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$BH/I=Matti Lepparanta (Professor, Division of Geophysics, University of Helsinki)
$BBj!!L\!'(BSea Ice Dynamics: Recent Results on Spectra and Scaling

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Sea Ice Dynamics: Recent Results on Spectra and Scaling (Matti Lepparanta) $BH/I=MW;](B :

  
 A brief introduction is given first into the dynamics of sea ice, 
 consisting the description of mechanical state of drift ice, rheology, 
 and the conservation laws of ice and momentum. Recent results are then 
 presented on two themes: scaling of sea ice dynamics and the variance 
 spectra of ice velocity. The momentum equation is analysed for scaling 
 and key non- dimensional quantities. So-called free drift is governed 
 by the roughness ratio of the upper and lower ice surfaces, while for 
 drift in the presence of internal friction the ratio ice strength to 
 external forcing provides a length scale, which classifies the 
 dynamics in different basins. The use of ice tanks to study mechanical 
 properties of drift ice floe fields is discussed with examples shown 
 of uniaxial compression tests. The frequency spectra of sea ice is 
 analysed based on analytical sea ice - ocean boundary layer (OBL) 
 modelling. The principal time scales are the response times of ice and 
 OBL, Coriolis period, and adjustment time of the ice volume. The full 
 two-body problem needs to be solved: an ice-only model gives too weak 
 inertial signal while a locked ice-ocean model puts the general 
 variance level too much down for the ice. The dominant property of 
 internal dynamics is to conserve energy in the feeded frequency since 
 the ice stress is at on/off state for converging/diverging motion but 
 the general sub- linear nature sea ice rheology has an additional 
 tendency to transfer kinetic energy toward lower frequencies. 
  
   

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mail-to:momoko@ees.hokudai.ac.jp / Tel: 011-706-2359