Particles and fields: Significant achievements

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Abstract
Space observations during 1964 and 1965 have led to discoveries in the physics of cosmic rays, the solar wind, and the magnetosphere. These results are particularly pertinent to a period of minimal solar activity. A regular sector structure, persisting for many solar rotations, was found to modulate the solar wind and its embedded magnetic field. Energetic protons up to about 10 Mev are emitted continuously from the sun in streams along certain magnetic field lines that corotate with the sector structure. The solar modulation of the propagation of galactic and solar cosmic rays was studied extensively, and theoretical explanations of this phenomenon have been derived on the basis of a diffusion model. It was discovered that low energy electrons (about 40 kev) are emitted by some solar flares, and substantial progress has been made in measuring the electron component of galactic cosmic rays. The existence of a neutral sheet in the geomagnetic tail has been demonstrated, and substantial progress was made in defining its properties as well as those of the transition region between the solar wind and the magnetopause. A short summary of spacecraft operation in 1965 is also given.