Effects of the postsunset vertical plasma drift on the generation of equatorial spread F

Abstract

Equatorial spread F (ESF) irregularities are caused by plasma instability processes in the equatorial ionosphere and especially related to plasma bubble phenomena in the topside F region. Plasma bubbles result from nonlinear evolution of the Rayleigh-Taylor instability. The prereversal enhancement (PRE) of the postsunset vertical plasma drift increases the height of the equatorial F layer, creating conditions conducive to the growth of the Rayleigh-Taylor instability, and is an important factor that controls the generation of ESF. Three different relationships of the quantitative connection between the PRE and ESF occurrence have been derived. (1) A threshold PRE must be reached for the occurrence of ESF. ESF will be generated when the PRE is larger than the threshold and will not be generated when the PRE is smaller than the threshold. (2) The occurrence probability of ESF increases approximately linearly with the PRE. (3) The occurrence probability of ESF is characterized by a continuous probability distribution as a function of the PRE magnitude. The second and third relationships imply that the PRE can be used to specify the occurrence probability of ESF. This paper will review these relationships and discuss how these relationships are connected to each other. The effects of seeding perturbations on the generation and global distribution of ESF will be briefly discussed.