Equatorial electrojet plasma irregularities observed during late afternoon by the 30MHz coherent scatter radar in S?o Luís, Brazil

摘要

Coherent scatter radar observations conducted right before twilight by the 30MHz radar in S?o Luís (Brazil) during both quiet (December 10, 2001) and disturbed (December 12, 2001) conditions detected type I echoes on the shoulders of broad type II spectra (near zero Doppler velocity). Zonal electric fields inferred from the S?o Luís ionosonde have a larger magnitude during the period where these spectral observations were made than on December 18, 2001 when type I echoes were not observed during late afternoon. The IMF B_z and AE index indicate that the extended geomagnetic disturbance in the afternoon of December 12, 2001 has allowed the interaction between disturbance dynamo and prompt penetration electric fields. The latter electric field component could have exceeded the former to give rise to the observed electric fields, and make possible observation of type I echoes.