Magnetospheric whistler-mode waves detected simultaneously by the DEMETER spacecraft and the Kannuslehto Station

Conjugate observations of magnetospheric whistler-mode waves provided by the DEMETER spacecraft at an altitude of about 660 km and the Kannuslehto station located near Sodankyla, Finland are analyzed. More than 500 DEMETER half-orbits between November 2006 and March 2008 overlap with the Kannuslehto data. The analysis includes waves at frequencies up to 16 kHz. We aim to determine the characteristic spatial scales of the waves and their propagation to the ground. For this purpose, correlations of wave intensities measured by both the spacecraft and the ground-based station are evaluated using two different approaches: i) direct correlations of wave intensities measured simultaneously at the same frequencies, and ii) correlations of wave patterns over a moving frequency-time window of a predefined size. The resulting correlations are studied as a function of the L-shell/geomagnetic longitude separation between the spacecraft and the ground-based station. The corresponding correlation lengths are determined as a function of frequency. Additionally, correlations of the wave intensities and the geomagnetic activity indices (Kp/AE) are calculated, demonstrating rather different dependence on the ground and at low altitudes.