气候平均值来施加季节性变化幅度阈值。修改的指数可以应用于各种分析，再分析或模型预测网格数据。在这里，修改的PA索引用于识别所有季节中的正北半球PA，并在ECMWF Era-Interim Reanalysic DataSet中计算PA频率，强度，位置和持续时间的趋势（1979-2016）。高度数据是下降的，并且异常用偏远纬度函数加权。除了先前（北太平洋，北大西洋和俄罗斯）鉴定的PA频率中的Maxima之外，北极出现了额外的夏季最大值;此功能尚未广泛分析。夏季阳性北极PA事件的复合性揭示了一种等同的波调结构，类似于为中间PAS记录的对策结构。北极PA频率在夏季最大;在38年的临时分析期间，它没有频率频率。实际上，在初级PA区域的分析期内，PA频率，强度或持续时间内没有可辨别的趋势，尽管北太平洋阳性PA活动的北方转变有所建议。

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    《Oceanographic Literature Review》 |2020年第4期|947-948|共2页
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