Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 3 6 2003 10.5194/acpd-3-5875-2003 http://www.atmos-chem-phys-discuss.net/3/5875/2003/ http://www.atmos-chem-phys-discuss.net/3/5875/2003/acpd-3-5875-2003.html http://www.atmos-chem-phys-discuss.net/3/5875/2003/acpd-3-5875-2003.pdf 5875 5918 2003-11-18 Analysis of a jet stream induced gravity wave associated with an observed ice cloud over Greenland S. Buss A. Hertzog C. Hostettler T. P. Bui T. Lüthi H. Wernli Institute for Atmospheric and Climate Science, Zürich, Switzerland Laboratoire de Météorologie Dynamique, Palaiseau, France NASA, Langley Research Center, Hampton VA, USA NASA Ames Research Center, Moffett Field CA, USA A polar stratospheric ice cloud (PSC type II) was observed by airborne lidar above Greenland on 14 January 2000. Is was the unique observation of an ice cloud over Greenland during the SOLVE/THESEO 2000 campaign. Mesoscale simulations with the hydrostatic HRM model are presented which, in contrast to global analyses, are capable to produce a vertically propagating gravity wave that induces the low temperatures at the level of the PSC afforded for the ice formation. The simulated minimum temperature is ~8 K below the driving analyses and ~3 K below the frost point, exactly coinciding with the location of the observed ice cloud. Despite the high elevations of the Greenland orography the simulated gravity wave is not a mountain wave. Analyses of the horizontal wind divergence, of the background wind profiles, of backward gravity wave ray-tracing trajectories, of HRM experiments with reduced Greenland topography and of several instability diagnostics near the tropopause level provide consistent evidence that the wave is emitted by the geostrophic adjustment of a jet instability associated with an intense, rapidly evolving, anticyclonically curved jet stream.<br> <br> In order to evaluate the potential frequency of such non-orographic polar stratospheric cloud events, an approximate jet instability diagnostic is performed for the winter 1999/2000. It indicates that ice-PSCs are only occasionally generated by gravity waves emanating from an unstable jet.