Gravity Waves and Convective Systems over the Alps and Andes

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

Workshop; OPAC-IROWG 2016; 2016

Gravity waves 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 ofgravity waves. 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 gravity waves 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 informationon gravity waves is limited in this respect. Observations of complex mountainwave events are based on measurement campaigns only. Different single cases ofgravity wave generation were analyzed and compared to model simulations. Major challenges related to the investigation of waves and convective systems are thelack of observations (with high vertical resolution and accuracy) and multi-model ensemble approaches. The GPS RO technique enables measurements ofthe 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. We analyze case studies of gravity waves generated during some identified Mesoscale Convective System (MCS) events near the Andes and Alps mountains, from GPS RO profiles collocated with radar observations, reanalyses and model simulations. Bending angle abrupt changes at cloud tops are identified from GPS RO. A comparison is performed with gravity waves at the same locations of the case studies, under clear sky conditions.