UPPER-OCEAN INERTIAL CURRENTS FORCED BY A STRONG STORM .1. DATA AND COMPARISONS WITH LINEAR-THEORY

A strong, isolated October storm generated 0.35-0.7 m s(-1) inertial f requency currents in the 40-m deep mixed layer of a 300 km x 300 km re gion of the northeast Pacific Ocean. The authors describe the evolutio n of these currents and the background how in which they evolve for ne arly a month following the storm. Instruments included CTD profilers, 36 surface drifters, an array of 7 moorings, and air-deployed velocity profilers. The authors then test whether the theory of linear interna l waves propagating in a homogeneous ocean can explain the observed ev olution of the inertial frequency currents. The subinertial frequency how is weak, with typical currents of 5 cm s(-1), and steady over the period of interest. The storm generates inertial frequency currents in and somewhat below the mixed layer with a horizontal saale much large r than the Rossby radius of deformation, reflecting the large-scale an d rapid translation speed of the storm. This scale is too large for si gnificant linear propagation of the inertial currents to occur. It ste adily decreases owing to the latitudinal variation in f, that is, beta , until after about 10 days it becomes sufficiently small for wave pro pagation to occur. Inertial energy then spreads downward from the mixe d layer, decreasing the mixed layer inertial energy and increasing the inertial energy below the mixed layer. A strong maximum in inertial e nergy is formed at 100 m (''the Beam''). By 21 days after the storm, b oth mixed layer inertial energy and inertial frequency shear maximum j ust below the mixed layer have been reduced to background levels. The total depth-average inertial energy decreases by about 40% during this period. Linear internal wave theory can only partially explain the ob served evolution of the inertial frequency currents. The decrease in h orizontal wavelength is accurately predicted as due to the beta effect The decrease in depth-average inertial energy is explained by southwa rd propagation of the lowest few modes. The superinertial frequency an d clockwise rotation of phase with depth are qualitatively consistent with linear theory. However, linear theory underpredicts the initial r ate at which inertial energy is lost from the mixed layer by 20%-50% a nd cannot explain the decrease of mixed layer energy and shear to back ground levels in 21 days.