Geophysical Research Letters
American Geophysical Union
Ulysses observed five coronal mass ejections (CMEs) and their associated disturbances while the spacecraft was immersed in the polar coronal hole (CH) flow above 70° N in late 2001. Of these CMEs, two were very fast (>850 km s−1) driving strong shocks in the wind ahead, and two others were over-expanding. The two fast CMEs were observed leaving the Sun by LASCO/SOHO, and were observed in the ecliptic by Genesis and ACE. These were large events, spanning at least from the northern heliospheric pole to the ecliptic. One-dimensional hydrodynamic simulations indicate that these could be described as overpressured CMEs launched from the Sun at speeds initially faster than ambient, but then decelerating to the ambient solar wind speed as they propagated outward. The two over-expanding CMEs mark their first occurrence since Ulysses’ first orbit when such CMEs were only observed in polar CH flow.