Eddy Memory Mode of Multidecadal Variability in Residual-Mean Ocean Circulations with Application to the Beaufort Gyre

摘要: Mesoscale eddies shape the Beaufort Gyre response to Ekman pumping, but their transient dynamics are poorly understood. Climate models commonly use Gent–McWilliams (GM) parameterization, taking eddy streamfunction Ψ* be proportional an isopycnal slope s and diffusivity K. This local-in-time parameterization leads exponential equilibration of currents. Here, idealized, eddy-resolving model is used demonstrate that carries a finite memory past ocean states, violating key GM assumption. As consequence, equilibrating gyre follows spiral sink trajectory implying existence damped mode variability—the (EM) mode. The EM manifests during spinup as 15% overshoot in (2000 km3 freshwater content overshoot) cannot explained by parameterization. An improved developed, such effective s*, carrying γof slopes. Introducing explains results brings light oscillation with period 2π√T_Eγ ≈ 50 yr, where diffusion time scale T_E ~ 10 yr γ 6 diagnosed from model. increases Ekman-driven variance γ/T_E 50% ± 15%, fraction stays relatively constant despite both scales decreasing increased mean forcing. study suggests general property rotating turbulent flows highlights need for better observational constraints on field characteristics.