The location of the high‐latitude polar cusp and the shape of the surrounding magnetopause

Hawkeye magnetic field measurements have been used to determine the location of the magnetopause in the vicinity of the polar cusp. We can clearly distinguish field lines above the cusp from those below the cusp and thus can well identify the statistical location of the cusp. As expected, we find that the location of the polar cusp depends strongly on the dipole tilt angle. However, there appears to be no indentation of the magnetopause surrounding the cusp in contrast to models of the cusp that are frequently drawn. At the magnetopause on the noon meridian the cusp is at a latitude of nearly 82° for northward interplanetary magnetic field (IMF) and 80° for southward IMF. This is more swept back than in models such as that of N. Tsyganenko but less swept back than in the computer simulation of C. C. Wu. In our study, both geocentric solar magnetospheric (GSM) and solar magnetic (SM) coordinates are used. GSM coordinates order the high‐altitude polar cusp position slightly better than SM coordinates.