The Cluster spacecraft's view of the motion of the high-latitude magnetopause

Abstract. The boundary between the interplanetary magnetic field and the terrestrial magnetic field is the magnetopause. This magnetopause is influenced by dynamic changes in the solar wind, that is different solar wind conditions lead to a change in the shape and location of the magnetopause. The interaction between the solar wind and the magnetosphere can be studied from in-situ spacecraft observations. Many studies focus on the equatorial plane, as this is where recent spacecraft constellations such as THEMIS or MMS operate. However, to fully capture the interaction, it is important to study the high latitude regions as well. The Cluster spacecraft allow us to collect a dataset of high-latitude magnetopause crossings and study magnetopause motion in this region, as well as deviations from established magnetopause models. We use multi-spacecraft analysis tools to investigate the direction of magnetopause motion in the high latitudes and compare the occurrence of crossings at different locations with the result in the equatorial plane. We find that the high-latitude magnetopause motion is generally consistent with previously reported values and seems to be more often associated with a closed magnetopause boundary. We show that on average the magnetopause moves faster inwards than outwards. Furthermore, the occurrence of magnetopause positions beyond those predicted by the Shue et al. (1998) model at high latitudes is found to be caused by the similar solar wind parameters as in the equatorial plane. Finally, we highlight the importance of the dipole tilt angle at high latitudes. Our results may be useful for the interpretation of plasma measurements from the upcoming SMILE mission (Branduardi-Raymont et al., 2018), as this spacecraft will also fly frequently through the high-latitude magnetopause.