A Study of Oceanic Boundary-Layer Characteristics Including Inertial Oscillation at Three Drifting Stations In the Arctic Ocean

View More View Less
  • 1 U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, NH 03755
© Get Permissions Rent on DeepDyve
Restricted access

Abstract

Measurements of surface drift and near-surface currents taken during August 1975, at drifting ice stations of the AIDJEX experiment in the central Arctic, are used to infer the response of the upper ocean to the passage of two frontlike wind events. As an aid in interpretation, a multilevel, time-dependent, dynamical boundary-layer model commensurate with earlier investigations of PBL turbulence and ice drift versus surface wind statistics is developed and shown to reproduce the main features observed, including energetic inertial oscillation of the ice cover and mixed layer, relatively small currents at 30 m (∼5 m into the pycnocline), and little inertial-period shear between the ice and currents measured at 2 m. The model employs an eddy viscosity dependent on the surface friction velocity (u *) and the nondimensional depth (fz/u *) in the well-mixed layer, and on the product of the local stress and the local Obukhov length in the upper pycnocline. When the dominant horizontal length scale (related to the Coriolis parameter and the propagation speed of the atmospheric system) is of the order 750.km, the phase and amplitude of the inertial motions across the 190 km span of the station array are observed to be more coherent than predicted by the locally driven (i.e., horizontally homogeneous) model. It is suggested that a small pressure term due to Ekman convergence could account for the discrepancy.

Abstract

Measurements of surface drift and near-surface currents taken during August 1975, at drifting ice stations of the AIDJEX experiment in the central Arctic, are used to infer the response of the upper ocean to the passage of two frontlike wind events. As an aid in interpretation, a multilevel, time-dependent, dynamical boundary-layer model commensurate with earlier investigations of PBL turbulence and ice drift versus surface wind statistics is developed and shown to reproduce the main features observed, including energetic inertial oscillation of the ice cover and mixed layer, relatively small currents at 30 m (∼5 m into the pycnocline), and little inertial-period shear between the ice and currents measured at 2 m. The model employs an eddy viscosity dependent on the surface friction velocity (u *) and the nondimensional depth (fz/u *) in the well-mixed layer, and on the product of the local stress and the local Obukhov length in the upper pycnocline. When the dominant horizontal length scale (related to the Coriolis parameter and the propagation speed of the atmospheric system) is of the order 750.km, the phase and amplitude of the inertial motions across the 190 km span of the station array are observed to be more coherent than predicted by the locally driven (i.e., horizontally homogeneous) model. It is suggested that a small pressure term due to Ekman convergence could account for the discrepancy.

Save