Tropopause Folding and the Variability of the Tropopause Height as Seen by the Flatland VHF Radar

Abstract

The Flatland radar, a VHF wind profiler located near Urbana, Illinois, has been used to study the variability of the tropopause over the period March 1987?April 1988. The vertically directed radar beam provides an indicator of tropopause height as well as measurements of the vertical velocity of the air. The sudden tropopause height changes previously seen in special campaigns are found to be relatively common features. Several case studies made under varying synoptic conditions are used to show that thew discontinuities are associated with tropopause folding events as revealed by cross-section analyses of potential temperature and potential vorticity based on radiosonde data. The vertical velocity in a typical tropopause fold is downward at up to 15 cm s?1. Finally, applications of the continuous data from VHF radars to develop quantitative climatologies of tropopause folding events are presented.