The inner magnetosphere ion composition and local time distribution over a solar cycle

Abstract

Using the Cluster/Composition and Distribution Function (CODIF) analyzer data set from 2001 to 2013, a full solar cycle, we determine the ion distributions for H+, He+, and O+ in the inner magnetosphere (L < 12) over the energy range 40 eV to 40 keV as a function magnetic local time, solar EUV (F10.7), and geomagnetic activity (Kp). Concentrating on L = 6–7 for comparison with previous studies at geosynchronous orbit, we determine both the average flux at 90° pitch angle and the pitch angle anisotropy as a function of energy and magnetic local time. We clearly see the minimum in the H+ spectrum that results from the competition between eastward and westward drifts. The feature is weaker in O+ and He+, leading to higher O+/H+ and He+/H+ ratios in the affected region, and also to a higher pitch angle anisotropy, both features expected from the long‐term effects of charge exchange. We also determine how the nightside L = 6–7 densities and temperatures vary with geomagnetic activity (Kp) and solar EUV (F10.7). Consistent with other studies, we find that the O+ density and relative abundance increase significantly with both Kp and F10.7. He+ density increases with F10.7, but not significantly with Kp. The temperatures of all species decrease with increasing F10.7. The O+ and He+ densities increase from L = 12 to L ~ 3–4, both absolutely and relative to H+, and then drop off sharply. The results give a comprehensive view of the inner magnetosphere using a contiguous long‐term data set that supports much of the earlier work from GEOS, ISEE, Active Magnetospheric Particle Tracer Explorers, and Polar from previous solar cycles.

The complex nature of storm‐time ion dynamics: Transport and local acceleration

“…Drifting plasma sheet ions are energized by the increased magnetic field strength (as well as temporarily energized by field fluctuations). Aging of the drifting plasma over a~24 h period led to an enhanced heavy ion content [Smith and Bewtra, 1978;Fok et al, 1991;Ebihara et al, 1998;Ferradas et al, 2015;Kistler and Mouikis, 2016]. This plasma mimics the presence of local in situ acceleration of the low-energy population.…”

“…Since O + is a major constituent of the ionosphere, and not of the solar wind, the presence of high-density O + (along with He + ) is strongly indicative of an ionospheric source. These losses result in changes in the composition that are energy (i.e., drift) dependent [Ferradas et al, 2015;Kistler and Mouikis, 2016]. (a) Direct and local acceleration of ionosphere and/or plasmasphere ions.…”

Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: implications for atmospheric escape on evolutionary timescales

“…For example, Yau et al (1988) parameterised the ionospheric ion outflow and found that the O + outflow rate increased exponentially with Kp as exp(0.5 Kp). Other studies that have shown a clear correlation between O + and geomagnetic activity are Peterson et al (2001), Cully et al (2003), and Kistler and Mouikis (2016). The O + density close to the mid-latitude magnetopause was shown by Bouhram et al (2005) to also increase exponentially with Kp.…”

The Impact of Oxygen on the Reconnection Rate

“…Spacecraft observation shows that the density of oxygen in the plasma sheet can be the dominating ion species during storm-time conditions (André & Cully, 2012;Kistler & Mouikis, 2016;Kistler et al, 2005Kistler et al, , 2006Mouikis et al, 2010). During such conditions, ionospheric outflow from high latitudes enriches the magnetospheric lobes with cold oxygen.…”