A two-dimensional, Boussinesq, nonhydrostatic model is used to investigate the evolution of filaments of potential vorticity (viewed in cross-section) in simple shear and strain background flows. At low shears and strains the temperature and along filament velocity are found to remain in semigeostrophic balance with the filament PV. In the case of a background shear flow the ageostrophic circulation advects the tips of the filament into stronger shear, causing filaments with realistic PV to become stretched to over twice the length of an initially comparable passive tracer in the same flow. The effect of this increased stretching on the realistic radiative dissipation of the PV is discussed. In the case of a background strain flow, the ageostrophic circulation is found to increase strain rate of the filament, and as a result the horizontal scale is found to decrease at a rate 15-25\% faster than expected for a passive tracer. The emission of gravity waves by filaments, and the breakdown of balance in high shear and strain flows and rapidly varying flows is also discussed.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics