Analysis of cloud-top height and cloud amount difference between spaceborne microwave radar and laser radar detection in boreal summer

Cloud is a critical factor for weather and climate change. Accurate estimation of the cloud top height and cloud amounts are very important for cloud characteristics analysis, precipitation forecast, and cloud radiative forcing study. Based on the measurements of the Cloud Profile Radar (CPR) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) carried by CloudSat and CALIPSO respectively, spatial distributions of global cloud top height and cloud amounts are investigated for the summer from June to August over the period of 2006-2010. The results show that the averaged cloud top height detected by CPR is 12 km against 16 km measured by CALIOP in the tropics. The cloud top heights detected by both CPR and CALIOP are mostly below 4 km in the subtropical ocean with large regional differences between measurements of CPR and CALIOP. Compared with the cloud top heights detected by the CALIOP, the CPR misdetected thin clouds, cloud anvils and clouds below 2.5 km, and underestimated the cloud top heights of thick clouds. The global mean cloud amount detected by CPR is 51.1%, which is 23.3% less than that by CALIOP. The results also show a significant sea-land difference in the distribution of cloud amounts with the largest difference occurring in the ocean. 80% of global clouds are found above the oceans based on CPR while more than 90% are over the oceans based CALIOP. Because of the short wavelength of CALIOP, it is sensitive to tiny particles, whereas CPR cannot detect relatively small particles. Therefore, CALIOP is better than CPR in detecting cloud top. Results of the present study not only enhance our understanding of detection principles of CPR and CALIOP, but also provide more information about the climatic characteristics of clouds.