Dynamics of proton and alpha-particle velocities and temperatures in the solar wind: Prognoz 7 observations

Abstract

The comparative behaviour of bulk velocities and kinetic temperatures of the solar wind protons and α-particles measured by the energy-mass-spectrometer on board the Prognoz 7 satellite is studied for various types of the solar wind streams which may be associated with solar wind and solar corona structures. Preferential acceleration and heating of α-particles and correlation of the temperature ratio TαTp and the absolute value of velocity difference |Vα−Vp| for α-particles and protons is observed, mainly, in the solar wind streams from coronal holes. A possibility of α-particle heating up to higher temperature than that of protons due to collisions is discussed for the case when the velocity distributions of the two components are shifted. The estimates show that the ion velocities and temperatures are equalized, on the average, at the heliocentric distances ∼ 7 and ∼ 20 AU, respectively, due to Coulomb collisions.