Global Flow Rates of 15-eV to 33-keV Ions Away From Earth Near the Polar Satellite Apogee Versus Perigee

As previously reported, the southern hemispheric outflow rates of 15-eV to 33-keV H⁺, O⁺ and He⁺ ions observed 1996-98 by the TIMAS instrument on the Polar satellite about two R E geocentric distance, near perigee, are significantly less than rates observed by instruments at somewhat higher altitudes, especially the H⁺ rates. In this paper a comparison is made with TIMAS observations in the northern hemisphere, at 4-9 R E, by scaling local flow densities along magnetic field lines in the combined IGRF-95 internal and Tsyganenko-95 external field models. The northern hemispheric outflow rates are indeed substantially greater within the given energy range, indicating continued acceleration of lower-energy ions above the Polar perigee altitude. Specifically, the northern rates for O⁺ and He⁺ ions are, respectively, about 3-5 and 6-10 times greater than their southern counterparts, the larger multiplier associated with summer season (April-September). In absolute numbers, in units of 10²⁵ s^-1, the northern outflow rates are in the range of 1-3 for the O⁺ and 0.3-1 for the He⁺, the larger numbers in the summer of 1998, about two years past solar minimum. The average Kp is about 2. The northern hemispheric outward flow rate of H⁺ ions is as much as 30-100 times greater than the southern counterpart, but that is largely due to solar origin ions with net flow away from the cusp region. Unlike the ionospheric H⁺ ions, the solar ions have much enhanced flow rate during the summer season (by almost a factor of three), presumably because the northern cusp is then tilted more toward the solar wind source.