Characteristics of tropical thin cirrus clouds deduced from joint CloudSat and CALIPSO observations

The joint detection characteristics of both the CloudSat radar and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar are used to study tropical thin cirrus observed between 20°N and 20°S. The thin ice cloud category (TIC-1) of cirrus consists of those clouds detected by the lidar but not the radar whereas the TIC-2 cirrus category consists of clouds detected by both sensors. Tropical TIC-1 cirrus clouds between 20°N and 20°S are high, are optically thin, and have an approximate cloud cover in the defined region of 30%. Almost a third of this occurrence is in the form of single layers of cloudiness without any clouds below. These TIC-1 clouds also exhibit a marked seasonal variation, especially away from the equator, consistent with the shifts in annual cycle of convection with latitude. Lidar-based estimates of optical depth, uncorrected for multiple scattering, suggest that the TIC-1 optical depths range between 0.02 and 0.3. The ice water path of TIC-1 clouds is also estimated to be between 0.5 and 4 g m-2. The radiative properties of the TIC-1 clouds are also deduced from CloudSat flux data products at the top, at the bottom, and within the atmosphere. The influence of these clouds on the instantaneous reflected solar fluxes is determined to be less than 2 W m-2. The effects of TIC-1 clouds on the instantaneous outgoing longwave fluxes are estimated to be ~20 W m-2, and the impact of these TIC-1 clouds on the tropics-wide average of the infrared heating is ~4 W m-2.