THE STRUCTURE OF NEAR-INERTIAL WAVES DURING OCEAN STORMS

Current meter data from two sites were analyzed for near-inertial moti ons generated by storms during the ten-month period of the Ocean Storm s Experiment in the northeast Pacific Ocean. The most striking feature of the inertial wave response to storms was the almost instantaneous generation of waves in the mixed layer, followed by a gradual propagat ion into the thermocline that often lasted many days after the initiat ion of the storm. The propagation of near-inertial waves generated by three storms in October, January, and March was studied by using group propagation theory based on the WKB approximation. It was found that wave frequencies were slightly superinertial, with inertial shifts 1%- 3% in October and March and around 1% in January. The phase of near-in ertial currents propagated upward below the mixed layer, confirming th e downward radiation of energy by these waves. The average downward en ergy flux during the storm periods was between 0.5 and 2.8 mW m(-2). T he vertical wavelengths indicated by the vertical phase differences ra nged from 150 to 1500 m. The vertical group velocity was estimated fro m the arrival times of the groups at successive depths. Using this in the dispersion relation, horizontal wavelengths ranging from 140 to 41 0 lan were obtained. A relation between density and velocity that give s the horizontal directionality of internal waves was derived During t he storm periods examined, the propagation directions of near-inertial waves mainly lay between northeast and south, indicating sources west of moorings. The directions tended to rotate clockwise with increasin g depth, consistent with the expected effect of the earth's curvature. The estimated horizontal wavelength and propagation direction were co nsistent with the horizontal phase difference between inertial current s at the two sites.