OSIRIS observations of a tongue of NOx in the lower stratosphere at the Antarctic vortex edge: comparison with a high-resolution simulation from the Global Environmental Multiscale (GEM) model

An optical spectrograph and infrared imager system (OSIRIS) aboard the Odin satellite measures limb-scattered sunlight in the 280 to 810 nm range. This paper addressed the challenge of interpreting nitrogen dioxide (NO2) profile observations in the polar lower stratosphere. Interpretations of these profile observations can be facilitated by first converting the measurements to NOx using a photochemical model in order to compare directly with simulated NOx from a 3-dimensional chemical transport model such as the Global Environmental Multiscale (GEM) model. In this study, GEM was used to simulate a tongue of NOx observed by OSIRIS as it circulated inside the Antarctic vortex edge. The objective was to clarify one of several OSIRIS observations of enhanced lower stratospheric NO2 in the Antarctic in early austral spring. Another objective was to demonstrate the variability in lower stratospheric NOx at polar latitudes due to dynamical processes. Selected NOx profiles of the Antarctic lower stratosphere inferred from OSIRIS NO2 observations were presented from the austral spring of 2003. A tongue of NOx at 100 hPa was observed, with a concentration typical of the middle stratosphere. GEM simulations revealed that this small-scale tongue of NOx-rich air descended into the lower stratosphere. The tongue was formed as a result of a Rossby wave breaking, transporting NOx from the pole, where larger concentrations had recently appeared, to the edge of the vortex. A detailed illustration of the 3-dimensional structure of the breaking wave was also presented. 17 refs., 1 tab., 10 figs