Fine structure of low-energy H+ in the nightside auroral region

Abstract

Low-energy H+ data with 6-s resolution from the retarding ion mass spectrometer instrument on DE 1 have been analyzed to reveal the fine structure at middle altitudes of the nightside auroral region. A new method for deconvolving the energy-integrated count rate in the spin plane of the satellite has been used to derive the two-dimensional phase space density. A detailed analysis reveals an alternating conic-beam-conic pattern with the observed conics correlated with large earthward currents in the auroral region. The strong downward current (>1 µA/m2 (equivalent 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.