STRUCTURE OF VELOCITY AND TEMPERATURE IN THE NORTHEAST PACIFIC AS MEASURED WITH LAGRANGIAN DRIFTERS IN FALL 1987

In October 1987, 49 Lagrangian surface drifters (TRISTAR-11) were rele ased in a 200-km x 200-km square area southeast of Ocean Station Papa as part of the OCEAN STORMS Experiment. The drifters measured temperat ure at the drogue level and reported their position through ARGOS appr oximately 11 times per day. Thirty-one of the drifters retained drogue s for longer than three months, and data from those instruments are us ed to describe the evolving fall 1987 pattern of current and temperatu re structures at 15 m in the area between 46-degrees and 49-degrees-N, 142-degrees-W and 132-degrees-W. Time variable currents were dominate d by mesoscale eddies of anticyclonic rotation with horizontal radii o f 53-86 km and rotational speeds of 10-20 cm s-1. These eddies persist ed for at least 90 days as evidenced by successive drifter trajectorie s through the eddies. Currents with periods longer than 1 day had a me an to the east of 4.4 cm s-1 and a mean to the north of 0.7 cm s-1. Ba ckground eddy kinetic energy levels were 40 cm2 s-2. Thus, eddy kineti c energy was four times larger than mean kinetic energy. The eastward single particle diffusivity was 1100 m2 s-1 and northward diffusivity was 1600 m2 s-1. The local change of thermal energy at 15-m depth was -2.9 W m-3, while on average, flow advected cold water to the east at a rate of 0.8 W m-3. Therefore, large-scale advective processes accoun ted for 28% of the thermal energy balance at 15 m. This horizontal hea t convergence in the open ocean is comparable in magnitude to that pro duced by powerful equatorial currents in the eastern Pacific cold tong ue.