A numerical investigation of the barotropic instability on the equatorial β-plane

Original Article

DOI: 10.1007/s00162-012-0260-3

Cite this article as:
Kacimi, A. & Khouider, B. Theor. Comput. Fluid Dyn. (2013) 27: 491. doi:10.1007/s00162-012-0260-3


The barotropic instability of horizontal shear flows is investigated by using two numerical algorithms to solve the equatorial β-plane barotropic equations. The first is the Arakawa Jacobian method (Arakawa, in J Comput Phys 1:119–143, 1966), which is a second-order-centered finite differences scheme that conserves energy and enstrophy, and the second is the fourth-order essentially non-oscillatory scheme for non-linear PDE’s of Osher and Shu (SIAM J Numer Anal 28:907–922, 1991), which is designed to track sharp fronts. We are interested in the performance of these two methods in tracking the long-time behavior of the instability, under the influence of the non-linearity, in the simple case of a Helmholtz shear layer. The associated linear problem is solved analytically, and the linear solution is used as an initial condition for the numerical simulations. We run a series of numerical simulations using both methods with various grid refinements and with two different amplitudes of the initial perturbation. A small viscosity term is added to the vorticity equation to damp the grid-scale waves for Arakawa’s method. This is not necessary for the high-order ENO-4 scheme, which has its own grid-scale dissipation. At high resolution, the two methods are in good agreement; they yield qualitatively and quantitatively the same solution in the long run: for small disturbances, the total flow stabilizes into a steady-state meridional shear with a smooth profile near the equator, while strong disturbances merge together to form a single large-scale vortex that propagates westward, along the equator, consistent with the African easterly waves and the monsoons trough circulation. At coarse resolution, however, Arakawa’s method seems to be much superior to the fourth-order ENO-4 scheme as it provides solutions that are more consistent with the fine resolution one.


Arakawa Jacobian Essentially non-oscillatory schemes Equatorial Rossby waves Atmospheric circulation Barotropic instability Vorticity Shear flow Stream function 


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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  1. 1.Laboratory AMNEDP, Department of MathematicsUniversity of Sciences and Technology Houari BoumedienneBab Ezzouar, AlgiersAlgeria
  2. 2.Department of Mathematics and StatisticsUniversity of VictoriaVictoriaCanada

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