Severe European Cyclones: A Storm-Prone Situation Perspective
Jennifer Owen*, Tomek Trzeciak and Peter Knippertz
*Contact: ee09jso@leeds.ac.uk; School of Earth and Environment, University of Leeds, LS2 9JT, UK
Introduction
Conclusions
• Intense winter storms are the most damaging weather phenomenon to afflict
Europe. Therefore, forecasting them in weather and climate models is a priority.
• The SEAMSEW project, financed through the AXA Research fund, aims to assess
uncertainties in future projections of severe storms.
• We can separate sources of uncertainty using the idea of a large-scale ‘stormprone situation’ (SPS), and evaluating their representation in climate models.
• First, we identified 31 severe European windstorms, based on the Storm Severity
Index, which calculates how unusual the wind speed is (Leckebusch et al., 2008).
• Selected 31 historic, severe European windstorms.
• Identified 4 jet stream types.
• Proposed new approach to storm-prone situations,
using existing idea of Eady Growth Rate.
• Included effects of moisture.
• Mixed success in detecting storms.
• Success potentially related to jet stream type.
Jet Stream Types
Kyrill
Klaus
• Once 31 storms selected, examined analysis
data and tracked each storm.
• Plotted jet stream in sections that move along
with the track of each storm.
• Four categories emerged.
• Here, one example of each is presented
Wind speed
(m/s) at
300hPa
Storm
Emma
Jet Type
Kyrill
Cross early
Emma
Edge
Klaus
Cross late
Xynthia
Split
Method
Xynthia
Four Versions of Growth Rate
Use Eady Growth Rate to quantify baroclincity.
Use quasi-geostrophic (QG) and semi-geostrophic (SG)
equations to describe atmosphere
Including effect of
moisture means four
versions identified.
Calculate the four
versions everywhere
Average over the box
(35-65oN, 40oE to 10oE) →
Search for high peaks,
followed by sudden drops.
QG dry
QG moist
SG dry
SG moist
QG moist
•
•
•
•
•
•
•
•
Shear
Dry stability
Coriolis parameter only
Lindzen & Farrell (1980).
Figure 2: Showing 4 versions of growth rate (σ) for 1 October 2006 to 31 March 2007.
Emma
σ
Figure 3: Showing 4 versions of growth rate (σ) for 1 October 2007 to 31 March 2008.
Shear
Moist stability
Coriolis parameter only
Whitaker and Davis (1994)
SG dry
SG moist
•
•
•
•
•
•
•
•
Shear
Dry stability
Vorticity
Emanuel, Fantini & Thorpe (1987)
Indentifying Storms
Kyrill
σ
QG dry
QG moist
SG dry
SG moist
QG dry
• Moisture accelerates growth
• SG moist is an upper limit, assuming
atmosphere totally saturated
σ
everywhere in the domain
• Expect σ to peak just before the
storm develops, and drop as the
baroclinic energy is removed.
• Objectively identify peaks (shown as
stars on plots) as exceeding 98th
percentile once in 48 hour period.
• Here, one storm of each jet stream
type is presented.
• e-folding times typically 0.5-1.0 days.
• Klaus: behaves as expected.
• Emma: peak apparent in some
σ
versions, not all.
Storm-Prone Situations
• Kyrill: large peak slightly after.
• Xynthia: no peak. Very different jet
stream configuration to the others.
• Overall, mixed results as to whether
there is a peak before every storm.
• Might be related to jet stream type.
QG dry
QG moist
SG dry
SG moist
Shear
Moist stability
Vorticity
Emanuel, Fantini & Thorpe (1987)
Klaus
Figure 4: Showing 4 versions of growth rate (σ) for 1 October 2008 to 31 March 2009.
QG dry
QG moist
SG dry
SG moist
Xynthia
Figure 5: Showing 4 versions of growth rate (σ) for 1 October 2009 to 31 March 2010.
Emanuel, K., M. Fantini, and A. Thorpe, 1987: Baroclinic instability in an environment of small stability to slantwise moist convection. Part I: Two-dimensional models. Journal of the Atmospheric Sciences, v. 44, pp. 1559–1573.
Leckebusch, G., D. Renggli, and U.Ulbrich, 2008: Development and application of an objective storm severity measure for the northeast Atlantic region. Meteorologische Zeitschrift, vol. 17 (5), pp. 575–587.
Lindzen, R. and B. Farrell, 1980: A simple approximate result for the maximum growth rate of baroclinic instabilities. Journal of the Atmospheric Sciences, vol. 37, pp.1648–1654.
Whitaker, J. and C. Davis, 1994: Cyclogenesis in a saturated environment. Journal of the Atmospheric Sciences, vol. 51, pp. 889–907.