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When the University of Bonn lidar on theEsrange (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 altitudeor 400 K potential temperature, where it persisted for two hours. The tropopausealtitude was 4 km below the cloud altitude. The cloud particles depolarized thelidar returns, thus must they have been aspherical and hence solid. Atmospherictemperatures near 230 K were approximately 40 K too high to support iceparticles at stratospheric water vapour pressures of a few ppmv. The isentropicback trajectory on 400 K showed the air parcels to have stayed clear of activemajor rocket launch sites. The air parcels at 400 K had traveled from theAleutians across Canada and the Atlantic Ocean arriving above central Europe andthen 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 pathabove eastern Canada. Apparently the cloud existed in a filament of air with anorigin different from those filaments both above and below. Possibly the 400 Klevel air parcels had carried soot particles from forest wild fires in northernCanada or volcanic ash from the eruption of the Korovin Volcano in the AleutianIslands.  <b>Key words:</b> Atmospheric composition and structure(aerosols and particles; biosphere-atmosphere interactions) · Meteorology andatmospheric dynamics (middle atmospheric dynamics

&lt;i&gt;Letter to the Editor:&lt;/i&gt; A strange cloud in the Arctic summer stratosphere 1998 above Esrange (68°N), Sweden

<i>Letter to the Editor:</i> A strange cloud in the Arctic summer stratosphere 1998 above Esrange (68°N), Sweden