HR: 10:35h
AN: OS12B-02    [Abstracts]
TI: Ageostrophic frontal secondary circulation with confluence and mixing
AU: * Tandon, A
EM: atandon@umassd.edu
AF: Physics Department (and SMAST), 285 Old Westport Road, North Dartmouth, MA 02747 United States
AU: Nagai, T
EM: tnagai@umassd.edu
AF: Physics Department (and SMAST), 285 Old Westport Road, North Dartmouth, MA 02747 United States
AB: Fronts are important sites for biological productivity and vertical exchanges of water masses in the upper ocean. The vertical velocity due to ageostrophic secondary circulation at fronts is a key factor for these processes. The ageostrophic flow near open ocean fronts has been previously diagnosed in observations using the quasi-geostrophic (QG) and balanced model Omega equations that assume inviscid adiabatic flow conditions. This study investigates two dimensional ageostrophic secondary circulation due to variable mixing and confluence ($\alpha$), using modified QG and SG equations. The two-dimensional modified SG equations used here differ from previous studies in that the confluence advected by along frontal ageostrophic flow is included. With these approaches, scalings for idealized fronts and the Azores front diagnostics are re-examined. The resulting ageostrophic frontal circulations indicate a strong dependency on the Burger number, $NH/fL$, where $H$ and $L$ are the vertical and horizontal scale of front, $N$ is the buoyancy frequency, and $f$ is the Coriolis parameter. The relative importance between deformation rate and vertical mixing can be parameterized by $\alpha H^2/A_v$, where $A_v$ is the vertical viscosity. The re-analyzed SeaSoar sections at Azores front with these equations indicate that vertical mixing intensifies the near surface secondary circulation.
DE: 4520 Eddies and mesoscale processes
DE: 4528 Fronts and jets
DE: 4568 Turbulence, diffusion, and mixing processes
DE: 4572 Upper ocean processes
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting