Evidence for inertia gravity waves forming polar stratospheric clouds over Scandinavia

Abstract

At three successive days at the end of January 2000 the Deutsches Zentrum für Luft‐ und Raumfahrt (DLR) airborne lidar Ozone Lidar Experiment explored mountain‐wave‐induced polar stratospheric clouds above the Scandinavian mountain ridge. Global analyses and mesoscale modeling are applied to explain their complex internal structure and their day‐to‐day variability. Depending on the synoptical‐scale meteorological conditions, stratospheric temperature anomalies of different amplitude and horizontal extent are generated by the upward propagating mountain waves. Short‐term excitation of about 6 hours resulted in localized stratospheric temperature anomalies directly above the mountain ridge as for 25 January 2000. In this case, the elevation of the observed clouds differed not much from the synoptic‐scale clouds upstream above the Norwegian Sea. On the other hand, long‐lasting flow past the Scandinavian mountain ridge formed huge 400‐km horizontally extending stratospheric ice clouds in altitudes as much as 5 km above the elevation of the upstream clouds just 1 day later. Inertia gravity waves with horizontal wavelengths of about 350 km are responsible for their formation. For the first time a predicted temperature minimum far downstream of the mountains could be proofed by the observation of an isolated stratospheric ice cloud above Finland. The observed particles are classified in terms of their measured optical properties such as backscatter ratio and depolarization. In all cases, mountain waves generated ice clouds. In contrast to the nitric acid trihydrate tail of the ice cloud on 25 January the same classification results in a tail of liquid supercooled ternary solutions droplets 1 day later. The particle structure downstream of the mountains is very complex and needs detailed microphyical modeling and interpretation.

A decadal satellite record of gravity wave activity in the lower stratosphere to study polar stratospheric cloud formation

“…Here, we are interested in gravity waves because they can provide significant local temperature fluctuations that can trigger the formation of PSCs, even if synoptic-scale temperatures are above formation thresholds. Case studies of mountain waves induced by the Scandinavian Mountains showed that the waves can cause localized cooling of up to 10-15 K (Carslaw et al, 1998b;Dörnbrack et al, 1999Dörnbrack et al, , 2002. The Antarctic Peninsula is another well-known hot spot for the formation of PSCs from mountain waves in the Southern Hemisphere (Wu and Jiang, 2002;Shibata et al, 2003;Höpfner et al, 2006b;Baumgaertner and McDonald, 2007;Eckermann et al, 2009;Orr et al, 2015).…”

Evidence of gravity waves into the atmosphere during the March 2006 total solar eclipse

“…The initiated by GWs convection, can result to formation of clouds (e.g. orographic cirrus, polar stratospheric and mesospheric; Dörnbrack et al, 2002), modify chemistry, and trigger numerous processes (e.g. Voigt et al, 2000).…”

Mesoscale temperature fluctuations in the stratosphere

“…Several studies of the implications of mesoscale temperature fluctuations and the microphysics of polar stratospheric cloud formation and evolution have been published (Wofsy et al, 1993;Murphy and Gary, 1995;Tabazedeh et al, 1996;Carslaw et al, 1998;Voigt et al, 2000;Gao et al, 2001;Doernbrack et al, 2002;Fueglistaler et al, 2003;Murphy, 2003;Karcher and Strom, 2003;Hoyle et al, 2005). Murphy and Gary (1995) use microphysical arguments involving time constants for various effects to conclude that rapid temperature fluctuations should affect the nucleation of polar stratospheric cloud droplets, and the large cooling rates experienced by air parcels have important implications for denitrification and dehydration.…”