Quality Assessment of Cloud-Top Height Estimates From Satellite IR Radiances Using the CALIPSO Lidar

This paper summarizes the studies performed using data from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) to verify cloud variables in the context of the European Centre for Medium-Range Weather Forecasts assimilation system. In the first part of this paper, the cloud-top height (CTH) derived from the Atmospheric Infrared Sounder (AIRS) radiances has been compared with the same quantity from CALIPSO exploiting the spatial and temporal coincidence guaranteed by the A-Train constellation. In the second part, the CTH from CALIPSO has been used to verify the wind height assignment (HA) for the atmospheric motion vectors (AMVs) derived from Meteosat geostationary cloudy radiances. Two different estimates from AIRS have been considered: one derived from the cloud detection scheme and the other used within the assimilation of infrared (IR) cloudy radiances. The verification of cloud detection for hyperspectral IR sounders has revealed some difficulties with cirrus clouds. The verification of CTH for the assimilation of IR cloudy radiances has shown a reasonable agreement when the lidar signal is fully attenuated but a larger scatter in other conditions. The verification of AMV HA revealed an overall tendency to produce CTHs lower than CALIPSO for high clouds and the opposite for low clouds. Interestingly, a similar behavior was observed in the validation of CTHs for the assimilation of IR cloudy radiances.