Observations of near-inertial current variability on the New England shelf

[1] Observations from the Coastal Mixing and Optics (CMO) moored array (deployed from August 1996 through June 1997) and supplemental moored observations are used to describe near-inertial current variability over the New England shelf. Near-inertial band current variance comprises 10–20% of the total observed current variance, and has episodic peak speeds exceeding 30 cm s . Near-inertial current variability during CMO is characterized by a first baroclinic mode vertical structure with one zero-crossing between 15 and 50 m. The zero-crossing is shallower during periods of stronger stratification. Laterally, near-inertial variability is coherent over the extent of the CMO moored array, and cross-shelf decorrelation scales for near-inertial currents are about 100 km, approximately the entire shelf width. The magnitude of near-surface near-inertial variability is stronger in the summer and weaker in the winter, following the seasonal variation in stratification and opposite the seasonal cycle in wind stress variance. During CMO, near-surface near-inertial kinetic energy is inversely related to surface mixed layer depth. Near-inertial variance decreases onshore, matching approximately the cross-shelf decrease in near-inertial energy predicted by a two-dimensional, linear, flat-bottom, twolayer, coastal wall model. In this model, the nullifying effects of a baroclinic wave emanating from the coastal wall play a dominant role in controlling the onshore decrease. Finally, strong persistent anticyclonic relative vorticity shifts near-inertial variability on the New England shelf to subinertial frequencies.