Research Aircraft Measurements of Jet Stream Geostrophic and Ageostrophic Winds

Abstract

Radar altimeter and inertial navigation wind velocity measurements from research aircraft are shown to give the ageostrophic wind velocity distribution within a jet stream system near the tropopause. Results from one case study reveal cross-height-contour ageostrophic winds exceeding 20 m s?1, and centripetal-acceleration-induced ageostrophic winds approaching 100 m s?1 in the exit region of a jet streak which has entered into the trough region of a synoptic wave. Diagnostic calculations are made of the horizontal velocity divergence and the geostrophic and ageostrophic components of the observed wind velocity acceleration. The results suggest caution in the application of near-straight jet-streak dynamics and the geostrophic momentum approximation to jet-streak systems embedded within large-amplitude synoptic wave regimes.