MILLIMETER-WAVE SPECTROSCOPIC MEASUREMENTS OVER THE SOUTH-POLE .1. A STUDY OF STRATOSPHERIC DYNAMICS USING N2O OBSERVATIONS

Millimeter wave measurements of N2O and O-3 [Cheng ef al., 1995], alon g with several other trace gases, have been made nearly continuously f rom February 1993 through early January 1994 at the Amundsen-Scott Sta tion, South Pole. In order to separate chemical and dynamical effects, this paper uses the observations of the long-lived tracer N2O to stud y stratospheric dynamics. The main emphasis is on the synoptic evoluti on of the polar vortex over an entire winter period, and quantitative results are given for various times and altitudes. Diabatic descent ra tes derived for different altitude levels showed the strongest descent in austral fall at high altitudes, agreeing fairly well with model pr edictions by Rosenfield et al. (1994). Subsidence was observed to cont inue until late October, well after polar sunrise. The breakdown of th e vortex occurred first in the upper stratosphere, marked in the intru sion of N2O rich air at these altitudes, consistent with trajectory ca lculations. Our calculated descent rates are not consistent with the i dea that the polar vortex is a ''flowing processor'', but instead shou ld be viewed as an isolated system.