Identification of precipitating clouds in the south and southwest of Iran using CALIPSO and CloudSat satellite observations

The main purpose of this study is to detect precipitating clouds and to analyze their vertical structures in the south and southwest of Iran using CALIPSO and CloudSat satellite observations. At First, events with high precipitation rates using the daily precipitation data of the synoptic stations in the area of interest during the statistical period from 2006 to 2016 were selected. The selection of these samples is based on two parameters: the average precipitation of the synoptic system and the number of stations involved in precipitation. The average precipitation of the system was calculated by the ratio of the total precipitation of all stations in one day to the number of stations involved in precipitation on the same day. In order to eliminate light precipitating samples, a precipitation threshold was set for the mentioned parameters. So that at least in one of the days of precipitating system activity, the number of stations involved in precipitation is not less than 15 stations and the average precipitation of the system is not less than 15 mm. This threshold is defined as the day of peak precipitation. In total, 74 precipitating systems that lasted from one day to one week were determined and 107 days of precipitation with the above specifications were selected. In order to ensure the occurrence of precipitation at the same time as the satellite orbit passing through the area, TRMM satellite level 3B precipitation data was used. These data have precipitation values in a temporal interval of 30 minutes and spatial resolution of 0.1 by 0.1 degrees. Considering the network precipitation values of peak days, three precipitating samples in three different paths where the precipitation occurred along the satellite path, were selected to analyze their cloud structures. Precipitation characteristics of the mentioned systems were extracted based on station and network precipitation values. In the next stage, three features including the total attenuated backscatter at 532 nm, the depolarization ratio and the color ratio were obtained by the use of CALIOP lidar level 1B data. The radar reflectivity feature was also extracted using data of CPR sensor of CloudSat. Then, using layers extracted from CALIOP and CPR sensors, the clouds of these samples were compared and analyzed in terms of cloud thickness and precipitation intensity. The results of the analysis showed that in the first sample (Path A), despite the large thickness of the cloud (approximately 10 km), the amount of precipitation is less than the other two samples. The cloud of this sample is different from the other two samples. Cloud layers in the vertical direction are not dense and integrated enough. Also, aerosol particles and ice crystals in the cloud are fewer and smaller. While in the other two samples, especially in path C, while the thick and dense cloud covers the atmosphere of the region, the concentrations of aerosols and ice crystals are much higher.