The South Georgia Wave Experiment (SG-WEX)
Lead Research Organisation:
University of Leeds
Department Name: School of Earth and Environment
Abstract
Gravity waves are an important type of atmospheric wave. They play a key role in many atmospheric processes, ranging from convection to the mixing of chemical species to influencing the global-scale circulation of the stratosphere and mesosphere. Because of this, it is essential to represent their effects in numerical weather prediction and climate models.
Gravity waves are generated by sources including winds blowing over mountains, jet-stream instabilities and strong convection. The waves can transport energy and momentum away from these sources and deposit them at greater heights, thus exerting a significant "drag" on the circulation and so coupling together different layers of the atmosphere.
Recent studies have shown that isolated mountainous islands in regions of strong winds can be intense sources of gravity waves that can have climatologically-significant effects on atmospheric circulation. However, most climate and numerical weather prediction models cannot accurately model waves from such small, intense island sources because the islands are too small compared to the resolution of the models - this is the "small island problem".
Here, we propose a major coordinated observational and modelling experiment to determine the nature and impacts of gravity waves generated by the most important of all these islands, South Georgia in the Southern Atlantic.
Our experiment will answer the following questions:
1. What is the nature of gravity waves generated by South Georgia and what is their variability?
2. What is the contribution of these gravity waves to the total field of gravity waves over the South Atlantic?
3. What is the influence of gravity waves from South Georgia on the mesosphere?
4. How can these observations be used to improve gravity-wave parametrizations in models?
5. How important is South Georgia in comparison to other gravity-wave sources and how does it impact local winds and the development of synoptic systems?
To answer these questions we will make measurements of gravity waves over and around South Georgia in two radiosondes campaigns in which meteorological balloons will be launched from South Georgia. We will place these observations in context with measurements made by satellite across the whole South Atlantic. Significantly, we will also deploy the first atmospheric radar on South Georgia. This is a meteor radar that will make the first ever measurements of gravity waves (and winds, tides and large-scale planetary waves) in the mesosphere over South Georgia at heights of 80 - 100 km.
These experimental results will be complemented by a programme of modelling work that will explore the propagation of gravity waves away from their sources. The observations will be used to help guide the development of new, improved, mathematical representations of gravity waves (so-called "parametrizations") allowing such islands to be better represented in the Met Office's Unified Model used for numerical weather prediction and climate studies. Finally, modelling studies will integrate these studies and determine the relative importance of South Georgia compared to other waves sources and investigate the impact of
Gravity waves from South Georgia on local winds and the development of synoptic (weather) systems.
Gravity waves are generated by sources including winds blowing over mountains, jet-stream instabilities and strong convection. The waves can transport energy and momentum away from these sources and deposit them at greater heights, thus exerting a significant "drag" on the circulation and so coupling together different layers of the atmosphere.
Recent studies have shown that isolated mountainous islands in regions of strong winds can be intense sources of gravity waves that can have climatologically-significant effects on atmospheric circulation. However, most climate and numerical weather prediction models cannot accurately model waves from such small, intense island sources because the islands are too small compared to the resolution of the models - this is the "small island problem".
Here, we propose a major coordinated observational and modelling experiment to determine the nature and impacts of gravity waves generated by the most important of all these islands, South Georgia in the Southern Atlantic.
Our experiment will answer the following questions:
1. What is the nature of gravity waves generated by South Georgia and what is their variability?
2. What is the contribution of these gravity waves to the total field of gravity waves over the South Atlantic?
3. What is the influence of gravity waves from South Georgia on the mesosphere?
4. How can these observations be used to improve gravity-wave parametrizations in models?
5. How important is South Georgia in comparison to other gravity-wave sources and how does it impact local winds and the development of synoptic systems?
To answer these questions we will make measurements of gravity waves over and around South Georgia in two radiosondes campaigns in which meteorological balloons will be launched from South Georgia. We will place these observations in context with measurements made by satellite across the whole South Atlantic. Significantly, we will also deploy the first atmospheric radar on South Georgia. This is a meteor radar that will make the first ever measurements of gravity waves (and winds, tides and large-scale planetary waves) in the mesosphere over South Georgia at heights of 80 - 100 km.
These experimental results will be complemented by a programme of modelling work that will explore the propagation of gravity waves away from their sources. The observations will be used to help guide the development of new, improved, mathematical representations of gravity waves (so-called "parametrizations") allowing such islands to be better represented in the Met Office's Unified Model used for numerical weather prediction and climate studies. Finally, modelling studies will integrate these studies and determine the relative importance of South Georgia compared to other waves sources and investigate the impact of
Gravity waves from South Georgia on local winds and the development of synoptic (weather) systems.
