Orographic and convective gravity waves above the Alps and Andes mountains during GPS radio occultation events – a case study

Abstract. Gravity waves (GW) and convective systems play a fundamental role in atmospheric circulation, weather, and climate. The main sources of GW are orographic effects triggering mountain waves and convective activity. We test the utility of Global Positioning System (GPS) radio occultation (RO) observations for the investigation of convective systems and GW over orographic regions in Europe and South America. We build a collocation database between RO events and convective systems over sub-tropical to mid-latitude mountain regions close to the Alps and Andes. Subsets of RO profiles are sampled and a case study is selected for each region. From mesoscale numerical simulations, we analyze relevant gravity waves features (main parameters, generation and propagation), mainly from orographic and convective activity origin for the case studies considered. Similar GW regimes and dominant vertical and horizontal wavelengths, from convective and orographic sources, are found in both regions. Mountain waves above the Alps are found to reach higher altitudes than close to the Andes, as the background subtropical jet above this region constrains the propagation of GW packets up to stratospheric heights. From recent results, the distortion introduced in the measured atmospheric vertical gravity wavelength by one of the RO events is illustratively discussed. In our analysis we take into account 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. In both case studies, a considerable distortion and underestimation of the vertical wavelengths measured by RO may be expected.