PONDEROMOTIVE EFFECTS ON DISTRIBUTIONS OF O-ZONE( IONS IN THE AURORAL)

Test particle calculations are used to compute the effects of gravity and ponderomotive acceleration by shear Alfven wave oscillations on th e distribution function of O+ ions along auroral field lines, assuming an ionospheric Maxwellian source of the ions at 2000 km altitude with similar to 0.5 eV of thermal energy in the parallel component of velo city. The electric field model corresponds to a standing wave oscillat ion with a frequency similar to 1 Hz in the azimuthal direction superi mposed on the background dipole field, in which the wave amplitude is either increasing or decreasing in time. The electric field is taken t o be primarily in the perpendicular direction. The time varying wave p roduces broad distributions with widths of 2 to 10 times the initial 0 .5-eV thermal energy of the Maxwellian source, and the density and flu x of upward going O+ ions at one Earth radius are both enhanced in thi s model. The oxygen ion distribution functions at 1 R(E) altitude resu lting from interaction with waves whose amplitudes are increasing in t ime have a more gradual lower energy cutoff than do the distribution f unctions resulting from decaying waves. The high-energy part of the di stribution functions in growing waves reflects the temperature of the Maxwellian source, while the high-energy part of the distributions res ulting from decaying waves steepens with time, independent of the sour ce temperature.