Adjustment of the Marine Atmospheric Boundary-Layer to the North Brazil Current during the EUREC4A-OA Experiment

The EUREC4A-OA experiment (January - February 2020. Bony et al., 2017) took place in the Northwest Tropical Atlantic. Atmospheric simulations were performed at kilometric scale during the EUREC4A-OA experiment (47 days) in order to estimate the sensitivity of the Marine Atmospheric Boundary-Layer (MABL) thermodynamics and circulation to the SST front associated with the North Brazil Current (NBC) and to the SST diurnal cycle. It will be shown that the NBC SST front and associated eddies «Couloir des Tourbillons» strongly control the MABL properties (Surface Pressure, Surface Heat Fluxes, Temperature, Wind, Vertical Shear, Precipitable Water, Liquid Water Content ...), while the diurnal cycle of the SST alters these properties by 5 to 10%.

A full MABL water budget has shown that the precipitable water (PW) results of the balance between the total Advection and entraiment at the MABL top, which drains water out the MABL, and surface evaporation that fills in the MABL. It will be shown that the NBC increases the loss of water by advection and by entrainment and increases the gain of water by surface evaporation, by 80 mm in 47 days. The diurnal cycle of SST amplifies these responses by 30 mm in the NBC.

Some components of the MABL energy budget will be also presented.