Large-Eddy simulations of airflow dynamics and physics over the island of Graciosa

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Description

Three-dimensional numerical experiments are performed to explore the mechanical and thermal impacts of Graciosa Island on the sampling of an oceanic airflow. Ideal and real configurations of flow and terrain are planned using high-resolution Cloud Model 1 (CM1) simulations. Ideal configurations include model initializations with a dry adiabatic as well as moist, constant-equivalent potential temperature profiles with a 3D island-like topography. Real configurations use observations from different climatological background states over the Eastern Northern Atlantic, Atmospheric Radiation Measurement (ENA-ARM) site on Graciosa Island. Large-eddy simulations (LES) of dry airflow with a Froude number of 0.33 (F = U / Nh; U = 10 m s-1, N = 0.01 s-1, and h = 3 km) result in a large cold pool upstream of 3D bell-shaped mountain and downstream propagating von Kármán vortices. Although the peak height of Graciosa is less than half a kilometer, the Azores island chain has a mountain over 2 km, which might be leading to a similar flow phenomenon. Smaller mountain height experiments result in downstream vortices as well as a highly non-linear region of airstream a couple of half-widths away from the mountain. Preliminary idealized low-resolution moist simulations indicate that the cloud field is significantly impacted due to the presence of the island. Further numerical experiments are planned to extend moist simulations to LES scale with realistic atmospheric profiles and observations of surface fluxes. This work is intended to produce a useful simulation framework coupled with instruments to guide airborne and ground sampling strategies during the ACE-ENA field campaign, which will be conducted in June-July, 2017.