Preprints
https://doi.org/10.5194/acp-2021-981
https://doi.org/10.5194/acp-2021-981

  09 Dec 2021

09 Dec 2021

Review status: this preprint is currently under review for the journal ACP.

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

Neil P. Hindley1, Neil Cobbett2, David C. Fritts3, Diego Janchez4, Nicholas J. Mitchell1,2, Tracy Moffat-Griffin2, Anne K. Smith5, and Corwin J. Wright1 Neil P. Hindley et al.
  • 1Centre for Space, Atmospheric and Oceanic Science, University of Bath, Bath, UK
  • 2British Antarctic Survey, Cambridge, UK
  • 3GATS, Boulder, CO, USA
  • 4NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 5National Center for Atmospheric Research, Boulder, CO, USA

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 ionosphere and space weather. 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 on the remote mountainous island of South Georgia (54° S, 36° W) in the Southern Ocean from 2016 to 2020. The goal of this study is to 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 explore the amplitudes and phases of the diurnal (24 h), semidiurnal (12 h) and terdiurnal (8 h) solar tides at this latitude. We also explore PW activity and find very large amplitudes up to 30 ms−1 for the quasi-2 day wave in summer and show that the dominant modes of the quasi-5, 10 and 16 day waves are westward W1 and W2. We investigate wind variance due to GWs in the MLT and use a new method to show an east-west tendency of GW variance of up to 20 % during summer and a weaker north-south tendency of 0–5 % during winter. This is contrary to the expected tendency of GW directions in the winter stratosphere below, which is a strong suggestion of secondary GW (2GW) observations in the MLT. Lastly, comparison of radar winds to a climatological Whole Atmosphere Community Climate Model (WACCM) simulation reveals a simulated summertime mesopause and zonal wind shear that occur at altitudes around 10 km lower than observed, and southward winds during winter above 90 km altitude in the model that are not seen in observations. Further, wintertime zonal winds above 85 km altitude are eastward in radar observations but in WACCM they are found to weaken and reverse to westward. Recent studies have linked this discrepancy to the impact of 2GWs on the residual circulation which are not included in WACCM. These measurements therefore provide vital constraints that can guide the development of GCMs as they extend upwards into this important region of the atmosphere.

Neil P. Hindley et al.

Status: open (until 20 Jan 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-981', Chris Meek, 03 Jan 2022 reply
  • RC2: 'Comment on acp-2021-981', Anonymous Referee #2, 04 Jan 2022 reply
  • RC3: 'Comment on acp-2021-981', Anonymous Referee #3, 06 Jan 2022 reply
  • RC4: 'Figures in RC3 for acp-2021-981', Anonymous Referee #3, 07 Jan 2022 reply

Neil P. Hindley et al.

Neil P. Hindley et al.

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Short summary
Here we present observations of winds in the mesosphere and lower thermosphere (MLT) from a recently installed meteor radar on the remote island of South Georgia (54° S, 36° W). We characterise mean winds, tides, planetary waves and gravity waves in the MLT at this location and compare our measured winds to a leading climate model. We find that the observed wintertime winds are unexpectedly reversed from model predictions, likely due to missing impacts of secondary gravity waves in the model.
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