Abstract
One of the significant challenges in physical oceanography is getting an adequate space/time description of the ocean surface currents. One possible solution is the maximum cross-correlation (MCC) method that we apply to hourly ocean color images from the Geostationary Ocean Color Imager (GOCI) over five years. Since GOCI provided a large number of image pairs, we introduce a new MCC search strategy to improve the computational efficiency of the MCC method saving 95% of the processing time. We also use an MCC current merging method to increase the total spatial coverage of the currents, proving a 25% increase. Five-year mean and seasonal time-average flows are computed to capture the major currents in the area of interest. The mean flows investigate the Kuroshio path, support the triple-branch pattern of the Tsushima Warm Current (TC), and reveal the origin of the TC. The evolution of a warm core ring shed by the Kuroshio near the northeast coast of Honshu, Japan, is clearly depicted by a sequence of three monthly MCC composites. We capture the evolution of the Kuroshio meander over seasonal, monthly, and weekly time scales. Three successive weekly MCC composite maps demonstrate how a large anticyclonic eddy, to the south of the Kuroshio meander, influences its formation and evolution in time and space. The unique ability to view short space/time scale changes in these strong current systems is a major benefit of the application of the MCC method to the high spatial resolution and rapid refresh GOCI data.
Highlights
Ocean currents represent a complex mixture of different types of aperiodic and periodic variability, ranging over wide ranges of horizontal size, velocities and time
Since Geostationary Ocean Color Imager (GOCI) provided a large number of maximum cross-correlation (MCC) image pairs to process we introduce a new MCC search strategy to improve the computational efficiency of the MCC method saving 95.9% of the processing time
The Taiwan Warm Current (TWC) flows northward along the Taiwan coast with a current speed of 7-50 cm s&' and it splits into two parts around 26.5°N, one flows northward into the East China Sea and one flows northeastward merging with the Kuroshio Current (KC)
Summary
Ocean currents represent a complex mixture of different types of aperiodic and periodic variability, ranging over wide ranges of horizontal size, velocities and time. These variations play significant roles in the global ocean circulation, and exert strong influence on ocean– atmosphere interactions [Semtner, 1995]. Shore-based High Frequency (HF) radars [Barrick et al, 1977; Georges et al, 1996] are deployed near the coast to provide high temporal and spatial resolution real-time surface currents with a range of up to ~180 km off the coast from the backscatter of the radar signals. Space-based satellite altimetry measures sea surface height from which mesoscale geostrophic currents can be calculated, with the limitation that altimetry does not work well in shallow waters or near coastlines [Roesler et al, 2013]
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