Barotropic instability of zonally varying flow forced by multimode topography

摘要: Abstract The linear stability characteristics of zonally varying basic flow forced by multimode topography are investigated with a quasigeostrophic, barotropic model on an infinite β-plane. Ekman pumping is the sole dissipative process. chosen to vary from one five zonal modes, amplitudes be representative those at middle latitudes in Northern Hemisphere. analysis reveals two distinct types most unstable disturbances: (1) nearly stationary instability (NSI) that associated flows near topographic resonance, parameter setting where single mode dominates state; (2) low frequency (LFI) occurs for dominated least waves similar amplitude. NSI characterized relatively large (small) growth rates which (in)sensitive small changes flow. importance resolution and disturbance-topography interaction system also examined. It shown solely responsible generating regions space states stable. disturbance important planetary vorticity advection approximately matches relative vorticity. Arbitrarily excluding eliminates LFI results overestimate range NSI. weakly non-linear equilibration briefly discussed.