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ANtarctic Gravity Wave Instrument Network (ANGWIN)

The 2022 workshop was hosted by the Korean Polar Research Institute (KOPRI), 5th-7th October. This meeting report contains a brief summary of each of the science talks given.

ANGWIN workshop web 

Wednesday 5th October

Our meeting was opened by SCAR president, Dr Yeadong Kim, and KOPRI president, Dr Sung-Ho Kang.

ANGWIN overview - Tracy Moffat-Griffin, British Antarctic Survey
Tracy, a member of the ANGWIN steering committee, presented a brief history of the network, where it fits within the Scientific Committee for Antarctic Research (SCAR) framework as a SCAR action group and the support they give to early career researchers. The development of an instrument database was also discussed. The ANGWIN action group page can be found here:

Interaction between planetary waves and gravity waves in the middle atmosphere (invited) - Hye-Yeong Chun, Yonsei University
The first of the science talks examined the role of gravity wave and planetary wave interactions, as observed in MERRA-2 data. The Transformed Eulerian Mean (TEM) equation was used in this study as in the TEM the zonal mean flow is influenced by planetary waves and gravity waves independently. They used a case study of the 2009 Sudden Stratospheric Warming (SSW) to examine the influence of gravity wave forcing on downward propagating planetary waves. They found that these planetary waves were likely generated by gravity wave drag and contributed to the zonal wavenumber 2 enhancement associated with the SSW.

Current status of the observations and research activities at KOPRI - Geonhwa Jee, KOPRI
This talk detailed the location of current KOPRI instrument sites in both the Arctic (Dasan station, KH Observatory and Kiruna) and Antarctic (Jang Bogo and King Sejong Station). In the Arctic they have auroral all sky imagers, FPI and GPS instrumentation. They also have access to the EISCAT radar which can measure ionospheric parameters down to mesospheric altitudes. In the Antarctic there is a wider range of ANGWIN relevant instruments, including: airglow imagers and temperature mappers, meteor wind radars, GPS, FPIs and an ionospheric radar.

Atmospheric Waves Experiment (AWE): a new NASA mission of opportunity for global gravity wave investigations - Mike Taylor, Utah State University.
AWE is a 2 year mission on the International Space Station running during 2024-2025. It will observe the airglow temperature at nighttime and there will be ~15 Orbits per day. A temperature map will be produced every second and will have a large 600km field of view. It will enable near-global measurements of gravity wave properties in the upper atmosphere and their impacts on the ionosphere-thermosphere-mesosphere (ITM) to be determined! It is the first NASA Heliophysics instrument on the ISS.

LODEWAVE (long-duration balloon experiment of gravity wave over Antarctica) – Yoshihiro Tomikawa (NIPR, SOKENDAI)
The focus next was on a ground-based campaign involving long-duration balloons in Antarctica called LODEWAVE. The super-pressure balloons were launched from Syowa station in January and February 2022 for 3 flights, recording T, p and GPS position and combined the data with the PANSY radar observations. They were able to identify waves within the data and have a campaign planned to launch again in 2024.

The first observation of metal ion layer by a resonance scattering lidar in the Antarctica - Mitsumu K. Ejiri (NIPR)
This talk showed the first observations of a Ca+ layer above Syowa. The layer was not present all the time and they investigated the possible reasons for this, comparing the data with geomagnetic activity, amount of meteors and also gravity waves. They concluded that a temperature decrease due to gravity waves was most likely responsible for shortening the lifetime of Ca+ and thus the disappearance of the layer.

Multi-instrument observation of a noctilucent cloud over Rio Grande, Argentina (53.8°S) - P.-Dominique Pautet (Utah State University)
A range of instrumentation (Advanced Mesospheric Temperature Mapper, lidar, meteor radar, NLC camera and airglow imager) observed a rare noctilucent cloud (NLC) event in January 2022. These events are rare but occur a few times every summer season. They showed that there was a ~35K temperature drop in one hour around the NLC observation and also surmised that a strong thermal tide transported ice particles from Antarctica northward causing the NLC event.

Airglow observations of the dynamics in the northern polar cap mesopause region - William Ward (University of New Brunswick)
An overview of the various instrumentation located at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka was given with a detailed focus on measurements from the mesosphere. They showed that there is a strong seasonal (and possibly solar cycle) trend in both winds and airglow emissions at this latitude and that there is also lots of short term variability in the airglow and wind data.

