春末夏初土壤状态对后期区域降水模拟的影响

Influence of Spring Soil Condition on Later Regional Precipitation Simulation

欧洲中期天气预报中心40 a的再分析资料(ERA40)对中国范围土壤湿度的表现好于美国国家环境预测中心/国家大气研究中心(NCEP/NCAR)再分析资料,尤其是在春末夏初阶段,对因融雪和土壤融冻产生的土壤湿度变化有着更好的表现.针对这一特点,分别用这两套再分析资料土壤温、湿度分布作为初始场驱动大气模式MM5,以1998年为例研究春末夏初不同的土壤状况对后期环流以及区域降水的影响.结果表明:土壤温、湿度分布对高空要素场的模拟有一定影响,运用ERA40土壤状况可以在一定程度上减小200 hPa高空急流的模拟误差,减小500 hPa位势高度场模拟误差,减小高原东侧向北的低空急流模拟误差,改进850 hPa温度场分布.运用ERA40土壤状况模拟的降水在长江中下游地区、西北干旱区以及青藏高原主体东侧的模拟不论从空间分布特征还是模拟误差方面均好于运用NCEP/NCAR土壤状况的模拟结果,运用ERA40土壤状况的模拟对季风雨带的演变时间和位置模拟都更接近于观测.

Previous studies have indicated that the European Center for Medium-Range Weather Forecasts（ECMWF） 40 years global reanalysis（ERA40） is better than the National Centers for Environmental Prediction-National Center for Atmospheric Research（NCEP-NCAR） Global Reanalysis（NCEP/NCAR） for describing the soil moisture over China,specially for the soil moisture variation due to snow melting and soil thawing at the end of spring and the beginning of summer.In this paper,two soil moisture and temperature data sets at the end of May 1998 are compared and used as land initialization.Soil moisture and temperature in June 1998 is simulated using the mesoscale model MM5 to investigate the influence of soil condition on circulation and water cycle simulation.The results indicate that soil condition influences the circulation to some extent.Errors of zonal wind at 200 mb,geopotential height at 500 mb,northward meridian wind and air temperature at 850 mb simulated by using ERA40 soil data are less than that by using NCEP/NCAR soil data.Precipitation simulation by using ERA40 soil data is improved both in the higher spatial correlation coefficient and error,as compared with that by using NCEP/NCAR soil data.The evolution of zonal mean precipitation simulated by using ERA40 soil data is closer to the observation than that simulated by using NCEP/NCAR soil data.