An extended investigation of Helios 1 and 2 observations: the interplanetary magnetic field between 0.3 and 1 AU.
Helios-1 and 2 spacecraft allowed a detailed investigation of the radial dependence of the interplanetary magnetic field components between 0.3 and 1 AU. The behaviour of the radial component B ris in a very good agreement with Parker's model (B r∼ r -2) and the azimuthal component B φalso shows a radial dependence which is close to theoretical predictions (B φ∼ r -1). Experimental results for the normal component B θand for the field magnitude B are consistent with those from previous investigations. The relative amplitude of the directional fluctuations with periods less than 12 hr is essentially independent of heliocentric distance, while their power decreases approximately as r -3 without any appreciable difference between higher and lower velocity regimes.