Ulysses observations of very different heliospheric structure during the declining phase of solar activity cycle 23

Abstract

This study examines the most recent observations from the solar wind experiment (SWOOPS) on the Ulysses spacecraft. In contrast to observations over the same locations in the declining phase of the previous solar activity cycle, these data show a more complicated heliospheric structure. Around the start of 2003, a band of slow solar wind resided at ∼20°–25°N latitude at all helio‐longitudes. Subsequently, Ulysses failed to observe a well‐organized corotating stream structure as it headed southward from the ecliptic plane, even though, in the previous solar cycle, Ulysses observed a regularly structured stream pattern. These observations show that the three‐dimensional structure of the heliosphere can differ significantly from one solar cycle to the next. Finally, we show that the solar wind dynamic pressure has been relatively stable throughout 2005, indicating that the termination shock distance will also likely be relatively stable throughout 2006.