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Observation of Mountain Waves and Secondary Gravity Waves in the Mesosphere Lower Thermosphere Above Patagonia.

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Title: Observation of Mountain Waves and Secondary Gravity Waves in the Mesosphere Lower Thermosphere Above Patagonia.
Authors: Reichert, Robert1,2 (AUTHOR) robert.reichert@physik.uni-muenchen.de, Pautet, Pierre‐Dominique3 (AUTHOR), Kaifler, Bernd1 (AUTHOR), Rhode, Sebastian4 (AUTHOR), Ungermann, Jörn4 (AUTHOR), Sato, Kaoru5 (AUTHOR), Janches, Diego6 (AUTHOR), Smith, Steven7 (AUTHOR)
Source: Journal of Geophysical Research. Atmospheres. 3/28/2026, Vol. 131 Issue 6, p1-28. 28p.
Subject Terms: Mountain wave, Gravity waves, Ray tracing, Atmospheric layers, Momentum transfer, Temperature measurements
Geographic Terms: Patagonia (Argentina & Chile), Tierra del Fuego (Argentina & Chile), Argentina
Abstract: We find observational evidence for mountain waves (MWs) and secondary gravity waves (2GWs) in the OH*(3‐1) layer above Tierra del Fuego, Argentina. On the night of 21–22 May 2018, the Advanced Mesospheric Temperature Mapper (AMTM) obtained temperatures at ∼84 ${\sim} 84$ km. During the westerly phase of the semi‐diurnal tide, arc‐shaped quasi‐stationary structures in temperature maps indicated MWs with horizontal wavelengths of 20–40 km. A co‐located temperature measurement from the COmpact Rayleigh Autonomous Lidar (CORAL) confirmed quasi‐stationary structures down to 15 km, also indicating MWs. Temperature profiles revealed a convectively unstable region within a MW phase front at 58–66 km—a sign of MW breaking, momentum deposition, local body forces, and generation of 2GWs. After a wind reversal in the mesosphere/lower thermosphere (MLT) observed by the Southern Argentina Agile Meteor Radar (SAAMER), a gravity wave propagated southeastward with an intrinsic phase speed >90ms−1 ${ >} 90\,{\text{ms}}^{-1}$. Using 1‐D cross‐wavelet analysis, we derived spectral properties of this fast wave and performed ray‐tracing, using the Japanese Whole Atmosphere Reanalysis as background. The fast wave likely originated near 63 km above the Torres del Paine region, known for large‐amplitude MWs. We conclude that tropospheric forcing excites MWs over Tierra del Fuego (observed) and over the Torres del Paine massif (not observed) ∼500 ${\sim} 500$ km northwest. The latter MWs likely generate 2GWs upon breaking in the lower mesosphere, observed over Tierra del Fuego after a turning‐level disappearance. A novel momentum‐flux (MF) retrieval, based on co‐located AMTM, CORAL, and SAAMER measurements, automatically identifies dominant wave features, incorporating measurement and OH*(3‐1) layer variability to infer realistic MF uncertainties. Plain Language Summary: On the night of 21–22 May 2018, atmospheric scientists observed mountain waves and secondary gravity waves above Tierra del Fuego, Argentina. Clear skies allowed continuous temperature measurements near 84 km altitude using a camera. The data showed patterns typical of mountain waves, triggered when strong winds blow over mountains. Additional temperature data from a co‐located laser system confirmed these waves extended downward to about 15 km. In one region between 58 and 66 km, the atmosphere was unstable—a sign that mountain waves were breaking and transferring energy into ambient wind. This process can generate new waves, known as secondary gravity waves. Later in the night, after a shift in wind direction, a fast‐moving wave was detected traveling southeast at over 90ms−1 $90\,{\text{ms}}^{-1}$. Analysis suggested this wave originated around 63 km altitude above the Torres del Paine mountains, about 500 km northwest. Breaking of mountain waves may have created the fast‐moving wave, classifying it as secondary. These conclusions were enabled by a new analysis method that automatically identifies and measures wave properties using co‐located temperature and wind observations. The method also accounts for measurement uncertainties, enabling an accurate estimate of how much momentum these waves carry into the upper atmosphere. Key Points: We observed mountain and secondary gravity waves in the OH layer above Tierra del Fuego using co‐located ground‐based instrumentsMountain wave breaking near 63 km likely generated fast secondary waves later seen above Tierra del Fuego after a turning level vanishedA novel retrieval method quantifies momentum flux from wave features and includes uncertainties from measurements and OH layer variability [ABSTRACT FROM AUTHOR]
