The Inner-Shelf Dynamics Experiment

17 USC 105 interim-entered record; under review.The article of record as published may be found at http://dx.doi.org/10.1175/BAMS-D-19-0281.1The inner shelf, the transition zone between the surfzone and the midshelf, is a dynamically complex region with the evolution of circulation and stratification driven by multiple physical processes. Cross-shelf exchange through the inner shelf has important implications for coastal water quality, ecological connectivity, and lateral movement of sediment and heat. The Inner-Shelf Dynamics Experiment (ISDE) was an intensive, coordinated, multi-institution field experiment from September–October 2017, conducted from the midshelf, through the inner shelf, and into the surfzone near Point Sal, California. Satellite, airborne, shore- and ship-based remote sensing, in-water moorings and ship-based sampling, and numerical ocean circulation models forced by winds, waves, and tides were used to investigate the dynamics governing the circulation and transport in the inner shelf and the role of coastline variability on regional circulation dynamics. Here, the following physical processes are highlighted: internal wave dynamics from the midshelf to the inner shelf; flow separation and eddy shedding off Point Sal; offshore ejection of surfzone waters from rip currents; and wind-driven subtidal circulation dynamics. The extensive dataset from ISDE allows for unprecedented investigations into the role of physical processes in creating spatial heterogeneity, and nonlinear interactions between various inner-shelf physical processes. Overall, the highly spatially and temporally resolved oceanographic measurements and numerical simulations of ISDE provide a central framework for studies exploring this complex and fascinating region of the ocean.U.S. Office of Naval Research (ONR)ONR Departmental Research Initiative (DRI)Inner-Shelf Dynamics Experiment (ISDE

Relating Lagrangian and Eulerian horizontal eddy statistics in the surfzone

The article of record as published may be located at http://dx.doi.org/10.1002/2013JC009415Concurrent Lagrangian and Eulerian observations of rotational, low-frequency (1024 to 1022 Hz) surfzone eddies are compared. Surface drifters were tracked for a few hours on each of 11 days at two alongshore uniform beaches. A cross-shore array of near-bottom current meters extended from near the shoreline to seaward of the surfzone (typically 100 m wide in these moderate wave conditions). Lagrangian and Eulerian mean alongshore velocities V are similar, with a midsurfzone maximum. Cross-shore dependent Lagrangian (rL) and Eulerian (rE) rotational eddy velocities, estimated from low-pass filtered drifter and current meter velocities, respectively, also generally agree. Cross-shore rotational velocities have a midsurfzone maximum whereas alongshore rotational velocities are distributed more broadly. Daily estimates of the Lagrangian time scale, the time for drifter velocities to decorrelate, vary between 40 and 300 s, with alongshore time scales greater than cross-shore time scales. The ratio of Lagrangian to apparent Eulerian current meter decorrelation times TL/TA varies considerably, between about 0.5 and 3. Consistent with theory, some of the TL/TA variation is ascribable to alongshore advection and TL/TA is proportional to V/r, which ranges between about 0.6 and 2.5. Estimates of TL/TA vary between days with similar V/r suggesting that surfzone Lagrangian particle dynamics vary between days, spanning the range from ‘‘fixed-float’’ to ‘‘frozen-field’’ [Lumpkin et al., 2002], although conclusions are limited by the statistical sampling errors in both TL/TA and V/r.This analysis was supported by NSF, ONR, and CA Sea Grant. The HB06 field work was supported by CA Coastal Conservancy, NOAA, NSF, ONR, and CA Sea Grant. R. T. Guza was a co-PI on the HB06 experiment. Staff and students from the Integrative Oceanography Division (B. Woodward, B. Boyd, K. Smith, D. Darnell, I. Nagy, D. Clark, M. Omand, M. Yates, M. McKenna, M. Rippy, and S. Henderson) and the Naval Postgraduate School (J. Brown and B. Swick) were instrumental in acquiring the field observations. The comments from three reviewers improved this manuscript and are greatly appreciated