FY 1982

Eddies detached from a jet crossing over a submarine ridge using a simple numerical model

Ikeda, M.

NOAA Tech. Memo. ERL PMEL-33, NTIS: PB82-217563, 38 pp (1981)

An eastward-flowing jet crossing over a submarine ridge is studied using a two-layer quasi-geostrophic model. The jet initially has small-amplitude meanders of one wavelength to the west of the ridge, and the lower layer is quiescent only at t = 0. The meanders grow propagating eastward, and the lower layer begins to move and feel bottom topography. Then, the ridge influences meanders and eddies that are detached from large-amplitude meanders. Detached, cyclonic eddies are strengthened south of the jet on the western slope of the ridge, as are anticyclonic eddies north of the jet on the eastern slope, because of vorticity generated by the topographic effects on the westward flows associated with two recirculating gyres which form on the north and south of the jet. Consistent with topographic Rossby wave theory, some of these eddies approach and coalesce with the jet. As a result the jet splits into two branches surrounding the cyclonic eddy. The two recirculating gyres are divided by the ridge and have shorter zonal length than do those in the no-ridge case. These specific flow patterns are observed in the Gulf Stream in the vicinity of the New England Seamount Chain and the Kuroshio over the Shatsky Rise.