Contrastive Study on Two Boundary Layer Parameterization Schemes Using TWP-ICE Experiment Data

TWP-ICE (Tropical Warm Pool International Cloud Experiment) is carried out at Darwin Station in northern Australia by Europe and the United States, observations can be used for numerical simulation study. High resolution WRF single column model is used to simulate a case during TWP-ICE with two boundary layer parameterization schemes (YSU and MYJ schemes). Simulation results of boundary layer structure, cloud and precipitation with these two boundary layer parameterization schemes are compared.The whole simulation process can be divided into two phases, which are monsoon active period and monsoon suppressed period. During monsoon active period, the boundary layer structure simulated by MYJ scheme is better than YSU scheme. Small turbulent exchange coefficient is simulated by YSU scheme leading to weak turbulent mixing and small heat flux in boundary layer during monsoon active period, which prevents the heat and moisture of surface from upward transporting. Therefore, the simulated potential temperature and vapor mixing ratio are significantly higher than observations at the bottom boundary layer, and the simulated vapor mixing ratio is lower than observation at the top of boundary layer. During monsoon suppressed period, great turbulent exchange coefficient is simulated by MYJ scheme at night, leading to strong turbulent mixing and large heat flux, and the simulated potential temperature and vapor mixing ratio variation with height are smaller than observations, so MYJ scheme cannot simulate the structure of nocturnal boundary layer well.Also, the simulation of cloud and precipitation is affected by the boundary layer parameterization schemes. During monsoon active period, weak turbulent mixing is simulated by YSU scheme, leading to the wet bias near the surface and dry bias above. As a result, YSU scheme simulates smaller cloud liquid water content and frozen water content, less cloud fraction and lower precipitation rate. During the same period, MYJ scheme simulates the boundary layer structure well, and can better simulate cloud and precipitation. During monsoon suppressed period, the cloud fraction and precipitation simulated with both schemes show no significant difference, both exceeding observations.