A simulation study of mesoscale coastal circulations in Mississippi Gulf coast

A numerical simulation of atmospheric mesoscale circulations in the Mississippi Gulf coast is carried out with non-hydrostatic WRF ARW meso-scale model to understand the flow and the boundary layer characteristics in the coastal environment. The model is used with three nested grids at 36, 12 and 4 km resolution covering the Mississippi Gulf coast and its adjoining regions for a typical summer period 01–03 June, 2006 having weak synoptic forcing. Results show development of sea-breeze circulation and formation of thermal internal boundary layer (TIBL) across the coast. The flow pattern shows regular occurrence of onshore winds in the day time and offshore winds in the late night/ early morning times. Simulated sea breeze extended horizontally up to 80 km inland and vertically up to 1 km. Height of the simulated internal boundary layer is 300 m near the coast and gradually merged with the mixing layer inland. Simulated winds and temperature distribution at the coast are found to agree with mesonet and upper air observations. Model simulated TIBL height is confirmed using observations from a boundary layer experiment. Performance of the Planetary Boundary layer (PBL) parameterization on the simulated circulation features is studied by conducting sensitivity experiments. The Yonsei University (YSU) nonlocal first order PBL scheme and a more complex Mellor–Yamada–Janjic (MYJ) TKE scheme are selected keeping the other model physics identical. Both the schemes have shown similar skills in simulating the mean characteristics of observed winds during sea breeze in the region. The YSU scheme shows improvement over MYJ in the simulation of internal boundary layer characteristics and the overall performance of predicted mean variables.