Abstract
Geometrical and optical characteristics of cirrus clouds using Raman lidar PollyXT measurements at different locations are presented. The PollyXT has been participated in two long-term experimental campaigns, one close to New Delhi in India and one at Elandsfontein in South Africa, providing continuous measurements and covering a wide range of cloud types. First results of cirrus cloud properties at different latitudes, as well as their temporal distributions are presented in this study. An automatic cirrus clouds detection algorithm is applied based on the wavelet covariance transform. The measurements at New Delhi performed from March 2008 to February 2009, while at Elandsfontein measurements were performed from December 2009 to January 2011.
Highlights
Cirrus clouds that are classified as high clouds have been characterized as having a significant double role in the Earth’s climate system, by cooling or heating the Earth [1]
Elastic backscatter and Raman lidars have been used for the retrieval of the geometrical and the optical properties of cirrus clouds already mentioned in literature [2]
The processing of the measurements and the detection of cirrus clouds geometrical boundaries was made by an automatic algorithm. This algorithm is based on a wavelet covariance transform (WCT) that is used to detect discontinuities in lidar signal as the base and the top of the cloud, with respect to the signal to noise ratio
Summary
Cirrus clouds that are classified as high clouds have been characterized as having a significant double role in the Earth’s climate system, by cooling or heating the Earth [1]. Systematic monitoring and detailed characterization of their geometrical and optical properties at different geographical locations is important in global climate analysis. Active remote sensing as lidar instruments are a useful tool for providing measurements of vertical distribution of the optical properties of cirrus clouds. Elastic backscatter and Raman lidars have been used for the retrieval of the geometrical and the optical properties of cirrus clouds already mentioned in literature [2]. From the reflected and transmitted polarized components of the backscattered light the profile of the depolarization ratio can be obtained as well, providing significant information about the sphericity of the retrieved particles and their liquid or solid phase. Measurements can be restricted to those days with the presence of low clouds and rain
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