Local organization of the turbulent energy cascade in geophysical flows

In stratified and rotating systems such as large scale geophysical flows, turbulent energy can cascade downscale, enhancing mixing and dissipation, or upscale, sustaining coherent structures such as eddies and gyres. Quantifying and, where possible, locally modulating the balance between these pathways could improve our ability to locally manage coastal mixing, pollution dispersion, and regional climate modeling. Here, we demonstrate in a 13-m-diameter rotating tank that the local direction and persistence of the energy cascade are governed by stress-strain alignment and can be locally modulated, based on a local Rossby number. A steady horizontal turbulent momentum jet injected at mid-depth was analyzed using high-resolution planar particle image velocimetry. After applying Gaussian filters over a range of scales, we computed subgrid-scale Reynolds stress and strain rate tensors and quantified their alignment angle. In nonrotating flows, the instantaneous energy flux is spatially intermittent but overall unbiased. As rotation increases, coherent inverse-cascade patches expand and their Lagrangian persistence grows. Statistical analyses show that faster rotation increases the fraction of inverse-cascade events, while making extreme bursts less frequent. These results support a tensor-geometry framework linking cascade direction to the angle between stress and strain eigenvectors and point toward practical strategies for engineering turbulent energy pathways in environmental and industrial applications.