Extended Abstract (1.1M)4.5
Simulations of A Real MCC Event over the Yellow Sea with COAMPS Model
Fanyou Kong, University of Oklahoma, Norman, OK; and B. Fiedler
The mesoscale cellular convection (MCC) system is common in wintertime when continental cold air mass flows through a warmer ocean surface, resulting in a maritime mixed layer capped by cellular pattern cloud cells. The ability for mesoscale models to explicitly simulate this MCC cloud system is important since cloud cells from such systems affect the radiation budgets and precipitation in the marine boundary layer in a great manner. In this study, the mesoscale cellular convection system during a real cold-air outbreak over the Yellow Sea on January 25, 2000 has been simulated with the atmospheric portion of the Naval Research Laboratory's Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS), a non-hydrostatic mesoscale numerical model. The numerical experiments are carried out in one single grid set with 2 km resolution in horizontal and 45 vertically stretched sigma levels ranging from 20 m near the surface to 790 m at the top at the height of about 14.8 km. The domain has 175 by 175 grids centered at 36.8N and 124.0E, covering a 350 km by 350 km region over the Yellow Sea. The model initial conditions are obtained directly from the Navy Operational Global Atmospheric Prediction System (NOGAPS) data, which also provide the lateral boundary conditions through the 24 h simulation process.
The simulation results show that the COAMPS model is able to produce the well developed mesoscale cellular cloud cells for the real case situation. However, in order for the stratiform cloud deck to fully break up into cellular cloud pattern in a timely manner, the eddy mixing coefficients resulted from the model's Mellor-Yamada TKE computation need to be reduced significantly. The Bougeault-Lacarrere mixing length method is implanted into the COAMPS model and tested in the simulation. It too requires adjustment of its parameters to generate proper level of eddy mixing for the model to produce well developed MCC. Sensitivity tests are also conducted, which show the important impact of latent heat flux on the resulting MCC development and structures.
Session 4, Atmospheric Processes
Friday, 9 November 2001, 8:30 AM-10:45 AM
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