Lidar observations of cirrus clouds in Buenos Aires

Abstract

Characterization of cirrus clouds over Buenos Aires (34.6°S, 58.5°W) using a ground based lidar is presented. The study, carried out for the period 2010?2011, reveals that cirrus are usually found in thealtitude region 8?11 km, with mid-cloud temperatures values varying between 75 °C and 55 °C. The clouds, whose bases altitudes display significant variability while their tops remains close to the tropopause, show geometrical thickness ranging from 1.2 to 5 km, with on average value 3.0 +/- 0.9 km. Most commonly observed cirri can be characterized as optically thin cirrus rather than dense ones, with a mean optical depth value of 0.26 7 0.11 and an applied multiple scattering factor η of 0.85 +/- 0.07. In this region, the optical depth increases with increasing geometrical thickness with a partially linear correlation. Lidar ratios are also analyzed and on average the value is 32 +/- 17 sr.