Gravity waves over Northern Scandinavia from AMTM data - Tracy Moffat-Griffin (BAS)
This talk gave an overview of a new project that is looking at how to improve predictive skill of the mesosphere in whole atmosphere models. One part of this project is looking at the long term variability of gravity waves in the mesosphere (and eventually comparing them to model output). Here preliminary results using the Matsuda Transform applied to AMTM data from Norway were presented.

Thursday 6th October

Ray tracing of gravity waves observed in the Arctic MLT - Dustin Fraser (University of New Brunswick)
This session was started off with a talk about mesospheric gravity waves above Eureka. Instruments used to observe the waves are the All-Sky Imager (ASI) and E-Region Wind Interferometer (ERWIN). Combining their observations with a model amtopshere they were able to use the GROGRAT gravity wave ray tracing to try to identify the likely sources of the waves. They showed that small-scale waves are likely to have originated in the near surface and large-scale, inertia GWs originate at the midlatitudes.

A modeling study on effects of secondary waves – In-Sun Song (Yonsei University)
This talk presented result examining the mesopause model bias and the role of gravity wave forcing. They investigated the effect of reducing primary gravity wave forcing in a model and including secondary waves generated from orographic waves. This updated gravity wave parametrisation scheme resulted in some improvement in the model bias but there is still lots of uncertainty and tuning to be done.

Connecting Antarctic gravity-wave observations to the WACCM model parameterization - Damian J. Murphy (AAD)
Next up was a talk that examined how well current parameterisations of gravity waves do in models compared to observations. The author presented work showing how a quasi-monochromatic gravity wave scheme was implemented in WACCM. This type of scheme was investigated due to the importance of large wave in transporting momentum. It can be tied to sources, so capturing intermittency better and can be compared with observations easier due to the way gravity wave variables are stored in the model.

Seasonal variation of Quasi-10-day wave activity during 2012-2016 in the Southern high-latitude MLT region based on meteor radar observations and SD-WACCM simulations - Wonseok Lee (Yonsei University)
This talk used meteor radar data from Davis and King Sejong stations (both ~60S and separated by 140 longitude) and wavelet analysis to examine the Quasi 10-day wave (Q10DW) and its variability. They show that its amplitude peaks around winter and the equinoxes. A comparison with SD-WACCM was also done and it was found that the Q10DW is unrealistic at high southern polar latitudes. It is thought that the reason for this is that the gravity wave parameterisation needs to be improved.

Medium-scale gravity waves observed over Antarctic peninsula in 2022 - Gabriel A. Giongo (NISR)
All-sky airglow observations from Comte Ferraz Station, at the tip of the Antarctic Peninsula, were used to study medium scale gravity waves in the mesosphere. These observations identified 28 individual medium scale waves with periods from 20mins – 1 hour. Raytracing of these events showed that ~30% were likely to be orographic in origin, with a similar amount likely to have been generated by the stratospheric polar vortex. Investigations as to the sources of the other waves is still ongoing.

Gravity waves climatology over McMurdo Station - Kenneth Zia (talk given by P.-Dominique Pautet) (USU) 
An Advanced Mesospheric Temperature Mapper has been operational at McMurdo since 2017, in this dataset they managed to find 96 hours of continuous, cloud-free data! These were analysed using the M-Transform and showed that although gravity waves are present continually, they also have quite a lot of short-term variability. They also performed a long-term climatology study and showed that the wave directionality observed was due to the strong influence of the stratospheric jet.

Investigation of acoustic gravity wave signatures in hydroxyl airglow images - P.-Dominique Pautet (USU)
This talks showed the work done to study acoustic gravity waves (very short period – 2-4minutes) in airglow data. Although quite weak, should be visible in mesosphere/D-region of ionosphere. As part of the AIRWaveS project they combined airglow and Low Frequency ionospheric observations. Initial comparisons suggest that they are seeing the same variability and oscillations in both datasets and identified several short-period waves.

Atmospheric Gravity Wave Detection Using Transfer Learning Techniques (Invited) - J. Yue (NASA, GSFC)
This talk presented work being done on using machine learning to detect gravity waves in airglow data from the VIIRS airglow data. They had challenges in terms of a very small labelled dataset for training purposes and also noisy data. By using ideas from other projects with small datasets (transfer learning) and using a pre-trained model they were able to get a 94% validation rate for the model.

Airglow imagery cleaning with machine learning classification - Kenneth Zia (talk given by P.-Dominique Pautet) (USU)
This talk also presented work being done on using machine learning techniques to remove the poor quality all-sky airglow imager data. They used a Light Gradient Boosted Machine Learning approach and trained it using the Themis aurora dataset. It worked well so was then applied to airglow data from Davis where it had a success rate of 98% in identifying bad data. Further work is ongoing to refine the method.

