Abstract
The temporal and spatial variation in submesoscale eddies in the coastal region of Lianyungang (China) is studied over a period of nearly two years with high-resolution (0.03°, about 3 km) observations of surface currents derived from high-frequency coastal radars (HFRs). The centers and boundaries of submesoscale eddies are identified based on a vector geometry (VG) method. A color index (CI) representing MODIS ocean color patterns with a resolution of 500 m is used to compute CI gradient parameters, from which submesoscale features are extracted using a modified eddy-extraction approach. The results show that surface currents derived from HFRs and the CI-derived gradient parameters have the ability to capture submesoscale processes (SPs). The typical radius of an eddy in this region is 2–4 km. Although no significant difference in eddy properties is observed between the HFR-derived current fields and CI-derived gradient parameters, the CI-derived gradient parameters show more detailed eddy structures due to a higher resolution. In general, the HFR-derived current fields capture the eddy form, evolution and dissipation. Meanwhile, the CI-derived gradient parameters show more SPs and fill a gap left by the HFR-derived currents. This study shows that the HFR and CI products have the ability to detect SPs in the ocean and contribute to SP analyses.
Highlights
Submesoscale processes (SPs) are frequently observed as eddies, filaments and fronts, where the approximate scale ranges are 0.1–10 km in the horizontal, 0.01–1 km in the vertical, and between hours and days in time over open oceans [1]
Submesoscale eddies were obtained from the high-frequency coastal radars (HFRs) velocity fields, with a total of 1102 cyclonic eddies and 886 anticyclonic eddies identified, based on the vector geometry (VG) eddy detection method
Submesoscale eddies were obtained from the HFR velocity fields, with a total of 1102 cyclonic Remedotde Sieesnsa. n20d208,8162,a7n1t1icyclonic eddies identified, based on the VG eddy detection method
Summary
Submesoscale processes (SPs) are frequently observed as eddies, filaments and fronts, where the approximate scale ranges are 0.1–10 km in the horizontal, 0.01–1 km in the vertical, and between hours and days in time over open oceans [1]. Submesoscale buoyancy flux in SPs enhances seasonal restratification and the mixing of the mixed layer [4]. The generation mechanisms of SPs may be summarized as: strain-induced frontogenesis, baroclinic instabilities in the mixed layer, turbulent thermal winds and topographic wakes [1,6,7]. Idealized numerical models under relevant theoretical frameworks may efficiently be employed in studies of SPs, which require high-resolution data of less than one hour in time and O(1) km in space [8,9]
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