Preliminary Analysis Of CloudSat CPR Data

Cloud-radiation interaction has a large impact on the Earth's weather and climate change, and clouds with different heights cause different radiative forcing. Thus, the information on the statistics of cloud height and its variation in space and time is very important to global climate change studies. CloudSat will provide, from space, the first global survey of cloud profiles and cloud physical properties, with seasonal and geographical variations, needed to evaluate the way clouds are parameterized in global models, thereby contributing to improved predictions of weather, climate and the cloud-climate feedback problem. The Cloud Profiling Radar (CPR) on CloudSat is a 94-GHz nadir-looking radar which measures the energy backscattered by clouds and precipitation within a 1.5 km across-track by 2.5 km along-track radar footprint and 500m vertical resolution.In this paper, cloud top height (CTH), cloud base height (CBH) and cloud thickness in the regions of Tibetan Plateau, Plateau south slope and South Asian Monsoon are analyzed based on the CloudSat data during the period from June 2006 to December 2007. The results show that frequency of cloud top and base heights in unit area over the studied regions have some certain space-time continuity. The CTH and CBH of different cloud types are in different range, and have significant seasonal variations. The cloud thickness is large (small) in summer (winter), and the percentage of different cloud types also have some certain regularity. The cloud heights and thicknesses of the same cloud type have some certain variation in the different study regions.We also use passive-sensing observation datas from the Moderate Resolution Imaging Spectroradiometer (MODIS) which boarded on Aqua (other A-Train satellite) to get the cloud top brightness temperature (TB) , and analyze the correlation between the MODIS TB and the CloudSat CTH. With a large number of cases, the results show that there is a negative correlation between TB and CTH, which means that the TB value will increase when the CTH is reduced. When the cloud is dense and thick, the correlation between the TB and the CTH is good. For improving the correlation, we set a more reasonable threshold to determine effective data. With this threshold, the correlation becomes much better, and a useful linear relationship is obtained.