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Discussion papers
https://doi.org/10.5194/acp-2019-371
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-371
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 15 May 2019

Research article | 15 May 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Gravity waves in the winter stratosphere over the Southern Ocean: high-resolution satellite observations and 3-D spectral analysis

Neil P. Hindley1, Corwin J. Wright1, Nathan D. Smith2, Lars Hoffmann3, Laura A. Holt4, M. Joan Alexander4, Tracy Moffat-Griffin5, and Nicholas J. Mitchell1 Neil P. Hindley et al.
  • 1Centre for Space, Atmospheric and Oceanic Science, University of Bath, Bath, UK
  • 2ndependent Researcher, Bath, UK
  • 3Jülich Supercomputing Centre, Forschungszentrum Jülich, Jülich, Germany
  • 4Northwest Research Associates, Boulder, Colorado, USA
  • 5Atmosphere, Ice and Climate Group, British Antarctic Survey, Cambridge, UK

Abstract. Atmospheric gravity waves play a key role in the transfer of energy and momentum between layers of the Earth's atmosphere. However, nearly all Global Circulation Models (GCMs) seriously under-represent the momentum fluxes of gravity waves at latitudes near 60° S. This can result in modelled winter stratospheres that are unrealistically cold – a significant bias known as the "cold-pole problem". There is thus a need for measurements of gravity-wave fluxes near 60S to test and constrain GCMs. Such measurements are notoriously difficult, because they require 3-D observations of wave properties if the fluxes are to be estimated without using significant limiting assumptions. Here we use 3-D satellite measurements of stratospheric gravity waves from NASA's AIRS/Aqua instrument. We present the first extended application of a 3-D Stockwell transform (3DST) method to determine localised gravity-wave amplitudes, wavelengths and directions of propagation around the entire region of the Southern Ocean near 60° S during austral winter 2010. We first validate our method using a synthetic wave field and two case studies of real gravity waves over the Southern Andes and the island of South Georgia. A new technique to overcome wave amplitude attenuation problems in previous methods is also presented. We then characterise large-scale gravity-wave occurrence frequencies, directional momentum fluxes and short-timescale intermittency over the entire Southern Ocean. Our results show that highest wave-occurrence frequencies, amplitudes and momentum fluxes are observed in the stratosphere over the mountains of the Southern Andes and Antarctic Peninsula. However, we find that around 60–80 % of total zonal-mean momentum flux is located over the open Southern Ocean during June–August, where a large "belt" of increased wave-occurrence frequencies, amplitudes and fluxes is observed. Our results also suggest significant short-timescale variability of fluxes from both orographic and non-orographic sources in the region. A particularly striking result is a widespread convergence of gravity-wave momentum fluxes towards latitudes around 60° S from the north and south. We propose that this convergence, which is observed at nearly all longitudes during winter, accounts for a significant part of the under-represented flux in GCMs at these latitudes.

Neil P. Hindley et al.
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Short summary
In this study, a 3D Stockwell transform is applied to AIRS/Aqua satellite observations in the first extended 3D study of stratospheric gravity waves over the entire Southern Ocean during winter. Our observations reveal a dynamic environment that contains some of the most intense gravity-wave sources on Earth. A particularly striking result is a large-scale meridional convergence of gravity-wave momentum flux towards latitudes near 60° S, something which is not generally considered in models.
In this study, a 3D Stockwell transform is applied to AIRS/Aqua satellite observations in the...
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