  Reduction of flow compressibility with the corresponding ideally invariant
helicities, universally for various fluid models of neutral and ionized gases,
can be argued statistically and associated with the geometrical scenario in the
Taylor-Proudman theorem and its analogues. A `chiral base flow/field', rooted
in the generic intrinsic local structure, as well as an `equivalence principle'
is explained and used to bridge the single-structure mechanics and the helical
statistics. The electric field fluctuations may similarly be depressed by the
(self-)helicities of the two-fluid plasma model, with the geometry lying in the
relation between the electric and density fields in a Maxwell equation.
