Catto Jennifer L, Raveh-Rubin Shira
1College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK.
2Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israel.
Clim Dyn. 2019;53(3):1873-1892. doi: 10.1007/s00382-019-04745-w. Epub 2019 May 7.
Cold fronts are a primary feature of the day-to-day variability of weather in the midlatitudes, and feature in conceptual extratropical cyclone models alongside the dry intrusion airstream. Here the climatological frequency and spatial distribution of the co-occurrence of these two features are quantified, and the differences in cold front characteristics (intensity, size, and precipitation) when a dry intrusion is present or not are calculated. Fronts are objectively identified in the ECMWF ERA-Interim dataset for the winter seasons in each hemisphere and split into three sub-types: central fronts (within a cyclone area); trailing fronts (outwith the cyclone area but connected to a central front); and isolated fronts (not connected to a cyclone). These are then associated with dry intrusions identified using Lagrangian trajectory analysis. Trailing fronts are most likely to be associated with a DI in both hemispheres, and this occurs more frequently in the western parts of the major storm track regions. Isolated fronts are linked to DIs more frequently on the eastern ends of the storm tracks, and in the subtropics. All front types, when co-occurring with a DI, are stronger in terms of their temperature gradient, are much larger in area, and typically have higher average precipitation. Therefore, climatologically the link with DIs increases the impact of cold fronts. There are some differences in the statistics of the precipitation for trailing and isolated fronts that are further investigated in Part II of this study from the front-centred perspective.
冷锋是中纬度地区日常天气变化的一个主要特征，并且在概念性温带气旋模型中与干侵入气流一同出现。在此，对这两种特征同时出现的气候学频率和空间分布进行了量化，并计算了存在或不存在干侵入时冷锋特征（强度、大小和降水量）的差异。在欧洲中期天气预报中心（ECMWF）的ERA-Interim数据集中，对每个半球冬季的锋面进行了客观识别，并分为三种亚型：中心锋（在气旋区域内）；尾随锋（在气旋区域外但与中心锋相连）；以及孤立锋（与气旋不相连）。然后将这些锋面与使用拉格朗日轨迹分析识别出的干侵入联系起来。在两个半球中，尾随锋最有可能与干侵入相关联，并且这种情况在主要风暴路径区域的西部更为频繁地发生。孤立锋在风暴路径的东端以及亚热带地区与干侵入的联系更为频繁。所有锋面类型在与干侵入同时出现时，其温度梯度更强，面积更大，并且通常平均降水量更高。因此，从气候学角度来看，与干侵入的联系增加了冷锋的影响。在尾随锋和孤立锋的降水统计方面存在一些差异，本研究的第二部分将从锋面中心的角度对此进行进一步研究。
