Monitoring the Dynamics of the Ionosphere–Plasmasphere System by Ground-Based ULF Wave Observations

Cross-spectral analysis of ULF wave measurements recorded at ground magnetometer
stations closely spaced in latitude allows accurate determinations of
magnetospheric field line resonance (FLR) frequencies. This is a useful tool for remote
sensing temporal and spatial variations of the magnetospheric plasma mass density. The
spatial configuration of the South European GeoMagnetic Array (SEGMA, 1.56 < L <
1.89) offers the possibility to perform such studies at low latitudes allowing to monitor the
dynamical coupling between the ionosphere and the inner plasmasphere. As an example of
this capability we present the results of a cross-correlation analysis between FLR frequencies
and solar EUV irradiance (as monitored by the 10.7-cm solar radio flux F10.7)
suggesting that changes in the inner plasmasphere density follow the short-term (27-day)
variations of the solar irradiance with a time delay of 1–2 days. As an additional example
we present the results of a comparative analysis of FLR measurements, ionospheric vertical
soundings and vertical TEC measurements during the development of a geomagnetic
storm.

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