Study on the Three Dimensional Cloud Region Diagnosis

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 occured in China. 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. RH threshold and its vertical distribution used for cloud diagnostic was analyzed from Threat score(TS) 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 Tbb observations overall. Diagnostic cloud depth consists with optical thickness and precipitation on ground better . 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.