The equations governing the nonlinear evolution of density fluctuations in a low-pressure weakly ionized plasma driven unstable by the E¿B or gradient-drift instability were derived by Sudan and Keskinen (1977, 1979) for addressing the electrostatic tubulence in E and F regions of the Earth's ionosphere. We have developed a subgrid model suitable for the numerical simulation of these equations which is closely related to renormalized diffusion caused by small-scale fluctuation spectrum. ''Dynamical Renormalization Group'' (RNG) methods are employed to obtain the renormalized diffusion. This procedure computes the long-wavelength, long-time behavior of density correlations generated by the evolution equation for the plasma stirred by a Gaussian random force characterized by a correlation function ∝ km where k is the wavenumber of the forcing function. The effect of small scales on the large-scale dynamics in the limit k→0 and infinite Reynolds number an be expressed in the form of renormalized coefficients; in our case, renormalized diffusion. If one assumes the power spectra to be given by Kolmogorov argument of cascading of energy through k space then one can derive a subgrid model based on the results of RNG. ¿American Geophysical Union 1995