Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 18, 505-509, 2000
© European Geosciences Union 2000
30 Apr 2000
Letter to the Editor: A strange cloud in the Arctic summer stratosphere 1998 above Esrange (68°N), Sweden
J. Siebert1, C. Timmis2, G. Vaughan2, and K. H. Fricke1 1Physikalisches Institut der Universität Bonn, Germany
2Physics Department, University of Wales, Aberystwyth, Wales
Abstract. When the University of Bonn lidar on the Esrange (68°N, 21°E), Sweden, was switched on in the evening of July 18, 1998, a geometrically and optically thin cloud layer was present near 14 km altitude or 400 K potential temperature, where it persisted for two hours. The tropopause altitude was 4 km below the cloud altitude. The cloud particles depolarized the lidar returns, thus must they have been aspherical and hence solid. Atmospheric temperatures near 230 K were approximately 40 K too high to support ice particles at stratospheric water vapour pressures of a few ppmv. The isentropic back trajectory on 400 K showed the air parcels to have stayed clear of active major rocket launch sites. The air parcels at 400 K had traveled from the Aleutians across Canada and the Atlantic Ocean arriving above central Europe and then turned northward to pass over above the lidar station. Parcels at levels at ±25 K from 400 K had come from the pole and joined the 400 K trajectory path above eastern Canada. Apparently the cloud existed in a filament of air with an origin different from those filaments both above and below. Possibly the 400 K level air parcels had carried soot particles from forest wild fires in northern Canada or volcanic ash from the eruption of the Korovin Volcano in the Aleutian Islands.

Key words: Atmospheric composition and structure (aerosols and particles; biosphere-atmosphere interactions) · Meteorology and atmospheric dynamics (middle atmospheric dynamics)

Citation: Siebert, J., Timmis, C., Vaughan, G., and Fricke, K. H.: Letter to the Editor: A strange cloud in the Arctic summer stratosphere 1998 above Esrange (68°N), Sweden, Ann. Geophys., 18, 505-509,, 2000.
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