Characterization of local time dependence of equatorial spread F responses to substorms in the American sector

Abstract

Substorms have been found to play an important role in ionospheric electrodynamics at low and equatorial latitudes. In this study, we have investigated the possible influence of substorm on the generation of equatorial spread F (ESF). Coherent backscatter radar (JULIA) and incoherent scatter radar measurements between 2000 and 2017 at the Jicamarca Radio Observatory (11.95° S, 76.87° W, ~0° dip lat) are used. In statistical analysis, 12,525 h of ESF measurements are considered and have been divided into two groups based on their local time: post-sunset (18–24 LT) and post-midnight (00–06 LT). The superposed epoch analysis shows that the substorm-caused disturbance on vertical plasma drift can last longer than 12 h, which further affects the occurrence rate of ESF during a substorm. The increase/decrease of ESF at the post-sunset/post-midnight sector with about a 1 h lag to the substorm commencement is attributed to the prompt penetration electric field (PPEF), while the disturbance dynamo electric field needs approximately 3.5 h to suppress/promote the post-sunset/post-midnight ESF after substorm. In addition, the absolute value of correlation coefficients between the AE index and the occurrence rate of ESF is the largest when a 3–3.5 h lag is considered, which implies that the effect of disturbance dynamo electric fields could be more significant than prompt penetration electric field for the generation (suppression) of post-midnight (post-sunset) ESF during a substorm.