This study separates the dry and moist components of the moist isentropic mass circulation (MIMC) on a daily timescale and investigates their relationships with extratropical surface temperature changes in winter (November to February). Results from ERA5 reanalysis data set (1979–2018) show that the MIMC is composed of a poleward warm branch in the upper layers and an equatorward cold branch below. The warm branch (WB) is dominated by the moist component in the mid‐latitude troposphere, but by the dry component in other regions. The stronger moist component of WB at 50°N‐70°N (WB_M) is a better precursory indicator than the dry component (WB_D) for the Arctic surface warming as a result of its dominant role in modifying the downward longwave radiation via water‐vapor‐related processes. The stronger WB_D is coupled with a negative Arctic Oscillation and a stronger, longer‐lasting equatorward transport of colder air, therefore a better precursory indicator of mid‐latitude cold events.

中文翻译：

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等熵质流的干湿成分在冬季改变温带表面温度中的作用

这项研究在每天的时间尺度上分离了湿等熵质量循环（MIMC）的干成分和湿成分，并研究了它们与冬季（11月至2月）的温带表面温度变化的关系。ERA5再分析数据集（1979-2018年）的结果表明，MIMC由上层的极地暖分支和下层的赤道冷分支组成。暖分支（WB）在中纬度对流层中以湿气为主，而在其他地区则以干气为主。由于北极在通过水改变向下的长波辐射中起主要作用，因此在50°N-70°N（WB_M）处，WB的较湿成分（WB_M）比干燥成分（WB_D）更好。与蒸气有关的过程。