Plasmapause, Convection, and Reconnection.

Being one of the first generation of space scientists who entered this field right after the space became accessible to in situ observations, I had good luck of addressing some of the basic questions in this field from the early years of my carrier. These are development of global convection in the magnetosphere when the interplanetary magnetic field has the southward polarity, changes in the structure of the magnetotail leading to the onset of substorm expansion phase, and physics of the plasmapause formation. My career culminated with promotion and implementation of the Geotail spacecraft mission. In this article I shall present my personal recollections on these efforts including interactions with colleagues worldwide who shared the common interest. Plain Language Summary: This article is a recollection of my contributions to space physics in early years of the space age. I chose this discipline for my career because I expected that exciting new problems will emerge out of observations made by Sputnik and numerous scientific satellite missions that should follow. The problems I addressed before 1980 included origin of the plasmapause, mechanism of substorms, and acceleration of trapped particles. (1) Plasmapause is a sharp drop in the plasma density that is always seen in the central region of the magnetosphere. I explained this feature by the combined action of the corotation of plasma with the Earth and the convection of plasma that is generated by the solar wind. I found in the process that this convection is generated when IMF (i.e., magnetic field in the solar wind) is directed southward, suggesting that reconnection of field lines (i.e., connection of field lines having different polarities) occurs at the boundary of the magnetosphere. (2) When this reconnection lasts and field lines are piled up in the magnetotail, another reconnection takes place among the piled‐up field lines, and expansion phase of substorm begins. (3) Plasmas in the magnetosphere can move not only by convection but also by field‐aligned motion and by diffusion. They can be energized from keV to higher energies by taking these trajectories in a gaining order. Since the 1980s, I organized the Geotail satellite mission as a joint program of ISAS of Japan with NASA of USA. This satellite, launched in 1992, covered the key regions of the magnetotail with advanced instruments and credited for deepening the space plasma physics from fluid dynamics to kinetics. Key Points: When IMF is southward, reconnection between IMF and geomagnetic field produces global convection in the magnetosphere named DP2Plasmapause is produced by combined action of DP2 convection and the flow accompanying the Earth's rotationWhen IMF turns southward and field lines are transported to the magnetotail, the plasma sheet becomes thinner and ensuing reconnection in the magnetotail drives the substorm expansion phase (DP1) [ABSTRACT FROM AUTHOR]