Open AccessEffects of instability waves in the mixed layer of the equatorial Pacific
Author(s) -
Baturin N. G.,
Niiler P. P.
Publication year - 1997
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/97jc02455
Subject(s) - equator , zonal and meridional , climatology , drifter , latitude , kinetic energy , atmospheric sciences , atmosphere (unit) , environmental science , longitude , energetics , geology , physics , meteorology , geodesy , lagrangian , quantum mechanics , mathematical physics , thermodynamics
Data from more than 1900 Lagrangian drifters in the equatorial Pacific Ocean from 1980 to 1994 together with velocity records from two Tropical Ocean‐Global Atmosphere ‐ Tropical Atmosphere Ocean (TOGA‐TAO) equatorial moorings at 11° and 140°W, advanced very high resolution radiometer (AVHRR) sea surface temperature (SST) product, and European Centre for Medium‐Range Weather Forecasts (ECMWF) winds were used to investigate the effects and energetics of currents associated with the tropical instability waves (TIWs). Adaptive multitaper spectral 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° longitude by 20° latitude centered at 0°N, 110°W and 0°N, 140°W to construct meridional profiles of energetics of the TIW region. High TIW energy values typically occurred around October when the South Equatorial Current (SEC) and the North Equatorial Countercurrent (NECC) both became stronger and the eddy kinetic and potential energy production at 140°W was noticeably larger. At 110°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°N from 150° to 100°W, with the largest values occurring between 110° and 140°W in longitude and around 5°N in latitude. The largest terms in the horizontal kinetic energy production equation wereu ′ υ ′ ¯U ¯ y andυ ′ υ ′ ¯V ¯ y with maxima in the region of anticyclonic shear between SEC and NECC, from 2° to 6°N. The temperature variance, or the potential energy production, peaked closer to the equator at 3°N. The linear growth timescale of the instability was about 10 days. The time‐variable wind supplied energy to the current fluctuations during the TIW off period, but for the TIW on period the wind energy input was reduced (at 110W) or even reversed (at 140°W, between 1°S and 7°N), suggesting that air‐sea interaction was important in the total energy balance of the waves. The effect of instability was to reduce the shear of the mean current and to warm the equatorial cold tongue. These calculations suggest that there exists a balance between energy production and dissipation in the TIWs.