Filaments of uniform quasi-geostrophic potential vorticity in pure strain

Three-dimensional filaments of quasi-geostrophic potential vorticity are generic features atmospheric and oceanic flows. They often generated during the strong interactions between three-dimensional vortices. contribute to a direct cascade enstrophy in spectral space. These correspond shear zones. Therefore they may be sensitive instabilities akin Kelvin–Helmholtz instability classical two-dimensional strip. are, however, subjected straining flow induced by surrounding This affects their robustness. paper focuses on simplified model this situation. We consider effect pure strain filament uniform vorticity. first quasi-static situation where strain, assumed small, only cross-sectional shape filament, but not velocity field. address linear stability that context also show examples filament's nonlinear evolution. then linearised dynamics strain. In particular we focus maximum perturbation amplification observed filament. conclude small moderate rates efficient at preventing large growth. Nonlinear effects can nevertheless leads roll-up weakly strained filaments.