Eddy Diffusion in the Antarctic Intermediate Water

In this paper the use of an eddy diffusivity tensor in the conservation of salt equation is investigated from two points of view. First it is found that the order of tensor assumed specifies the amount of information that can be obtained about the eddy flux. Secondly a method is developed for calculating each component of the eddy diffusivity tensor and/or its derivative from a record of the mean salinity and velocity fields. This method in essence treats the components of the diffusivity tensor as coefficients in a regression equation. This procedure allows confidence limits to be established for the tensor. In order to apply these results to observations from the ocean an objective analysis scheme was developed. This scheme provided a means for estimating the salinity and geostrophic current fields along sigma t surfaces of the Antarctic Intermediate Water. The picture of the Intermediate Water obtained from this analysis is discussed and compared with the classic Meteor reports. Using this objective procedure five different methods for calculating diffusivity were employed to determine the components of the diffusivity tensor. These methods included simple one dimensional diffusion, a balance of horizontal and vertical diffusion in the absence of a mean current, the general methods developed in this research which allowed for both horizontal and vertical mixing, and a finite difference scheme. The magnitude of the coefficients obtained by each one of the different methods were comparable with each other and with those of previous investigators. However, in general the confidence limits on the estimates of the components of the diffusivity tensor were of the same order of magnitude as the estimates themselves. Significant improvement in the confidence limits was obtained by analyzing a much smaller region. An error analysis was made for the entire computational procedure. This analysis indicated that a combination of errors and/or terms neglected in the diffusion equation could account for the large uncertainties in the calculations.