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Does strong tropospheric forcing cause large amplitude mesospheric gravity waves? : a deepwave case study / by Martina Bramberger
VerfasserBramberger, Martina
Betreuer / BetreuerinnenStiperski, Ivana ; Dörnbrack, Andreas
UmfangIV, 122 S. : Ill., graph. Darst., Kt.
HochschulschriftInnsbruck, Univ., Master-Arb., 2015
Datum der AbgabeNovember 2015
Schlagwörter (EN)Gravity-Waves / Mesosphere / Deepwave / Wave-breaking / Gravity-Waves - Mesosphere - Deepwave - Wave-breaking
Schlagwörter (GND)Neuseeland / Mesosphäre / Gravitationswelle / Troposphäre
URNurn:nbn:at:at-ubi:1-2716 Persistent Identifier (URN)
 Das Werk ist frei verfügbar
Does strong tropospheric forcing cause large amplitude mesospheric gravity waves? [51.38 mb]
Zusammenfassung (Englisch)

The goal of this thesis is to investigate whether large amplitude mesospheric gravity waves over New Zealand (NZ) are connected to strong tropospheric forcing. For this reason a case study of the 4 July 2014 during the DEEPWAVE campaign is presented. On that day a pronounced low-pressure system south of NZ provided strong forcing conditions with horizontal wind speeds up to 30 m/s across the Southern Alps between 03 and 12 UTC. During this time, DLR Rayleigh lidar measurements conducted in Lauder showed stationary gravity waves up to an altitude of about 55 km which amplified strongly up to an altitude of about 80 km with maximum amplitudes of about 20 K. Also, ECMWF operational analyses and short-term forecasts for this day indicate that gravity wave propagation from the ground up to the mesosphere might be possible. The lidar measurements together with the ECMWF simulations raise the question whether these large amplitude mesospheric gravity waves are directly related to the strong tropospheric forcing. For this purpose, in-situ measurements of the DLR Falcon aircraft and the NSF/NCAR GV aircraft are analysed in order to determine energy and momentum fluxes. Additionally a scale analysis with the help of wavelets is conducted on the in-situ flightlevel data. To gain information on altitudes above and below the flight tracks also radiosondes launched in Haast and Lauder are taken into account as well as WRF simulated data along the flight track. ECMWF operational analysis and short-term forecasts are used to describe the synoptic situation as well as the upstream background flow. The analysis of the DLR Falcon and the NSF/NCAR in-situ data revealed largest measured vertical energy fluxes during DEEPWAVE. In contrast to the Eliassen-Palm relation momentum fluxes were not constant with altitude and changed the sign above the tropopause between the first and second research flight of the Falcon. Radiosondes launched in Haast detected wave breaking regions in the lower stratosphere above the southern NZ island which were also shown in WRF simulations along the flight track. The breaking regions are locally confined and distributed in a scattered pattern. Due to this turbulent region a conclusive statement cannot be made as to whether the excited primary mountain waves propagated up to the mesosphere.

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