Dynamics of the Bottom Boundary Layer on the Northern California Shelf,
Abstract
Time-series measurements of velocity, temperature and conductivity on the northern California shelf during two winter seasons permit an observational test, in vertically integrated form, of a simple set of subinertial momentum and heat balances for the bottom boundary layer, which have resulted from recent theoretical work. These are: (1) an along-isobath momentum equation that reduces to a classical Ekman balance; (2) a cross-isobath momentum equation in which the Ekman balance is modified by a buoyancy force caused by distortion of the isopycnal surfaces within the boundary layer; and (3) a heat balance in which variability of temperature is produced by cross-isobath advection. The measurements confirm the importance of buoyancy in the cross-isobath momentum equation, and, as has recently been predicted theoretically, they indicate that buoyancy is a dominant effect when the boundary layer is thick, which typically occurs during downwelling-favorable flows. An Ekman balance describes subinertial fluctuations in the along-isobath momentum equation with moderate success. The mean along-isobath momentum equation is significantly influenced by a buoyancy force caused by an along-isobath temperature gradient, and along-isobath advection is as important as cross-isobath advection in the heat balance. Thus along-isobath variability of temperature, which has been neglected in most theoretical work, is fundamental to the structure of the velocity field and the evolution of the temperature field.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 31, 1996
- Accession Number
- ADA326047
Entities
People
- J. H. Trowbridge
- S. J. Lentz
Organizations
- Woods Hole Oceanographic Institution