A Half Century of Magnetic Helicity in the Solar Wind

Abstract:

Using NASA’s “OMNI” dataset, this work presents observations of the net magnetic helicity and the normalized helicity spectrum at 1 AU over the period 1965 – 2014. Past studies (1,2) reported that the helicity at large scales has a definite dominant sign organized with respect to the heliospheric current sheet, with negative helicities occurring north of the current sheet, and positive helicities south. The present study confirms this pattern and extends it by more than two solar cycles and past the most recent solar maximum. Particle scattering by turbulence with finite magnetic helicity is one of only two known particle transport mechanisms that are sensitive to particle charge sign and magnetic field polarity. Implications to cosmic ray transport will be discussed. References: (1) Bieber, Evenson, and Matthaeus, Geophys. Res. Lett. , Vol 14, p 864, 1987. (2) Smith and Bieber, Proc. 23rd Internat. Cosmic Ray Conf. (Calgary), Vol 3, p 493, 1993.