Optical classification, existence temperatures, and coexistence of different polar stratospheric cloud types

Year: 1999

Authors: Stein B., Wedekind C., Wille H., Immler F., Müller M., Wöste L., Del Guasta M., Morandi M., Stefanutti L., Antonelli A., Agostini P., Rizi V., Readelli G., Mitev V., Matthey R., Kivi R., Kyrö E.

Autors Affiliation: Institut für Experimentalphysik, Freie Universität Berlin, 14195 Berlin, Germany; Ist. Ric. Onde Elettromagnetiche/CNR, Firenze, Italy; Ente Nuove Tecnologie, l\’E., Camugnano, Italy; Dipartimento di Fisica, Universita degli Studi di L\’Aquila, L\’Aquila, Italy; Observatoire Cantonal Neuchatel, Neuchatel, Switzerland; Finnish Meteorological Institut, Sodankylä Observatory, Ilmala, Sodankylä, Finland; ENEA C.R. Brasimone, P.O. Box 1, I-40032 Camugnano, Italy; IROE/CNR, Via Panciatichi 64, I-50127 Firenze, Italy; Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany; Finnish Meteorological Institut, Sodankylä Observatory, Ilmala, FIN- 99600, Sodankylä, Finland; Observatoire Cantonal Neuchatel, Rue de l\’Observatoire 68, CH-2000 Neuchatel, Switzerland; Dipartimento di Fisica, Universita degli Studi di L\’Aquila, Piazza Vincenzo Rivera 1, I-67100 L\’Aquila, Italy

Abstract: Multispectral lidar measurements of polar stratospheric clouds (PSCs) from two winter campaigns in 1994/1995 and 1996/1997 at Sodankylä, Finland, have been evaluated together with temperature data from local radiosondes to find optical parameters for a PSC classification of different particle types and their existence temperatures. Precise depolarization measurements show that both solid and liquid particles exist below the NAT (nitric acid trihydrate) temperature. A comparison of temperatures at the PSC base and at the cloud top shows a good agreement with the NAT-existence temperature for solid type Ia clouds and a 3-4 K lower temperature for liquid type Ib clouds. The two particle families are therefore consistent with solid NAT particle formation and condensational growth of HNO3, H2O and H2SO4 liquid ternary solutions. The coexistence of solid and liquid particles has been observed by means of the temporal development of parallel and perpendicular polarized lidar signals. These time series of subsequent lidar measurements show stronger and faster fluctuations in the liquid particle mode compared to the solid particles and thus indicate a higher sensitivity toward temperature fluctuations for the liquid PSCs. While the optical properties of most observations are consistent with the definition of PSC type Ia (solid) and type Ib (liquid) clouds, a third type has been observed which does not fit into the current type Ia/Ib optical classification. This cloud type consists of solid particles but has a higher backscatter than type Ia PSC. Copyright 1999 by the American Geophysical Union.

Journal/Review: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES

Volume: 104 (D19)      Pages from: 23983  to: 23993

KeyWords: LIDAR observations; Artic Stratosphere; Size distributions; Winter; Depletion; Particles; Aerosols; Droplets; Growth; Easoe
DOI: 10.1029/1999JD900064

Citations: 44
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