EFFECTS OF INSTABILITY WAVES IN THE MIXED-LAYER OF THE EQUATORIAL PACIFIC

Data from more than 1990 Lagrangian drifters in the equatorial Pacific Ocean from 1980 to 1994 together with velocity records from two Tropi cal Ocean-Global Atmosphere - Tropical Atmosphere Ocean (TOGA-TAO) equ atorial moorings at 110 degrees and 140 degrees W, advanced very high resolution radiometer (AVHRR) sea surface temperature (SST) product, a nd European Centre for Medium-Range Weather Forecasts (ECMWF) winds we re used to investigate the effects and energetics of currents associat ed with the tropical instability waves (TIWs). Adaptive multitaper spe ctral analysis was used to estimate how spectral energy varied in the 15-to-30-day period TIW band. The drifter data was analyzed separately for high and low values of the TIW energy in regions of 20 degrees lo ngitude by 20 degrees latitude centered at 0 degrees N, 110 degrees W and 0 degrees N, 140 degrees W to construct meridional profiles of ene rgetics of the TIW region. High TIW energy values typically occurred a round October when the South Equatorial Current (SEC) and the North Eq uatorial Countercurrent (NECC) both became stronger and the eddy kinet ic and potential energy production at 140 degrees W was noticeably lar ger. At 110 degrees W the eddy kinetic and potential energy production existed all the time without large differences between the periods of high and low TIW activity. The meridional kinetic energy was enhanced in the region between the equator and 10 degrees N from 150 degrees t o 100 degrees W, with the largest values occurring between 110 degrees and 140 degrees W in longitude and around 5 degrees N in latitude. Th e largest terms in the horizontal kinetic energy production equation w ere <(u'v'U)over bar>(y) and <(v'v'V)over bar>(y) With maxima in the r egion of anticyclonic shear between SEC and NECC, from 2 degrees to 6 degrees N. The temperature variance, or the potential energy productio n, peaked closer to the equator at 3 degrees N. The linear growth time scale of the instability was about 10 days. The time-variable wind sup plied energy to the current fluctuations during the TIW off period, bu t for the TIW on period the wind energy input was reduced (at 110 degr ees W) or even reversed (at 140 degrees W, between 1 degrees S and 7 d egrees N), suggesting that air-sea interaction was important in the to tal energy balance of the waves. The effect of instability was to redu ce the shear of the mean current and to warm the equatorial cold tongu e. These calculations suggest that there exists a balance between ener gy production and dissipation in the TIWs.