Study of Meso-Scale Coastal Circulations in Mississippi Gulf coast with Mesonet Observations and Modeling

Mesoscale simulations of land-sea breeze circulation are carried out in the Mississippi Gulfcoast region using the Weather Research and Forecast (WRF ARW) model using high resolution nested domains for application to atmospheric dispersion. In the present study a meso-net observation network consisting of automatic weather stations installed along the Mississippi Gulfcoast are used to capture the meteorological fields. Data from this network is used in conjunction with available surface and upper air observations for model assimilation. A series of simulations are conducted for different seasons under varying synoptic conditions. Surface fluxes of heat, moisture, momentum, turbulent kinetic energy (TKE) and the state variables – temperature, humidity and winds are compared with observations. Data collected from boundary layer profilers at a number of locations across the coast from a field experiment are used to evaluate the model simulations and to study the thermal internal boundary layer characteristics.

Simulated features show well developed onshore and off-shore flow associated with land-sea breeze circulation and formation of thermal internal boundary layer near the coast. The onset, strength and inland penetration of sea breeze are found to vary in different seasons. Summer weak synoptic conditions associated with strong solar heating and land-sea temperature contrast favored intense land-sea breeze development and TIBL formation. Simulated sea breeze strength is about 6 m s-1 and its horizontal extent is about 100 km across the coast. Simulated vertical extent of internal boundary layer is about 300 m spreading about 50 km across the coast. Simulations suggest that the presence of these complex meso-scale coastal circulations could influence the trajectory of air pollutants parcels originating at the coast. The trajectory pathways are expected to affected by the onshore and offshore winds and the consequent recirculation. Also the shallow mixing depths near the coast as revealed by the model could cause enhanced ground level pollution concentrations from the locally emitted releases.

Keywords : Coastal circulation, Mesonet, WRF, sea breeze, dispersion.