Lidar observation of spherical particles in a – 65°cold cirrus observed above Sodankyla (Finland) during S.E.S.A.M.E.

Year: 1998

Authors: Del Guasta M., Morandi M., Stefanutti L., Balestri S., Kyro E., Rummukainen M., Kivi R., Rizi V., Stein B., Wedekind C., Mielke B., Matthey R., Mitev V., Douard M.

Autors Affiliation: Ist. Ric. Onde Elettromagnetiche C., Florence, Italy; Universita\’ l\’Aquila, L\’Aquila, Italy; Freie Universitat Berlin, Berlin, Germany; Observatoire Cantonal Neuchatel, Neuchatel, Switzerland; Universite\’ Lyon I, Villeurbanne, France

Abstract: The absence of LIDAR depolarization in a polar cirrus observed above Sodankyla (Finland) showed the presence of spherical particles at -65°C. The presence of pure liquid water is excluded, since homogeneous freezing should occur at or above -40°C. The cirrus layer was detected at the tropopause, during the horizontal and vertical advection above northern Scandinavia of warm and wet oceanic air. Two alternative explanations are suggested, the first one involving the presence of large, deliquescent tropospheric CN, freezing at very low temperature, and the second one involving the presence of metastable, spherical ice-particles produced in the fast adiabatic cooling of the airmasses. The second hypothesis is less reasonable because the absence of depolarized LIDAR signal implies a strict cylindrical symmetry in the particles, a symmetry that is difficult to maintain during the freezing process.

Journal/Review: JOURNAL OF AEROSOL SCIENCE

Volume: 29 (3)      Pages from: 357  to: 374

More Information: This work was supported by the European Commission, under contract EV5V CT930355 (M.O.A.N.A. project), and by the Programma Nazionale di Ricerche in Antartide (P.N.R.A.). We are very grateful to the Finnish Meteorological Institute (F.M.I.) for having hosted the LIDAR experiment in Sodankyla, and to the entire, friendly team of the Sodankyla station. We are also grateful to the European Center for Midrange Weather Forecasting (ECMWF) for the meteorological data, and to the Norvegian Meteorological Institute (KNMI) that supplied the model for the trajectory calculations.
KeyWords: Clouds; Freezing; Optical radar; Particles (particulate matter); Troposphere, Spherical particles, Atmospheric aerosols, ice, air monitoring; air temperature; airborne particle; article; cloud; cooling; depolarization; finland; freezing; hypothesis; priority journal; troposphere
DOI: 10.1016/S0021-8502(97)10008-8

Citations: 10
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