Kinetic properties of solar wind minor ions and protons measured with SOHO/CELIAS

Abstract

Using observations of the Charge Time‐of‐Flight(CTOF) charge and mass spectrometer of the Charge, Element and Isotope Analysis System (CELIAS), and of CELIAS/proton monitor on board the Solar and Heliospheric Observatory (SOHO), we present an overview of speeds and kinetic temperatures of minor ions and protons in the solar wind near solar minimum, covering the Carrington Rotations 1908 to 1912. In the case of a collision‐dominated solar wind the speed of minor ions is expected to be lower or equal to the speed of the protons, and all species are expected to have equal temperatures. On the other hand, minor ions can be accelerated and heated by wave‐particle interaction. In this case, equal thermal speeds of all species are expected. CTOF data allow the determination of the kinetic parameters of various ions with high accuracy and with high time resolution. The mean O 6+ speed of the observed period is 390 km s −1 . The speeds of Si 7+ and Fe 9+ correlate well with O 6+ , the linear correlation coefficient being 0.96 or higher. Our results also indicate that silicon and iron tend to lag behind oxygen with a speed difference of ∼20 km s −1 at 500 km s −1 . At the same time, the kinetic temperature of the ions under investigation exhibit the well‐known mass proportionality, which is attributed to wave‐particle interactions. During the period of low solar activity in consideration, many cases are observed where the kinetic temperature is extraordinarily low (10 4 K for O 6+ ).