Event Study on Pre-Substorm Phases and Their Relation to the Energy Coupling Between Solar Wind and Magnetosphere

摘要

A sudden southward turning of the interplanetary magnetic field, immediately followed by a worldwide intensification of convection, is documented. Observations within the auroral zone and polar cap show enhanced activity ending in a localized substorm. Large fluctuations in ionospheric parameters starting before the substorm onset, and subsequent high energy particle precipitation (recorded by balloon X-ray detectors), with changes in maximum ionospheric current density and in electrojet halfwidth and total electrojet current, are resolved, together with the increase in auroral brightness prior to final breakup. Observations during this trigger phase are discussed. The energy coupling function correlates with the Joule heating rate at first, but subsequently increases as the heating rate decreases. This suggests that the start of the trigger phase is internally controlled while the length of the phase and onset of the final substorm are influenced by changes in the energy coupling function.