A world without Greenland: impacts on the Northern Hemisphere winter circulation in low- and high-resolution models
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To investigate the effect of Greenland’s orography on the northern hemisphere winter circulation experiments with an atmospheric GCM are conducted: a perturbed integration where standard orography is reduced to sea level in the Greenland area is compared to a standard orography control integration. The outcome of these experiments suggests that the existence of high mountains at Greenland causes a reinforcement of the stationary wave field in the Atlantic sector, colder temperatures to the west of Greenland and warmer temperatures to the east and south, over the North Atlantic. The impact on the flow field cannot be understood in the framework of standing Rossby waves, but it indicates a resonance between remotely forced stationary waves and local (thermo-) dynamics. The pattern of the North Atlantic Oscillation (NAO), in particular the northern centre, lies further to the east in the flat-Greenland experiment compared to the control run and the observations. Together with the fact that the climatological low-pressure system around Iceland hardly shifts, this suggests that the location of the NAO is not necessarily tied to the time mean pressure distributions. Considering the model resolution as a parameter, experiments with a high resolution (T106) suggest that the near-field changes are represented sufficiently by a T42 resolution, a standard resolution used in state-of-the-art coupled climate models. In contrast, far-field changes depend critically on model resolution. Hemispheric circulation and temperature changes differ substantially from low to high resolution, and generalized statements about the impact of Greenland’s orography cannot be made.
KeywordsGeopotential Height North Atlantic Oscillation North Atlantic Oscillation Index Teleconnection Pattern Geopotential Height Field
We are greatly indebted to the Model and Data group, Hamburg, for providing the reanalysis data (ECMWF/DWD/DKRZ: 1996). We would like to thank the two anonymous reviewers for their constructive suggestions and comments on the manuscript. They helped to improve the presentation of our results. We thank Rita Seiffert for providing the cyclone-track statistics. This work was funded by the Deutsche Forschungsgemeinschaft (DFG) within the Sonderforschungsbereich 512: Tiefdruckgebiete und Klimasystem des Nordatlantiks.
- Charney J, Eliassen A (1949) A numerical model for prediciting the perturbations of the middle latitude westerlies Tellus 1:38–54Google Scholar
- Christoph M, Ulbrich U, Oberhuber JM, Roeckner E (2000) The Role of Ocean Dynamics for Low-Frequency Fluctuations of the NAO in a Coupled Ocean-Atmosphere GCM. J Climate 13:2536–2549Google Scholar
- Dong B, Valdes PJ (2000) Climates at the Last Glacial Maximum: Influence of Model Horizontal Resolution. J Climate 13:1554–1573Google Scholar
- Held IM (1983) Stationary and quasi-stationary eddies in the extratropical troposphere. In: Hoskins BJ, Pearce DP (eds) Large-Scale dynamical processes in the atmosphere. Academic Press, London pp 127–168Google Scholar
- May W (2001) Impact of horizontal resolution on the simulation of seasonal climate in the Atlantic/European area for present and future times. Climate Research 16:203–223Google Scholar
- Roeckner E, Arpe K, Bengtsson L, Christoph M, Claussen M, Dümenil L, Esch M, Giorgetta M, Schlese U, Schulzweida U (1996) The atmospheric general circulation model ECHAM-4 Tech rep. Max-Planck-Institut für Meteorologie, HamburgGoogle Scholar
- Schwierz CB (2001) Interactions of Greenland-scale orography and extra-tropical synoptic-scale flow Tech rep. Swiss Federal Institute of Technology, Zurich, SwitzerlandGoogle Scholar
- Thompson DWJ, Wallace JM (2000) Annular modes in the extratropical circulation Part I: month-to-month variability. J Climate 13:1000–1016Google Scholar