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Extreme Storms in the North Atlantic and Europe
Stockholm University, Faculty of Science, Department of Meteorology .
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A study of the most extreme cyclones affecting the North Atlantic and Europe is presented with particular focus on extreme windstorms over the densely populated area of Western Europe, whose associated high surface wind speeds are capable of causing extensive structural damage and occasionally a loss of life.

A novel cyclone identification and tracking algorithm is presented which explicitly recognises ‘multi-centre cyclones’ (MCCs), defined as cyclonic systems which contain two or three sea-level pressure minima. The method also recognises cyclone merging and splitting events and reduces the number of tracks which would have been spuriously split at some point in their life-cycle. MCC frequency is shown to increase with storm intensity, with approximately 60% of the top 30% of cyclones constituting MCCs at some point in their life-cycle.

The first findings of the IMILAST (Inter-comparison of MId-LAtitudeSTorm diagnostics) project, an intercomparison study of 15 cyclone identification and tracking algorithms, are presented. Each method was applied to a 20 year period of the ERA-Interim dataset and results for cyclone frequency, intensity, life-cycle and track location were compared across the methods.

The relationship between the evolution of the most intense wind storms affecting Western Europe (Britain and Ireland, Scandinavia, and Western Continental Europe) and the large-scale atmospheric flow is investigated using an automated cyclone tracking algorithm and an objective measure of cyclone destructiveness applied to ERA40 and ERA-Interim reanalysis data as well as EC-Earth model output data at two different spatial resolutions. Composite analyses reveal a clear connection between the precise location of upper-level anti-cyclonic wave breaking and cold air intrusion from the north and the position and orientation of an intense jet; this, in turn, plays a crucial role in determining into which region a developing extreme storm will be steered.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University , 2013. , 44 p.
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-86533ISBN: 978-91-7447-630-9 (print)OAI: oai:DiVA.org:su-86533DiVA: diva2:587214
Public defence
2013-02-05, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Epub ahead of print. Paper 4: Manuscript.

 

Available from: 2013-01-15 Created: 2013-01-14 Last updated: 2013-06-12Bibliographically approved
List of papers
1. Objective identification and tracking of multi-centre cyclones in the ERA-Interim reanalysis dataset
Open this publication in new window or tab >>Objective identification and tracking of multi-centre cyclones in the ERA-Interim reanalysis dataset
2012 (English)In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 138, no 664, 612-625 p.Article in journal (Refereed) Published
Abstract [en]

We present a novel cyclone identification and tracking method that explicitly recognizes multicentre cyclones (MCCs), defined as a cyclonic system with two or three sea-level pressure minima within its outermost contour. The method allows for the recognition of cyclone merger and splitting events in a natural way, and provides a consistent measure of the cyclone extent. Using the ERA-Interim reanalysis dataset, we compute a climatology using this method and show that MCCs occur in about 32 of all cyclone tracks and are much more prevalent in more intense storms. We also show that the method permits reconnection of tracks that would have been spuriously split using a conventional method. We present spatial maps of cyclone mergers, splitting, genesis and lysis using the method and also compute statistics of precipitation falling within cyclones, showing that it is strongly concentrated in the most intense cyclones.

Keyword
cyclone identification, cyclone tracking, multi-centre cyclones
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-66404 (URN)10.1002/qj.948 (DOI)000302714500005 ()
Note

2

Available from: 2011-12-19 Created: 2011-12-19 Last updated: 2017-12-08Bibliographically approved
2. IMILAST A Community Effort to Intercompare Extratropical Cyclone Detection and Tracking Algorithms
Open this publication in new window or tab >>IMILAST A Community Effort to Intercompare Extratropical Cyclone Detection and Tracking Algorithms
Show others...
2013 (English)In: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 94, no 4, 529-547 p.Article in journal (Refereed) Published
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-90377 (URN)10.1175/BAMS-D-11-00154.1 (DOI)000318074700008 ()
Note

AuthorCount:36;

Available from: 2013-06-12 Created: 2013-06-03 Last updated: 2017-12-06Bibliographically approved
3. The role of large-scale atmospheric flow and Rossby wave breaking in the evolution of extreme windstorms over Europe
Open this publication in new window or tab >>The role of large-scale atmospheric flow and Rossby wave breaking in the evolution of extreme windstorms over Europe
2012 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, L21708- p.Article in journal (Refereed) Published
Abstract [en]

We investigate the relationship between large-scale atmospheric flow and the evolution of the most extreme windstorms affecting Western Continental Europe. The 25 most destructive Western Continental European wind storms are selected from a 43-year climatology. 22 of these storms are grouped as having a similar trajectory and evolution. We show that these storms typically occur during particularly strong and persistent positive NAO anomalies which peak approximately 2 days before the storms' peak intensity; the NAO pattern then shifts eastward to a position over the European continent when the storms strike Europe. A temporal composite of potential temperature on the 2-PVU surface suggests that this NAO shift is the result of simultaneous cyclonic and anticyclonic wave breaking penetrating further to the east than during a typical high-NAO event. This creates an extremely intense, zonally-orientated jet over the North Atlantic whose baroclinicity favours explosive intensification of storms while steering them into Western Continental Europe.

National Category
Geosciences, Multidisciplinary
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-83809 (URN)10.1029/2012GL053408 (DOI)000310963000001 ()
Note

AuthorCount:2;

Available from: 2012-12-14 Created: 2012-12-14 Last updated: 2017-12-06Bibliographically approved
4. Rossby wave breaking and extreme windstorms overWestern Europe
Open this publication in new window or tab >>Rossby wave breaking and extreme windstorms overWestern Europe
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We investigate the role of upper-level Rossby wave breaking in the evolution ofthemost extreme windstorms affecting three regions inWestern Europe: Britainand Ireland, Scandinavia and Western Continental Europe. Using ERA40and ERA-Interim reanalysis data along with EC-Earth model output at twodifferent spatial resolutions, we first construct an extreme wind climatologyover the selected regions and inter-compare the model climatology with thatcomputed from the reanalysis data. Using a storm destructiveness measure, wethen select the top 25 most destructive storms in each region from a multidecadalclimatology in each of our four datasets; track-by-track analysis revealsa good agreement in the trajectories and evolution of these storms in bothmodel resolutions compared to the reanalysis data. Temporal MSLP reanalysiscomposites demonstrate that in each region, there exists a set of large-scaleconditions conducive to the development of these storms; similar composites ofmodel output data show that these surface conditions are broadly well capturedby both model resolutions. Temporal composites of potential temperature onthe 2-PVU surface using reanalysis data reveal that these regional large-scalesurface patterns can be associated with exceptional cyclonic and anti-cyclonicwave breaking occurring contemporaneously in the North Atlantic; the preciselocation of these wave breaking events controls the position and orientation ofan intense upper-level jet which in turn determines into which region the stormsare steered. Similar composites using model output data show qualitativelythe same picture, but with an overall positive bias most likely due to a lowertropopause height in the model.

Keyword
Rossby wave breaking, Extreme windstorms, Western Europe
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-86519 (URN)
Available from: 2013-01-14 Created: 2013-01-14 Last updated: 2013-01-14

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