The diurnal cycle of high-frequency temperature variability at 0*, 140*W on seasonal and interannual time scales
Brainard, Russell E.
Garwood, Roland W.
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The diurnal cycle of high-frequency temperature fluctuations attributable to turbulence and internal waves in the upper central equatorial Pacific Ocean is found to persist over most of the period November 1983 - October 1987. Moored temperature and velocity data in the upper 300 m at 0 deg, 140 deg W during this four-year period were used to: (1) determine the vertical extent of the diurnal cycle of turbulence and internal waves and evaluate its contribution to the equatorial zonal momentum balance, and (2) determine whether the diurnal cycle of turbulence and internal waves varied seasonally and interannually in response to varying surface forcing and ambient stability conditions. Using 15-minute spot-sampled temperature data at 35 m. 60 m, 100 m, 140 m. 200 m, and 300 m, isotherm displacement variance (IDV) was computed for each six-hour time period as a proxy for vertical overturning and displacement associated with turbulence and internal waves. The time series of monthly mean IDV for each of the six-hour time bins showed the magnitude of the diurnal cycle of turbulence and internal waves (Delta(IDV)) as a function of season and depth. The diurnal change in IDV was pronounced at both the 35-m and the 60-m depths, with nighttime IDV significantly greater than daytime IDV. This result is consistent with TROPIC HEAT microstructure observations over two periods of a few days to weeks. showing that IDV is a useful proxy for turbulence and internal wave energy during periods when microstructure measurements are not available. Equatorial ocean dynamics, Turbulence, Internal waves, Diurnal cycle of upper ocean process, Seasonal and interannual variability of upper ocean.
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