The magnitudes of the density and electric field fluctuations and their spectral characteristics were studied with a three-dimensional nonlinear model of the structuring in high-latitude patches caused by the primary gradient drift instability. The simulations were compared with the simultaneous density and electric field spectra obtained from noon-midnight and dawn-dusk orbits of the Dynamic Explorer 2 (DE 2) satellite [ Basu et al., 1990 ]. The magnitudes of the simulated density and electric field fluctuations were found to be in very good agreement with the measured data. In the directions parallel and perpendicular to convection, the similarities in the spectral slope distributions of both simulated and observed density and electric field fluctuations were demonstrated. These findings together with our earlier results [ Gondarenko and Guzdar, 1999 , 2001, 2003; Gondarenko et al., 2003 ] provide a significant evidence for coexistence of the primary gradient drift instability and subsequent secondary Kelvin-Helmholtz and tertiary shear-flow instabilities.