FLOW DYNAMICS OF A WIDE ARCTIC CANYON

We extend and interpret acoustic Doppler current profiler and conducti vity-temperature-depth data collected in the summer of 1993 over Barro w Canyon in order to implement a high resolution (1.5 to 5 km) model o f the Beaufort and Chukchi Seas. This paper addresses physical process es relevant to the Barrow Canyon region using common dynamical analyse s of both field data and numerical results. The field data reveal the dominant physical processes that guide the design of our numerical exp eriments. The observed velocity field shows an intense and variable do wn canyon flow with transports ranging from 0.5 to 1.4 Sv. A momentum analysis reveals that the cross-canyon dynamic balance for the barotro pic component is primarily geostrophic. Conversely, the baroclinic cro ss-canyon momentum balance is ageostrophic and secondary flow results from a local imbalance between the vertically varying; Coriolis accele ration and the cross-canyon pressure gradient. In addition to the mode rate influence of stratification (Froude number of 0.4 and Burger numb er of 0.06), the barotropic pressure gradient component across the can yon (inferred from the large magnitude and little vertical variability of the residuals) is dynamically important for both upcanyon and down canyon flows that occur at different locations concurrently. The along -canyon dynamic balance is ageostrophic since the time derivative and the Coriolis term are of the same order of magnitude (temporal Rossby number is approximately 1). An analysis of the longitudinal density an d velocity fields from the model reveals that the main driving mechani sm for generating the observed upcanyon flow is the nonlinear interact ion of the variable barotropic flow with the steep topography. Stratif ication is maintained by the downcanyon advection of fresh and warm wa ter from the Bering and Chukchi Seas and the upcanyon advection of sal tier and colder water from the Arctic.