Multidecadal climatological investigations
of storms in the Northeast North Atlantic
and in the North Sea
Matthias Zahn1,2, Ralf Weisse1, Hans v. Storch1,2, Frauke Feser1
(1) University Hamburg, Meteorological Institute, Bundesstrasse 55, 20146 Hamburg, Germany
(2) GKSS Research Centre, Institute for Coastal Research, Max­Planck­Str.1, 21502 Geesthacht, Germany
Outline:
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Introduction •
Reconstruction of the atmosphere's state •
Quality of reconstructions
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Change of storm frequency
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Reconstruction of particular mesoscale features
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Summary/Conclusion
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Introduction Reconstruction of the atmosphere's state Quality of reconstructions
Change of storm frequency Reconstruction of particular mesoscale features
• Why do we care about storms in maritime areas?
(storms, sea state and storm surges)
• How did the number of such extreme events change? •
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Introduction Reconstruction of the atmosphere's state Quality of reconstructions
Change of storm frequency Reconstruction of particular mesoscale features
• Comprehensive measurements are required to address such questions (long in time, high in spatial detail, homogeneous)
• Such measurements are usually not available
• Use of numerical models in combination with existing measurements to reconstruct the past state of the atmosphere •
Introduction •
Reconstruction of the atmosphere's state •
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Quality of reconstructions
Change of storm frequency NCEP Global Reanalyses ( 210 km x 210 km )
1958 ­ 2001
Model chain used for reconstructions
Area: North Sea and Eastern North Atlantic
REMO Windspeed and Direction 21.02.1993 12 UTC
BAW ­ TELEMAC 2D
Water level and barotropic current 21.02.1993 12 UTC
Reconstruction of WAM sig. Waveheight and particular mesoscale direction 21.02.1993 12 UTC
features
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Resolution about 50 x 50 km
Resolution between about 100 m and 5km
Hourly archiving of the complete model output
Resolution about 5 x 5 km
Ralf Weisse, pers. com.
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Introduction Reconstruction of the atmosphere's state Quality of Wind speed and direction at K13
reconstructions
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Change of storm frequency Reconstruction of particular mesoscale features
Wind speed [m/s]
Wind direction [degrees]
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observations – black;
Hindcast - green
Weisse, R. and H. Günther, 2006
Weisse, R. and H. Günther, Wave climate and long­term changes for the Southern North Sea obtained from a high­resolution hindcast 1958­2002, Ocean Dynamics, 2006, submitted.
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Introduction Reconstruction of the atmosphere's state Example: high wind speed
Quality of Hipocas
Reconstruction of particular mesoscale features
SON
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xr90
xr
24.38
25.86
28.44
22.50
23.76
25.67
23.29
24.89
26.68
25.17
27.28
31.33
23.16
24.82
28.00
24.15
26.32
30.70
xr90
Waves [m ]
Hipocas
Observed
Observed
xr90
xr
xr90
25.96
24.05 25.21 26.37
28.70
25.75 27.64 29.53
34.22
28.09 32.77 37.45
23.82
23.16 24.03 24.90
25.88
24.33 25.94 27.55
30.33
26.43 29.75 33.07
25.01
23.11 24.03 24.95
27.75
24.15 25.94 27.73
34.72
26.42 29.75 33.08
Weisse, R. and H. Günther, 2006
2, 5, and 25­annual return values with a confidence interval of 90% based on 10.000 Monte Carlo simulations.
K13
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Change of storm frequency EUR
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Years
reconstructions
Wind [m /s]
2
5
25
2
5
25
2
5
25
xr90
xr
xr90
xr90
7.12
7.49
7.86
7.84
8.44
9.04
8.99 10.35 11.71
5.89
6.15
6.41
6.34
6.83
7.32
6.90
8.20
9.50
6.78
7.06
7.34
7.37
7.79
8.21
8.04
9.03 10.02
6.41
6.93
7.52
5.52
5.89
5.99
5.60
5.97
6.34
xr
6.77
7
7.54
8
9.21 10
5.84
6
6.46
7
7.88
9
5.84
6
6.46
6
7.88
9
Weisse, R. and H. Günther, Wave climate and long­term changes for the Southern North Sea obtained from a high­resolution hindcast 1958­2002, Ocean Dynamics, 2006, submitted.
Trends in storm activity
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Introduction Reconstructed trends of the annual total
number of storms from 1958-2002
Reconstruction of the atmosphere's state Quality of reconstructions
Change of storm frequency •
Reconstruction of particular mesoscale features
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Weisse et al. 2005
Weisse, R., H. von Storch, and F. Feser, Northeast Atlantic and North Sea storminess as simulated by a regional climate model 1958­2001 and comparison with observations, J. Climate, 18(3), 465­479, 2005.
Trends in storm activity
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Introduction Reconstructed trends of the annual total
number of storms from 1958-2002
Reconstruction of the atmosphere's state Stormindex based on geostrophic Wind
speed derived from measurements of air
pressure
Quality of reconstructions
Change of storm frequency •
Reconstruction of particular mesoscale features
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Weisse et al. 2005
Alexandersson et al. 2000
H. Alexandersson, H. Tuomenvirta, T. Schmidth, and K. Iden. Trends of storms in NW Europe derived from an updated pressure data set. Climate Res., 14:71­73, 2000
Weisse, R., H. von Storch, and F. Feser, Northeast Atlantic and North Sea storminess as simulated by a regional climate model 1958­2001 and comparison with observations, J. Climate, 18(3), 465­479, 2005.
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Introduction Possible piecewise linear trends
Reconstruction of the atmosphere's state Quality of reconstructions
Change of storm frequency •
Reconstruction of particular mesoscale features
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T
a1*xT + b1 = a2*xT + b2 at time T
Piecewise linear trends
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Introduction Reconstruction of the atmosphere's state Quality of reconstructions
Change of storm frequency •
Reconstruction of particular mesoscale features
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Weisse et al. 2005
Weisse et al. 2005
Weisse, R., H. von Storch, and F. Feser, Northeast Atlantic and North Sea storminess as simulated by a regional climate model 1958­2001 and comparison with observations, J. Climate, 18(3), 465­479, 2005.
Trends and variability in extratropical mesoscale •
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Introduction Reconstruction of the atmosphere's state Quality of reconstructions
Change of storm frequency Reconstruction of particular mesoscale features
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cyclones (VI EXTROP)
POLAR LOWS:
• intense maritime mesoscale cyclones • strong winds (>15m/s), severe weather, heavy precipitation • are also called Arctic Hurricanes
Simulation of a Polar Low Case, Oct. 1993
POLAR LOWS:
• intense maritime mesoscale cyclones • strong winds (>15m/s), severe weather, heavy precipitation • are also called Arctic Hurricanes
Simulation of a Polar Low Case, Oct. 1993
Simulation of a Polar Low Case, Oct. 1993
Berliner Wetterkarte, October 15th , 1993, 7:00 MEZ
• The number of storms per year in the NA •
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Introduction Reconstruction of the atmosphere's state Quality of reconstructions
Change of storm frequency •
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Reconstruction of particular mesoscale features
and in the NSea arose in the last 4 decades
• This rise attenuated or even turned into a decrease
• Possibly the NA storm track was displaced farther south
• CLM probably can reproduce mesoscale features like Polar Lows
Thank you