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Statistical analysis of high-resolution drifter data collected just beyond the surf-zone in the Santa Barbara Channel
J. C. Ohlmann
University of California, Santa Barbara
cohlmann@ucsd.edu(Abstract received 04/29/2005 for session A)
ABSTRACT
New drifter technology utilizing GPS and terrestrial cellular communications allows inexpensive collection of high-resolution trajectories in the near-shore region to address questions related to small-scale advection and dispersion. A total of 21 deployments of a fleet of up to 15 GPS-cellular drifters over the inner shelf of the Santa Barbara Channel during 2003 yielded near 300 tracks comprised of position measurements, accurate to ~5 m, recorded every 10 minutes. Tracks are mostly a few hours in length. The combined resolution in time and space, along with drifter density, make for a unique data set enabling examination of the flow field on extremely small scales. The drifters generally move up coast and on-shore, in opposition to the prevailing wind direction, suggesting that pressure or Coriolis forces play a significant role in the local momentum balance despite the very nearshore region. Velocity variance is the same order as mean values indicating the importance of high frequency fluctuations in both time and space. Eddy kinetic computed on a typical HF radar scale (hourly in a 2 by 2 km box) reaches nearly 30 cm2 s-2. Lagrangian time and space scales are near 40 min and 100 m, respectively. Mean square pair separations grow exponentially in time from the smallest resolved scale (~10 m) to ~100 m with an e-folding time of near 60 min. Subsequently, dispersion grows exponentially with an e-folding time near 280 min up to scales of 1 km. Along-shore dispersion is slightly greater than cross-shore growth. The underlying dynamics are presently being investigated.
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2005 LAPCOD Meeting, Lerici, Italy, June 13-17, 2005