Gravity Waves and Convective Systems over the Alps and Andes

HIERRO, R., A.K. STEINER, A. DE LA TORRE, P. ALEXANDER, AND P. LLAMEDO

Graz

Workshop; OPAC-IROWG 2016; 2016

Universidad de Graz

Gravity waves (GWs) and convective systems play a fundamental role in atmospheric circulation, weather, and climate. They initiate fast vertical transport which alters the thermal structure of the troposphere and the stratosphere including a redistribution of water vapor and atmospheric constituents. Topographic terrain represents a source for the generation of GWs. Due to orographic effects so-called mountain waves are generated over large mountain ranges, such as the European Alps or the Andes in South America. The connection between GWs and the development of convective systems is a topic of current active research. Initial investigations of orographic effects related to deep convection over the Andes region provided evidence that mountain waves supply energy sufficient for the initiation of convective events, sometimes with hail production. Over the European Alps the information on GWs is limited in this respect. Major challenges related to the investigation of waves and convective systems are the lack of observations (with high vertical resolution and accuracy) and multi-model ensemble approaches. The GPS RO technique enables measurements of the atmospheric density structure during extreme weather events with high vertical resolution and accuracy in any meteorological conditions since the radio wave signal is almost unaffected by clouds. Here we present two case studies on GW generation during identified convective events near the Andes and Alps mountains. We analyze GPS RO profiles collocated with convective cloud observations from geostationary satellites and identify cloud tops from abrupt changes in RO bending angle. We investigate GW generation for the two cases with model simulations.