The Study of Mesoscale Land-Air Interaction Processes Using a Nonhydrostatic Model
The main objectives of this study are to understand the effects of land-air-sea interaction on mesoscale processes. To achieve these goals, the compressible nonhydrostatic atmospheric component of the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) (Hodur, 1993) has been modified to include orography, surface moisture and energy budgets. Efforts were also made to improve the model efficiency. Validation tests indicate that the COAMPS is capable of simulating different phenomena associated with mountains. Effects of a Gulf Stream filament (GSF) on mesoscale circulations were examined using the model. The GSF is found to play an important role in the initiation and maintenance of convective clouds and precipitation in a time scale of several hours. Heavy precipitation occurs for a short time. High resolution SST distribution is necessary for a successful meteorological forecasting over the ocean. Influence of ground surface moisture on sea breeze circulations, convection and subsequent precipitation during the Convection and Precipitation Electrification experiment (CaPE) was also investigated using the COAMPS. Surface energy and moisture budgets were added to the COAMPS to simulate the diurnal cycle of ground surface temperature and wetness. The surface moisture is found to have a significant impact on the formation, strength, maintenance, and the location of convection and precipitation induced by the sea breezes. To correctly simulate the sea breeze and the associated rainfall, inclusion of surface energy and moisture budget in the model is necessary. Finally, effects of topography and air-sea interaction processes on atmospheric circulations were investigated over the Pacific Northwest (PNW) region using a triple -nested version of the COAMPS. Real data were used in this case study. The COAMPS is able to reasonably simulate the observed mesoscale circulations and the precipitation in a region with complex terrain features. The blocking of low-level air mass by topography plays a very significant role in modifying the large scale and mesoscale circulations. Due to the three-dimensional shape of the Olympic Mountains, incoming low-level flow is steered around it. Air-sea interaction has a significant impact on the large scale as well as on mesoscale systems. Unlike over the Gulf Stream region where heat fluxes are transferred from warm ocean to the atmosphere, heat fluxes here are transferred from the warm sectors of the atmosphere to the cold ocean. To realistically predict mesoscale circulations over the PNW region, at least two factors are found important. These are representation of topographical features, using fine model resolution and inclusion of air-sea interaction processes.
- Pub Date:
- January 1995
- Physics: Atmospheric Science; Physics: Fluid and Plasma; Mathematics; Physical Oceanography