Investigation of Boundary Layer Scheme Usage Impact to Seasonal Precipitation over the Philippines Using 24-km WRF Model Simulations

Abstract:

Boundary layer schemes in Weather Research and Forecast (WRF) model control the surface processes that determine the boundary layer environment necessary for convective initiation. This indirect impact of boundary layer scheme modulate some part of convection and precipitation. This study investigated the sensitivity impact of boundary layer scheme usage in predicting seasonal precipitation over the Philippines. The study used a 24-km resolution single-year hindcast experiment from June 2005 to May 2006. Ten boundary layer schemes were investigated from WRF version 3.5.1. This study evaluated the seasonal precipitation and 2-meter air temperature using 0.25 degree daily APHRODITE product. Diurnal cycle of surface variables were investigated to evaluate the capability of the boundary layer scheme in simulating surface processes in the simulations. Air temperature and relative humidity profiles were also compared against AIRS satellite data to validate the simulated atmospheric structure. Additionally, heat and moisture budget profile analysis using ERA-Interim as a reference was also done to investigate the coupling impact of default Grell-Freitas scheme with different boundary layer schemes. The evaluation of precipitation, atmospheric structure, and budget profiles allows better understanding of the impact of boundary layer scheme usage impact on the seasonal precipitation. The results of boundary layer scheme sensitivity show that it controls the modulation on the intensity of seasonal precipitation and modulation of heating and drying profiles. Mean precipitation structure and budget profiles are mainly dependent on the cumulus scheme used. Also, local TKE type schemes showed least overestimation in seasonal precipitation while non-local type schemes showed relatively high overestimation. This overestimation tendency seen on seasonal precipitation was also observed to be consistent with overestimation tendencies in the results of heat and moisture budget profile analysis.