Secondary gravity waves generated by breaking mountain waves over Europe

A strong mountain wave, observed over Northern European on the 12th Jan 2016, is simulated in 2D under 2 fixed background wind conditions representing opposite tidal phases. The aim of the simulation is to investigate the breaking of the mountain wave and subsequent generation of non-primary waves in the upper atmosphere. It is found that the mountain wave first breaks as it approaches a mesospheric critical level creating turbulence on horizontal scales of 8-30km. These turbulence scales couple directly to horizontal secondary waves scales, but those scales are prevented from reaching the thermosphere by the tidal winds which act like a filter. Initial secondary waves which can reach the thermosphere range from 60-120km in horizontal scale and are influenced by the scales the horizontal and vertical forcing associated with wave breaking at mountain wave zonal phase width, and horizontal wavelength scales. Large scale non-primary waves dominate over the whole duration of the simulation with scales from 107-300km and periods from 11-22 minutes. The thermosphere winds heavily influence the time-averaged spatial distribution of wave forcing in the thermosphere, which peaks at 150km altitude and occurs both westward and eastward of the source in the 2 UT background simulation and primarily eastward of the source in the 7 UT background simulation. The forcing amplitude is 2x that of the primary mountain wave breaking and dissipation. This suggests that non-primary waves play a significant role in gravity waves dynamics and improved understanding of the thermospheric winds is crucial to understanding their forcing distribution.Key Points:Mountain wave breaking in the MLT couples directly to secondary wavesTidal winds act like a filter for secondary wave spectra reaching the thermosphereNon-primary wave forcing is significant and distribution is governed by thermospheric winds This collection hosts the data associated with the journal article, Secondary gravity waves generated by breaking mountain waves over Europe. The full-text manuscript is published in JGR: Atmospheres. DOI: https://doi.org/10.1029/2019JD03166