A Spectral Rotary Analysis of Gravity Waves: An Application during one of the SOUTHTRAC Flights

Abstract

To understand the main orographic and non-orographic sources of gravity waves (GWs) over South America during an Experiment (Rapp et al, 2021, https://doi.org/10.1175/BAMS-D-20-0034.1), we propose the application of a rotational spectral analysis based on methods originally developed for oceanographic studies. This approach is deployed in a complex scenario of large-amplitude GWs by applying it to reanalysis data. We divide the atmospheric region of interest into two height intervals. The simulations are compared with lidar measurements during one of the flights. From the degree of polarization and the total energy of the GWs, the contribution of the upward and downward wave packets is described as a function of their vertical wavenumbers. At low levels, a larger downward energy flux is observed in a few significant harmonics, suggesting inertial GWs radiated at polar night jet levels, and below, near to a cold front. In contrast, the upward GW energy flux, per unit area, is larger than the downward flux, as expected over mountainous areas. The main sub-regions of upward GW energy flux are located above Patagonia, the Antarctic Peninsula and only some oceanic sectors. Above the sea, there are alternating subregions dominated by linearly polarized GWs and sectors of downward GWs. At the upper levels, the total available GW energy per unit mass is higher than at the lower levels. Regions with different degrees of polarization are distributed in elongated bands. A satisfactory comparison is made with an analysis based on the phase difference between temperature and vertical wind disturbances.

The Mission Support System (MSS v7.0.4) and its use in planning for the SouthTRAC aircraft campaign

“…The scientific objectives were very diverse, ranging from examining air polluted by biomass burning in the tropics (Johansson et al, 2022) (and, as a target of opportunity, Australia; Ohneiser et al, 2022), the breakdown of the Antarctic polar vortex and the associated chemical and physical structure, the general chemical composition of the Southern Hemisphere's upper troposphere-lower stratosphere (Johansson et al, 2022), to studying gravity waves. Some exemplary outcomes from the gravity wave part of the SouthTRAC campaign include clear-air turbulence studies (Rodriguez Imazio et al, 2022;Dörnbrack et al, 2022), gravity wave propagation from the Southern Andes and the Antarctic peninsula into the mesosphere (Reichert et al, 2021;Conte et al, 2022), gravity wave observation and model intercomparison (Gisinger et al, 2022;Dörnbrack et al, 2022;Liu et al, 2022;Alexander et al, 2022), mountain waves drifting upwind of the Andes (Krasauskas et al, 2022), gravity wave refraction due to wind shear (Geldenhuys et al, 2022), and gravity waves from orographic and non-orographic sources (Alexander et al, 2022;de la Torre et al, 2022).…”