Solar wind influence on the oxygen content of ion outflow in the high‐altitude polar cap during solar minimum conditions

Abstract

Abstract. We correlate solar wind and interplanetary magnetic field (IMF) properties with the properties of O+ and H+ during early 1996 (solar minimum) at altitudes between 5.5 and 8.9 R E geocentric using the Thermal Ion Dynamics Experiment (TIDE) on the Polar satellite. Throughout the high-altitude polar cap we observe H+ to be more abundant than O+. O+ is found to be more abundant at lower latitudes when the solar wind speed is low (and Kp is low), while at higher solar wind speeds (and high Kp), O+ is observed across most of the polar cap. The O+ density and parallel flux are well organized by solar wind dynamic pressure, both increasing with solar wind dynamic pressure. Both the O+ density and parallel flux have positive correlations with both VswBiM F and Esw. No correlation is found between O+ density and IMF Bz, although a nonlinear relationship with IMF By is observed, possibly due to a strong linear correlation with the dynamic pressure. H+ is not as highly correlated with solar wind and IMF parameters, although H+ density and parallel flux are negatively correlated with IMF By and positively correlated with both VswBiM F and Esw. In this solar minimum data set, H+ is dominant, so that contributions of this plasma to the plasma sheet would have very low O+ to H+ ratios.

Solar wind control of Earth's H+ and O+ outflow rates in the 15‐eV to 33‐keV energy range

“…The difference is the largest in Figure 4, where the O + flow rate is mostly 3 times greater with negative B z . This is significantly more of a difference than previously reported about both polar region O + outflows in various energy ranges [e.g., Abe et al, 1996;Øieroset et al, 2000;Elliott et al, 2001;Cully et al, 2003] and the 0.1-to 16-keV O + concentration in the plasma sheet [Lennartsson, 1995]. The larger difference may be caused by a combination of two circumstances: (1) The ±3 nT or stronger B z is a more discerning condition than most previously used, and (2) the 15-min averaging may be a fortuitous choice.…”

“…That interpretation is also consistent with the locally enhanced O + flow density in the cusp regions of Figure 1, and it meshes quite well, in fact, with earlier reports on the outflow of O + ions with energies below 15 eV, since the rate of outflow of so-called ''suprathermal'' O + ions has been found to be especially strong in the cusp regions (''ion fountains'' [Lockwood et al, 1985]) and rather well correlated with the solar wind dynamic pressure, especially with its standard deviation, more so than with several other solar wind parameters [e.g., Moore et al, 1999;Elliott et al, 2001;Cully et al, 2003]. In terms of solar wind power input it might seem then that the kinetic energy flow density K ought to be especially important, a conjecture that can indeed be drawn from the comparison of K and S in Figures 4 and 5 as well.…”

Change of the plasma sheet ion composition during magnetic storm development observed by the Geotail spacecraft

“…Recent studies employing the Polar spacecraft have also shown that ionospheric plasma outflow responds to the solar wind dynamic pressure [Moore et al, 1999Elliott et al, 2001]. Moore et al [1999] have reported a correlation between upwelling O + escape flux and the standard deviation in the solar wind dynamic pressure.…”

“…Moore et al [1999] have reported a correlation between upwelling O + escape flux and the standard deviation in the solar wind dynamic pressure. Elliott et al [2001] have found that density of outflowing O + correlated best with the solar wind dynamic pressure. Ions escaping from the polar ionosphere (in particular, from the dayside cusps) are transported to the plasma sheet, according to the results of particle tracing by Cladis and Francis [1985], Cladis [1986Cladis [ , 1988, and Chappell et al…”

“…These results indicate that when the number density of ions of ionospheric origin in the plasma sheet was (was not) increased, the solar wind dynamic pressure had (had not) been enhanced. Thus a probable scenario for event 1 is that the enhancement of solar wind dynamic pressure causes a flux increase of upwelling ionospheric ions, as reported by Giles [1993], Moore et al [1999], and Elliott et al [2001]; then these ionospheric ions are transported to the plasma sheet where the ions are accelerated. We suggest that enhancement of solar wind dynamic pressure can be another reason for the increase of the energy density ratios.…”