HR: 11:20h
AN: OS32B-05    [Abstracts]
TI: Non-Linear Internal Tides Move Cool sub-Surface Waters From the mid-Shelf to the Beach
AU: * Noble, M
EM: mnoble@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AU: Jones, B
AF: University of Southern California, HIMS, Los Angeles, CA 90089 United States
AU: Xu, J
AF: U.S. Geological Survey, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AU: Rosenfeld, L
AF: Naval Postgraduate School, 833 Dyer Rd, Monterey, CA 93943 United States
AU: Hamilton, P
AF: SAIC, 615 Oberlin Rd, Raleigh, NC 27605 United States
AU: Robertsib, G
AF: Orange County Sanitation District, 10844 ellis Ave, Fountain Valley, CA 92708 United States
AU: Largier, J
AF: Scripps Institution of Oceanography, Sverdrup Hall, La Jolla, CA 92093 United States
AB: In the summer of 2001, a dense array of moorings measured currents, salinity and temperature over the entire water column for 4 months across the southern San Pedro shelf in southern California. An associated hydrographic program periodically monitored synoptic temperature and salinity distributions over the entire shelf. The measurement program was designed in part to determine the characteristics of the semidiurnal internal tide in the region. Initial results show that although the semidiurnal barotropic tidal currents were oriented alongshelf, the baroclinic, or internal, tidal currents were oriented cross-shelf. Approximately 6 times during the summer, the energy in the internal tides over the outer shelf was much larger than normal for the region. The energetic internal tides usually consisted of a series of amplified tidal pulses that lasted for a few days to more than a week. On average, the cross-shelf excursions associated with the energetic internal tides moved water and suspended material less than 2 km across the 7 km wide shelf. However, during three of the energetic internal tidal events, measurements from the moored array and hydrographic program showed that cool, subthermocline water from the mid-shelf was carried 2-3 km into the nearshore region. Subsequent mixing/shoaling processes transported these cool nearshore waters into the surfzone and onto the beach. Surf zone temperature measurements showed cool waters in the surfzone for the several days that the energetic internal tidal pulses were present in the nearshore. While near-bottom water from the shelf break was carried toward shore, this did not reach the nearshore. Subtidal currents over the shelf were always strongly downcoast when cool waters were observed at the beach. When the subtidal currents were not downcoast during a multiday energetic event, the internal tide pulses did not deliver cool water to the nearshore. Presumably, the uptilted thermocline associated with the downcoast subtidal flows is necessary to allow this process to exist.
DE: 4219 Continental shelf processes
DE: 4512 Currents
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting