Boundaries in space plasma provide an interface between various plasma regimes. These boundaries are often associated with current sheets where there are strong electric fields and hence particle acceleration. The physics of such usually very thin boundaries in collisionless magnetospheric plasmas include important microscopic kinetic processes, which might in fact control the overall dynamics of the entire magnetospheric system.
The narrowness of the boundaries and their high mobility in space make experimental study of them a rather complicated problem. The Cluster mission to be launched by 2001 will consist of four closely-spaced spacecraft flying together through these boundaries with the aim of separating spatial and temporal effects, determining boundary structure, and measuring in three dimensions the local plasma processes.
The global shape and dynamics of the magnetopause and other boundaries is also a subject on which the IACG/ISTP missions can unveil important information. There have been case studies and statistical studies using data from one or two satellites, but magnetopause and other boundaries can show complicated deformations which cannot be fully monitored by one or two satellites. Multi-satellite and ground monitoring of the shape of the boundaries provides vital information.
The second IACG campaign is now divided into two stages. The original plan will be realized in the second stage which starts after the launch of Cluster in early years of the next millennium. The first stage, which started in the spring of 1997, mainly aims at studying the overall shape of the magnetopause, and the transfer of mass, momentum, and energy across and/or along the magnetopause and adjacent boundary layers, using data from all the missions currently running. Similar studies are also planned for the bow shock and plasma sheet boundary layer.
Geotail and the Interball-1/Magion-4 pair provide in-situ measurements of the low and high latitude magnetopause and boundary layers, plasma sheet boundary layer and bow shock. The latter pair traverse the outer cusp as well. Wind and IMP-8 provide solar wind input monitoring along with interplanetary shock and other solar wind boundaries studies. Wind also will observe the bow shock, and the near-tail magnetopause, and plasma sheet boundary layer during perigee passes. Polar and Interball-2 will supply the data on the boundary layer, the plasma sheet, and the various boundary regions of the inner magnetosphere. The ground-based together with ionospheric (e.g. aboard Fast) and geostationary measurements complete the survey of magnetospheric boundaries and their interaction with interplanetary disturbances.