Millimeter wave spectroscopic measurements over the South Pole: 1. A study of stratospheric dynamics using N2O observations

Millimeter wave measurements of N2O and O3 [Cheng et al., 1995], along with several other trace gases, have been made nearly continuously from February 1993 through early January 1994 at the Amundsen-Scott Station, South Pole. In order to separate chemical and dynamical effects, this paper uses the observations of the long-lived tracer N2O to study stratospheric dynamics. The main emphasis is on the synoptic evolution of the polar vortex over an entire winter period, and quantitative results are given for various times and altitudes. Diabatic descent rates derived for different altitude levels showed the strongest descent in austral fall at high altitudes, agreeing fairly well with model predictions by Rosenfield et al. (1994). Subsidence was observed to continue until late October, well after polar sunrise. The breakdown of the vortex occurred first in the upper stratosphere, marked in the intrusion of N2O rich air at these altitudes, consistent with trajectory calculations. Our calculated descent rates are not consistent with the idea that the polar vortex is a “flowing processor”, but instead should be viewed as an isolated system.