Analysis of a jet stream induced gravity wave associated with an observed ice cloud over Greenland 1Institute for Atmospheric and Climate Science, ETH Zürich, Switzerland
2Swiss Federal Office of Meteorology and Climatology (MeteoSwiss), Zürich, Switzerland
3Laboratoire de météorologie dynamique, Palaiseau, France, Switzerland
4NASA, Langley Research Center, Hampton VA, USA
5NASA Ames Research Center, Moffett Field CA, USA
6Institut für Physik der Atmosphäre, Universität Mainz, Germany
Abstract. A polar stratospheric ice cloud (PSC type II) was observed by airborne
lidar above Greenland on 14 January 2000. It 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 ~4.5 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 diagnostics
near the tropopause level provide evidence that the wave
is emitted from an intense, rapidly evolving, anticyclonically
curved jet stream. The precise physical process responsible for the wave
emission could not be identified definitely, but geostrophic
adjustment and shear instability are likely candidates.
In order to evaluate the potential frequency of such non-orographic
polar stratospheric cloud events, the non-linear balance equation
diagnostic is performed for the winter 1999/2000. It
indicates that ice-PSCs are only occasionally generated by gravity waves
emanating from spontaneous adjustment.
Citation: Buss, S., Hertzog, A., Hostettler, C., Bui, T. B., Lüthi, D., and Wernli, H.: Analysis of a jet stream induced gravity wave associated with an observed ice cloud over Greenland, Atmos. Chem. Phys., 4, 1183-1200, doi:10.5194/acp-4-1183-2004, 2004.