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The missing link between alpine potential vorticity banners and banded convection : a case study of a severe alpine snow storm / by Simon Karl Siedersleben
VerfasserSiedersleben, Simon Karl
Begutachter / BegutachterinGohm, Alexander
GutachterGohm, Alexander
ErschienenInnsbruck, January 2016
Umfangvi, 55 Blätter : Illustrationen, Diagramme
HochschulschriftUniversität Innsbruck, Masterarbeit, 2016
Datum der AbgabeJanuar 2016
Schlagwörter (EN)banded convection / potential vorticity / PV
Schlagwörter (GND)Südalpen / Föhn / Wolke / Schneesturm / Lawine / Geschichte 2014
URNurn:nbn:at:at-ubi:1-3113 Persistent Identifier (URN)
 Das Werk ist frei verfügbar
The missing link between alpine potential vorticity banners and banded convection [11.58 mb]
Zusammenfassung (Englisch)

On 01 February 2014, the southern side of the Alps was affected by a severe snowstorm which forced authorities to issue the highest level of avalanche danger in southern partsof Austria. The northern side of the Alps was mostly dry. Nevertheless, radar imagery captured the evolution of quasi-steady convective cloud bands over the northern Alpine foreland with a remarkable length of up to 300 km. This study illuminates the processes that generated these cloud bands based on numerical simulations. The storm was associated with a deep large-scale trough that caused strong southwesterly cross-Alpine flow, orographic precipitation on the southern side, and foehn-like subsidence on the northern side of the Alps. Orographic potential vorticity (PV) banners eveloped at small-scale topographic features embedded in the Alps and extended downstream over the northern Alpine foreland. Convective cloud bands were aligned parallel to these PV banners. They formed in an environment of inertial instability (negative absolute vorticity) and conditional instability. Sensitivity experiments reveal that the structure and size of these cloud bands are strongly sensitive to the small-scale terrain roughness. Removing small-scale topographic features suppresses the formation of orographic vorticity banners, which in turn suppresses the development of cloud bands. These results suggest that the release of inertial instability at negative orographic vorticity banners was crucial for establishing circulations and associated uplift that triggered conditional instability. To summarize, inertial instability was responsible for the banded structure and conditional instability for the convective nature of these cloud bands.