L. Goldfarb, P. Keckhut, M.-L. Chanin, and A. Hauchecorne

Service d'Aéronomie du CNRS BP 3, 91371 Verrières-le-Buisson CEDEX, FRANCE

Quantification of cirrus occurrences and their optical properties is essential in the calculation of the heating rates, but long-term studies, especially of optically thin cirrus, are limited. We have constructed a climatology of cirrus clouds over the Observatoire de Haute Provence from ground-based lidar measurements taken between 1997 to 1999. During this time the Rayleigh-Mie lidar collected nearly 400 nights of measurements and cirrus profiles are detected in about half of these cases. Subvisible cirrus ( < 0.03) constitute a significant portion ( 20 %) of the cirrus cloud occurrence. Our high-resolution (75 m vertically and 3 minutes temporally) results show a sizable fraction of cirrus clouds occur near the tropopause. Preliminary results from phase function determinations, using data from the Raman and Rayleigh-Mie lidars, will also be presented.