Central plasma sheet ion properties as inferred from ionospheric observations

Abstract

Abstract. A method of inferring central plasma sheet (CPS) temperature, density, and pressure from ionospheric observations is developed. The advantage of this method over in situ measurements is that the CPS can be studied in its entirety, rather than only in fragments. As a result, for the first time, comprehensive two-dimensional equatorial maps of CPS pressure, density, and temperature within the isotropic plasma sheet are produced. These particle properties are calculated from data taken by the Special Sensor for Precipitating Particles, version 4 (SSJ4) particle instruments onboard DMSP F8, F9, F10, and Fll satellites during the entire year of 1992. Ion spectra occurring in conjunction with electron acceleration events are specifically excluded. Because of the variability of magnetotail stretching, the mapping to the plasma sheet is done using a modified Tsyganenko [1989] magnetic field model (T89) adjusted to agree with the actual magnetotail stretch at observation time. The latter is inferred with a high degree of accuracy (correlation coefficient -0.9) from the latitude of the DMSP b2i boundary (equivalent to the ion isotropy boundary). The results show that temperature, pressure, and density all exhibit dawn-dusk asymmetries unresolved with previous measurements. The ion temperature peaks near the midnight meridian. This peak, which has been associated with bursty bulk flow events, w.idens in the Y direction with increased activity. The temperature is higher at dusk than at dawn, and this asymmetry increases with decreasing distance from the Earth. In contrast, the density is higher at dawn than at dusk, and there appears to be a density enhancement in the low-latitude boundary layer regions which increases with decreasing magnetic activity. In the near-Earth regions, the pressure is higher at dusk than at dawn, but this asymmetry weakens with increasing distance from the Earth and may even reverse so that at distances X < --10 to -12 Roe, depending on magnetic activity, the dawn sector has slightly higher pressure. The temperature and density asymmetries in the near-Earth region are consistent with the ion westward gradient/curvature drift as the ions ExB convect earthward. When the solar wind dynamic pressure increases, CPS density and pressure appear to increase, but the temperature remains relatively constant. Comparison with previously published work indicates good agreement between the inferred pressure, temperature, and density and those obtained from in situ data. This new method should provide a continuous mechanism to monitor the pressure, temperature, and density in the magnetotail with unprecedented comprehensiveness.

3-D Force-balanced Magnetospheric Configurations

“…In this paper we present results with equatorial P (R, φ, Z = 0) = P (R, Z = 0), where R is the distance from Earth in the equatorial plane. This should not be an unreasonable choice, since observations [e.g., Wing and Newell , 1998] report the pressure further than about 7 R E to vary little in the azimuthal (φ) direction. Closer to Earth on the other hand, the plasma β generally tends to be quite low, and therefore the pressure does not influence much the magnetic field configuration.…”

“…Observing the distribution of field-aligned precipitating ions in the ionosphere one thus obtains an accurate reflection of their isotropic distribution function in the plasma sheet. Based on the theory of Sergeev et al [1993], Wing and Newell [1998] have inferred the plasma sheet pressure contribution due to protons by observing particle precipitation in the ionosphere at latitudes higher than the so-called "isotropy boundary." Their method relies on the technique, commonly employed in the space physics community, of relating the 2-D pressure measurements to different points in space (thus obtaining a 3-D distribution) by "mapping" the pressure using empirical magnetic field models.…”

“…Finally, probably the most extensive observations of plasma sheet pressure are those of the GEOTAIL mission [e.g., Hori et al, 2000]. Besides in situ plasma sheet measurements, a novel technique [Wing and Newell , 1998] has allowed imaging of plasma sheet ions by analyzing their precipitation at low altitudes in the ionosphere. The theoretical background of the method relies on the isotropization of plasma sheet ions when the ratio of their gyroradius to the magnetic field curvature exceeds a certain value [Sergeev et al, 1993].…”

Heat flux in magnetospheric convection: A calculation based on adiabatic drift theory

“…Including this effect in (28) - (30) exacerbates the earthward decreases of p and n. At any rate, the above solution is a demonstration that the heat flux terms do lead to significant sub-adiabaticity, but are not purported to be realistic representations of the true magnetosphere, which must be solved in two dimensions and with (25) incorporated. Comparisons with empirical studies such as those by Wing and Newell [1998] and Wang et al [2006] need to be carried out. We will deal with this rather extensive problem in a separate study.…”

Sensitivity studies of the E region neutral response to the postmidnight diffuse aurora

“…Even larger E region winds, of around 350 to 400 m/s at 30-km altitude, have been observed during rocket campaigns within the aurora on the premidnight side (Mikkelsen et al, 1987(Mikkelsen et al, , 1981. The postmidnight diffuse aurora will be investigated here, which may have brighter emissions than the premidnight diffuse aurora due to the larger precipitating electron energy fluxes, resulting from the tendency of plasma sheet electrons to drift towards the dawn side (Wing and Newell 1998;Wang et al 2001). This larger precipitation will result in increased E region ion densities, enhanced coupling to the neutrals, and enhanced Joule heating.…”