Satellite Observation on Rainfall Enhancement in Stratiform Clouds over Shaanxi Province in Spring 2009

Because of the advantages of cloud detection with satellite,the cloud structure and precipitation formation process can be analyzed from different configurations of cloud thickness,particle size and cloud top properties by the retrieval and multi-spectral analysis of satellite data,and consequently the potential of rainfall enhancement can be investigated based on the assumptions of rainfall enhancement and the available research achievements.A new applicable tool will be provided for satellite detection of the conditions of precipitation enhancement.A precipitation process of stratiform clouds from 7 to 8 February,2009 was selected to analyze rainfall enhancement with MODIS polar orbiting satellite data.The retrieval microphysical characteristics of the clouds are as follows:(1) The cloud top temperature was about-10 ℃,the effective radius(Re) of cloud top was around 10 μm,the cloud body was thick,and the clouds were rich in supercooled water but lack of ice crystals or large drops at daytime of 7 February;(2) Rainfall occurred under the participation of high clouds;(3) There was a good opportunity for rainfall enhancement because of the existence of sustained and stable low-level stratiform clouds.Cloud tracking with FY2C geostationary satellite revealed that the cloud system lasted for 30 hours,in which clouds grew thick gradually with stable Re and less rainfall from the daytime to the night of 7 February.Although precipitation process of such clouds was weak,there was a good potential for precipitation enhancement operation.After the comprehensive analysis,the suitable criteria for detecting rainfall enhancement of supercooled stratiform clouds with satellite can be summarized as: the thickness of clouds is about 2 km,and cloud top temperature ranges from-10 ℃ to-20 ℃ with Re less than 15 μm.