Comparative experiments with MAPS on different-parameterization schemes for surface moisture flux and boundary-layer processes

Abstract

A modified formula for computing the surface moisture flux is proposed based on the assumption that the layer below the lowest model computational level can be represented by three "physical' layers, of which the bottom one is the molecular layer. This three-layer aerodynamic (3LAD) scheme is compared with two-layer aerodynamic (2LAD) as well as flux matching and Penman-Monteith potential evapotranspiration (PM) schemes. Both a 10-day forecast period (3D) and case simulations demonstrate that the 3LAD scheme gives the best prediction in latent heat flux from the ground and mixing ratio in the atmosphere. The moisture flux produced by the 2LAD scheme is too large, especially over warm and moist surfaces. The mean 12-h forecast rms errors in relative humidity at the surface (10 m AGL) are 15.6%, 21.5%, and 26.0%, respectively, for the 3LAD, PM, and 2LAD schemes in a 10-day parallel test period using MAPS. -from Authors