Microphysical Structure of the Marine Boundary Layer under Strong Wind and Spray Formation as Seen from Simulations Using a 2D Explicit Microphysical Model. Part II: The Role of Sea Spray

Abstract

he effect of sea spray on the thermodynamics and microphysical structure of the lowest 400-m layer under strong wind speeds is investigated using a 2D hybrid Lagrangian?Eulerian model with spectral bin microphysics. A large number of adjacent and interacting Lagrangian parcels move within a turbulent-like flow with the largest vortices being interpreted as large eddies (LE) with characteristic velocity of a few meters per second.It is shown that sea spray effect strongly depends on the environmental conditions, and largely on relative humidity (RH). When RH < ~90%, spray evaporates and contributes to moistening and cooling of the boundary layer, as well as to an increase in surface fluxes. When RH > ~90% the effects of spray on the BL thermodynamics substantially decrease. Spray leads to formation of drizzle by collisions with droplets formed on background aerosols.It is also shown that LE transport about 20% of large spray drops with radius exceeding 150 ?m to the upper levels of the atmospheric mixed layer. It is hypothesized that this effect is of much importance with regard to the spray effect on the microphysics and dynamics of deep convective clouds typical of a hurricane eyewall.