Impact of Land Surface Parameters on the Evaluation of East Asia Monsoon Precipitation

Abstract:

Land surface has crucial impact on air movement through momentum, energy and mass exchange. Leaf area index (LAI), one of important variable in the land surface processes, involves in canopy radiative transfer, momentum transfer, precipitation interception loss, and transpiration, which affect on land surface energy and water partition processes. Therefore, it crucially affects the ability of models to adequately simulate land-surface interaction. In this study, Long-term Global Mapping LAI (GLOBMAP LAI) and its corresponding land cover and greenness fraction are introduced into WRF_NMM/SSiB2. Compared with the control simulation based on the original specified LAI that is based on limited survey. The simulation with GLOBMAP LAI produced better precipitation distribution and rain belt movement. The improvements of the East Asia monsoon precipitation simulation are mainly attributed to the correction of the position of subtropical high. The north edge of subtropical high is related to the position of East Asia Westerly Jet. In the control simulation, weak westerlies lead subtropical high to move northward. Therefore compared with observations, more precipitation is in high latitudes. With imposed remote sensing LAI, the model produces larger meridional temperature gradient in surface and upper air, leading to stronger thermal westerlies. The Southward of Westerly Jet blocks the subtropical high, which amends the position of monsoon rain belt. This study directly takes advantage of recently available remote sensing products, and attributes the improved regional model simulation to proper LAI specification, which leads to adequate land/atmosphere interactions.