Phase velocity spectral analysis of gravity waves: application of M-transform to various airglow imaging data - Takuji Nakamura (NIPR)
This talk presented the wide range of data sets that the M-Transform has been applied to in order to study gravity wave horizontal phase velocity spectra. Studies have been done using all-sky airglow data around Antarctica and also to examine latitudinal variations in the gravity wave field. It has also been applied to other airglow emissions than OH, there have been studies using 630nm emissions in the thermosphere and show the wave spectra there. Additionally it has been applied to TEC data and SuperDARN, identifying Travelling Ionospheric Disturbances. It shows how versatile this technique is. The software is also freely available.

Inertia-gravity waves revealed in radiosonde data at Jang Bogo Station, Antarctica: characteristics and potential sources - J.-H. Yoo (Yonsei University)
Moving lower in the atmosphere this talk presented observations of lower stratospheric gravity waves above Jang Bogo station. Several years of data was used to show that the prevalent direction of inertia gravity waves was eastward but that there was strong seasonal variation in gravity wave characteristics and propagation direction. Some ray tracing of the waves was also performed and they showed that the waves generated by different sources (e.g. orography, convection etc) had different characteristics.

A statistical study of inertia gravity waves over Syowa Station: comparison between the pansy radar and the ERA5 reanalysis - L. Yoshida (SOKENDAI)
This presentation showed work that was being done to see how well reanalysis data captured inertia gravity wave events observed in the troposphere and lower stratosphere. Comparisons between pansy observations and ERA5 data showed that ERA5 underestimated both the momentum flux and vertical wavelength. However it was able to capture the correct propagation direction.

Study of gravity wave activities in a wide height range of 60-110 km over Syowa Station, Antarctic - M. Tsutsumi (NIPR)
Here an advanced meteor echo measurement technique is explained, where they combine two techniques to extend the MF radar’s observational altitude range. Work is ongoing and the current observations show a mean wind above 100km altitude that the wave driven scenario may not explain. They also showed analysis about the gravity wave activity as measured from the radar. Below 100km it displayed the expected annual and semi-annual pattern but above 100km there was little variability.

Activities of small-scale gravity waves in the upper mesosphere observed from meteor radar at King Sejong Station, Antarctica (62.22°S, 58.78°W) and their potential sources – B.-G. Song (Yonsei University)
This presentation showed results of an analysis of 10 year gravity wave variances above King Sejong Station and their work identifying the sources. They showed that the winds displayed the expected annual and semi-annual variations and used a range of diagnostic methods to identify the likely sources of these waves (storms, polar night jet and orography). Further investigations into secondary gravity waves in the mesosphere was also done using a co-located airglow imager and ray tracing. They found that secondary gravity waves mainly occur in winter and are likely to be linked to breaking orographic waves.

Mesospheric short-period gravity waves in the Antarctic peninsula observed in all-sky airglow images and their possible source locations - Hosik Kam (KASI)
Here a more detailed analysis of airglow imager data from King Sejong Station was presented using the M-Transform. They showed that there was a clear seasonal variation in direction of propagation and magnitude of waves and that there was also increased intensity in the winter months. They showed, through wind blocking diagrams, the likelihood of some waves been generated at higher altitudes and also identified the likely secondary gravity waves.

Gravity wave horizontal phase velocity spectra in the mesosphere over the Antarctic stations, Syowa and Davis - M. Kogure (Kyushu University)
Here a comparison of a year of all-sky airglow data using the M-Transform was presented. They showed that the two sites, although separated by 40 degrees longitude, showed similar phase velocity spectra distributions. This was attributed to the polar night jet. Although the distributions were similar, Davis data showed less power. This is thought to be different critical level filtering conditions at Davis.

Comparison of gravity wave activities between two mesospheric layers using satellite and ground-based airglow data - Yucheng Zhao (USU)
This presentation showed work that had been done studying gravity wave energy using both the CIPS satellite (observations at ~50-55km altitude) and airglow imager data from Davis station (~87 km altitude) in 2020. A combination of machine learning and M-Transform were used to analyse the data sets. They showed that there was lots of variability seen at both altitudes and a wider range of wave propagating directions were observed at Davis compared to other studies at McMurdo. They plan to extend their analysis to other years to allow intra-seasonal variability to be determined and extend to other ANGWIN sites.