Influence of interplanetary disturbances on the terrestrial ionospheric outflow

Following the discovery of the terrestrial ionospheric outflow in the early 1970s, and the confirmation of its significance in the late 1970s and the 1980s, a large number of studies investigated the processes leading to the escape of ionospheric ions to the magnetosphere. In general, ionospheric ou tflow was found to increase proportionally with geomagnetic activity. In th e late 1980s and the 1990s several studies showed that whenever the abundan ce of ionospheric origin ions in the magnetosphere is extraordinarily high, their effects on geospace activity are substantial. It has been suggested that the large abundance of ionospheric origin ions regulates major dynamic processes like storms and substorms. This appears to be the case during gr eat magnetic storms. A number of factors have been identified, which have a critical influence on the extent and the characteristics of ionospheric ou tflow. There are certainly several internal geospace factors, but a major i nfluence on ionospheric outflow presumably originates in certain interplane tary structures. Such structures are for example high-speed streams, magnet ic clouds, and coronal mass ejections. We will discuss the relationship bet ween interplanetary structures and ionospheric outflow, on the basis of bot h theoretical expectations and observational facts. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.