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Titel MST radar and polarization lidar observations of tropical cirrus
VerfasserIn Y. Bhavani Kumar, V. S. Siva Kumar, A. R. Jain, P. B. Rao
Medientyp Artikel
Sprache Englisch
ISSN 0992-7689
Digitales Dokument URL
Erschienen In: Annales Geophysicae ; 19, no. 8 ; Nr. 19, no. 8, S.873-882
Datensatznummer 250014298
Publikation (Nr.) Volltext-Dokument vorhandencopernicus.org/angeo-19-873-2001.pdf
 
Zusammenfassung
Significant gaps in our understanding of global cirrus effects on the climate system involve the role of frequently occurring tropical cirrus. Much of the cirrus in the atmosphere is largely due to frequent cumulus and convective activity in the tropics. In the Indian sub-tropical region, the deep convective activity is very prominent from April to December, which is a favorable period for the formation of deep cumulus clouds. The fibrous anvils of these clouds, laden with ice crystals, are one of the source mechanisms for much of the cirrus in the atmosphere. In the present study, several passages of tropical cirrus were investigated by simultaneously operating MST radar and a co-located polarization lidar at the National MST Radar Facility (NMRF), Gadanki (13.45° N, 79.18° E), India to understand its structure, the background wind field and the microphysics at the cloud boundaries. The lidar system used is capable of measuring the degree of depolarization in the laser backscatter. It has identified several different cirrus structures with a peak linear depolarization ratio (LDR) in the range of 0.1 to 0.32. Simultaneous observations of tropical cirrus by the VHF Doppler radar indicated a clear enhancement of reflectivity detected in the vicinity of the cloud boundaries, as revealed by the lidar and are strongly dependent on observed cloud LDR. An inter-comparison of radar reflectivity observed for vertical and oblique beams reveals that the radar-enhanced reflectivity at the cloud boundaries is also accompanied by significant aspect sensitivity. These observations indicate the presence of anisotropic turbulence at the cloud boundaries. Radar velocity measurements show that boundaries of cirrus are associated with enhanced horizontal winds, significant vertical shear in the horizontal winds and reduced vertical velocity. Therefore, these measurements indicate that a circulation at the cloud boundaries suggest an entrainment taking place close to these levels. The analysis of simultaneous lidar and MST Radar observations can thus yield valuable information on the structure and dynamics of the cirrus, specifically near the boundaries of such clouds.

Key words. Atmospheric composition and structure (cloud physics and chemistry; instruments and technique) - Meteorology and atmospheric dynamics (tropical meteorology)
 
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