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

Abstract

[1] Earth's high-latitude outflow of H + and O + ions has been examined with the Toroidal Imaging Mass-Angle Spectrograph instrument on the Polar satellite in the 15-eV to 33-keV energy range over an almost 3-year period near solar minimum (1996)(1997)(1998). This outflow is compared with solar wind plasma and interplanetary 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 magnetic fieldaligned ion flow densities. When the flow data are arranged according to the polarity of the IMF B z (in GSM coordinates) and limited to times with B z > 3 nT or B z < À3 nT, the total rate of ion outflow is seen to be significantly enhanced with negative B z , typically by factors of 2.5-3 for the O + and 1.5-2 for the H + , more than previously reported from similar but less extensive comparisons. With either IMF B z polarity the rate of ion outflow is well correlated with the solar wind energy flow density, especially well 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, increasing almost threefold from perigee (R $ 2 R E ) toward apogee (R $ 4-9 R E ) for O + ions, i.e., up to 10 26 ions s À1 or more per hemisphere. The apogee enhancement may be still larger for the H + , but it is obscured by mantle flow of cusp origin solar H + . Ion mean energy also increases with altitude, leading to about a twentyfold increase in the O + energy flow rate from Polar perigee to apogee altitude, reaching values of 20 GW or more per hemisphere. While the perigee outflow of H + has little or no seasonal modulation, in terms of ions s À1 the O + outflow rates at both altitudes do increase during local summer and so does the rate of cusp origin H + flow near apogee. The latter rate, in fact, has very similar seasonal modulation as the O + rates, suggesting that it has a significant influence on the O + outflow.

Survey of cold ionospheric outflows in the magnetotail

“…10 and 11. Lennartsson et al (2004) presented a study on solar wind control of ion outflow, where significant enhancement of the ion outflow during southward IMF (increase by a factor of 2 for H + ) were observed. There was also a strong dependence on the solar wind kinetic flow density and the Poynting flux.…”

“…As was mentioned in the introductory section, there have been a large number of studies on ion outflow from the polar caps at low altitudes using different spacecraft: DE-1 (Nagai et al, 1984;Chandler et al, 1991), Akebono (Abe et al, 1993(Abe et al, , 1996(Abe et al, , 2004Cully et al, 2003a), and Polar (Moore et al, 1997;Su et al, 1998;Chappell et al, 2000;Lennartsson et al, 2004;Liemohn et al, 2005;Huddleston et al, 2005;Peterson et al, 2006Peterson et al, , 2008. The study at highest altitude so far was conducted by Su et al (1998) using Polar data at apogee altitude at 8 R E above the polar caps.…”

“…The current understanding of the high-latitude ion outflows, including the polar wind, can mainly be attributed to a wealth of studies from Akebono (Abe et al, 1993(Abe et al, , 1996(Abe et al, , 2004Cully et al, 2003a) and Polar (e.g. Moore et al, 1997;Su et al, 1998;Chappell et al, 2000;Lennartsson et al, 2004;Liemohn et al, 2005;Huddleston et al, 2005;Peterson et al, 2006). More details on the previous measurements of the high-latitude ion outflows can be found in the recent review articles by Yau et al (2007) and Moore and Horwitz (2007).…”

Relative outflow enhancements during major geomagnetic storms – Cluster observations

“…However, the scaled O + outflow that we estimate is not considerably higher than during less disturbed conditions. Indeed, Nilsson et al (2012) found that the oxygen ion flux at a high cusp altitude is 5 × 10 12 m −2 s −1 , and Lennartsson et al (2004) observed O + flux in the cusp regions of approximately 10 12 m −2 s −1 above 65…”

Oxygen ion energization by waves in the high altitude cusp and mantle

“…The relatively sporadic appearance of enhanced wave activity presented in Waara et al (2011) may make it difficult to observe the actual heating, so it is not obvious that we should have a good correlation between wave activity and perpendicular temperature for each measurement point. The sporadic nature of the cusp and polar cap ion energization is also discussed by Lennartsson et al (2004). They discussed energization of ions, which was random in both onset and location, as a plausible explanation of their data.…”