Large-Scale Control in Arctic Modelling –

A suggestion for aReconstruction of the Recent

Past Hans von Storch

Institute for Coastal ResearchGKSS Research CentreGeesthacht, Germany

Open Science Meeting (OSM) for the Study of Environmental Arctic Change (SEARCH), Seattle, 25-31. October 2003

Lars Bärring, pers. comm.

Storm proxies, derived from local air pressure readings

stormproxies 1820-2001

Regional atmospheric modelling: nesting into a global state

Dynamical downscaling of known large-scale state given by, e.g., NCEP re-analyses.

Concept: Regional space-time details form as a response to large scale conditioning and response to regional physiographic detail. This formation is described by RCMs.

The Rinke & Dethloff study on regional modelling of the Arctic atmosphere

Rinke, A., and K. Dethloff, 2000: On the sensitivity of a regional Arctic climate model to initial and boundary conditions. Clim. Res. 14, 101-113.

Ensemble standard deviation 500 hPa height [m²/s²]

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Concept of Dynamical DownscalingRCM Physiographic detail

3-d vector of state

Known large scale state

projection of full state on large-scale scale

Large-scale (spectral) nudging

Well resolved

Insufficiently resolved

Spatial scales

vari

ance

regional model

Added value

We use …

• REMO, 0.5 deg

• Europe

• NCEP forcing with spectral nudging – wave numbers k = 1-3, applied to wind components above 850 hPa

Mean monthly

precipitation [mm/month]

for 1999.

REMO

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NCEP

Marcos Garcia Sotilla, 2003

Assimilated into NCEP(Atlantic)

Not assimilated into NCEP (Ionic Sea)

Wind speed at two bouys

Buoy data

Temperature at two locations:

PEÑAS buoy: Atlantic buoy located at 43.73N, 6.16W (North coast of Iberian Peninsula).

BMAHO buoy: Mediterranean buoy located at 39.72N,4.44E (In front of island of Menorca).

Not assimilated by NCEP

Comparison of local data with NCEP and REMO/downscaled.

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BM

AH

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NCEP vs. obsNCEP vs. obs

REMO vs. obs REMO vs. obs

Marcos Garcia Sotillo (2003)

Buoy data

Wind speed at two locations:

ZSANT buoy located at 36.26N,25.50W (close to the greek island of Santorini)

ESTAC buoy located at 44.06N,7.62W (North coast of Iberian Peninsula).

Not assimilated by NCEP

Comparison of local data with NCEP and REMO/downscaled.

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ZS

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TMarcos Garcia Sotillo (2003)

NCEP vs. obs NCEP vs. obs

REMO vs. obs REMO vs. obs

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

DWD REMO

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Ocean wave height

reconstruction Solid: HIPOCAS RCM/NCEP reconstruction

Dashed: WASA/DNMI SLP reconstruction

Red: Local observations

50%, 90%, 95% and 99%iles.

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DWD analysis

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1958-2002 assessment• Regional atmospheric modeling, combined

with appropriate nesting into a large scale regime, allows for a reasonable, space-time detailed reconstruction of marine weather stream of the past 40, or so, years.

• This reconstruction may be used to study the dynamics of weather-sensitive environmental aspects, such as ocean waves.

• This success has been demonstrated for the “through-flow” area of Europe, for which the lateral boundaries play a stronger role than in the more isolated area of the Artic.

Suggestion

• Same approach for the Artic• Using NCEP or ERA large scale states• Prescribed lower boundary conditions

(in particular sea ice parameters properties)

• Validate with local data and with ice cores and other proxies

• Use as forcing in sea ice, ocean, and ice shelf studies (proxy generation)

30 year mean estimated wave energy impinging on the west coast of Jutland, derived from

• WASA wave reconstruction (1955-93) and statistical extrapolation backward until 1900, and

• empirical downscaling from 200 year control global climate simulation („T42 control“) and,

• empirical downscaling from 150 year climate change global simulation („T42 transient“)

Pfizenmayer, 2002

Spectral nudging vs. standard formulation

Spectral nudging vs. standard formulation