Global mapping of diapycnal diffusivity in the deep ocean based on fine-scale vertical shear observed by expendable current profilers
Abstract
skip=0pt % hspace*{1em} We examine the distribution of diapycnal diffusivity in the thermocline over a large area in the North Pacific and the North Atlantic obtained by incorporating the fine-scale vertical shear of horizontal velocity measured by expendable current profilers (XCP) into the empirical formula proposed by Gregg [1989]. hspace*{1em} One of the remarkable findings from the XCP survey is that diapycnal diffusivity strongly depends on the latitude. For example, the estimated diapycnal diffusivities over the Hawaiian Ridge and the Izu-Ogasawara Ridge (at latitudes lower than 30^oN) exceed 10-4m^2s-1, whereas those over the Aleutian Ridge, the Emperor Seamounts and the Mid-Atlantic Ridge (at latitudes higher than 30^oN) are of the order of 0.1×10-4m^2s-1, even though the available semidiurnal internal tidal energy is similar among all of these prominent topographic features. The latitudinal dependence of the diapycnal diffusivity obtained from these estimates is consistent with the numerical prediction by Hibiya et al. [1996, 1998, 2002] that the cascade of semidiurnal internal tidal energy down to dissipation scales is dominated by the resonant interaction, parametric subharmonic instability which is expected to occur only below 30^oN. hspace*{1em} To examine whether or not this observed result reflects a universal feature, the XCP survey has recently been extended to the Southern Hemisphere, namely, the South Pacific and the South Indian Ocean. The spatial distribution of the estimated diapycnal diffusivity is discussed with emphasis on the latitudinal dependence.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....8675H