We propose a new class of models for the mean motion of ideal incompre
ssible fluids in three dimensions, including stratification and rotati
on. In these models, the amplitude of the rapid fluctuations introduce
s a length scale, alpha, below which wave activity is filtered by both
linear and nonlinear dispersion. This filtering enhances the stabilit
y and regularity of the new fluid models without compromising either t
heir large scale behavior, or their conservation laws. These models al
so describe geodesic motion on the volume-preserving diffeomorphism gr
oup for a metric containing the H-1 norm of the fluid velocity.