A model for long-term response of the plasmasphere to the magnetospheric activity and related measurement plans by EXOS-D

Abstract Recent advances in the understanding of ionosphere-plasmasphere coupling are briefly reviewed with the emphasis on the refilling of flux tubes after depletion caused by a severe geomagnetic storm. The effects of microscopic processes such as the ion and electron heating by, for example, wave-particle interactions, on the macroscopic process like the refilling of the magnetic flux tubes have been discovered to be important ingredients from both theoretical and experimental studies. A plan for observations of the low-energy ions by the 12th Japanese scientific satellite (EXOS-D) is introduced which emphasizes plasmasphere-ionosphere coupling investigations. For this mission, we have developed a new type of ion energy-mass spectrometer which has a high mass resolution and a wide dynamic range both of which are indispensable in measuring the magnetospheric and ionospheric ions extending from thermal to several keV in energy. Also given is a brief description of the satellite and its instrumentation.