Overestimated Eddy Kinetic Energy in the Eddy‐Rich Regions Simulated by Eddy‐Resolving Global Ocean–Sea Ice Models

Abstract

The performance of eddy‐resolving global ocean–sea ice models in simulating mesoscale eddies is evaluated using six eddy‐resolving experiments forced by different atmospheric reanalysis products. Interestingly, eddy‐resolving ocean general circulation models (OGCMs) tend to simulate more (less) energetic eddy‐rich (eddy‐poor) regions with a smaller (larger) spatial extent than satellite observation, which finally shows that larger (smaller) mesoscale energy intensity (EI) is simulated in the eddy‐rich (eddy‐poor) regions. Quantitatively, there is an approximately 27%–60% overestimation of EI in the eddy‐rich regions, which are mainly located in the Kuroshio–Oyashio Extension, the Gulf Stream, and the Antarctic Circumpolar Currents regions, although the global mean EI is underestimated by 25%–45%. Apparently, the eddy kinetic energy in the eddy‐poor region is underestimated. Further analyses based on coherent mesoscale eddy properties show that the overestimation in the eddy‐rich regions is mainly attributed to mesoscale eddies’ intensity and is more prominent when mesoscale eddies are in their growth stage.

A century-long eddy-resolving simulation of global oceanic large- and mesoscale state

“…The spatial patterns and magnitudes of global mesoscale eddies are successfully simulated, with high SPCCs exceeding 0.70, except for EL, for which the SPCC is only 0.45. Similar to what we have learned from observation and previous research 71,72,[106][107][108] , the high values of EKE and eddy amplitude simulated in this eddy-resolving simulation are located in the western boundary currents and their eastward extensions, and the Southern Ocean, suggesting extensive eddy activity in these regions of strong and unstable currents; the simulated spatial distribution of eddy radius shows an essentially monotonic decrease from about 180 km in the near-equatorial areas to about 60 km at 60° latitude; and for eddy frequency and EL, it is obvious that coherent eddies are simulated almost everywhere in the global ocean, with notable exceptions in the northeast and southeast Pacific Ocean, which we usually refer to as "eddy deserts" 71,72 . The spatial distributions for both CEs and AEs resemble Fig.…”

“…The underestimation also happens for the eddy occurrence number (EON), but the bias for AEON (36.8%) is slightly smaller than that of CEON (40.1%). This underestimation of eddy frequency has been investigated and discussed in previous studies [106][107][108] . In general, the intensity of global mesoscale eddies (shown by the eddy amplitude, radius, and lifetime) in this eddy-resolving simulation is also quantitatively similar to that in the satellite observations 71,72 and other eddy-resolving simulations [106][107][108] .…”

“…This underestimation of eddy frequency has been investigated and discussed in previous studies [106][107][108] . In general, the intensity of global mesoscale eddies (shown by the eddy amplitude, radius, and lifetime) in this eddy-resolving simulation is also quantitatively similar to that in the satellite observations 71,72 and other eddy-resolving simulations [106][107][108] . The global statistics in Table 3 show that the intensities of CEs (AEs) are underestimated (overestimated) by 0%-17% (4.5%-9%).…”

Estimating Three‐Dimensional Structures of Eddy in the South Indian Ocean From the Satellite Observations Based on the isQG Method

“…In particular, the skill scores are mostly higher than 0.5 near 60°E in July 2015 when the strong AE caught the drifter, suggesting that the reconstructed velocity performs well in describing the eddy velocities. Regions with lower skill scores are typically eddy poor or the strong western current system (Ding et al., 2022), where the drifter may occasionally be affected by high‐frequency ageostrophic processes.…”

“…Even though the sea level fluctuations in these eddies are small, the anomalous subsurface velocities were between 10 and 30 cm/s around the eddy cores. Finally, the cruise reached the western coast of Australia, which is also regarded as an eddy‐rich area (Ding et al., 2022). The eddy activities on the west side of the Leeuwin Current were weak at the time, but our reconstructed velocities effectively capture them.…”