Dissipation effects in North Atlantic Ocean modeling

Numerical experiments varying lateral viscosity and diffusivity between 20 and 150 m 2 /s in a North Atlantic Ocean ( NAO ) model having 4th‐order accurate numerics, in which the dense deep current system ( DCS ) from the northern seas and Arctic Ocean is simulated directly show that Gulf Stream ( GS ) separation is strongly affected by the dissipation of the DCS. This is true even though the separation is highly inertial with large Reynolds number for GS separation flow scales. We show that realistic NAO modeling requires less than 150 m 2 /s viscosity and diffusivity in order to maintain the DCS material current with enough intensity to get realistic GS separation near Cape Hatteras ( CH ). This also demands accurate, low dissipation numerics, because of the long transit time (1–10 years) of DCS material from its northern seas and Arctic Ocean source regions to the Cape Hatteras region and the small lateral and vertical scales of DCS.