Stratospheric Mountain Waves over the South Andes: Observations & Application of Linear Theory

The South Andes mountain range is a global hot spot for stratospheric gravity waves. Here, we identify two selected case study flows over the South Andes, using data from the ERA5 reanalysis, one featuring extensive vertical and downstream wave propagation with a characteristic cellular pattern, and the other with little to no wave propagation. Core features of these two flow fields are identified and shown to correspond to different analytical solutions to the linear Taylor-Goldstein equation: one with vertical wave propagation (with and without rotation), and one with trapped waves propagating downstream. The importance of rotation is emphasised for its ability to suppress mountain waves at low altitudes, and wave trapping is identified as potentially contributing to the downstream propagation of waves in the stratosphere for one of the flow snapshots. The dimensionless number γ , the ratio of the height-scale of the Scorer parameter and the mountain’s horizontal length-scale, is highlighted as playing a critical role in the behaviour of trapped waves in multiple analytical models.