Large-Scale Control in Arctic Modelling – A suggestion for a Reconstruction of the Recent Past Hans von Storch Institute for Coastal Research GKSS Research Centre Geesthacht, Germany Open Science Meeting (OSM) for the Study of Environmental Arctic Change (SEARCH), Seattle, October 2003

Lars Bärring, pers. comm. Storm proxies, derived from local air pressure readings stormproxies

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, Ensemble standard deviation 500 hPa height [m²/s²]

Concept of Dynamical Downscaling RCM 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 variance 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 REMO Frauke Feser, pers. comm. 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. Peñas BMAHO NCEP 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. ESTAC ZSANT Marcos Garcia Sotillo (2003) NCEP vs. obs REMO vs. obs

Extreme wind speeds 20-year return values of wind speed, based on daily data (color codes) plus from station data in NL (numbers in black) Southern North Sea DWD REMO Feser, pers. comm.

Weisse, pers. comm. Ocean wave height reconstruction Solid: HIPOCAS RCM/NCEP reconstruction Dashed: WASA/DNMI SLP reconstruction Red: Local observations 50%, 90%, 95% and 99%iles.

Beate Müller, pers. comm. DWD analysis ) )

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 ( ) 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