Scaling turbulent dissipation in an Arctic fjord

In September 2003, microstructure and fine-scale shear (vertical derivative of horizontal current) and strain (vertical derivative of isopycnal displacements) profiles were collected in Storfjorden, Svalbard Archipelago. Storfjorden is a sill-fjord of significant dense water production and the period of observations corresponds to weak overflow conditions of the dense water. The data set comprises fine-scale measurements combined with simultaneous dissipation and buoyancy frequency profiles and allows for evaluation of various turbulence scalings and internal wave-wave interaction models. Microstructure profiles identified high levels of background vertical diffusivity, K-p, O(10(-4))m(2)s(-1), which increased by one order within the overflow. Fine-scale shear and strain spectral levels were found to be elevated above those of Garrett-Munk, consistent with the observed enhanced mixing, whereas their average ratio was comparable to that of Garrett-Munk. Among the internal wave-wave interaction models, a shear-strain model agreed with the observations (between the surface and bottom mixed layers) within a factor of 2, on the average. A scaling of the dissipation, epsilon, in the form of total-energy x N suggests that approximately 0.5% of the energy is dissipated per buoyancy period, 2 pi/N. The best-fit power-law scaling between diffusivity and N is K-p proportional to N-1.4 ((+/- 0-2)). For this environment, a parameterization of the form of Pacanowski-Philander is suggested with background levels of eddy viscosity and diffusivity elevated by an order of magnitude. (c) 2006 Elsevier Ltd. All rights reserved.