Refraction in the horizontal is the process whereby a GW phase front changes in orientation. Such changes in orientation are linked with changes in the wavelength in the x-direction and y-direction (Durran, 2009), which has been shown to have important implications for GW propagation (e.g., Dunkerton & Butchart, 1984;Ehard et al., 2017;Sato et al., 2009). A literature survey shows a very small amount of papers on GW refraction compared to GW dissipation and GW breaking. This indicates that a large portion of the academic effort does not include refraction. This article uses high-resolution observational data from the lower troposphere to the lower mesosphere to quantify refraction and show the importance there-of for wave-mean flow interaction.

Atmospheric gravity waves (GWs) are usually excited by processes such as flow over orography (e.g., Ecker-

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.

Refraction in the horizontal is the process whereby a GW phase front changes in orientation. Such changes in orientation are linked with changes in the wavelength in the x-direction and y-direction (Durran, 2009), which has been shown to have important implications for GW propagation (e.g., Dunkerton & Butchart, 1984;Ehard et al., 2017;Sato et al., 2009). A literature survey shows a very small amount of papers on GW refraction compared to GW dissipation and GW breaking. This indicates that a large portion of the academic effort does not include refraction. This article uses high-resolution observational data from the lower troposphere to the lower mesosphere to quantify refraction and show the importance there-of for wave-mean flow interaction.

Abstract. Following the current understanding of gravity waves (GWs) and especially mountain waves (MWs), they have high potential of horizontal propagation from their source. This horizontal propagation and therefore the transport of energy is usually not well represented in MW parameterizations of numerical weather prediction and general circulation models. The lack thereof possibly leads to shortcomings in the model's prediction as e.g. the cold pole bias in the Southern Hemisphere and the polar vortex breaking down too late. In this study we present a mountain wave model (MWM) for quantification of the horizontal propagation of orographic gravity waves. This model determines MW source location and associates their parameters from a fit of idealized Gaussian shaped mountains to topography data. Propagation and refraction of these MWs in the atmosphere is modeled using the ray-tracer GROGRAT. Ray-tracing each MW individually allows for an estimation of momentum transport due to both vertical and horizontal propagation. This study presents the MWM itself and gives validations of MW induced temperature perturbations to ECMWF IFS numerical weather prediction data and estimations of gravity wave momentum flux (GWMF) compared to HIRDLS satellite observations. The MWM is capable of reproducing the general features and amplitudes of both of these data sets and, in addition, is used to explain some observational features by investigating MW parameters along their trajectories.