Transcript Institut für Küstenforschung

Activities at GKSS related
to D&A problems
Hans von Storch
Institute for Coastal Research
GKSS Research Centre
Geesthacht, Germany
INTERESTED IN WIND OVER SEA
Overview
• Millennial forced runs "Erik the Red" and
"Christof Columbus"
• 1958-2000 regional
downscaling/reconstruction
• Changes storminess / WASA
• Ocean waves and detection for (erosion
relevant) wave energy change.
Forced Simulation
1550-2000 simulation
Changing solar forcing and
time variable volcanic aerosol load;
greenhouse gases
Atmosphere: ECHAM4
horizontal resolution T30 ~ 300 km at mid latitudes
Ocean: HOPE-G
horizontal resolution T42 ~ 200 km at mid latitudes
increased resolution in the tropics
Model provided as community climate by
Model & Data Group at MPI for Meteorology
and run at German Climate Computing Centre (DKRZ)
and computing facilities at FZ Jülich
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Climate model used
IfK
Control 1990 equilibrium
Erik the Red
Christoph Columbus
More actual data via internet
Information provided by
Fidel González-Rouco and
Simon Tett
ECHO-G
HadCM3
differences relative to the
1550-1800 average and are a
25-year running average.
forced
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control
IfK
1958-2000 regional
downscaling/reconstruction
• Spectral nudging
• Dutch coast extremes (maps)
• K13 extremes wind & waves (return
values)
State space equation
Ψ t 1  F(Ψ t ;ηt )  εt
Observatio n equation
d t  G(Ψ t )  δt
Known large scale
statewit h
 t ,  t  model and observatio n errors
F  dynamical model
projection of full state on
G  observatio n model
large-scale scale
Ψ t*1  F(Ψ t ;ηt )
Forward integratio n :
d t*1  G (t*1 )
 Ψ t 1  Ψ t*1  K(d t*1  d t 1 )
with a suitable operator K .
Large-scale
(spectral) nudging
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Concept of Dynamical Downscaling
RCM
Physiographic
3-d vector of state
detail
IfK
Skill in representing marine winds
[days]
wave direction
[days]
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significant wave height
Red: buoy, yellow: radar, blue: wave model run with REMO winds
IfK
Southern
North Sea
Feser, pers. comm.
Extreme wind speeds
DWD
REMO
20-year return values of wind speed,
based on daily 1992-97 data (color codes)
plus from station data in NL (numbers in black)
Skill in representing marine winds
Extreme value analysis of significant wave height at
platform K13 (southern North Sea)
2
2
5
10
25 years
5
10
25 years
[m]
simulated
January 1980-January 1997
IfK
Weisse, pers. comm.
observed
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[m]
Changing storminess / WASA
• Geostrophic wind + pressure
tendencies
• Ekofisk
• SMHI scenario
Trends in storminess
intra-annual 99% quantiles
of geostrophic wind,
averaged over many
triangles.
North Sea
Baltic Sea
Alexandersson, SMHI, 2003
Bärring, 2003
Weisse, pers. comm.
99%
99%
95%
95%
90%
90%
50%
50%
Wind speed
Significant wave height
red: local observations
solid: RCM reconstruction (downscaling NCEP) + WAM
dashed: WASA estimate + WAM
Scenario for changed wind conditions in the
wider North Sea area, end of 21st century
(A2)
Mean wind speed
Storm wind speeds
m/sec
Rossby Center, Norrköping, Sweden
Anthropogenic climate change shown by local
wave conditions in the North Sea
(Arnt Pfizenmayer, Hans von Storch)
ABSTRACT: In the central North Sea we have observed an increase in the
frequency of eastwardly propagating waves in the last 4 decades. To assess
the significance of this change, wave statistics for the 20th century were
reconstructed with a statistical model. With a linear multivariate technique
(redundancy analysis), monthly mean air pressure fields over the North
Atlantic and Western Europe were downscaled on the intramonthly
frequency of directional wave propagation. When compared against this
reference, the recent change appears statistically significant at the 5%
level. In order to investigate the reason for this local climatic change, the
reconstruction was compared with the downscaled results of control and
transient GCM scenarios (ECHAM4-OPYC3) and with the results obtained in
a high-resolution time-slice experiment with increased concentrations of
greenhouse gases and aerosols. Both estimates are qualitatively consistent
with the changes observed in the last 4 decades. We suggest that the
recent increase in eastward propagation is a local manifestation of
anthropogenic global climate change.
Pfizenmayer and von Storch, 2002
Comparison of the 30 yr running mean of the monthly frequency of eastwardly
propagating waves (3 h time steps, anomalies). The reconstruction of the 20th
century (black line), the transient T42 run (dotted line), the T42 control run
(grey line) and the time-slice experiment T106 (star) are shown. Dashed lines
are the estimated 5, 95 and 99% confidence intervals.
Pfizenmayer, 2002