Multi-Spacecraft Observations of the Mid-Altitude Cusp

Many aspects of the magnetospheric cusps, from how it should be defined to how various altitude measurements relate to each other, remain to be resolved. The Cluster mission, with its unique multi-spacecraft capabilities offer exciting new insights into the nature and structure of the mid-altitude cusps. Previous studies have shown the low-altitude cusps to be consistent with the Crooker antiparallel merging model. At high-altitudes, observations reported by Savin using Interball and Prognoz data indicate large amplitude, low-frequency waves in the Turbulent Boundary Layer just at and outside the magnetopause. Recent Cluster observations made at mid-altitudes (~5 RE) will be presented which are consistent with the narrow, wedge-shaped cusp of Crooker and contain persistent wave signatures that are compatible with the previously reported high-altitude measurements. Thus, the cusp signatures observed at a wide range of altitudes begin to present a coherent picture of the cusp as the focus of open field lines from the entire magnetopause current layer.