Spectra of polar heliospheric fields and implications for field structure

Abstract

The predictions of the “Fisk” model for a peak at the equatorial solar rotation frequency in the spectrum of the latitudinal component of the heliospheric magnetic field were found to give values significantly larger than those observed. The observed values were statistically the same as observed in the ecliptic and were consistent with random fluctuations about the (null) Parker field component. These conclusions are based on spectra of field and plasma quantities using Ulysses data from the first southern and northern polar passes. There was also no evidence for solar photospheric differential rotation in the latitudinal component. A related search for signatures of the differential rotation (not directly part of the Fisk magnetic field model) yielded the strongest evidence for a photospheric influence on the radial component of the solar wind velocity and related “compressive” quantities.