Annual variations of the probability distributions of solar wind parameters using Helios data near 0.3 AU

Abstract

We have sorted the Helios 1 hourly average data into six yearly bins (late 1974-1975, 1976, 1917, 1978, 1979 and 1980). Probability distribution curves were then obtained for each yearly bin for the solar wind parameters: velocity, temperature and number density at perihelion (0.3 -0.5 AU). These curves show the evolution of these solar wind parameters from solar minimum through solar maximum for the region close to the sun. We find a clear separation between the low-speed and high-speed distributions. The low-speed distributions can de well fit by a Gaussian distribution. The low-speed peak velocity obtained by Gaussian fit is independent of the solar cycle. We also find that the transition years, 1978 and 1979, show an unusual intermediate-speed distribution not previously recognized.