A New Variable-Threshold Persistent Anomaly Index: Northern Hemisphere Anomalies in the ERA-Interim Reanalysis
A New Variable-Threshold Persistent Anomaly Index: Northern Hemisphere Anomalies in the ERA-Interim Reanalysis
复制标题
新的可变阈值持续异常指数：ERA 中期再分析中的北半球异常
作者：
R. L. Miller;G. Lackmann;W. Robinson
以异常温度或降水为特征的持续天气状况通常与对流层位势高度场的持续异常（PA）有关。为了确定整个年度周期的 PA，对早期的定义进行了修改，以应用季节性变化的震级阈值，该阈值基于每日 500 hPa 位势高度变化的平滑、每日变化的气候平均值。修改后的索引可应用于各种分析、再分析或模型预测网格数据。此处，修改后的 PA 指数用于识别所有季节的北半球正 PA 和负 PA，并计算 ECMWF ERA-中期再分析数据集（1979-2016）中 PA 频率、强度、位置和持续时间的趋势。高度数据被去趋势化，异常值通过纬度反正弦函数进行加权。除了先前确定的 PA 频率最大值（北太平洋、北大西洋和俄罗斯）之外，北极地区还出现了额外的夏季最大值；此功能尚未得到广泛分析。夏季北极 PA 正事件的综合结果揭示了等效的正压结构，类似于中纬度 PA 记录的结构。北极 PA 频率在夏季最高；在 38 年 ERA 中期分析期内，它没有表现出频率趋势。事实上，在主要 PA 区域的分析期间，PA 频率、强度或持续时间没有明显的趋势，尽管有迹象表明北太平洋积极的 PA 活动向北移动。
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.
影响因子：
4.9
作者：
Adam A. Scaife;T. Woollings;J. Knight;G. Martin;T. Hinton
通讯作者：
Adam A. Scaife;T. Woollings;J. Knight;G. Martin;T. Hinton
影响因子：
4.9
作者：
G. Masato;B. Hoskins;T. Woollings
通讯作者：
G. Masato;B. Hoskins;T. Woollings
影响因子：
4.9
作者：
Sillmann, Jana;Croci-Maspoli, Mischa;Katz, Richard W.
通讯作者：
Katz, Richard W.