Cross-Shore Thermally Driven Exchange Flows: Dynamic
Regimes and Variability
University of California at San Diego
La Jolla, CA
Observations of the velocity structure at the Kilo Nalu Observatory on the south shore of Oahu, Hawaii show that thermally driven baroclinic exchange is a dominant mechanism for cross-shore transport for this tropical forereef environment. Although cross-shore wind stress influences the diurnal cross-shore exchange, surface heat flux is identified as the primary forcing mechanism from the phase relationships and from analysis of momentum and buoyancy balances for the record-averaged diurnal structure. Dynamic flow regimes are characterized based on a two-dimensional theoretical framework and the observations of the thermal structure at Kilo Nalu are shown to be in the unsteady temperature regime. Diurnal phasing and the cross-shore momentum balance suggest that turbulent stress divergence is dominant. While the thermally driven exchange has a robust diurnal profile in the long term, there is high temporal variability on shorter time scales. Some of this variability can be accounted for by influence of strong along-shore flow that is forced at semidiurnal frequencies. The along-shore flow affects the cross-shore exchange through its influence on turbulent diffusivity and via Coriolis driven cross-shore accelerations. A theoretical model is developed to examine the role of multi-frequency forcing. The solution uses a linear perturbation to the baseline pressure-stress divergence balance introducing a time-dependent eddy viscosity and Coriolis accelerations associated with a semidiurnal along-shore flow.
Wednesday, January 18, 2017
Seaver Science Library, Room 150 (SSL 150)
Refreshments will be served at 3:15 pm.