Cosmic Ray and Solar Particle Investigations Over the South Polar Regions of the Sun

Abstract

Observations of galactic cosmic radiation and anomalous component nuclei with charged particle sensors on the Ulysses spacecraft showed that heliospheric magnetic field structure over the south solar pole does not permit substantially more direct access to the local interstellar cosmic ray spectrum than is possible in the equatorial zone. Fluxes of galactic cosmic rays and the anomalous component increased as a result of latitude gradients by less than 50% from the equator to -80 degrees . Thus, the modulated cosmic ray nucleon, electron, and anomalous component fluxes are nearly spherically symmetric in the inner solar system. The cosmic rays and the anomalous nuclear component underwent a continuous, -26 day recurrent modulation to -80.2 degrees , whereas all recurring magnetic field compressions and recurring streams in the solar wind disappeared above approximately 55 degrees S latitude.

Ulysses COSPIN observations of cosmic rays and solar energetic particles from the South Pole to the North Pole of the Sun during solar maximum

“…(This effect is visible most clearly in the integral intensity trace for the slow latitude scan in Fig. 2d; see Simpson et al, 1995 for a fuller discussion.) At the same time, periodic enhancements of low energy particles accelerated by the shocks bounding the CIRs were also observed.…”

“…1, and no effect at all was detectable for the low energy galactic cosmic rays (panel c). Together with other evidence, such as observations near the poles of periodic variations in the intensity of high energy cosmic rays (McKibben et al, 1995;Kunow et al, 1995;Simpson et al, 1995) and of low energy interplanetary accelerated particles produced by near-equatorial solar wind stream corotating interaction regions (CIRs) (Sanderson et al, 1995;Roelof et al, 1996), the observations led to the conclusion that transport of energetic charged particles across the mean interplanetary magnetic field between the equatorial and polar regions was much more efficient than existing models had contemplated (e.g. Fisk, 1996;Kóta and Jokipii, 1998;McKibben, 1998;Potgeiter, 1998).…”

Statistical study of low‐energy heliosphere particle fluxes from 1.4 to 5 AU over a solar cycle

“…During solar minimum, except near apogee in its orbit, Ulysses will neither measure particles in the near‐ecliptic current sheet nor the effects of the current sheet in accelerating particles (including at corotating interactions regions (CIRs)). Above the heliosphere current sheet, the fluxes of particles are measured to be very low [e.g., Lanzerotti et al , 1995; Simpson et al , 1995]. However, this solar minimum limitation in the statistics is not a serious limitation of this study in that the solar maximum fluxes (which become the particle reservoirs) are of sufficient intensity to be the dominant player when determining the longer‐term implications of the heliosphere radiation environment beyond Earth orbit.…”

Theory of cosmic ray modulation

“…In a Fisk-type field, magnetic field lines exhibit extensive excursions in heliographic latitude, and this has been cited as a possible explanation for recurrent energetic particle events observed by the Ulysses spacecraft at high latitudes (see, e.g., Simpson et al 1995;Zhang 1997;Paizis et al 1999), as well as the smaller than expected cosmic-ray intensities observed at high latitudes (Simpson et al 1996). The Fisk field and the physics behind it have been discussed in a series of papers (see, e.g., Fisk & Schwadron 2001, and references therein) where it is assumed that the polar coronal hole is symmetric with respect to the solar magnetic axis, and that the magnetic field expands nonradially.…”