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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.

Submitted as: research article 15 May 2019

Submitted as: research article | 15 May 2019

Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.

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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Interactive discussion
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Neil P. Hindley et al.
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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