Abstract
The Kuroshio Extension (KE) shifts between elongated and convoluted states on interannual to decadal time scales. The nature of this low frequency variability (LFV) is still under debate since it is known to be driven by intrinsic oceanic mechanisms, but it is also synchronized with the Pacific Decadal Oscillation (PDO). In this analysis we present the results from two present-climate coupled simulations performed with the CMCC-CM2 model under the CMIP6 HighResMIP protocol and differing only by their atmospheric component resolution. The impact of increased atmospheric resolution on the KE LFV is assessed inspecting several aspects: the KE bimodality, the large-scale variability and the air–sea interactions. The KE LFV and the teleconnection mechanism that connects the KE and the PDO are well captured by both configurations. However, higher atmospheric resolution favors the occurrence of the elongated state and leads to a more realistic PDO representation. Moreover, both simulations qualitatively capture the signatures of atmosphere-driven and ocean-driven regimes over the North Pacific Ocean, even if the higher resolution induces an excessively strong ocean–atmosphere coupling that leads to an overestimation of the air–sea feedbacks. This work highlights that the small scale atmospheric variability (resolution lower than 1°) does not substantially contribute to improve the realism of the KE LFV, but causes significant differences in the air–sea interaction over the KE region likely related to the strengthening of the coupling. The eddy-permitting ocean resolution shared by both configurations is likely responsible for the degree of realism exhibited by the simulated KE LFV in the two analyzed simulations.
Highlights
The Kuroshio Extension (KE) is the eastward meandering jet formed by the convergence of the Kuroshio and Oyashio WBCs in the Northern Pacific Ocean and is known for exhibiting low frequency variability (LFV) over interannual and decadal time scales
It has been shown that the frontal-scale variability contributes to changes in the KE jet speed which can be generated by intrinsic oceanic mechanisms, highlighting that while the linear Rossby wave theory explains the timing of the bimodality, nonlinear ocean dynamics plays an essential role in organizing the spatial frontal structure (Nonaka et al 2006, 2012; Taguchi et al 2007; Tsujino et al 2006, 2013)
The specific goal of our analysis is to investigate the impact of model resolution on the representation of KE LFV, analyzed in terms of both frontal-scale and broad-scale variability, making a step forward into assessing the role of the horizontal atmospheric resolution on the degree of realism of the KE jet
Summary
The KE is the eastward meandering jet formed by the convergence of the Kuroshio and Oyashio WBCs in the Northern Pacific Ocean and is known for exhibiting LFV over interannual and decadal time scales. Taguchi et al (2007), with the use of an eddy-resolving ocean general circulation model (OGCM), showed that the KE LFV is coherent with the large-scale atmospheric variability via the propagation of Rossby waves (RWs) from the East-Central Norther Pacific In this context, it has been shown that the frontal-scale variability contributes to changes in the KE jet speed which can be generated by intrinsic oceanic mechanisms, highlighting that while the linear Rossby wave theory explains the timing of the bimodality, nonlinear ocean dynamics plays an essential role in organizing the spatial frontal structure (Nonaka et al 2006, 2012; Taguchi et al 2007; Tsujino et al 2006, 2013). From other ongoing studies in the HighResMIP community (see some preliminary results reported in Tsartsali et al 2019), this one-to-one gridpoint matching impacts on the strength of the ocean–atmosphere coupled interaction Both intrinsic and atmospheric processes play a fundamental role in the KE LFV, it is necessary to inspect the role of the horizontal atmospheric model resolution in the representation of coupled ocean–atmosphere processes over this region.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
