HR: 14:25h
AN: OS33D-04    [Abstracts]
TI: The dynamics and cross-frontal circulation at a tidal mixing front under well-mixed and stratified conditions
AU: * Lerczak, J A
EM: jlerczak@whoi.edu
AF: Woods Hole Oceanographic Institution, MS#21, Woods Hole, MA 02543 United States
AU: Beardsley, R C
EM: rbeardsley@whoi.edu
AF: Woods Hole Oceanographic Institution, MS#21, Woods Hole, MA 02543 United States
AU: Schlitz, R J
EM: rschlitz@whsun1.wh.whoi.edu
AF: Northeast Fisheries Science Center, NOAA/NMFS, Woods Hole, MA 02543 United States
AB: We use current, temperature, salinity and bottom pressure data from an array of moorings deployed on the southern flank of Georges Bank to estimate the cross-bank momentum budget and the tidal and sub-tidal circulation in the vicinity of the tidal mixing front (TMF) that is often present in that region. The array of eight moorings was deployed for a 160 day period during the spring and summer of 1999, spanning approximately 20 km in the cross-bank direction and centered on the 60 m isobath, the typical location of the TMF on the southern flank. The tight spacing between moorings (2 to 3 km), allowed us to determine the dominant balance in the sub-tidal, cross-front momentum equation and the detailed structure of the tidal and sub-tidal cross-front and along-front circulation during the spring, when the water column was well-mixed and the TMF was not present, and during the summer, when a strong thermal TMF was observed. Notably, we directly calculate the cross-frontal tidal stress terms associated with tidal rectification. During well-mixed conditions with weak winds, the cross-frontal tidal stress is uniform with depth and approximately balances the Coriolis term associated with the along-bank circulation. When a strong thermal tidal mixing front is present during weak winds, tidal stress, cross-front baroclinic pressure gradient and Coriolis are dominant terms in the cross-front momentum budget. The different dynamical balances between spring and summer conditions lead to differences in the cross-frontal and along-frontal circulation. During the spring, the along-bank, sub-tidal circulation is clockwise (to the southwest), uniform with depth, with an amplitude of about 8 cm/s. The cross-front circulation is mode-one in structure, with onbank flow near the bottom and offbank flow near the surface, and with an amplitude of about 2 cm/s. During the summer, a strong subsurface along-bank jet with an amplitude of 30 cm/s was observed at the TMF. The sub-tidal, cross-front circulation is stronger and more complicated than during the spring. At the location of the jet, the cross-front flow is on-bank in the middle of the water column, with an amplitude of 5 cm/s. The flow is offbank near the surface and bottom of the water column. We explore the implications of the variations in the cross-frontal circulation to the cross-frontal heat flux and the heat budget.
DE: 4219 Continental shelf processes
DE: 4528 Fronts and jets
DE: 4560 Surface waves and tides (1255)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting