A Technique for Comparing Solar Wind Structures Observed by ACE and Ulysses

Comparison of solar wind observations from the ACE spacecraft, in the ecliptic plane at ∼1 AU, and the Ulysses spacecraft as it orbits over the Sun's poles, may provide valuable information about the latitudinal extent and variation of solar wind structures in the heliosphere. While qualitative comparisons can be made using average properties observed at these two locations, comparison of specific, individual structures requires a procedure to determine if a given structure has been observed by both spacecraft. Before addressing the challenge of comparing such structures at different latitudes, we seek to benckmark our procedure by comparing solar wind structures observed when both spacecraft were near the ecliptic plane. In this paper we assess the use of a 1-D hydrodynamic code to propagate ACE plasma measurements out to the distance of Ulysses and develop a procedure for compensating for the differing longitudes of the ACE and Ulysses spacecraft. In addition to comparing the plasma parameters and their characteristic profiles, we examine superthermal electron measurements and magnetic field polarity to determine if the same features are encountered at both ACE and Ulysses. We find that when both spacecraft are near the ecliptic plane; they frequently observe the same features.