2017/10/22 by Hussein Aluie, Matthew Hecht, Geoffrey K. Vallis
Earth and Planetary Sciences · Environmental Science · Physics and Astronomy · #Cascade #Climate variability and models #Data assimilation #Energy budget #Energy cascade #Energy flux #Extratropical cyclone #Homogeneity (statistics) #Measure (data warehouse) #Ocean Waves and Remote Sensing #Oceanographic and Atmospheric Processes #Scale (ratio) #Turbulence #physics.flu-dyn #physics.geo-ph
paper · pdf · doi:10.1175/jpo-d-17-0100.1
45 pages, 11 figures, accepted in the Journal of Physical Oceanography
arxiv created 2017/10/22 · openalex created_date 2017/11/10 · openalex publication_date 2017/11/14 · arxiv updated 2018/02/14 · openalex updated_date 2026/08/05
Abstract A coarse-graining framework is implemented to analyze nonlinear processes, measure energy transfer rates, and map out the energy pathways from simulated global ocean data. Traditional tools to measure the energy cascade from turbulence theory, such as spectral flux or spectral transfer, rely on the assumption of statistical homogeneity or at least a large separation between the scales of motion and the scales of statistical inhomogeneity. The coarse-graining framework allows for probing the fully nonlinear dynamics simultaneously in scale and in space and is not restricted by those assumptions. This paper describes how the framework can be applied to ocean flows. Energy transfer between scales is not unique because of a gauge freedom. Here, it is argued that a Galilean-invariant subfilter-scale (SFS) flux is a suitable quantity to properly measure energy scale transfer in the ocean. It is shown that the SFS definition can yield answers that are qualitatively different from traditional measures that conflate spatial transport with the scale transfer of energy. The paper presents geographic maps of the energy scale transfer that are both local in space and allow quasi-spectral, or scale-by-scale, dynamics to be diagnosed. Utilizing a strongly eddying simulation of flow in the North Atlantic Ocean, it is found that an upscale energy transfer does not hold everywhere. Indeed certain regions near the Gulf Stream and in the Equatorial Countercurrent have a marked downscale transfer. Nevertheless, on average an upscale transfer is a reasonable mean description of the extratropical energy scale transfer over regions of O (10 3 ) km in size.