Solar cycle invariance in solar wind proton temperature relationships

The relationships between solar wind proton temperature and velocity and between temperature and momentum flux density at 1 AU are examined using National Space Science Data Center IMP 8 solar wind data obtained from late 1984 to early 1985. These relationships are compared with similar ones obtained from a variety of solar wind data spanning 14 years, from 1966 to 1980. It is found that these relationships, particularly the one between temperature and velocity, are very stable over the solar cycles from which these data were drawn. This suggests that the basic physical processes which accelerate and heat the solar wind have remained unchanged for the last 20 years. Over this same period, the energy, momentum, and mass fluxes produced by the Sun to generate the solar wind varied by about 60%. A qualitative explanation of these results is given in the context of a model for solar wind generation that includes significant postsonic momentum and energy deposition and assumes that solar wind protons are heated by magnetohydrodynamic waves of solar origin.

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