This talk presents various aspects of coastal surface circulation based on multi-year observations of high-frequency radar-derived surface currents off the U.S. West coast. The dynamics of the surface currents are governed by tides, winds, Coriolis force, low-frequency pressure gradients (less than 0.4 cycles per day (cpd)), and nonlinear interactions of those forces. Alongshore surface currents show poleward propagating signals with phase speeds of O(10) and O(100 to 300) km day−1 and time scales of 2 to 3 weeks. The signals with slow phase speed are only observed in southern California. It is hypothesized that they are scattered and reflected by shoreline curvature and bathymetry change and do not penetrate north of Point Conception. The seasonal transition of alongshore surface circulation forced by upwelling‐favorable winds and their relaxation is captured in fine detail. Submesoscale eddies, identified using flow geometry, have Rossby numbers of 0.1 to 3, diameters in the range of 10 to 60 km, and persistence for 2 to 12 days. The HFR surface currents resolve coastal surface ocean variability continuously across scales from submesoscale to mesoscale (O(1) km to O(1000) km). Their spectra decay with k−2 at high wave number (less than 100 km) in agreement with theoretical submesoscale spectra below the observational limits of present‐day satellite altimeters. In addition, the diagnostic characterizations of recent submesoscale observations of surface currents and chlorophyll concentrations are discussed.
Sung Yong Kim is an Assistant Professor in the Department of Mechanical Engineering at Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Republic of Korea and the director of the Environmental Fluid Mechanics Laboratory at KAIST. He received B.S. degree in Naval Architecture and Ocean Engineering from Seoul National University, Seoul, Republic of Korea, in 1999 and Ph.D. degree in Applied Ocean Science from Scripps Institution of Oceanography/University of California -- San Diego, La Jolla, USA, in 2009. His present research interests are in the areas of coastal circulation, sub-mesoscale processes, statistical and dynamical data analysis, environmental parameterization, and operational coastal ocean observing system. He has served as a member of Technical Committee (MONITOR) in the North Pacific Marine Science Organization (PICES) since 2014. He is elected as a member of the Young Korean Academy of Science and Technology in 2017. He is the recipient of the Young Frontier Research Scientists Award in the Korean Academy of Science and Technology in 2013, the Young Scientist Award in the Korean Society of Oceanography in 2014, and the Young Scientist Award to brighten Korea for next 30 years (selected as one of 30 persons in Natural Sciences, particularly, Oceanography) in the Pohang University of Science and Technology in 2016.