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- Title
The Impact of Slantwise Descending Dry Intrusions on the Marine Boundary Layer and Air‐Sea Interface Over the ARM Eastern North Atlantic Site.
- Authors
Ilotoviz, E.; Ghate, V. P.; Raveh‐Rubin, S.
- Abstract
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. Key Points: Synoptic‐scale dry and cold intrusions descend slantwise behind cold fronts trailing from extratropical cyclones into the boundary layerUpon mixing into the boundary layer, dry intrusions lead to enhanced vertical mixing, increased boundary layer height and inversion depthDry intrusions enhance the latent and sensible surface fluxes and increased boundary‐layer cloudiness, despite the dry anomaly they induce
- Subjects
AIRSTREAM trailers; SYNOPTIC climatology; TROPOSPHERE; BOUNDARY layer (Aerodynamics); OCEAN-atmosphere interaction
- Publication
Journal of Geophysical Research. Atmospheres, 2021, Vol 126, Issue 4, p1
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1029/2020JD033879