Sources and transport pathways of precipitating waters in cold-season deep North Atlantic cyclones
Sources and transport pathways of precipitating waters in cold-season deep North Atlantic cyclones
复制标题
冷季北大西洋深层气旋降水水源及输送路径
DOI：
10.1175/jas-d-21-0105.1
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发表时间：
2021
影响因子：
3.1
通讯作者：
H. Wernli
中科院分区：
文献类型：
--
作者：
L. Papritz;F. Aemisegger;H. Wernli
温带气旋是中纬度地区降水的主要来源，对水循环的特点产生了深远的影响。在这项研究中，我们使用ERA5再分析和气旋跟踪方案并结合拉格朗日诊断来确定1979年至2018年冬季676个北大西洋深处气旋中心附近的水汽来源。湿气吸收主要发生在最初在北大西洋上空加热的冷干空气中，特别是在墨西哥湾流的温暖水域，而来自陆地或亚热带的更偏远的来源则不那么重要。通过对吸湿动力环境的分析，发现气旋加强阶段的水汽降水来源于前气旋冷区和气旋-反气旋相互作用区的前气旋环境。这些水汽来源通过所谓的支流与气旋的上升区域联系在一起，支流是一种东北气旋相对气流，由于气旋传播超过低层背景气流的平流而产生。在衰变阶段，越来越多的水汽来自气旋自身的冷区。因此，降水在气旋中的停留时间较短(中位数为≈2天)，输送距离通常小于气旋本身的移动距离。这些发现强调了通过气旋前环境中的地表通量进行预适应对气旋中降水形成的重要性，并表明了在风暴路径内将水汽从一个气旋传递到下一个气旋的重要作用。
Extratropical cyclones are responsible for a large share of precipitation at mid-latitudes and they profoundly impact the characteristics of the water cycle. In this study, we use the ERA5 reanalysis and a cyclone tracking scheme combined with a Lagrangian diagnostic to identify the sources of moisture precipitating close to the center of 676 deep North Atlantic cyclones in winters 1979 to 2018. Moisture uptakes occur pre-dominantly in originally cold and dry air heated over the North Atlantic, in particular, over the warm waters of the Gulf Stream, whereas more remote sources from land or the subtropics are less important. Analysing the dynamical environment of moisture uptakes, we find that moisture precipitating during the cyclone intensification phase originates in the pre-cyclone environment in the cold sectors of preceding cyclones and the cyclone-anticyclone interaction zone. These moisture sources are linked to the cyclone’s ascent regions via the so-called feeder airstream, a north-easterly cyclone-relative flow that arises due to the cyclone propagation exceeding the advection by the low-level background flow. During the decay phase more and more of the moisture originates in the cyclone’s own cold sector. Consequently, the residence time of precipitating waters in cyclones is short (median of ≈ 2 days) and transport distances are typically less than the distance travelled by the cyclone itself. These findings emphasize the importance of pre-conditioning by surface fluxes in the pre-cyclone environment for the formation of precipitation in cyclones, and suggest an important role for the hand-over of moisture from one cyclone to the next within a storm track.