Mesoscale Eddy-Induced Ocean Dynamic and Thermodynamic Anomalies in the North Pacific

Abstract

Oceanic mesoscale eddies are associated with large thermodynamic anomalies, yet so far they are most commonly studied in terms of surface temperature and in the sense of composite mean. Here we employ an objective eddy identification and tracking algorithm together with a novel matching and filling procedure to more thoroughly examine eddy-induced thermodynamic anomalies in the North Pacific, their relationship with eddy amplitude (SSH), and the percentage of variability they explain on various timescales from submonthly to interannual. The thermodynamic anomalies are investigated in terms of sea surface temperature (SST), isothermal layer depth (ITD), and upper ocean heat content (HCT). Most eddies are weak in amplitude and are associated with small thermodynamic anomalies. In the sense of composite mean, anticyclonic eddies are generally warm eddies with deeper isothermal layer and larger heat content, and the reverse is true for cyclonic eddies. A small fraction of eddies, most probably subsurface eddies, exhibits the opposite polarities. Linear relationships with eddy amplitude are found for each of the thermodynamic parameters but with different level of scatter and seasonality. HCT-amplitude relation scatters the least and has the smallest seasonal difference, ITD-amplitude relation has the largest scatter and seasonality, while SST-amplitude relation is in between. For the Kuroshio and Oyashio Extension region, the most eddy-rich region in the North Pacific, eddies are responsible for over 50% of the total SSH variability up to the intra-seasonal scale, and ITD and HCT variability up to interannual. Eddy-induced SST variability is the highest along the Oyashio Extension Front on the order of 40–60% on submonthly scales. These results highlight the role of mesoscale eddies in ocean thermodynamic variability and in air-sea interaction.

Decadal‐Scale Influence of the Kuroshio and Oyashio Extension Fronts on Atmospheric Circulation and Storm Track

“…Both the KEF and OEF exhibit synchronized decadal variability of position and strength, that is, they both strengthen while shifting northward. For the KEF, the stronger and northerly (weaker and southerly) stage is known as the stable (unstable) state because it is associated with damped (enhanced) eddy activity (e.g., Qiu et al., 2014; Zhou, Zhou, et al., 2021). SST changes associated with the KEF index is shown in Figure 2a, which reveals that the strengthening/northward excursion of the KEF is comprised of both cooling to the north of the front west of 150°E and heating to the south.…”

“…Qiu and Chen (2005) pointed out that the position of the KE could be fittingly defined by the 170-cm SSH contour in the northwestern North Pacific. Since their SSH data is referenced to 70 cm below the reference geoid of AVISO, here we follow Zhou, Li, and Cheng (2021) and use the latitude of the 100-cm ADT contour averaged between 142 and 156°E to define the KE and KEF position. The strength of the KE/KEF is correspondingly measured by the latitudinal width between the 90-cm and 110-cm contours averaged within the same longitudinal range.…”

Impact of greenhouse warming on mesoscale eddy characteristics in high-resolution climate simulations

“…However, recent advancements in eddy detection algorithms have enabled a more comprehensive exploration of eddy characteristics. Recent studies have also focused on examining the long-term variations in other crucial attributes of eddies, including their quantity, radius, and amplitude (Oliver et al 2015, Zhou et al 2021. Oliver et al (2015) observed an increase in anticyclonic eddies in the East Australian Current (EAC), which could contribute to a higher frequency of sudden extreme warming events.…”

Documentation of gill net operation and major fish landings at Andaman Islands, India, during 2014 - 2018

“…Phytoplankton biomass, the primary food source within the sea, is another important factor (Karuppusamy et al, 2020). According to Zhou et al (2021), the thermodynamic anomalies are investigated in terms of sea surface temperature (SST), isothermal layer depth (ITD), and upper ocean heat content (HCT). Mesoscale eddies increase biological productivity by vertical and horizontal mixing of the water column in the pelagic zone (Yoder et al, 1981).…”