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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 4 | Copyright
Ann. Geophys., 18, 505-509, 2000
https://doi.org/10.1007/s00585-000-0505-0
© European Geosciences Union 2000

  30 Apr 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 J. Siebert et al.
  • 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)

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