ULF turbulence in magnetospheric boundary layers during April 1997 as measured aboard Magion-4 subsatellite Original Research Article

Our study is based on complete data set from ULF electromagnetic measurements carried aboard the Magion-4 subsatellite of the Inerball-1 spacecraft, when the high-latitude near-Earth magnetotail and magnetopause regions were encountered. For the first time purely electrostatic broadband ULF waves with frequencies below the ion cyclotron frequency are observed in the high-latitude near-Earth magnetotail region. At the mantle-magnetopause region the ULF fluctuations are in general electromagnetic, the wave spectrum being around the ion cyclotron frequencies. The ULF wave activity is characterized by a broadband spectrum and discrete bursts with minute duration. Possible generation and propagation mechanisms for the observed ULF waves are discussed. A plasma gradient mechanism for the electrostatic ULF wave generation in the high-latitude near-Earth magnetotail is suggested.