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Low-Frequency Variability of Polar Atmosphere due to Blocking Formations: A Numerical Experiment of Blocking,

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Arctic climate in winter depends on occurrence of large-scale atmospheric blocking and amplification of planetary waves. Understanding the development of blocking formations is an important research subject in polar regions as well as in middle latitudes for time scales of a month to a season. In this study, we carried out nonlinear numerical simulations of amplification of low-frequency planetary waves and the concurrent development of blocking. The simulations were conducted using a barotropic spectral model derived from three-dimensional spectral primitive equations with a basis of vertical structure functions and Hough harmonics. The model is truncated to include only barotropic Rossby components of the atmosphere with simple physics including biharmonic diffusion, topographic forcing, baroclinic instability, and zonal surface stress. We find that these four physical processes are sufficient to produce a realistic and persistent dipole blocking with a sharp transition from zonal to meridional flows on a sphere. The simulations confirmed an amplification of the meridional dipole mode due to the up-scale energy cascade from synoptic disturbances under an environment of persistent wavenumber 2. The energy supply from synoptic disturbances contributes to the sharp transition from zonal to meridional flows.

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This article is from 'Proceedings of the International Conference on the Role of the Polar Regions in Global Change Held in Fairbanks, Alaska on 11-15 June 1990. Volume 1', AD-A253 027, p170-175.



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