Low-frequency oscillations on the outer shelf in the southern Mid-Atlantic Bight

Current meter data collected during the SEEP-II spring experiment off the coasts of Delaware, Maryland and Virginia were analyzed to examine the low-frequency phase propagation on the outer shelf and upper slope. In the low frequency band (periods between 24 and 12 days), there was a distinct offshore phase propagation in the data. The amplitude was nearly constant on the shelf and decreased offshore on the slope. In the vertical direction, there was an upward phase propagation on the shelf. These oscillations were probably topographic waves generated near the shelf-slope front. In the synoptic band (periods between 8 and 4.8 days), oscillation amplitudes were higher on the slope than on the shelf; the phase was nearly constant across the shelf and slope. The coherent motions were probably associated with the oscillations of the shelf-slope front. In the wind band with periods shorter than 4 days, the amplitude decreased rapidly offshore, similar to coastally trapped waves. Offshore veering of curents in the bottom boundary layer was observed at the 400 and 1000 m isobaths and was probably related to low-frequency oscillations at mid-depths.