Ulysses observations of latitude gradients in the heliospheric magnetic field

• Published in: Advances in space research 1995-01, Vol.16 (9), p.165-170
• Main Authors: Smith, E.J., Balogh, A., Lepping, R.P., Neugebauer, M., Phillips, J., Tsurutani, B.T.
• Format: Article
• Language: English
• Subjects: Solar Physics
• ISSN: 0273-1177; 1879-1948
• DOI: 10.1016/0273-1177(95)00328-C

Several parameters measured by Ulysses as it traveled southward to heliographic latitudes of −50° are presented and analyzed. The radial component of the magnetic field, averaged over 5° latitude increments and extrapolated back to 1 AU, is found to agree with baseline measurements provided by IMP-8. There is little, if any, evidence of a latitude gradient, a result consistent with the dominance of the magnetic field associated with the heliospheric current sheet and with recent models which include the effect of the current sheet as well as of source surface fields. Thus far, the spiral angle agrees with the Parker spiral assuming a rate of rotation of the field lines at the Sun equal to the equatorial value. No evidence is seen of either a change in rotation rate with latitude or an unwinding of the spiral as suggested by a recent analysis. Hourly variances in the field magnitude and in the sum of the variances in the components, normalized to the square of the observed field strength, show the former to be independent of latitude while the latter shows a strong increase with latitude. These two observations are shown to be associated with Alfvén waves that are continuously present at high latitudes. The waves have large amplitudes, extend to long periods, and have important implications for galactic cosmic rays and the solar wind.