LOW-FREQUENCY ELECTROMAGNETIC TURBULENCE OBSERVED NEAR THE SUBSTORM ONSET SITE

On the basis of wave and plasma observations of the Geotail satellite, the instability mode of low-frequency (1-10 Hz) electromagnetic turbu lence observed at the neutral sheet during substorms has been examined . Quantitative estimation has also been made for the anomalous heating and resistivity resulting from the electromagnetic turbulence. Four p ossible candidates of substorm onset sites, characterized by the near- Earth neutral line, are found in the data sets obtained at substorm on set times. In these events, wave spectra obtained by the search-coil m agnetometer and the spherical double-probe instrument clearly show the existence of electromagnetic wave activity in the lower hybrid freque ncy range at and near the neutral sheet. The linear and quasi-linear c alculations of the lower hybrid drift instability well explain the obs erved electromagnetic turbulence quantitatively, The calculated charac teristic electron heating time is comparable to the timescale of the e xpansion onset, while that of ion heating time is much longer. The est imated anomalous resistivity fails to supply enough dissipation for th e resistive tearing mode instability.