利用TWP-ICE试验资料对比两种边界层参数化方案

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

利用高分辨率WRF单气柱模式,选取了两种边界层参数化方案(YSU,MYJ),对TWP-ICE(Tropical Warm Pool International Cloud Experiment)试验期间的个例进行数值模拟,比较了两种方案对边界层结构、云和降水模拟的影响。结果表明:季风活跃期,YSU方案模拟的湍流交换系数较小,湍流混合偏弱,边界层内热通量偏小,使地表热量和水汽不易向上输送,水汽含量在近地表明显偏多,而在边界层及其以上大气层具有显著的干偏差,因此该方案模拟的云中液态水和固态水含量偏低,云量偏少,降水率偏小;MYJ方案对于季风活跃期的边界层结构具有较好的模拟能力,其模拟的云和降水更为准确。季风抑制期,MYJ方案模拟的夜间边界层结构存在较大误差,这是因为该方案模拟的夜间湍流交换系数较大,湍流混合偏强,边界层内热通量偏大,模拟的位温和水汽混合比在边界层内随高度变化较小,而观测廓线在边界层内存在较大梯度。季风抑制期两种方案模拟的云和降水均比观测值偏多,方案之间的差异较小。

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 po-tential temperature and vapor mixing ratio are significantly higher than observations at the bottom bounda-ry layer,and the simulated vapor mixing ratio is lower than observation at the top of boundary layer.Dur-ing 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 struc-ture 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 precip-itation.During monsoon suppressed period,the cloud fraction and precipitation simulated with both schemes show no significant difference,both exceeding observations.