Impact of Dry Intrusions on the Marine Boundary Layer

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Description

Intrusions of dry air from the upper troposphere into the boundary layer are known to cause significant changes in the boundary layer thermodynamic and wind fields (Raveh-Rubin, 2017). The dry intrusions (DIs) are slantwise descending airstreams from the midlatitude upper troposphere towards the boundary layer at lower latitudes. DIs occur mainly during winter months over the mid-latitude oceanic storm track regions. These regions are also home to marine boundary clouds that are an important component of the Earth’s radiation budget as they reflect much higher radiation back to the space compared to the ocean surface thereby cooling the Earth’s surface. Although subsidence is generally an inherent feature of the subtropical marine boundary layer, it is unclear how the marine boundary layer reacts to the transient, dynamically distinct DI, differently from the nominal subtropical subsidence resulting from the descending branch of Hadley circulation. In this study we use the observations made at the Atmospheric Radiation Measurement (ARM) Eastern North Atlantic (ENA) site (39N, 28W) to characterize the impact of dry intrusions on marine boundary layer cloud, thermodynamic and dynamic properties. We used the data from the European Center for Medium-range Weather Forecasts (ECMWF) reanalysis ERA Interim to identify DI trajectories during the years 2016-2018. The cloud macro- and micro-physical properties are retrieved by combining the data from the vertically pointing Doppler cloud radar, lidar and microwave radiometer. The boundary layer thermodynamic structure is characterized using observations from the radiosondes and Raman Lidar. The boundary layer dynamic structure and wind fields will be retrieved from the data collected by Doppler Lidar and Radar Wind Profiler (RWP). The observations made before, during, and after the arrival of the DI at the site will be contrasted to quantify the impact of DI on the boundary layer properties. Raveh-Rubin, S., 2017: Dry Intrusions: Lagrangian Climatology and Dynamical Impact on the Planetary Boundary Layer. J. Climate, 30, 6661–6682,https://doi.org/10.1175/JCLI-D-16-0782.1