29th Conference on Hurricanes and Tropical Meteorology


Spray microphysics and effects on surface fluxes as seen from simulations using a Lagrangian model with spectral bin microphysics

Jacob Shpund, The Hebrew University of Jerusalem, Jerusalem, Israel

The spatial evolution of spray size distribution, as well as effects of spray on temperature, humidity and surface fluxes are investigated using the Lagrangian model of maritime boundary layer. In this model, the computational area of 300m x 400 m is covered by more than 1500 Largangian adjacent with characteristic linear size of 8 m moving within a turbulent-like flow under a given background wind speed. Turbulent properties of the boundary layer are determined according to the observed realistic data. The model takes into account various processes such as condensation/evaporation, drop collision, gravitational sedimentation of drops and turbulent mixing between parcels, heat and moisture surface fluxes. The size distribution of spray droplets at a characteristic level of (~ 5-10 m) is determined within a wide range from ~0.01 micron to ~400 microns based on a wave-breaking/energy dissipation model as well as laboratory simulations. In droplet size distribution sense, the model is being parameterized as Ocean-Atmosphere coupled model. To describe the process of evaporation/condensation as well as collisions accurately, size distribution of aerosols and droplets is calculated at mass grid containing up to 500 mass bins. Soluble mass is calculated within spray particles, so that distribution of salinity of droplets is determined at each time step (~0.1 s). The simulations provide spray size distributions at different levels, including that at the top of the surface level, as well as at the cloud base level. This allows one to evaluate the concentration and size distribution of aerosols including giant cloud condensational nuclei at cloud base at different wind speeds. The ways to parameterize the results for utilization in the cloud models and TC models for simulation of precipitation and surface fluxes are discussed.

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Session 2C, Hurricane Aerosol and Microphysics Program (HAMP)
Monday, 10 May 2010, 10:15 AM-12:00 PM, Arizona Ballroom 10-12

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