Radar observations of winds, waves and tides in the mesosphere and lower thermosphere over South Georgia island (54°S, 36°W) and comparison with WACCM simulations

Neil P. Hindley, Nicholas J. Mitchell, Neil Cobbett, Anne K. Smith, Dave C. Fritts, Diego Janches, Corwin J. Wright, Tracy Moffat-Griffin

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9 Citations (SciVal)

Abstract

The mesosphere and lower thermosphere (MLT) is a dynamic layer of the earth's atmosphere. This region marks the interface at which neutral atmosphere dynamics begin to influence the upper atmosphere and ionosphere. However, our understanding of this region and our ability to accurately simulate it in global circulation models (GCMs) is limited by a lack of observations, especially in remote locations. To this end, a meteor radar was deployed from 2016 to 2020 on the remote mountainous island of South Georgia (54°S, 36°W) in the Southern Ocean. In this study we use these new measurements to characterise the fundamental dynamics of the MLT above South Georgia including large-scale winds, solar tides, planetary waves (PWs), and mesoscale gravity waves (GWs). We first present an improved method for time-height localisation of radar wind measurements and characterise the large-scale MLT winds. We then determine the amplitudes and phases of the diurnal (24°h), semidiurnal (12°h), terdiurnal (8°h), and quardiurnal (6°h) solar tides at this latitude. We find very large amplitudes up to 30°m°s-1 for the quasi 2°d PW in summer and, combining our measurements with the meteor SAAMER radar in Argentina, show that the dominant modes of the quasi 5, 10, and 16°d PWs are westward 1 and 2. We investigate and compare wind variance due to both large-scale "resolved"GWs and small-scale "sub-volume"GWs in the MLT and characterise their seasonal cycles. Last, we use our radar observations and satellite temperature observations from the Microwave Limb Sounder to test a climatological simulation of the Whole Atmosphere Community Climate Model (WACCM). We find that WACCM exhibits a summertime mesopause near 80°km altitude that is around 10°K warmer and 10°km lower in altitude than observed. Above 95°km altitude, summertime meridional winds in WACCM reverse to poleward, but this not observed in radar observations in this altitude range. More significantly, we find that wintertime zonal winds between 85 to 105°km altitude are eastward up to 40°m°s-1 in radar observations, but in WACCM they are westward up to 20°m°s-1. We propose that this large discrepancy may be linked to the impacts of secondary GWs (2GWs) on the residual circulation, which are not included in most global models, including WACCM. These radar measurements can therefore provide vital constraints that can guide the development of GCMs as they extend upwards into this important region of the atmosphere.

Original languageEnglish
Pages (from-to)9435-9459
Number of pages25
JournalAtmospheric Chemistry and Physics
Volume22
Issue number14
Early online date22 Jul 2022
DOIs
Publication statusPublished - 31 Dec 2022

Bibliographical note

Funding Information:
Author contributions. The South Georgia meteor radar at KEP was installed by NJM and NC in 2016. It was supported by the SG-WEX grant for which NJM and TMF were investigators, and later the DRAGON WEX grant for which NJM, TMF, and CJW were investigators. The WACCM data were provided by AKS, and the SAAMER meteor radar data are provided by DCF and DJ. The radar, satellite, and model data analysis, written manuscript and publication figures were produced by NPH, and all authors contributed to the final manuscript wording.

Funding Information:
Acknowledgements. We would like to thank the government of South Georgia and the South Sandwich Islands for their cooperation. In addition we would like to thank the relevant staff at GENESIS, King Edward Point, British Antarctic Survey, and University of Bath for all their help in ensuring the successful delivery of the instrument campaign. The SG-WEX project that deployed the radar was supported by the United Kingdom Natural Environment Research Council (NERC) under grants NE/K015117/1, NE/K012584/1, and NE/K012614/1. Its continuation was supported by the NERC DRAGON-WEX project under grants NE/R001391/1 and NE/R001235/1. The WACCM data used here derive from the CESM project, which is supported primarily by the United States National Science Foundation (NSF) and is based upon work supported by the National Center for Atmospheric Research (NCAR) sponsored by the NSF under Cooperative Agreement No. 1852977. Computing and data storage resources, including the Cheyenne supercomputer (https://doi.org/10.5065/D6RX99HX), were provided by the Computational and Information Systems Laboratory (CISL) at NCAR. Finally, we would like to thank the three anonymous reviewers for their helpful comments on the manuscript, and to also provide a special mention for Erich Becker for his friendly support and technical advice on the topics presented in this study.

Funding Information:
Financial support. This work was supported by the UK Natural Environment Research Council (NERC) under grants NE/K015117/1, NE/K012614/1, NE/R001391/1, NE/R001235/1 and NE/S00985X/1 and the Royal Society under grant number UF160545.

ASJC Scopus subject areas

  • Atmospheric Science

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