Planned Impact
There are three main groups of beneficiaries:
a) The academic community who work in tropospheric, stratospheric and mesospheric science. We will present our results and make a particular effort to bridge the gaps between experimental scientists studying different regions of the atmosphere and those modellers working in numerical weather prediction.
b) The general public, who will be informed of the nature of our project and kept up to date on its development by a dedicated web site and the Press Office and Public Engagement Unit of The University of Bath. The public will also ultimately benefit from the improvements in numerical weather prediction and climate modelling.
c) The Met Office, who will benefit by being able to use the knowledge generated by the project to assess and improve the representation of gravity waves in future Model development for numerical weather prediction and climate research.
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a) The academic community who work in tropospheric, stratospheric and mesospheric science. We will present our results and make a particular effort to bridge the gaps between experimental scientists studying different regions of the atmosphere and those modellers working in numerical weather prediction.
b) The general public, who will be informed of the nature of our project and kept up to date on its development by a dedicated web site and the Press Office and Public Engagement Unit of The University of Bath. The public will also ultimately benefit from the improvements in numerical weather prediction and climate modelling.
c) The Met Office, who will benefit by being able to use the knowledge generated by the project to assess and improve the representation of gravity waves in future Model development for numerical weather prediction and climate research.
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Organisations
Publications
Hindley N
(2021)
Stratospheric gravity waves over the mountainous island of South Georgia: testing a high-resolution dynamical model with 3-D satellite observations and radiosondes
in Atmospheric Chemistry and Physics
Hindley N
(2022)
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
in Atmospheric Chemistry and Physics
Jackson D
(2018)
The South Georgia Wave Experiment: A Means for Improved Analysis of Gravity Waves and Low-Level Wind Impacts Generated from Mountainous Islands
in Bulletin of the American Meteorological Society
Moffat-Griffin T
(2017)
The South Georgia Wave Experiment ( SG-WEX ): radiosonde observations of gravity waves in the lower stratosphere. Part I: Energy density, momentum flux and wave propagation direction
in Quarterly Journal of the Royal Meteorological Society
Vosper S
(2020)
Sampling Errors in Observed Gravity Wave Momentum Fluxes from Vertical and Tilted Profiles
in Atmosphere
| Description | Studied the wake formed downwind of South Georgia using numerical simulations and satellite measurements of surface winds over the ocean. This shows that high resolution models capture this fairly well, although it has also identified biases surface winds in the widely used ECMWF analysis over this region. Work on comparing satellite and radiosonde observations of gravity waves with high resolution numerical model simulations are promising. Comparison are generally good. Using this combined approach we have demonstrated that due to sampling issues using radiosondes alone to estimate momentum fluxes due to gravity waves is unreliable. This is important as often these are the only routine in-situ measurements available. The radiosondes are valuable in validating model simulations though, and these simulations can be used to measure momentum fluxes. Correctly observing these fluxes is necessary in order to calculate where gravity wave drag is being applied in the atmosphere and to validate gravity wave parametrisations. New 3D satellite retrievals of wave fluxes have been compared with the high resolution numerical simulations and are in good agreement when compared at the same resolution, but the results are sensitive to the resolution of the input model / satellite data sets. |
| Exploitation Route | Project still ongoing, but work is hoped to feed into further research project. It is also planned that the results will lead to changes in the way the Met Office weather and climate models parametrise gravity waves. This is important as errors in the way gravity waves are represented can lead to systematic errors climate simulations. |
| Sectors | Environment |
| Description | The results from the high resolution simulations conducted as part of this project have contributed to ongoing work at the Met Office to make the MetUM gravity wave drag parametrisation scheme scale aware. In the longer term this will help improve the representation of gravity wave breaking the MetUM leading to more accurate weather and climate forecasts. |
| First Year Of Impact | 2019 |
| Sector | Environment |
| Impact Types | Policy & public services |
| Description | Radio interview on Paul Hudson Weather Show |
| Form Of Engagement Activity | A broadcast e.g. TV/radio/film/podcast (other than news/press) |
| Part Of Official Scheme? | No |
| Geographic Reach | Regional |
| Primary Audience | Public/other audiences |
| Results and Impact | Interview on gravity waves in the atmosphere for the Paul Hudson weather show on BBC local radio in the Yorkshire / Lincolnshire area. Talked about gravity waves in general, and specifically about the SG-WEX project. |
| Year(s) Of Engagement Activity | 2015 |