Simultaneous multi-layer retrievals of ice and liquid water cloud properties using passive measurements

Abstract

Cirrus are recognized as having a major, yet poorly understood impact on the Earth-atmosphere radiation balance. The precise study of their properties is thus necessary nowadays, in order to supply accurate information to climate models. Therefore, many studies have been conducted during the past decades to characterize cirrus properties more accurately. Amongst them, the A-Train mission has proven to be particularly important, thanks to a multitude of active and passive instruments. Aiming to take advantage of these new possible of synergies, variational methods, such as optimal estimation, have become commonly used to retrieve properties of ice or liquid water cloud layers. Simultaneous retrievals of ice and liquid clouds properties nevertheless remain rare. In this study, an algorithm dedicated to performing such simultaneous multi-layer retrievals is presented. This algorithm uses the information contained in five channels situated in the visible, near infrared and thermal infrared regions, to retrieve the ice water content of one ice cloud layer, and the optical thickness and droplet effective radius of two possible liquid cloud layers. This paper presents preliminary results of the algorithm that correspond to one month of retrievals, under several CALIOP orbits. Comparisons with products of operational algorithms such as MODIS or DARDAR show good agreement with our retrievals.