Abstract. Gravity waves (GWs) and convective systems play a fundamental role in
atmospheric circulation, weather, and climate. Two usual main sources of GWs
are orographic effects triggering mountain waves and convective activity. In
addition, GW generation by fronts and geostrophic adjustment must also be
considered. The utility of Global Positioning System (GPS) radio occultation
(RO) observations for the detection of convective systems is tested. A
collocation database between RO events and convective systems over
subtropical to midlatitude mountain regions close to the Alps and Andes is
built. From the observation of large-amplitude GW structures in the
absence of jets and fronts, subsets of RO profiles are sampled. A
representative case study among those considered at each region is selected
and analyzed. The case studies are investigated using mesoscale Weather Research and Forecasting (WRF)
simulations, ERA-Interim reanalysis data, and measured RO temperature
profiles. The absence of fronts or jets during both case studies reveals
similar relevant GW features (main parameters, generation, and propagation).
Orographic and convective activity generates the observed GWs. Mountain waves
above the Alps reach higher altitudes than close to the Andes. In the Andes
case, a critical layer prevents the propagation of GW packets up to
stratospheric heights. The case studies are selected also because they
illustrate how the observational window for GW observations through RO
profiles admits a misleading interpretation of structures at different
altitude ranges. From recent results, the distortion introduced in the
measured atmospheric vertical wavelengths by one of the RO events is
discussed as an illustration. In the analysis, both the elevation angle of
the sounding path (line of tangent points) and the gravity wave aspect ratio
estimated from the simulations and the line of sight are taken into account.
In both case studies, a considerable distortion, over- and underestimation of
the vertical wavelengths measured by RO, may be expected.
First Direct Observational Evidence for Secondary Gravity Waves Generated by Mountain Waves Over the Andes