FINE-STRUCTURE OF LOW-ENERGY H+ IN THE NIGHTSIDE AURORAL REGION

Low-energy H+ data with 6-s resolution from the retarding ion mass spe ctrometer instrument on DE 1 have been analyzed to reveal the fine str ucture at middle altitudes of the nightside auroral region. A new meth od for deconvolving the energy-integrated count rate in the spin plane of the satellite has been used to derive the two-dimensional phase sp ace density. A detailed analysis reveals an alternating conic-beam-con ic pattern with the observed conics correlated with large earthward cu rrents in the auroral region. The strong downward current (>1 muA/m2(e quivalent value at ionosphere)) provides a free energy source for the perpendicular ion heating, that generates the ion conics with energies from several eV to tens of eV. The bowl shape distribution of the low -energy H+ is caused by the extended perpendicular heating. The strong correlation between conics and large downward currents suggests that the current-driven electrostatic ion cyclotron wave is an appropriate candidate for the transverse heating mechanism.