Intraseasonal variability in a barotropic model with seasonal forcing

Abstract

Steady-state solutions of the model include multiple unstable equilibria that sustain oscillatory instabilities with periods of 10-15 days, 35-50 days, and 150-180 days, for a realistic forcing pattern. Time-dependent solutions exhibit chaotic behavior with episodic oscillations, featuring both the intraseasonal (35-50 day) and biweekly (10-15 day) modes. The former is dominated by standing spatial patterns, the latter by traveling wave patterns. The phases of the intraseasonal oscillation are robust for all cases, exhibiting a clear oscillatory exchange of atmospheric angular momentum with the solid earth via mountain torque. It is demonstrated, through linear stability analysis on the sphere, that the intraseasonal oscillations are induced by topographic instabilities. -from Authors