Angular Distribution of Solar Wind Magnetic Field Vector at 1 Au

We study the angular distribution of the solar wind magnetic field vector at 1 AU and its solar cycle dependence using ACEobservations. A total of twelve27.27 day(the duration of a solar rotation) intervals during the solar maximum, the solar minimum, as well as the ascending and descending phases of solar cycle 23 are examined. For all selected intervals, we obtain the angular distribution function a t f ( ), where α is the angle between the instantaneous solar wind magnetic field vector and the average background magnetic field vector, and τ is the period length for the averaging. Our results show that in all periods a t f ( ) has two populations, one at small angles and one at large angles. We suggest that the second population is due to the presence of current sheets in the solar wind. The solar-cycle dependence of a t f ( ) and a τ-scaling property of the second population of a t f ( ) are discussed. The τscaling shows a clear dependence on the solar wind type. The implication of a t f ( ) for particle acceleration at interplanetary shocks driven by coronal mass ejections, such as those in solar energetic particle events, is also discussed.