On the dynamical coupling between atmospheric blocks and heavy precipitation events: A discussion of the southern Alpine flood in October 2000

Lenggenhager, Sina; Croci-Maspoli, Mischa; Brönnimann, Stefan; Martius, Olivia (2019). On the dynamical coupling between atmospheric blocks and heavy precipitation events: A discussion of the southern Alpine flood in October 2000. Quarterly Journal of the Royal Meteorological Society, 145(719), pp. 530-545. Royal Meteorological Society 10.1002/qj.3449

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In October 2000, a high‐impact lake flood event occurred in southern Switzerland. During the month prior to the flood event three heavy precipitation events (HPEs) occurred. The first two events preconditioned the catchment and brought the lake close to its flood level. During the third event the lake level rose above the flood threshold. At the same time, anomalously high blocking activity was observed in the northern North‐Atlantic/European region. This study describes the synoptic development during the month prior to the flood and investigate the role of atmospheric blocking for the formation of the HPEs using ERA‐Interim data. Atmospheric blocks are identified as persistent negative potential vorticity (PV) anomalies in the upper troposphere. All three heavy precipitation events were forced by upper‐level equatorward elongated streams of stratospheric high‐PV air (PV streamers). These PV streamers formed in the strong deformation field upstream and downstream of single blocks or in between two blocks. During the third and most persistent heavy precipitation episode the eastward propagation of the PV streamer was prevented by a downstream block for several days leading to a stationary upper‐level north‐eastward flow and a prolonged period of heavy precipitation over the catchment. The study identifies and quantifies a potential feedback between heavy precipitation and blocks via diabatic depletion of PV. It is shown that a substantial fraction of the diabatically modified low PV air (63%) that reached and strengthened the blocks over the Atlantic and Europe during this month experienced heating in HPE areas.

Item Type:

Journal Article (Original Article)

Division/Institute:

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

UniBE Contributor:

Lenggenhager, Sina; Brönnimann, Stefan 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:

Hélène Christine Louise Barras

Date Deposited:

12 Feb 2019 15:04

Last Modified:

21 Mar 2019 10:34

Publisher DOI:

10.1002/qj.3449

Uncontrolled Keywords:

Atmospheric blocking, rainfall, floods, mid-latitude, extra-tropical weather systems, troposphere, dynamic/processes, Switzerland

BORIS DOI:

10.7892/boris.123106

URI:

https://boris.unibe.ch/id/eprint/123106

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