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Abstract:We find observational evidence for mountain waves (MWs) and secondary gravity waves (2GWs) in the OH*(3‐1) layer above Tierra del Fuego, Argentina. On the night of 21–22 May 2018, the Advanced Mesospheric Temperature Mapper (AMTM) obtained temperatures at ∼84 ${\sim} 84$ km. During the westerly phase of the semi‐diurnal tide, arc‐shaped quasi‐stationary structures in temperature maps indicated MWs with horizontal wavelengths of 20–40 km. A co‐located temperature measurement from the COmpact Rayleigh Autonomous Lidar (CORAL) confirmed quasi‐stationary structures down to 15 km, also indicating MWs. Temperature profiles revealed a convectively unstable region within a MW phase front at 58–66 km—a sign of MW breaking, momentum deposition, local body forces, and generation of 2GWs. After a wind reversal in the mesosphere/lower thermosphere (MLT) observed by the Southern Argentina Agile Meteor Radar (SAAMER), a gravity wave propagated southeastward with an intrinsic phase speed >90ms−1 ${ >} 90\,{\text{ms}}^{-1}$. Using 1‐D cross‐wavelet analysis, we derived spectral properties of this fast wave and performed ray‐tracing, using the Japanese Whole Atmosphere Reanalysis as background. The fast wave likely originated near 63 km above the Torres del Paine region, known for large‐amplitude MWs. We conclude that tropospheric forcing excites MWs over Tierra del Fuego (observed) and over the Torres del Paine massif (not observed) ∼500 ${\sim} 500$ km northwest. The latter MWs likely generate 2GWs upon breaking in the lower mesosphere, observed over Tierra del Fuego after a turning‐level disappearance. A novel momentum‐flux (MF) retrieval, based on co‐located AMTM, CORAL, and SAAMER measurements, automatically identifies dominant wave features, incorporating measurement and OH*(3‐1) layer variability to infer realistic MF uncertainties. Plain Language Summary: On the night of 21–22 May 2018, atmospheric scientists observed mountain waves and secondary gravity waves above Tierra del Fuego, Argentina. Clear skies allowed continuous temperature measurements near 84 km altitude using a camera. The data showed patterns typical of mountain waves, triggered when strong winds blow over mountains. Additional temperature data from a co‐located laser system confirmed these waves extended downward to about 15 km. In one region between 58 and 66 km, the atmosphere was unstable—a sign that mountain waves were breaking and transferring energy into ambient wind. This process can generate new waves, known as secondary gravity waves. Later in the night, after a shift in wind direction, a fast‐moving wave was detected traveling southeast at over 90ms−1 $90\,{\text{ms}}^{-1}$. Analysis suggested this wave originated around 63 km altitude above the Torres del Paine mountains, about 500 km northwest. Breaking of mountain waves may have created the fast‐moving wave, classifying it as secondary. These conclusions were enabled by a new analysis method that automatically identifies and measures wave properties using co‐located temperature and wind observations. The method also accounts for measurement uncertainties, enabling an accurate estimate of how much momentum these waves carry into the upper atmosphere. Key Points: We observed mountain and secondary gravity waves in the OH layer above Tierra del Fuego using co‐located ground‐based instrumentsMountain wave breaking near 63 km likely generated fast secondary waves later seen above Tierra del Fuego after a turning level vanishedA novel retrieval method quantifies momentum flux from wave features and includes uncertainties from measurements and OH layer variability [ABSTRACT FROM AUTHOR]
ISSN:2169897X
DOI:10.1029/2025JD045172