Radial profiles of quiet time magnetospheric parameters

Abstract

Magnetospheric plasma parameters during geomagnetically quiet conditions are studied with ion measurements covering energies from ~1 keV to ~4 MeV from the Charge Composition Explorer. It is found that the observed quiet time plasma pressure in the midnight sector is comparable (within a factor of 2) to that deduced by Spence et al. (1989) and Kan et al. (1992) from inverting the magnetic field models of Tsyganenko and Usmanov (1982) and Tsyganenko (1987). The radial profile of the total plasma pressure shows a peak generally at L = 3 to 4 and decreases from L = 4 to L = 9 rather monotonically. No largescale earthward decrease in plasma pressure occurs in these outer L shells, contrary to some theoretical expectation for the magnetospheric closure of the region 2 field-aligned current system. The plasma pressure within L ~ 9 is generally anisotropic with a larger pressure component perpendicular to the magnetic field than parallel to the field. This anisotropy tends to increase with smaller L. While the anisotropy is always below the fire hose instability threshold during all quiet time passes studied, it is near the mirror instability threshold in the midnight sector at large L shells due mostly to the large value of plasma beta (>1) there. The radial profile of the azimuthal volume current density is also computed, with the result suggesting that the current density associated with the quiet time ring current population is distributed broadly over the L shells between L = 3.5 and L = 7 with average values in the range of ~1 to 4 nA/m 2 and peak values in the range of ~4 to 8 nA/m 2. Another current region situated beyond L = 7, which may be related to the inner portion of the quiet time cross-tail current, is also apparent and has average and peak current density values similar to those of the ring current.

Computational analysis of the near‐Earth magnetospheric current system during two‐phase decay storms

“…The asymmetric current component can reach 15-20 MA during the main phase of a storm and the symmetric portion can rise up to several MA during the recovery phase. These differences are expected, though, because Tsyganenko [2000] assumed quiet time ring current ion distributions (those of Lui and Hamilton [1992]). Therefore the results from that study and this one are not at odds but are actually quite consistent.…”

Empirical modeling of the quiet time nightside magnetosphere

“…At the inner edge of the ring current, the plasma pressure decreases rapidly inward, producing an eastward-flowing ring current in the inner magnetosphere [Lui and Hamilton, 1992]. This ring current is featured in neither the T87L nor T89 model.…”

“…The observed anisotropy of plasma pressure taken from Lui and Hamilton [1992] is shown in Figure 2 together with an empirical fit. The anisotropy is seen to be large in the inner region and decreases rather systematically at further downstream distances.…”

“…The ISEE-2 data are taken from Spence et al [1989] for the K p = 1-condition, the CCE data from Lui and Hamilton [1992], the ATS-5 data from Deforest and Mcllwain [1971], and the Explorer 45 data from Spence et al [1989] using measurements of 1-872 keV protons presented by Smith and Hoffman [1973]. The range of pressure values from Explorer 45 data indicated by the error bars actually spans the observed pressure taken during geomagnetically quiet to disturbed conditions and thus the lower limit should be used for comparison with the model calculation.…”

Azimuthally asymmetric ring current as a function of <i>D<sub>st</sub></i> and solar wind conditions

“…Statistical studies are not so numerous. Lui and Hamilton (1992) obtained plasma pressure radial proCorrespondence to: Y. P. Maltsev (maltsev@pgi.kolasc.net.ru) files from L=2 to L=9 at noon and at midnight for quiet conditions. De Michelis et al (1999), using AMPTE CCE data, have built energetic plasma profiles in four LT sectors for two AE ranges.…”