Activities at GKSS related to D&A problems

Hans von StorchInstitute for Coastal Research

GKSS Research CentreGeesthacht, 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.

1550-2000 simulation

Changing solar forcing and time variable volcanic aerosol load; greenhouse gases

Forced Simulation

Climate model usedAtmosphere: ECHAM4

horizontal resolution T30 ~ 300 km at mid latitudesOcean: HOPE-G

horizontal resolution T42 ~ 200 km at mid latitudesincreased resolution in the tropics

Model provided as community climate by Model & Data Group at MPI for Meteorologyand run at German Climate Computing Centre (DKRZ)and computing facilities at FZ Jülich

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More actual data via internet

Control 1990 equilibrium

Erik the Red

Christoph Columbus

Information provided byFidel González-Rouco andSimon Tett

HadCM3

ECHO-G

differences relative to the 1550-1800 average and are a 25-year running average.

control

forced

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1958-2000 regional downscaling/reconstructi

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• Spectral nudging• Dutch coast extremes (maps)• K13 extremes wind & waves

(return values)

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Concept of Dynamical DownscalingRCM Physiographic detail3-d vector of state

Known large scale state

projection of full state on large-scale scale

Large-scale (spectral) nudging

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Skill in representing marine winds

Red: buoy, yellow: radar, blue: wave model run with REMO winds

wave direction

significant wave height

[days]

[days]

Extreme wind speeds

20-year return values of wind speed, based on daily 1992-97 data (color codes)plus from station data in NL (numbers in black)

Southern North Sea

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Extreme value analysis of significant wave height at platform K13 (southern North Sea)

January 1980-January 1997

simulated

observed

Skill in representing marine winds

2 5 10 25 years

2 5 10 25 years

[m]

[m]

Changing storminess / WASA

• Geostrophic wind + pressure tendencies

• Ekofisk• SMHI scenario

Trends in storminess

Alexandersson, SMHI, 2003

intra-annual 99% quantiles of geostrophic wind, averaged over many triangles.

North Sea

Baltic Sea

Bärring, 2003

red: local observationssolid: RCM reconstruction (downscaling NCEP) + WAMdashed: WASA estimate + WAM

Weisse, pers. comm.

99%

95%90%50%

99%

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Wind speed

Significant wave height

Scenario for changed wind conditions in the wider North Sea area, end of 21st century (A2)

Rossby Center, Norrköping, Sweden

Mean wind speed Storm wind speeds m/sec

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.

Anthropogenic climate change shown by localwave conditions in the North Sea(Arnt Pfizenmayer, Hans von Storch)

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 and von Storch, 2002

Pfizenmayer, 2002