Magnetic storm associated disturbance dynamo effects in the low and equatorial latitude ionosphere

Abstract

During geomagnetic storms, magnetospheric energy injection at high latitudes leads to global scale disturbances in ionospheric electric fields and thermospheric winds. Over middle and low latitudes the disturbance dynamo (DD) electric field sets in within a few hours from the high latitude energy deposition. As a result, the major low latitude ionospheric phenomena, such as the ionization anomaly, the electrojet and the plasma bubbles irregularity processes, can be inhibited during times of their normal developments, while enhancing them at other times. Depending upon the strength and duration of the magnetospheric disturbances, the disturbance dynamo effects could last from several hours to a few days. An empirical model has been developed which successfully describes the diurnal pattern of the DD electric field. The basic theory has been successfully used in simulation models to predict the typical diurnal behavior of this electric field. However, the precise relationship of the intensity and duration of the effects at low latitudes to ' that of the causative storm seems poorly known, for validation purpose in case studies. This paper reviews our present state of knowledge on the disturbance dynamo effects in the low/equatorial latitude ionosphere, and discusses some new results from data obtained in the South American longitudinal sector. The DD electric field characteristics in response to magnetic disturbances arising from the CIRs (co-rotating interaction regions) and co-rotating streams, that are of significantly longer duration than those arising from the CMEs (Coronal mass ejections), are also discussed in some detail.