We examine the mapping of magnetospheric and ionospheric electric fields in a kinetic model of magnetospheric-ionospheric electrodynamic coupling proposed for the aurora by . A new feature is the generalization of the kinetic current-po tent is1 relationship to the returncurrent region (identified as a region where the parallel potential drop from magnetosphere to ionosphere is positive); such a return current always exists unless the ionosphere is electrically charged to grossly unphysical values.We are able for the first time to give a coherent phenomenological picture of both the low-energy return current and the high-energy precipitation of an inverted-V.The mapping between magnetospheric_ and ionospheric electric fields is phrased in terms of a Green's function which acts as a filter, emphasizing magnetospheric latitudinal spatial scales of order (when mapped to the ionosphere) 50-150 km. This same length, when multiplied by Perpendicular electric fields just above the ionosphere, sets the scale for parallel potential drops between the ionosphere and equatorial magnetosphere.

We assess the principal statistical and physical uncertainties associated with the determination of magnetic field strengths in clusters of galaxies from measurements of Faraday rotation (FR) and Compton-synchrotron emissions. In the former case a basic limitation is noted, that the relative uncertainty in the estimation of the mean-squared FR will generally be at least one third. Even greater uncertainty stems from the crucial dependence of the Faraday-deduced field on the coherence length scale characterizing its random orientation; we further elaborate this dependence, and argue that previous estimates of the field are likely to be too high by a factor of a few. Lack of detailed spatial information on the radio emission-and the recently deduced nonthermal X-ray emission in four clusters-has led to an underestimation of the mean value of the field in cluster cores. We conclude therefore that it is premature to draw definite quantitative conclusions from the previously-claimed seemingly-discrepant values of the field determined by these two methods.

No abstract

Under current solar minimum conditions at Arecibo, Puerto Rico, large (∼1000–2000 K) enhancements in electron temperature are observed in the winter, nighttime ionosphere when high‐power 3‐MHz radio waves reflect near the F region peak. Computational modeling has been performed to determine the cause of the unusually large temperature enhancements. The results indicate that low collisional cooling rates combined with strong thermal conduction along geomagnetic field lines play a key role in elevating F region temperatures and spreading the electron temperature enhancements far outside of the region where radio wave energy is deposited. Thus, the dramatically large temperature enhancements are attributable primarily to expected low cooling rates of the electron gas, rather than unexpectedly high heating rates.