Berthomier, M. and Fazakerley, A. N. and Forsyth, C. and Pottelette, R. and Alexandrova, O. and Anastasiadis, A. and Aruliah, A. and Blelly, P.-L. and Briand, C. and Bruno, R. and Canu, P. and Cecconi, B. and Chust, T. and Daglis, I. and Davies, J. and Dunlop, M. and Fontaine, D. and Génot, V. and Gustavsson, Bjorn and Haerendel, G. and Hamrin, M. and Hapgood, Mike and Hess, S. and Kataria, D. and Kauristie, K. and Kemble, S. and Khotyaintsev, Y. and Koskinen, H. and Lamy, L. and Lanchester, B. S. and Louarn, P. and Lucek, E. and Lundin, R. and Maksimovic, M. and Manninen, J. and Marchaudon, A. and Marghitu, O. and Marklund, G. and Milan, S. and Moen, J. and Mottez, F. and Nilsson, H. and Ostgaard, N. and Owen, C. J. and Parrot, M. and Pedersen, A. and Perry, C. and Pinçon, J.-L. and Pitout, F. and Pulkkinen, T. and Rae, I.J. and Rezeau, L. and Roux, A. and Sandahl, I. and Sandberg, I. and Turunen, E. and Vogt, J. and Walsh, A. and Watt, C. E. J. and Wild, James and Yamauchi, M. and Zarka, P. and Zouganelis, I. (2012) Alfvén: magnetosphere-ionosphere connection explorers. Experimental Astronomy, 33 (2-3). pp. 445-489. ISSN 0922-6435
Abstract
The aurorae are dynamic, luminous displays that grace the night skies of Earth’s high latitude regions. The solar wind emanating from the Sun is their ultimate energy source, but the chain of plasma physical processes leading to auroral displays is complex. The special conditions at the interface between the solar wind-driven magnetosphere and the ionospheric environment at the top of Earth’s atmosphere play a central role. In this Auroral Acceleration Region (AAR) persistent electric fields directed along the magnetic field accelerate magnetospheric electrons to the high energies needed to excite luminosity when they hit the atmosphere. The “ideal magnetohydrodynamics” description of space plasmas which is useful in much of the magnetosphere cannot be used to understand the AAR. The AAR has been studied by a small number of single spacecraft missions which revealed an environment rich in wave-particle interactions, plasma turbulence, and nonlinear acceleration processes, acting on a variety of spatio-temporal scales. The pioneering 4-spacecraft Cluster magnetospheric research mission is now fortuitously visiting the AAR, but its particle instruments are too slow to allow resolve many of the key plasma physics phenomena. The Alfvén concept is designed specifically to take the next step in studying the aurora, by making the crucial high-time resolution, multi-scale measurements in the AAR, needed to address the key science questions of auroral plasma physics. The new knowledge that the mission will produce will find application in studies of the Sun, the processes that accelerate the solar wind and that produce aurora on other planets.