Formation of ice supersaturation by mesoscale gravity waves P. Spichtinger, K. Gierens, and A. Dörnbrack Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
Abstract. We investigate the formation and evolution of an ice-supersaturated region
(ISSR) that was detected by means of an operational radiosonde sounding
launched from the meteorological station of Lindenberg on 21 March 2000,
00:00 UTC. The supersaturated layer was situated below the local tropopause,
between 320 and 408 hPa altitude. Our investigation uses satellite imagery
from METEOSAT and the Advanced Very High Resolution Radiometer (AVHRR) and
analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF).
Mesoscale simulations reveal that the ISSR was formed by a temporary vertical
uplift of upper tropospheric air parcels by 20 to 40 hPa in 1 to 2 h. This
resulted in a significant local increase of the specific humidity by the
moisture transport from below. The ascent was triggered by the superposition
of two internal gravity waves, a mountain wave induced by flow past the
Erzgebirge and Riesengebirge south of Lindenberg, and an inertial gravity
wave excited by the anti-cyclonically curved jet stream over the Baltic
Sea. The wave-induced ISSR was rather thick with a depth of about 2 km. The
wave-induced upward motion causing the supersaturation also triggered the
formation of a cirrus cloud. METEOSAT imagery shows that the cirrus cloud
got optically thick within two hours. During this period another longer
lasting thin but extended cirrus existed just beneath the tropopause. The
wave-induced ISSR disappeared after about half a day in accordance with the
decaying wave activity.
Citation: Spichtinger, P., Gierens, K., and Dörnbrack, A.: Formation of ice supersaturation by mesoscale gravity waves, Atmos. Chem. Phys., 5, 1243-1255, doi:10.5194/acp-5-1243-2005, 2005.