Cosmic Ray Observations in the 3-D Heliosphere through the Solar Cycle: New Insights from Ulysses

Abstract

The Ulysses spacecraft has been the first to orbit the Sun over its poles and to explore the heliosphere at high heliolatitudes. It has completed three fast-latitude scans, the first and the most recent one at solar minimum, the second one at solar maximum. The Ulysses observations over 17 of the 22 years of a solar magnetic cycle have produced unexpected surprises. Contrary to pre-mission expectations, the energy spectrum of cosmic ray nucleons was found to be highly modulated even over the solar poles. At solar minimum, only small positive latitudinal cosmic ray gradients were found in the A positive cycle. No latitudinal gradient was seen in the current A negative cycle, At solar maximum, the cosmic ray fluxes were dominated by temporal fluctuations. The Ulysses observations of cosmic rays, the solar wind and the heliospheric magnetic field have significantly contributed to the theoretical understanding of solar modulation in the inner heliosphere, especially at high heliolatitudes.