Correlations of magnetospheric ion composition with geomagnetic and solar activity

Abstract

A large ion composition data set consisting of 1‐month averages has been assembled for the energy per charge range 0.9–15.9 keV/e. It includes 48 months of data taken by the Ion Composition Experiments on the ESA/GEOS 1 and 2 satellites at or near geostationary orbit. Data were obtained during the rising and maximum phases of the current solar cycle from May 1977 through November 1981 inclusive. Five ion species are routinely identifiable: H+, He++, He+, O++, and O+, above a limiting density ∼10−3 ions cm−3. Ion densities exhibit a number of very striking statistical correlations with one another and with both Kp and solar EUV as measured by F10.7. One principal result is that increases in the densities of magnetospheric He+, O++, and O+ are observed that are apparently due entirely to increased solar EUV fluxes associated with the rising phase of the current solar cycle. There is a marked rise in O+ density by a factor of ∼8 with increasing geomagnetic activity, but no corresponding increase in either He+ or O++ and only a small increase in H+. The He++/H+ ratio is found to be remarkably constant at ≈0.01. Contrary to ion density results, little or no variation is found in mean energy. These observations are interpreted in terms of the composition and dynamics of two sources of magnetospheric plasma: the solar wind and the high‐latitude topside ionosphere.

Ring Current Energy Input and Decay

“…Because of their heavier mass, oxygen ions carry more energy per unit number density than protons. The enhanced ionospheric outflow during storms (e.g., Moore et al, 1999) enriches the O + content in the plasma sheet, and this stormtime variation is clearly seen in composition measurements (e.g., Young et al, 1982;Lennartsson and Shelley, 1986;Nose et al, 2001;Fu et al, 2001;Pulkkinen et al, 2001). However, these studies show substantial scatter about the mean trends.…”

“…Variations in the observed plasma sheet density are taken to represent temporal variations of a spatially uniform nightside plasma sheet (see Liemohn et al (1999) for details of this method). The composition of the MPA density or flux (n b or φ b ) of species α is assumed to vary with solar and magnetic activity according to the statistical relationship derived by Young et al (1982) while the SOPA data is assumed to be mostly H + (with kappa function high-energy tails for the other species through the SOPA energy range; note that these kappa tails are invariably much lower than the SOPA observations).…”

“…The plasma sheet is an essential participant in magnetic storm dynamics as a reservoir of ring current particles. Depending on the solar wind driving, the plasma sheet can become superdense (up to 10 cm −3 ) , heated (temperatures of >10 keV in the nearEarth region, rather than 5-8 keV), and enriched in ionospheric ions (Young et al, 1982;Moore and Delcourt, 1995;Fu et al, 2001). The energy density in the plasma sheet, in general, is higher during magnetic storms than quiet times (e.g., Nose et al, 2001) but, it is also highly variable, modulating the relative geoeffectiveness of comparable southward IMF intervals even within a single magnetic storm (Liemohn et al, 2001a;Kozyra et al, 2002).…”

Model of electromagnetic ion cyclotron waves in the inner magnetosphere

“…In this study we use flux measurements from the Magnetospheric Plasma Analyzer (MPA) (up to 50 keV) [Bame et al, 1993] and the Synchronous Orbit Particle Analyzer (SOPA) (above 50 keV) [Belian et al, 1992] instruments on the geosynchronous LANL satellites during the modeled event. These instruments measure the total ion flux only, and we use a parametric formula derived by Young et al [1982] to split the total measured flux between H + , O + , and He + . The Young et al formula is based on the observations at geosynchronous orbit by the GEOS-1 and GEOS-2 satellites.…”

Auroral Ionospheric Ion Feeding of the Inner Plasma Sheet during Substorms

“…Most of the previous studies had used long-time averages of AE indices or the Kp index (e.g. Young et al, 1982;Lennartsson and Sharp, 1985;Lermartsson and Shelley, 1986). However, within a time interval of 3 or more hours, several substorms can take place and both the magnetospheric conditions and the ionospheric state can undergo a series of dramatic changes.…”