Analysis of a jet stream induced gravity wave associated with an observed ice cloud over Greenland

Abstract

A polar stratospheric ice cloud (PSC type II) was observed by airborne lidar above Greenland on 14 Jan-uary 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 orog-raphy 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 .

Variability in the altitude of fast upper tropospheric winds over the Northern Hemisphere during winter

“…Jet stream variability also influences stratosphere-troposphere exchange [Hoerling et al, 1993;Langford, 1999;Wimmers et al, 2003], the intensity and track of synoptic-scale storms [Nakamura, 1992;Christoph et al, 1997], the development of severe convective storms [Uccellini and Johnson, 1979;Kloth and Davies-Jones, 1980], the occurrence of heavy rain [Smith and Younkin, 1972] and snow [Uccellini and Kocin, 1987], and the development of tornados [Fawbush et al, 1951;Skaggs, 1967]. Jet streams also produce gravity waves associated with clear air turbulence [Knox, 1997] and polar stratospheric clouds [Hitchman et al, 2003;Buss et al, 2004].…”

Meteorological effects of ionospheric disturbances from vertical radio sounding data

“…Jet streams (JS) can be sources of GWs as well (Bertin et al, 1975;Bertin et al, 1978;Thomas et al, 1999;Fritts and Alexander, 2003;Plougonven et al, 2003;Buss et al, 2004;Zulicke and Peters, 2007;Plougonven and Snyder, 2005;Manney et al, 2011). A jet stream is defined as a flat tubular current of air, quasi-horizontal, whose axis is directed along a line of maximum speed, and that is characterized not only by high speeds, but also by strong transverse (horizontal and vertical) speed gradients (World Meteorological Organization, http://www.wmo.int/pages/themes/climate/understanding_climate.php).…”

Polar stratospheric ice cloud above Spitsbergen

“…Since strong and nearly unidirectional winds throughout the troposphere and stratosphere favor the upward wave propagation, mountain wave-induced stratospheric temperature fluctuations leading to PSC formation are enhanced at the inner edge of the polar vortex [Dörnbrack and Leutbecher, 2001]. Alternatively, PSCs can be induced by jet stream instabilities in breaking Rossby waves and by shear instabilities in the tropopause region [Teitelbaum et al, 2001;Hitchman et al, 2003;Buss et al, 2004].…”