Abstract Measurements of the heliospheric magnetic field made over the last several years are surveyed with emphasis on Pioneer 11 observations near 35 AU and Ulysses observations between 1 and 5 AU. The increase in field magnitude at 1 AU near the recent sunspot maximum is also seen at Pioneer 11. Extrapolation of the magnitude and azimuthal component of the field as measured at Pioneer back to 1 AU, assuming the Parker model of a time stationary, spherically symmetric solar wind, leads to values which are systematically lower than the 1 AU measurements. This flux deficit is not confirmed by Voyager measurements and the origin of the discrepancy is unknown. The sector structure continues to be well-defined at large distances. There is evidence at 35 AU of a reduction in the peak-to-peak quasi-periodic (∼25 day) variations which are characteristic of the magnetic field structure at lesser radial distances. In 1991, the structure at Pioneer 11 was dominated by a large long-lasting increase associated with the major solar events of March–May. Those events are clearly seen in the Ulysses observations at 2.2 AU and consist of several coronal mass ejections and accompanying shocks. In the latter half of 1991, a sequence of recurrent corotating interaction regions appears with their companion forward and reverse shocks. Contrary to what might have been expected, the March events did not cause a significant restructuring of the heliospheric current sheet, specifically, a change in its inclination. As a consequence, the interval is of particular interest to studies of the solar modulation of galactic cosmic rays and to the effect of global merged interaction regions. The search for ion cyclotron waves resulting from the pick-up of freshly ionized interstellar hydrogen, carried out most recently using Voyager data, continues to be unsuccessful. Thus, there is still no evidence in magnetic field measurements at large distances of the purported interaction between the solar wind and the interstellar medium.
Magnetic fields throughout the heliosphere
Advances in Space Research ; 13 , 6 ; 5-14
01.01.1993
10 pages
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
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