A statistical description method of global sub-grid topography for numerical models

Abstract Slope and aspect are important topographic elements for thermodynamics dynamics of atmospheric circulation, especially local radiation precipitation. We propose a simple realistic statistical method based on trigonometric function transformation to calculate sub-grid slope describing the orographic characteristics complex areas over globe. It is found that transformed conditional probability density conforms Gaussian distribution in most global (~ 98%), this feature not eliminated with increasing horizontal resolution. The reasonability tested Tibetan Plateau. results show improvement ratio surface solar downward (SSRD) Plateau improved significantly compared from grid average scheme, autumn. root mean square error approximately 18.2 W/m 2 , reached 38.4%. improvements maximum regional-averaged SSRD whole were ~ 130 44.3 respectively. Although we only consider effect shortwave radiation, which has certain bias observation data, it sufficient prove rationality unobstructed surfaces scheme.