Low-Latitude Pi2 Waves according to Observations on SWARM Satellites and Ground Stations

We considered wave disturbances of the Pi2 type geomagnetic field (periods of 1–2 min) recorded simultaneously by magnetometers at low-latitude stations in Africa and on low-orbit SWARM satellites both during the beginning of a substorm and in non-substorm periods. At night, Pi2 waves in the upper ionosphere and on Earth are almost identical in amplitude and in phase. These waves on the satellite mainly manifest themselves in longitudinal (along the geomagnetic field) and radial magnetic components. A comparison of the observational results with the model of the interaction of MHD waves with the ionosphere–atmosphere–Earth system shows that night low-latitude Pi2 signals are generated by magnetospheric fast magnetosonic waves propagating to the Earth through the opacity region. The results of analytical estimates and numerical simulations are consistent with the properties of Pi2 signals recorded in the upper ionosphere and on Earth.