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Abstract Parameterization of mesoscale eddies in coarse resolution ocean models is necessary to include the effect of eddies on the large‐scale oceanic circulation. We propose to use a multiple‐scale Quasi‐Geostrophic (MSQG) model to capture the eddy dynamics that develop in response to a prescribed large‐scale flow. The MSQG model consists in extending the traditional quasi geostrophic (QG) dynamics to include the effects of a variable Coriolis parameter and variable background stratification. Solutions to this MSQG equation are computed numerically and compared to a full primitive equation model. The large‐scale flow field permits baroclinically unstable QG waves to grow. These instabilities saturate due to non‐linearities and a filtering method is applied to remove large‐scale structures that develop due to the upscale cascade. The resulting eddy field represents a dynamically consistent response to the prescribed background flow, and can be used to rectify the large‐scale dynamics. Comparisons between Gent‐McWilliams eddy parameterization and the present solutions show large regions of agreement, while also indicating areas where the eddies feed back onto the large scale in a manner that the Gent‐McWilliams parameterization cannot capture. Also of interest is the time variability of the eddy feedback which can be used to build stochastic eddy parameterizations. 

Abstract. This paper contains a description of recent changes tothe formulation and numerical implementation of the Quasi-GeostrophicCoupled Model (Q-GCM), which constitute a major update of the previousversion of the model (Hogg et al., 2014). The Q-GCM model has been designedto provide an efficient numerical tool to study the dynamics of multi-scalemidlatitude air–sea interactions and their climatic impacts. The presentadditions/alterations were motivated by an inquiry into the dynamics ofmesoscale ocean–atmosphere coupling and, in particular, by an apparent lackof the Q-GCM atmosphere's sensitivity to mesoscale sea-surface temperature (SST)anomalies, even at high (mesoscale) atmospheric resolutions, contrary toample theoretical and observational evidence otherwise. Major modificationsaimed at alleviating this problem include an improved radiative-convectivescheme resulting in a more realistic model mean state and associated modelparameters; a new formulation of entrainment in the atmosphere, whichprompts more efficient communication between the atmospheric mixed layer andfree troposphere; and an addition of a temperature-dependent windcomponent in the atmospheric mixed layer and the resulting mesoscalefeedbacks. The most drastic change is, however, the inclusion of moistdynamics in the model, which may be key to midlatitude ocean–atmospherecoupling. Accordingly, this version of the model is to be referred to as theMQ-GCM model. Overall, the MQ-GCM model is shown to exhibit a rich spectrumof behaviors reminiscent of many of the observed properties of the Earth'sclimate system. It remains to be seen whether the added processes are ableto affect in fundamental ways the simulated dynamics of the midlatitudeocean–atmosphere system's coupled decadal variability. 

Abstract The structure and variations of the North Equatorial Counter Current (NECC) in the far western Pacific Ocean during 2014-2016 are investigated using repeated in-situ hydrographic data, altimeter data, Argo data, and reanalysis data. The NECC shifted ~1 degree southward and intensified significantly with its transport exceeding 40 Sv (1 Sv = 10 6 m 3 s -1 ), nearly double its climatology value, during the developing phase of the 2015/16 El Niño event. Observations show that the 2015/16 El Niño exerted a comparable impact on the NECC with that of the extreme 1997/98 El Niño in the far western Pacific Ocean. Baroclinic instability provided the primary energy source for the eddy kinetic energy (EKE) in the 2015/16 El Niño, which differs from the traditional understanding of the energy source of EKE as barotropic instability in low latitude ocean. The enhanced vertical shear and the reduced density jump between the NECC layer and the subsurface North Equatorial Subsurface Current (NESC) layer renders the NECC–NESC system baroclinically unstable in the western Pacific Ocean during El Niño developing phase. The eddy-mean flow interactions here are diverse associated with various states of the El Niño Southern Oscillation (ENSO). 

Abstract We describe a form of Atlantic Meridional Overturning Circulation (AMOC) variability that we believe has not previously appeared in observations or models. It is found in an ensemble of eddy‐resolving North Atlantic simulations that the AMOC frequently reverses in sign at ∼35°N with gyre‐wide anomalies in size and that reach throughout the water column. The duration of each reversal is roughly 1 month. The reversals are part of the annual AMOC cycle occurring in boreal winter, although not all years feature an actual reversal in sign. The occurrence of the reversals appears in our ensemble mean, suggesting it is a forced feature of the circulation. A partial explanation is found in an Ekman response to wind stress anomalies. Model ensemble simulations run with different combinations of climatological and realistic forcings argue that it is the atmospheric forcing specifically that results in the reversals, despite the signals extending into the deep ocean. 

Abstract. With the increase in computational power, ocean models with kilometer-scale resolution have emerged over the last decade. These models have been used for quantifying the energetic exchanges between spatial scales, informing the design of eddy parametrizations, and preparing observing networks. The increase in resolution, however, has drastically increased the size of model outputs, making it difficult to transfer and analyze the data. It remains, nonetheless, of primary importance to assess more systematically the realism of these models. Here, we showcase a cloud-based analysis framework proposed by the Pangeo project that aims to tackle such distribution and analysis challenges. We analyze the output of eight submesoscale-permitting simulations, all on the cloud, for a crossover region of the upcoming Surface Water and Ocean Topography (SWOT) altimeter mission near the Gulf Stream separation. The cloud-based analysis framework (i) minimizes the cost of duplicating and storing ghost copies of data and (ii) allows for seamless sharing of analysis results amongst collaborators. We describe the framework and provide example analyses (e.g., sea-surface height variability, submesoscale vertical buoyancy fluxes, and comparison to predictions from the mixed-layer instability parametrization). Basin- to global-scale, submesoscale-permitting models are still at their early stage of development; their cost and carbon footprints are also rather large. It would, therefore, benefit the community to document the different model configurations for future best practices. We also argue that an emphasis on data analysis strategies would be crucial for improving the models themselves. 

Abstract The “eddying” ocean, recognized for several decades, has been the focus of much observational and theoretical research. We here describe a generalization for the analysis of eddy energy, based on the use of ensembles, that addresses two key related issues: the definition of an “eddy” and the general computation of energy spectra. An ensemble identifies eddies as the unpredictable component of the flow, and permits the scale decomposition of their energy in inhomogeneous and non‐stationary settings. We present two distinct, but equally valid, spectral estimates: one is similar to classical Fourier spectra, the other reminiscent of classical empirical orthogonal function analysis. Both satisfy Parseval's equality and thus can be interpreted as length‐scale dependent energy decompositions. The issue of “tapering” or “windowing” of the data, used in traditional approaches, is also discussed. We apply the analyses to a mesoscale “resolving” (1/12°) ensemble of the separated North Atlantic Gulf Stream. Our results reveal highly anisotropic spectra in the Gulf Stream and zones of both agreement and disagreement with theoretically expected spectral shapes. In general, we find spectral slopes that fall off faster than the steepest slope expected from quasi‐geostrophic theory. 

Abstract A wavelet‐based method is re‐introduced in an oceanographic and spectral context to estimate wavenumber spectrum and spectral flux of kinetic energy and enstrophy. We apply this to a numerical simulation of idealized, doubly periodic quasi‐geostrophic flows, that is, the flow is constrained by the Coriolis force and vertical stratification. The double periodicity allows for a straightforward Fourier analysis as the baseline method. Our wavelet spectra agree well with the canonical Fourier approach but with the additional strengths of negating the necessity for the data to be periodic and being able to extract local anisotropies in the flow. Caution is warranted, however, when computing higher‐order quantities, such as spectral flux.