Gravity Waves and Convective Systems over the Alps and Andes

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

Graz

Congreso; Occultations for Probing Atmosphere and Climate 6; 2016

Gravity waves and convective systems play a fundamental role inatmospheric circulation, weather, and climate. They initiate fast verticaltransport which alters the thermal structure of the troposphere and thestratosphere including a redistribution of water vapor and atmosphericconstituents. Topographic terrain represents a source for the generation ofgravity waves. Due to orographic effects so-called mountain waves are generatedover large mountain ranges, such as the European Alps or the Andes in SouthAmerica. The connection between gravity waves and the development of convectivesystems is a topic of current active research. Initial investigations oforographic effects related to deep convection over the Andes region providedevidence that mountain waves supply energy sufficient for the initiation of convectiveevents, 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. Majorchallenges related to the investigation of waves and convective systems are thelack of observations (with high vertical resolution and accuracy) andmulti-model ensemble approaches. The GPS RO technique enables measurements ofthe atmospheric density structure during extreme weather events with highvertical resolution and accuracy in any meteorological conditions since theradio wave signal is almost unaffected by clouds. We analyze case studies ofgravity waves generated during some identified Mesoscale Convective System (MCS)events near the Andes and Alps mountains, from GPS RO profiles collocated withradar observations, reanalyses and model simulations. Bending angle abruptchanges at cloud tops are identified from GPS RO. A comparison is performedwith gravity waves at the same locations of the case studies, under clear skyconditions.