Dry intrusions (DIs) are synoptic‐scale slantwise descending airstreams from the midlatitude upper troposphere toward the boundary layer at lower latitudes. Typically occurring behind cold fronts, such intrusions of dry air often reach the boundary layer and cause its deepening, thereby affecting boundary‐layer clouds. Although subsidence is generally an inherent feature of the subtropical marine boundary layer (MBL), it is unclear how the MBL reacts to the transient, dynamically distinct DI. In this study, reanalysis data were combined with observations from the Atmospheric Radiation Measurement Eastern North Atlantic (ENA) site (39.1°N,28.0°W) to characterize the impact of DIs on MBL characteristics and clouds. Specifically, an objective criterion is applied to the observations made during the winter months of 2016–2018 to identify the DI days from those before and following DIs, and reference periods without DIs. The analyses suggest substantial deepening of the well‐mixed boundary layer accompanied by changes in the cloud, precipitation and thermodynamic properties during the DI events. During the DI, the lower troposphere cooled and dried substantially thereby inducing strong surface sensible and latent heat fluxes. All while a strong inversion builds up at the elevated MBL top affecting cloud occurrence. The results show DIs to affect the boundary layer and cloud structure at the ENA site ∼21% of the time in winter months, with the response of the cloud fields to the DI‐fronts substantially different than that to the non‐DI fronts. Hence, the DI events should be considered while studying boundary layer and cloud processes in the region.

中文翻译：

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倾斜下降的干侵入对ARM东北部大西洋站点海洋边界层和海海界面的影响

干侵入（DI）是天气尺度从中纬度对流层上的低层向边界层倾斜的气流。这种干空气入侵通常发生在冷锋之后，经常到达边界层并引起其加深，从而影响边界层云。尽管沉陷通常是亚热带海洋边界层（MBL）的固有特征，但尚不清楚MBL对瞬态，动态不同的DI的反应。在这项研究中，再分析数据与来自北大西洋东部辐射测量（ENA）站点（39.1°N，28.0°W）的观测资料相结合，以表征DI对MBL特征和云的影响。具体来说，将客观标准应用于2016-2018年冬季的观测值，以从DI之前和之后的DI日以及没有DI的参考期中识别出DI日。分析表明，DI事件期间，充分混合的边界层显着加深，同时伴有云，降水和热力学性质的变化。在DI期间，对流层下部基本冷却并干燥，从而产生了强烈的表面敏感和潜热通量。同时，强烈的反演会在升高的MBL顶部建立，从而影响云的发生。结果表明，在冬季，DI影响ENA站点边界层和云结构的时间约为21％，而云场对DI前沿的响应与对非DI前沿的响应大不相同。因此，