Evaluation of MM5 Forecasts of Near-Surface Parameters: Sensitivity to Land-Surface Parameterization and Planetary Boundary Layer Schemes

Abstract

The specific purpose of the research is to evaluate the performance of the MM5 model in the forecasting of near-surface parameters, such as 2-meter temperature, 2-meter dew point, and 1000-850 mb thickness. The evaluation will include a comparison of the MM5 against the Eta model, and a comparison of the forecasting skill of the MM5 with three different land-surface parameterization schemes. Three different soil moisture scaling techniques will be applied to the MM5, and their forecasts will be evaluated against observations taken from 7-9 December 2001.

The MM5 displayed an inability to capture the full magnitude of the diurnal cycle of 2-meter temperature and dew point. The Eta model performed better than the MM5 in the forecasts of near-surface parameters. The MM5 forecasts of near-surface parameters can be improved by adjusting the vertical profile of the soil moisture in the model initial conditions. By removing soil moisture from the initial conditions of the MM5, a more realistic Bowen ratio was simulated, leading to an improved forecast of the diurnal cycle of temperature and dew point. The results of this research suggest that the cause of the damped diurnal cycle in the MM5 forecasts may be inadequate ventilation of the upper planetary boundary layer, an inaccurate representation of surface evapotranspiration, or incorrect assignment of soil type and land use categories.