Temporal Variation and Spatial Structure of the Kuroshio-Induced Submesoscale Island Vortices Observed from GCOM-C and Himawari-8 Data

Abstract

Dynamics of ocean current-induced island wake has been an important issue in global oceanography. Green Island, a small island located off southeast of Taiwan on the Kuroshio path was selected as the study area to more understand the spatial structure and temporal variation of well-organized vortices formed by the interaction between the Kuroshio and the island. Sea surface temperature (SST) and chlorophyll-a (Chl-a) concentration data derived from the Himawari-8 satellite and the second generation global imager (SGLI) of global change observation mission (GCOM-C) were used in this study. The spatial SST and Chl-a variations in designed observation lines and the cooling zone transitions on the left and right sides of the vortices were investigated using 250 m spatial resolution GCOM-C data. The Massachusetts Institute of Technology general circulation model (MITgcm) simulation confirmed that the positive and negative vortices were sequentially detached from each other in a few hours. In addition, totals of 101 vortexes from July 2015 to December 2019 were calculated from the 1-h temporal resolution Himawari-8 imagery. The average vortex propagation speed was 0.95 m/s. Totals of 38 cases of two continuous vortices suggested that the average vortex shedding period is 14.8 h with 1.15 m/s of the average incoming surface current speed of Green Island, and the results agreed to the ideal Strouhal-Reynolds number fitting curve relation. Combined with the satellite observation and numerical model simulation, this study demonstrates the structure of the wake area could change quickly, and the water may mix in different vorticity states for each observation station.

Solution of Shallow-Water Equations by a Layer-Integrated Hydrostatic Least-Squares Finite-Element Method

“…Shipboard ADCP-CTD profiling was conducted to investigate the surface patterns, vertical structures, the evolution of the Green Island vortices [22,23]. The ERS-1 SAR images and Moderateresolution Imaging Spectroradiometer (MODIS) satellite images [24][25][26][27], and numerical modelling [28][29][30][31][32] have also been used to study Kuroshio-induced island vortex of Orchid Island and Green Island. Figure 5a shows a composite ERS-1 SAR image of the Kuroshioinduced vortex of Orchid Island and Green Island, taken in one-week intervals, sequentially,…”

“…Kuroshio passes Orchid Island and Green Island off the southeastern coast of Taiwan. Kuroshio-induced Green Island vortices have previously been studied with in-situ measurements [22,23], such as ERS-1 SAR images, moderate-resolution imaging spectroradiometer (MODIS) satellite images [24][25][26][27], and numerical modelling [28][29][30][31][32].…”

Retrieval of Daily Mean VIIRS SST Products in China Seas

“…With the development of remote sensing technology, satellite-retrieved SST products are widely used with wide coverage and strong real-time performance. In addition, they are mainly utilized in the studies of water mass properties [6], ocean circulation [7], tropical cyclone [8], weather prediction [9] and ocean numerical simulation [10,11]. In these research areas, the quality of satellite SST products has becoming a prerequisite influencing the scientific findings.…”

Preface: Earth Observations for Environmental Sustainability for the Next Decade

“…Achieving the SDGs by turning knowledge into action is the critical challenge for scientists and other subject matter experts throughout the world. This monograph, Earth Observations for Environmental Sustainability for the Next Decade, gathers original viewpoints and knowledge advances in the use of Earth observations to address a number of urgent issues of great concern for humanity, including land use/land cover (LULC) classification [1], debris-flow assessment [2,3], precipitation estimates [4], drought assessment [5], hyperspectral image classification [6], Kuroshio-induced wakes [7], sea water primary production [8], weather system (tropical cyclone) interaction [9], and habitat suitability and biodiversity conservation [10]. In this editorial, a brief overview of the collected papers is presented.…”

“…An improved understanding of ocean current-induced island waves is needed in the study of oceanic environments. Using high-temporal-resolution imagery from the Himawari-8 satellite, the study in [7] presented the temporal variation and spatial structure of the Kuroshio-induced Green Island wakes. Green Island is a small island located near southeast Taiwan that is on the main path of the Kuroshio.…”