We investigate the influence of turbulence anisotropy and rotation on the d
iffusion of a low-concentration passive scaler in a turbulent medium. Using
the renormalization the diffusion tensor over the spectrum of turbulent fl
uctuations, we show that enhanced horizontal mixing reduces the vertical di
ffusion transport of a passive scalar. Allowance for rotation results in tw
o effects? which have not been noted previously: (1)under the influence of
Coriolis forces, horizontal turbulence also produces a vertical diffusion f
lux. with the horizontal and vertical diffusions being of the same order of
magnitude for rapidly rotating stars and (2) in the case of rapid rotation
, all diffusion fluxes of a passive scalar decrease in inverse proportion t
o the square root of the Coriolis number. (C) 2001 MAIK "Nauka/Interperiodi
ca".