Solar cycle changes, geomagnetic variations, and energetic particle properties in the inner magnetosphere

The causes and effects of geospace variability during recent years have been studied using coordinated measurements from an international constellation of Sun-Earth spacecraft. Particular emphasis is placed on long-term, homogeneous data sets from recent NASA spacecraft missions. It is found that even for modest geomagnetic storms, radiation belt electron fluxes can be rapidly enhanced within the Earth's inner magnetosphere. Remote-sensing solar data identify the eruptive or recurrent coronal features that produce the upstream drivers that, in turn, cause episodes of intense geomagnetic activity. Continuous solar wind data allow study of the principal drivers of magnetospheric acceleration processes. The Earth's radiation belts and inner magnetosphere show pronounced differences in their characteristics as the interplanetary magnetic field and solar wind properties change over the 11-year solar cycle. Solar coronal holes produce regular, recurrent solar wind streams, almost invariably enhancing highly relativistic electrons when solar wind speeds exceed 500 km/s. These phenomena are characteristic of the several-year approach to solar minimum. This contrasts with major geomagnetic disturbances associated with aperiodic coronal mass ejections that occur most frequently around solar maximum. As a practical consequence of Sun-Earth connection events, it is found that many adverse space weather episodes have contributed significantly to spacecraft operational anomalies and failures. We discuss how present and future space missions can address International Living With a Star (ILWS) goals and improve space weather forecasts. (C) 2007 Elsevier Ltd. All rights reserved.