Gravity wave and orographic wave activity observed around the Antarctic and Arctic stratospheric vortices by the COSMIC GPS‐RO satellite constellation

Abstract

Polar stratospheric gravity wave activity is studied using data from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Global Positioning System Radio Occultation (GPS‐RO). Waves with vertical wavelengths of ∼2 to 15 km are considered. The temperature variance σ2 is used as a measure of wave activity and is studied on isentropic surfaces. Large intermittent orographic wave activity is identified during austral spring 2007 above the Patagonian Andes and the Antarctic Peninsula, where σ2 in the stratosphere increases by up to a factor of 5 for periods of 5 days to a few weeks. The σ2 are also investigated in equivalent latitudes to allow a direct comparison with the changing vortex structure. The October 2007 σ2 inside the Antarctic vortex boundary region at 400–600 K is one and a half times that outside the vortex. This region of enhanced σ2 descends in time and is not observed during the decay of the Arctic vortex. During the boreal winter of 2006/2007, orographic wave activity is observed above Scandinavia and Greenland. An analysis of the 400 K and the 450 K levels in both hemispheres shows a strong relationship between enhanced σ2 and the location of the vortex edge, suggesting that the waves observed are propagating poleward and are guided to higher altitudes by the vortex. The line of sight of the occultations shows a preference for north‐south alignment, indicating that COSMIC favors the detection of orographic waves above the north‐south oriented mountain ranges considered here.