Radial variation of the interplanetary magnetic field between 0.3 AU and 1.0 AU - observations by the Helios-1 spacecraft

Abstract

We have investigated the radial dependence of the radial and azimuthal components and the magnitude of the interplanetary magnetic field obtained by the Technical University of Braunschweig magnetometer experiment on-board of Helios-1 from December 10, 1974 to first perihelion on March 15, 1975. Absolute values of daily averages of each quantity have been employed. The regression analysis based on power laws leads to 2.55 γ x r^-2.0 , 2.26 γ x r^-1.0 and F = 5.53 γ x r^-1.6 with standard deviations of 2.5 γ, 2.0 γ and 3.2 γ for the radial and azimuthal components and magnitude, respectively. Here r is the radial distance from the Sun in astronomical units. The results are compared with results obtained for Mariners 4, 5 and 10 and Pioneers 6 and 10. The differences are probably due to different epochs in the solar cycle and the different statistical techniques used.

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