Diffusion of small‐scale density irregularities during equatorial spread F

Abstract

The diffusion of small‐scale density irregularities (i.e., those with density gradient scale lengths less than several hundred meters) is investigated during the decay phase of equatorial spread F. Both classical and anomalous diffusion processes are considered. The anomalous diffusion coefficient is based upon the transport properties associated with the universal drift instability. It is found that anomalous diffusion can smooth out small‐scale density irregularities on time scales τ, consistent with observational results, i.e., few minutes is ≲τ≲ few hours. On the other hand, classical diffusion is much too slow a process to be important. Also, anomalous diffusion is unable to diffuse large‐scale irregularities, i.e., those with scale lengths greater than a kilometer, on time scales τ≲ few hours and another mechanism must occur to smooth out these irregularities, e.g., shorting out to the E region.