Oceanic Eddy Characteristics and Generation Mechanisms in the Kuroshio Extension Region

20 pages, 19 figures, 1 appendixThe Kuroshio Extension region is well known for its strong eddy activity. In this paper, using satellite altimetry-measured sea surface height anomaly data from 1993 to 2012 in an extended Kuroshio Extension region (140–180°E, 25–45°N), we analyze eddy characteristics: eddy size, polarity, lifetime, intensity, trajectory, and spatial and temporal distributions. Using temperature and salinity vertical profiles measured by Argo floats, we examine the eddy impact on vertical stratification. During the 20-year period, 7,574 eddies are identified (based on following complete eddy trajectories) with a lifetime equal to or longer than 4 weeks. The numbers of cyclonic and anticyclonic eddies are found to be approximately the same. The distribution of eddy sizes peaks at a radius of about 40 km. The radius at the peak is at the same order as the first baroclinic deformation radius or the horizontal shear scale of the Kuroshio flow. The normalized eddy statistical characteristics show that eddies have different characteristics at different stages of their lifetimes. Among eddies with lifetimes longer than 50 weeks, more anticyclonic (cyclonic) eddies are found north (south) of 35°N. In contrast, among eddies with lifetimes shorter than 20 weeks, more cyclonic (anticyclonic) eddies are found north (south) of 35°N. The asymmetric distribution of eddies suggests two different eddy generation mechanisms: (1) the development of meanders in the Kuroshio path leading to the pinch off of eddies with longer lifetime (larger size) and (2) horizontal shear instability (barotropic instability) leading to eddies of shorter life (smaller size). We further apply an eddy-resolved numerical product to quantitatively investigate the eddy generation mechanismsThis research work was supported by National Key Research Program of China (2017YFA0604100, 2016YFC1401407, and 2016YFA0601803), NSFC (41476022, 41490643, 41621064 and 91528304), Jiangsu Province Science Foundation for Youths (BK20150897), Startup Foundation for Introducing Talent of Nanjing University of Information Science and Technology (2013r121, 2014r072), Program for Innovation Research and Entrepreneurship Teams in Jiangsu Province, the National Basic Research Program (2013CB430302), the National Natural Science Foundation of China (41321004, 91528304, and 41606022,the National ScienceFoundation of China for Outstanding Young Scientist under Grant 41622604,the Excellent Youth Science Foundation of Jiangsu Province under Grant BK2016090,), the National Program on Global Change and Air‐Sea Interaction (GASI‐ IPOVAI‐02, GASI‐ IPOVAI‐04 and GASI‐ IPOVAI‐05) National 973 Program of China (2014CB745000),Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYLX16_0925), China Ocean Mineral Resources Research and Development Association program (DY135‐E2‐3‐01), and the Natural Science Foundation of Jiangsu Province (BK20150897)Peer Reviewe