Lidar studies of the microphysical and optical properties of thin cirrus clouds

摘要

Cirrus clouds are routinely observed by lidar at Chung-Li (25°N, 121°E). Their optical and microphysical properties are investigated by the height and temperature distributions, optical thickness, extinction, and depolarization ratios. Cirrus clouds with optical thickness smaller than 0.03, which are classified as subvisual cirrus clouds, have high probability of occurrence. Thin cirrus clouds have their optical thickness exponentially correlates with temperature in the region of -60 to -80C. Depolarization ratio is an important property of cirrus clouds. Although depolarization ratio for ice particle is large, vanishing depolarization ratios have been found for some clouds as high as 12 km. Depolarization ratio for all cirrus clouds distributed widely, and thin cirrus clouds near the tropopause above 16 km seem to have limited depolarization ratios. The microphysics of ice particles is discussed.