NEW ALGORITHMS FOR THE DETERMINATION OF SOLAR RADIATION, SURFACE TEMPERATURE AND PBL HEIGHT IN CALMET

摘要

CALMET (Scire et al., 1999) is a diagnostic meteorological model that parametrises slope flows, kinematic terrain effects, terrain blocking effects, and includes a divergence minimisation procedure. CALMET contains also a micrometeorological model for the calculation of the planetary boundary layer parameters both overland and overwater. Since 1999 CALMET is the diagnostic meteorological model suggested by the US-EPA. This work presents new algorithms thought to overcome some limitations currently present into the model. The modifications concern the energy balance equation, the temperature interpolation and the PBL height calculation. The original version of CALMET considers only the direct radiation impinging over the ground and does not include shadowing effects. New routines were added in order to take into account topography induced shadows and to calculate direct, diffuse and reflected radiation. Moreover CALMET determines ground temperature at grid points doing a pure spatial interpolation of measurements that does not consider the different heights above the sea level of the points themselves. New routines were added to take into account the vertical temperature gradient, topography properties such as slope and aspect and the vegetation cover. Finally the algorithm originally present in CALMET to calculate the planetary boundary layer height were substituted with those described by Batcharova and Gryning (1991) for daytime conditions and by Zilitinkevich (1989) for nighttime conditions. The algorithms for the calculation of the PBL parameters will be not described in the following of this paper. A comprehensive description of these algorithms can be found for example in Seibert et al. (2000).