Depolarization Ratio Measurements From the CALIPSO Spaceborne Lidar

Thanks to its sensitivity to optically thin atmospheric layers and its vertical variability, the lidar is a instrument perfectly suited to the study of cirrus clouds and aerosols. Moreover, most recent lidars are equipped with polarization-sensitive detectors that allow the retrieval of the depolarization ratio. Being, on a first approximation, only sensitive to the shape of particles, this measurement gives unique insights into the microphysical properties of probed atmospheric layers. Launched in late April 2006, the CALIPSO platform holds a 532 nm lidar with polarization abilities. This instrument, which circles the globe 14 times a day, allows to obtain, for the first time, coherent depolarization measurements all around the world - even in high-latitude areas like Antarctica. Moreover, the location of the CALIPSO lidar allows it to observe high-altitude clouds that are typically masked from ground-based observations by e.g. thick convective systems. Finally, its continuous operation will allow the creation of comprehensive cloud climatologies over long periods of time. An overview of the depolarization ratios observed from the CALIPSO lidar will be presented, including individual atmospheric features such as thick PSCs and aerosol layers. Overall statistics over longer periods, including latitude and temporal variability, will be discussed and compared to existing, ground-based climatologies.