利用2007-2008年Cloudsat云检测产品与ECMWF再分析资料的相对湿度进行统计分析, 得出了中国云內外相对湿度判別阈值及其随高度的变化, 提出了基于再分析资料的三维云场分布诊断方法, 应用于实例三维云场诊断, 并与卫星、雷达、地面云降水观测等资料进行了对比分析, 得到的主要结论有: (1)Cloudsat云判别有效值>20的云区位置与Cloudsat辅助产品给出的ECWMF再分析资料的相对湿度高值区有较好的时空对应; (2)不同高度范围的云内相对湿度都呈单峰型分布, 峰值在相对湿度100%附近, 晴空相对湿度受当地大气环境影响, 各地各高度都有差别; (3)通过相对湿度对云区和晴空的TS评分测试, 得出了诊断云区的相对湿度阈值及其垂直分布; (4)利用NCEP再分析资料对中国三维云场的分布进行个例诊断应用, 与卫星、雷达和地面云降水观测的对比表明, 云区附近的湿度梯度大, 相对湿度阈值法诊断的云区总体比较稳定; (5)诊断的云区与上升气流区对应较好, 云区和晴空的分布与卫星TBB观测大致对应, 云厚(即云格点总数)与光学厚度和地面降水的分布比较一致; (6)云场垂直剖面可以清晰地看出其分布同天气系统的关系, 诊断的云区与地面云观测比较一致, 云层密实深厚的区域通常对应着地面降水; (7)单点的云垂直结构随时间演变与当地的雷达和地面云降水观测都比较一致。
Cloud mask and relative humidity (RH) provided by Cloudsat products from 2007 to 2008 are statistical analyzed to get RH Threshold between cloud and clear sky and its variation with height.A diagnosis method is proposed based on reanalysis data and applied to three-dimensional cloud field diagnosis of a real case.Diagnostic cloud field was compared to satellite, radar and other cloud precipitation observations.Main results are as follows.Cloud region where cloud mask is bigger than 20 has a good space and time corresponding to the high value relative humidity region, which is provide by ECWMF AUX product.Statistical analysis of the RH frequency distribution within and outside cloud indicated that, distribution of RH in cloud at different height range shows single peak type, and the peak is near a RH value of 100%.Local atmospheric environment affects the RH distribution outside cloud, which leads to RH distribution vary in different region or different height.RH threshold and its vertical distribution used for cloud diagnostic was analyzed from Threat Score method The method is applied to a three dimension cloud diagnosis case study based on NCEP reanalysis data, and the diagnostic cloud field is compared to satellite, radar and cloud precipitation observation on ground.It is found that, RH gradient is very big around cloud region and diagnosed cloud area by RH threshold method is relatively stable.Diagnostic cloud area has a good corresponding to updraft region.The cloud and clear sky distribution corresponds to satellite the TBB observations overall.Diagnostic cloud depth, or sum cloud layers distribution consists with optical thickness and precipitation on ground better.The cloud vertical profile reveals the relation between cloud vertical structure and weather system clearly.Diagnostic cloud distribution correspond to cloud observations on ground very well.Precipitation on ground usually can be observed at deep-developed cloud area.The time series of cloud vertical structure evolution at single point is well consistent with local radar and surface cloud and precipitation observations.In summary, diagnosis of three-dimensional cloud field and its distribution by relative humidity threshold from the reanalysis data are in good agreement with the development and movement of cloud precipitation and weather systems.It can be well applied to weather, climate and weather modification research.
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