Abstract
Abstract. Nearly all general circulation models significantly fail to reproduce the observed behaviour of the southern wintertime polar vortex. It has been suggested that these biases result from an underestimation of gravity wave drag on the atmosphere at latitudes near 60° S, especially around the "hot spot" of intense gravity wave fluxes above the mountainous Southern Andes and Antarctic peninsula. Here, we use Global Positioning System radio occultation (GPS-RO) data from the COSMIC satellite constellation to determine the properties of gravity waves in the hot spot and beyond. We show considerable southward propagation to latitudes near 60° S of waves apparently generated over the southern Andes. We propose that this propagation may account for much of the wave drag missing from the models. Furthermore, there is a long leeward region of increased gravity wave energy that sweeps eastwards from the mountains over the Southern Ocean. Despite its striking nature, the source of this region has historically proved difficult to determine. Our observations suggest that this region includes both waves generated locally and orographic waves advected downwind from the hot spot. We describe and use a new wavelet-based analysis technique for the quantitative identification of individual waves from COSMIC temperature profiles. This analysis reveals different geographical regimes of wave amplitude and short-timescale variability in the wave field over the Southern Ocean. Finally, we use the increased numbers of closely spaced pairs of profiles from the deployment phase of the COSMIC constellation in 2006 to make estimates of gravity wave horizontal wavelengths. We show that, given sufficient observations, GPS-RO can produce physically reasonable estimates of stratospheric gravity wave momentum flux in the hot spot that are consistent with measurements made by other techniques. We discuss our results in the context of previous satellite and modelling studies and explain how they advance our understanding of the nature and origins of waves in the southern stratosphere.
Highlights
Gravity waves are propagating mesoscale disturbances that transport energy and momentum in fluid environments
That the leeward region of increased Ep over 70◦ W–90◦ E in Fig. 4 is likely dominated by (1) primary orographic waves with λH > 350 km from the southern Andes or Antarctic Peninsula that have been advected downwind, (2) secondary waves with non-zero phase speeds generated in the breaking zones of primary orographic waves and (3) non-orographic wave activity associated with storm tracks over the oceanic sectors
Our results demonstrate that, given sufficient sampling density, COSMIC Global Positioning System radio occultation (GPS-RO) can provide physically reasonable estimates of stratospheric gravity wave momentum flux that are consistent with results from HIgh Resolution Dynamics Limb Sounder (HIRDLS), CRISTA and Vorcore
Summary
Gravity waves are propagating mesoscale disturbances that transport energy and momentum in fluid environments. The mountains of the southern Andes and Antarctic Peninsula are a hot spot of stratospheric gravity wave momentum flux Accompanying the momentum flux hot spot is a long leeward distribution of increased gravity wave energy stretching eastwards from the southern Andes, Drake Passage and Antarctic Peninsula far over the Southern Ocean. This feature has puzzled researchers since it was first seen in spaceborne observations. Our results are discussed in the context of other studies in Sect. 5, and in Sect. 6 the key results of the present study are summarised
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