Einfluss von Zyklonen auf das Meereis in der zentralen Arktis: Modellstudien und Beobachtungen (Impact of cyclones on sea ice in the central Arctic: model studies and observations)

• Main Author: Kriegsmann, A.
• Format: Doctoral or Postdoctoral Thesis
• Language: German
• Published: Universität Hamburg 2011
• Subjects: Arctic Ocean; Arktis; Arktis*; Atlantic Arctic; Atlantic-Arctic; North Atlantic; Sea ice
• Online Access: http://hdl.handle.net/11858/00-001M-0000-0024-61AA-3; http://hdl.handle.net/11858/00-001M-0000-0024-61AC-0

Arctic sea-ice is a barrier between ocean and atmosphere and as such, plays an important role in the climate system. In winter, a closed ice cover reduces the sensible and latent heat fluxes between ocean and atmosphere to a great extent. In summer, the sea ice reflects the most part of the incoming shortwave radiation. Strong winds, as they occure in cyclones, lead to sea-ice drift and influence the fraction of ocean surface which is covered by sea ice. This study investigates the impact of cyclones on sea ice, with a focus an the sea-ice concentration in the central Arctic. The impact of cyclones is analyzed on the basis of observations of the field campaigns DAMOCLES 2007 and DAMOCLES 2008, on the basis of satellite measurements (AMSR-E ice concentrations) and furthermore on the basis of simulations with a coupled sea-ice-ocean model. For the simulations the dynamic-thermodynamic model NAOSIM (North Atlantic Arctic Ocean Sea Ice Model) is forced with 6-hourly ECMWF-analyses (European Centre for Medium- Range Weather Forecasts). The comparison of simulated ice drift and concentration with observations made clear that the choosen model configuration is appropriate for the performed studies. Sensitivity studies were performed with a wind field that represents a cyclone passing through the Arctic. The experiments show, that the ice concentration is reduced in general under the influence of a cyclone. The reduction is the stronger, (1) the slower the cyclone, (2) the higher the pressure difference between core and surrounding, (3) the smaller the deviation angle between 10 m-wind and geostrophic wind, and (4) the higher the initial ice concentration is. Between reduction of ice concentration and initial ice thickness no correlation has been found. The comparison of simulated ice drift with data of drift buoys reveals, that the model overestimates the drift speed in general whereas extreme events like storms are unterestimated. A systematic deviation in simulated and observed drift direction is found. Furthermore ...