X-ray Image Data Research Articles

The auroral energy deposition over the polar ionosphere during substorms

The global Joule heating distributions for the period of 23–24 July 1983 are estimated through the magnetogram-inversion method developed by Kamide et al. (1981, J. geophys. Res. 86, 801). Unlike previous work which mostly used one of statistically-determined conductance models, this study employs instantaneous ionospheric conductance distributions deduced from the DMSP-F6 Bremsstrahlung X-ray image data. Also estimated from the X-ray data are instantaneous global particle heating distributions. The two heating distributions thus obtained allow us to investigate various aspects of heat energy processes over the polar ionosphere on an instantaneous basis. A special emphasis is placed on their spatial and temporal behaviors. Several important results of this study are summarized as follows. (1) Regions of significant Joule heating are closely associated with the auroral electrojets prominently in the dawn and dusk sectors. (2) The major Joule heating usually occurs poleward of the major particle heating region particularly in the morning sector. On the other hand, the two heating patterns are complementary in the longitudinal direction. (3) There is a higher correlation between the global Joule heating rate U j and AE (12) than between the global particle heating rate ( U A ) and AE(12). (4) The particle heating rate tends to be more prominent during the maximum phase of substorms and afterward than during the preexpansion phase. (5) The U J U A ratio varies by more than a factor of 10, suggesting the wide variability in the relative importance of the two heating rates. On average, however, U J is larger than U A by a factor of 6.

EXOSAT observations of the Perseus cluster

EXOSAT CMA and GSPC observations of the Perseus Cluster of galaxies are reported. The soft X-ray image data confirm the earlier Einstein Observatory results in terms of the density distribution radially outward from NGC1275. We have used the GSPC spectral data at higher energies to study the strength of the X-ray continuum and of the Fe line emission over the cluster. An asymmetry is found in the distribution of the hot gas around NGC1275, which is consistent with the E-W direction of the ellipticity discovered at soft X-rays by the Einstein Observatory.