WRF4.0模式陆气耦合对不同物理参数化方案的敏感性初探

A preliminary study on the sensitivity of WRF 4.0 model land-atmosphere coupling to different physical parameterization schemes

摘要:

模式的不同参数化方案会对模拟的天气和气候产生影响,但如何影响陆气耦合还不是很清楚。利用WRF 4.0模式设计了一组16种不同参数化方案组合的集合试验,对华北地区2013年夏季气候进行模拟。结果表明,不同积云对流参数化方案对模拟的降水平均态影响较大,其次是短波辐射方案,而微物理方案影响较小。进一步利用潜热通量(LH,Latent Heat flux)和土壤湿度(SM,Soil Moisture)、抬升凝结高度(LCL,Lifting Condensation Level)的相关系数R_(SM,LH)和R_(LH,LCL)表征陆气耦合过程,评估了陆气耦合对不同参数化方案的敏感性。模式模拟的R_(SM,LH)在不同区域随着平均降水、相对湿度的增加以及平均短波辐射的减少而减小,而R_(LH,LCL)的变化正好相反。它们内在的物理机制类似,与气候态的干湿变化密切相关,即随着土壤湿度趋于饱和,蒸散发过程逐渐受太阳辐射的限制,陆面对大气的影响减弱。另外,陆气耦合强度受积云对流方案、微物理方案和短波辐射方案的影响而产生差别,这与不同参数化方案模拟的气候态的不同密切相关,因此本研究对于WRF 4.0模式中参数化方案特别是积云对流方案的选择同样有着重要的指导意义。

关键词:陆气耦合;WRF4.0;参数化方案;抬升凝结高度

Abstract:

Different model parameterization schemes affect the simulation of weather and climate,but their effect on the simulated land-atmosphere coupling is still unclear.In this study,16 different physical parameterization schemes are used with the WRF 4.0 model to simulate the climate in northern China during the summer of 2013.The simulated mean precipitation is found to be most affected by cumulus schemes,least affect by microphysics schemes,and affected in between by shortwave radiation schemes.The correlation coefficients between soil moisture and latent heat flux (R_(SM,LH)) and between latent heat flux and lifting condensation level height (R_(LH,LCL))are used to represent land-atmosphere coupling,and their sensitivities to different parameterization schemes are investigated.The study shows that R_(SM,LH)decreases with precipitation and relative humidity and increases with downward shortwave radiation,while the change in R_(LH,LCL)is opposite.The changes in both metrics are similar and are related to the mean wetness changes.As the soil moisture tends to saturate,evapotranspiration is limited gradually by solar radiation,and the influence of land processes on the atmosphere weakens.Besides,the strength of the simulated land-atmosphere coupling varies with the physical parameterization schemes,including the cumulus schemes,microphysics schemes,and shortwave radiation schemes.These differences in coupling are also closely related to the different mean climates simulated by different parameterization schemes.Therefore,this study has important guidance for choosing parameterization schemes in WRF 4.0,especially cumulus schemes.

Key words:land-atmosphere coupling;WRF 4.0;parameterization scheme;lifting condensation level