Relative concentration of He⁺ in the inner magnetosphere as observed by the DE 1 retarding ion mass spectrometer

Abstract

Abstract. With observations from the retarding ion mass spectrometer on the Dynamics Explorer 1 from 1981 through 1984, we examine the He + to H + density ratios as a function of altitude, latitude, season, local time, geomagnetic and solar activity. We find that the ratios are primarily a function of geocentric distance and the solar EUV input. The ratio of the densities, when plotted as a function of geocentric distance, decrease by an order of magnitude from 1 to 4.5 RE. After the He + to H + density ratios are adjusted for the dependence on radial distance, they decrease nonlinearly by a factor of 5 as the solar EUV proxy varies from about 250 to about 70. When the mean variations with both these parameters are removed, the ratios appear to have no dependence on geomagnetic activity, and weak dependence on local time or season, geomagnetic latitude, and L shell.

Thermal plasmaspheric morphology: Effect of geomagnetic and solar activity

“…Early studies [Horwitz et al, 1986] concluded that the ratio of helium ion density to hydrogen ion density is relatively constant. A more recent examination of the DE 1 observations [Craven et al, 1997] revealed strong statistical relationships between the heliumto-hydrogen density ratio and both geocentric distance and solar activity. On the other hand, only a weak dependence on magnetic activity and local time was observed.…”

“…These generalizations should significantly improve the agreement between the model and observations. We demonstrate this with a comparison to in situ measurements of the helium-to-hydrogen ion density ratio by the Dynamics Explorer 1 (DE 1) satellite [Craven et al, 1997]. It should be noted that, in its present version, MSKPM is not intended to reproduce plasmaspheric morphology during the refilling process (for example, no possibility of shocks is included).…”

Space Weather

“…This fixed profile while not very realistic allows the outflow physics and the solar wind controlling influences to be properly isolated. Dynamic ionospheric composition [Craven et al, 1997;Gallagher et al, 1998] are now just becoming available. Future models need to incorporate dynamic changes in the ionospheric com position, but quantitative models for such changes as a function of the solar wind conditions presently do not exist.…”

Lower hybrid resonances stimulated by the four CLUSTER relaxation sounders deep inside the plasmasphere: observations and inferred plasma characteristics

“…The magnetic field amplitude can be estimated from a model, or measured with a good accuracy. The electron density and effective mass (related to composition in terms of the fractional abundance of ions present in the medium) are dependent on the geophysical situation encountered, while empirical, statistical, or theoretical models, are being elaborated (Craven et al, 1997;Gallagher et al, 2000;Pierrard and Lemaire, 2001). Actual measurements of the F lh variable in the regions explored by CLUSTER thus form a valuable data set, bringing complementary information to current models.…”