Journal of Geophysical Research: Atmospheres

Fragmentation of stratospheric intrusions


  • C. Appenzeller,

  • H. C. Davies,

  • W. A. Norton


Evidence is presented pointing to the existence of rich and coherent subsynoptic and mesoscale flow features at tropopause levels. These features are related to, and evolve from, the classical V-shaped intrusions of stratospheric air down to tropospheric elevations. It is shown that intrusions can develop into elongated (∼2000–3000 km) and slender (∼200 km) streamers, and that thereafter such a streamer can roll up to form a train of stalactite-shaped vortex subentities with an accompanying substantial thinning of the intervening filament. In addition there are indications that the vortices themselves can develop a spirallike interior structure of interleaved stratospheric and tropospheric air. These inferences are based upon two independent but complementary sources: analysis of the potential vorticity distribution on tropopause transcending isentropic surfaces derived from the analysis fields of the European Centre for Medium-Range Weather Forecasts either directly, or indirectly using a contour advection technique; and imagery from the water vapor channel of the European Space Agency Meteosat 4 satellite. Streamers were observed to occur with a frequency of approximately one per week over central and southern Europe during the winter of 1991–1992. The fragmentation is linked to the instability or self-development of a filament of enhanced potential vorticity and it can modify or instigate surface weather systems. Moreover, by inducing a substantial and rapid enlargement of the intrusion's surface area it greatly enhances the potential for local irreversible mixing of stratospheric and tropospheric air.