A nonlinear calculation is made of the saturated (self-limited) fractional density fluctuation Δ&rgr;/&rgr;0 of gravity waves. The result is Δ&rgr;/&rgr;0= (&ggr;-1)/[1+0.4⋅&ggr;2k2zH2Δ>1/2, &ggr;=specific heats ratio, kz=vertical wave no., H=scale height, Δ∝ spectral width of gravity waves. The calculation is based on a method developed for plasma waves. In addition, a calculation is made of the enhancement of atmospheric diffusion by finite amplitude gravity waves. It is shown that such diffusion is very much anisotropic and has the proper magnitude to explain some observations in the mesosphere.