The circulation and internal tide of Indian Arm, B.C

Bradley De Young
The wintertime deepwater exchange in a silled fjord is described. Bottom-water renewal took place in the third year of the study, 1984/85. Hydraulic control of the exchange was consistent with the observations. This control is exerted over the long sill, which restricts access to the fjord. The maximum density at the sill was observed during neap tides. No distinct peaks in the velocity at the sill were observed during the inflows. During each inflow, associated with a neap tide, about 20% of
more » ... e water in the fjord was replaced. These exchanges occurred over periods of 5 — 10 days. An internal tide was observed in Indian Arm in all three winters studied. In the winter of 1983/84, this internal tide was observed to change from a predominantly M₂ internal response to a predominantly K₁. This change in the response is explained as a partial resonance response of the system. During the 1983/84 winter, the resonance period steadily increased from 14 hours at the start, to 22 hours at the end. It is suggested that the enhanced internal response at the K₁ frequency, late in the winter, is due to resonance. Fitting of normal modes was done to look at the energy flux in Indian Arm. About 20 — 30% of the energy flux is found to propagate from the head of the inlet, supporting the resonance hypothesis, which requires energy to be reflected from the head. The energy sinks for the barotropic tide are investigated using a variety of data. From an analysis of the tidal data, it is estimated that a total of 10 — 15 % of the barotropic tidal energy which enters Burrard Inlet is dissipated. About 0.7 MW is lost from the barotropic tide in the vicinity of the Indian Arm sill. About 0.3 MW was found in internal waves propagating away from the sill. Of this flux about 60 % was in the internal tide, with 40 % in high frequency internal waves. The vertical diffusion coefficient (K[sub v]) is determined from an analysis of the density data. K[sub v] is found to be related to the buoyancy frequency N by the relationship, K[sub v] ∝ N[s [...]
doi:10.14288/1.0053318 fatcat:goe2xebaprdmvbhqnkctbmdv5y