Dynamics of a local Alpine flooding event in October 2011: moisture source and large-scale circulation

Piaget, Nicolas; Froidevaux, Paul Arnaud; Giannakaki, Paraskevi; Gierth, Franziska; Martius, Olivia; Riemer, Michael; Wolf, Gabriel; Grams, Christian M. (2015). Dynamics of a local Alpine flooding event in October 2011: moisture source and large-scale circulation. Quarterly Journal of the Royal Meteorological Society, 141(690), pp. 1922-1937. Royal Meteorological Society 10.1002/qj.2496

[img] Text
qj2496.pdf - Published Version
Restricted to registered users only
Available under License Publisher holds Copyright.

Download (11MB) | Request a copy

Alpine heavy precipitation events often affect small catchments, although the circulation pattern leading to the event extends over the entire North Atlantic. The various scale interactions involved are particularly challenging for the numerical weather prediction of such events. Unlike previous studies focusing on the southern Alps, here a comprehensive study of a heavy precipitation event in the northern Alps in October 2011 is presented with particular focus on the role of the large-scale circulation in the North Atlantic/European region. During the event exceptionally high amounts of total precipitable water occurred in and north of the Alps. This moisture was initially transported along the flanks of a blocking ridge over the North Atlantic. Subsequently, strong and persistent northerly flow established at the upstream flank of a trough over Europe and steered the moisture towards the northern Alps. Lagrangian diagnostics reveal that a large fraction of the moisture emerged from the West African coast where a subtropical upper-level cut-off low served as an important moisture collector. Wave activity flux diagnostics show that the ridge was initiated as part of a low-frequency, large-scale Rossby wave train while convergence of fast transients helped to amplify it locally in the North Atlantic. A novel diagnostic for advective potential vorticity tendencies sheds more light on this amplification and further emphasizes the role of the ridge in amplifying the trough over Europe. Operational forecasts misrepresented the amplitude and orientation of this trough. For the first time, this study documents an important pathway for northern Alpine flooding, in which the interaction of synoptic-scale to large-scale weather systems and of long-range moisture transport from the Tropics are dominant. Moreover, the trapping of moisture in a subtropical cut-off near the West African coast is found to be a crucial precursor to the observed European high-impact weather.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geography > Physical Geography > Unit Impact
10 Strategic Research Centers > Oeschger Centre for Climate Change Research (OCCR)
08 Faculty of Science > Institute of Geography

Graduate School:

Graduate School of Climate Sciences

UniBE Contributor:

Froidevaux, Paul Arnaud; Giannakaki, Paraskevi and Romppainen-Martius, Olivia

Subjects:

500 Science > 550 Earth sciences & geology
900 History > 910 Geography & travel

ISSN:

0035-9009

Publisher:

Royal Meteorological Society

Language:

English

Submitter:

Monika Wälti-Stampfli

Date Deposited:

21 Sep 2015 13:00

Last Modified:

14 Nov 2016 08:26

Publisher DOI:

10.1002/qj.2496

BORIS DOI:

10.7892/boris.71841

URI:

https://boris.unibe.ch/id/eprint/71841

Actions (login required)

Edit item Edit item
Provide Feedback