Characterization of cirrus clouds in central Amazon (2.89ºS, 59.97ºW): Firsts results from observations in 2011

Abstract

In 2011 a UV Raman-Lidar station become operational in the central Amazon region. The instrument is installed 30 km up-wind from Manaus-AM and remotely senses the troposphere using a 95 mJ NdYag laser at 355 nm. Receiving optics consists of a cassegrain telescope with 400 mm and 4000 mm focal length. During the first year of operation, a narrow field of view was used to allow a reasonable signal to noise ratio near the tropopause. This study focuses on the characterization of tropical cirrus clouds observed during the first year of operation (February to December 2011). A cloud detection algorithm developed by Barja and Aroche (2001) was adapted for this system and used to determine the cloud base and top heights, and cloud thickness. The method based on the lidar transmittance factor was used to derive the cirrus optical depth. The occurrence of cirrus clouds is about 63% of the total observation time, and these are located between 10 and 16 km height typically. This result agrees with those derived by Sassen et al (2008) from Calipso data. We also found that around 26% of all cirrus were subvisual cirrus (τ<0.03), 43 % were thin cirrus (0.03<τ< 0.3) and 31% were cirrus stratus (τ.0.3).