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Oblique propagation of mountain waves to the upwind side of the Andes observed by GLORIA and ALIMA during the SouthTRAC campaign
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  • Lukas Krasauskas,
  • Bernd Kaifler,
  • Sebastian Rhode,
  • Jörn Ungermann,
  • Wolfgang Woiwode,
  • Peter Preusse
Lukas Krasauskas
Institute of Energy and Climate Research (IEK-7: Stratosphere), Forschungszentrum Jülich

Corresponding Author:l.krasauskas@fz-juelich.de

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Bernd Kaifler
Institute of Atmospheric Physics, German Aerospace Center
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Sebastian Rhode
Forschungszentrum Jülich
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Jörn Ungermann
Institute of Energy and Climate Research - Stratosphere (IEK-7), Research Centre Jülich
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Wolfgang Woiwode
Karlsruhe Institute of Technology
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Peter Preusse
Juelich Research Center
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Gravity waves (GW) carry energy and momentum from troposphere to the middle atmosphere and have a strong influence on the circulation there. Global atmospheric models cannot fully resolve GWs, and therefore rely on highly simplified GW parametrizations that, among other limitations, account for vertical wave propagation only and neglect refraction. This is a major source of uncertainty in models, and leads to well-known problems, such as late break-up of polar vortex due to the “missing” GW drag around 60°S. To investigate these phenomena, GW observations over Southern Andes were performed during SouthTRAC aircraft campaign. This paper presents measurements from a SouthTRAC flight on 21~September 2019, including 3-D tomographic temperature data of the infrared limb imager GLORIA (8-15 km altitude) and temperature profiles of the ALIMA lidar (20-80 km altitude). GLORIA observations revealed multiple overlapping waves of different wavelengths. 3-D wave vectors were determined from the GLORIA data and used to initialise a GW ray-tracer. The ray-traced GW parameters were compared with ALIMA observations, showing good agreement between the instruments and direct evidence of oblique (partly meridional) GW propagation. ALIMA data analysis confirmed that most waves at 25-40 km altitudes were indeed orographic GWs, including waves seemingly upstream of the Andes. We directly observed horizontal GW refraction, which has not been achieved before SouthTRAC. Refraction and oblique propagation caused significant meridional transport of horizontal momentum as well as horizontal momentum exchange between waves and the background flow all along the wave paths, not just in wave excitation and breaking regions.