Abstract
Using high-resolution satellite-derived sea surface temperature (SST) data from September 1981 to December 2015, the present study develops a new index to detect the long-term variation in mesoscale eddy activity over the Kuroshio Extension (KE) region. This eddy activity index (EAI) highlights the strength of eddy-induced poleward heat transport and has obvious advantages over the other existing KE indices in depicting the low-frequency changes in KE eddy activity. An analysis of the EAI shows that over the long term, the KE eddy activity variability presents a significant spectral peak of about 8 years and is not directly modulated by wind-driven oceanic Rossby waves generated in the central North Pacific. When the EAI is positive, the strengthened KE eddy activity significantly enhances the heat release from ocean to atmosphere over the Kuroshio–Oyashio confluence region (KOCR). This induces an anomalous dipole pattern of near-surface baroclinicity over this region that can persist for up to 6 months, favoring a weakened and northward-moving East Asian jet, and vice versa. It is believed that the new EAI will facilitate future studies focusing on the climatic effects of the KE eddy activity variation.
Highlights
Mesoscale oceanic eddies are ubiquitous in the global ocean and account for a large portion of the ocean’s energy [1,2]
The sea surface temperature (SST) data were obtained from the monthly National Oceanic and Atmospheric Administration (NOAA) optimum interpolation SST (OISST) data product [20] for the period from September 1981 to December 2015, which is based on Advanced Very High-Resolution Radiometer (AVHRR) infrared satellite data and has a high spatial resolution of 0.25◦
We found that the eddy activity index (EAI) is related to significant easterly-wind anomalies that lead to a weakened East Asian jet but with a more northern position compared with those associated with the BDI
Summary
Mesoscale oceanic eddies are ubiquitous in the global ocean and account for a large portion of the ocean’s energy [1,2]. The three black boxes denote the regions used to represents the mean KE jet axis, which is defined as the 110-cm SSH contour. (c) Time series of the EAI (blue line) and denote the regions used to define the new eddy activity index (EAI) (see text for details). Some studies have reported that anomalous KE eddy activity alters the poleward heat transport, satellite-derived SSH data. Some studies have reported that anomalous KE eddy activity alters the poleward heat (KOCR; 34◦ –42◦ N, 141◦ –150◦ E) [18,19] Inspired by these works, we have constructed the new transport, leading to a change in sea surface temperature (SST) over the Kuroshio–Oyashio index of KE eddy activity from its related SST anomalies using high-resolution satellite-derived SST confluence region
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