New statistics on the solar wind control of Earth's ion outflow

Earth's high-latitude outflow of H⁺ and O⁺ ions has been examined with the TIMAS instrument on the Polar satellite in the 15-eV to 33-keV energy range over a nearly three-year period. This outflow is compared with solar wind plasma and magnetic field (IMF) data from the WIND spacecraft, the latter having been time shifted to the subsolar magnetopause and averaged for 15 min prior to each sampling of Earth's ion outflows. When the outflow data are arranged according to the polarity of the IMF B_z and limited to times with B_z > 3 nT or B_z < -3 nT, the total rate of ion outflow is seen to be significantly enhanced with negative B_z, typically by factors of 3 for the O⁺ and 1.5-2 for the H⁺, more than previously reported from similar but less extensive comparisons. With either B_z polarity, the rate of ion outflow is well correlated with the solar wind energy flow density, especially with the density of kinetic energy flow. The rate of ion outflow within the instrument's energy range is a strong function of the Polar satellite altitude, being up to five times larger toward apogee (R∼ 4 to 9 R_E) than at perigee (R∼ 2 R_E) for O⁺ ions. The apogee enhancement may be still larger for the H⁺, but it is somewhat obscured by cusp origin solar H⁺. When ion mean energy is taken into account, the O⁺ ions are seen to gain a 20- to 30-fold increase in energy flow rate from Polar perigee to apogee altitude.