Poynting flux measurements on a satellite: A diagnostic tool for space research

Abstract

The first satellite observations of the total field‐aligned component of the quasi‐dc Poynting flux are presented for two passes over the polar region, one in the noon sector and one in the afternoon. The energy input due to electron precipitation is also presented. In the noon pass the downward Poynting flux in the auroral oval was comparable to the kinetic energy input rate. The peak electromagnetic energy input rate of 6 ergs/(cm² s) equaled the peak particle input while the integrated electromagnetic value along the trajectory was 60% that of the particles. In the afternoon pass the peak electromagnetic energy input was also about 6 ergs/(cm² s), but the peak particle energy was 6 times this value. The average electromagnetic input was 10% of the particle input for the pass. In this study we can measure the Poynting flux only over a limited range of scale sizes; thus the contribution to the total energy budget in the polar cap cannot be determined. Both passes show small regions characterized by upward Poynting flux suggesting a neutral wind dynamo. There is also evidence during part of the noontime pass that the external generator acted in opposition to an existing wind field since the Poynting flux was greater than the estimate of Joule heating from the electric field measurement alone (i.e., from ΣpE²). In the course of deriving Poynting's theorem for the geophysical case we also present a proof that ground magnetometer systems respond primarily to the Hall current which does not depend upon geometric cancellation between the field generated by Pedersen and field‐aligned currents.

High-latitude electromagnetic and particle energy flux during an event with sustained strongly northward IMF

“…For this event however, the maximum electromagnetic energy flux was 50 mW/m 2 , considerably higher than typical maxima inferred from radars and assimilation techniques. It is also at the high end of energy fluxes observed from satellites which were observed at auroral latitudes (Kelley et al, 1991;Gary et al, 1995). Our result implies that the localized heating near the magnetic pole during this event was particularly strong and should be associated with a strong localized thermospheric temperature enhancement and corresponding upwelling comparable in intensity to that occurring at auroral latitudes during active times.…”

Direct measurements of the Poynting flux associated with convection electric fields in the magnetosphere

“…Moreover, surveys of large-scale Poynting fluxes were primarily performed in the ionospheric altitudes. Low-altitude satellite data and global circulation models showed that these are directed predominantly downward, which means dominance of the magnetospheric driver [Kelley et al, 1991;Gary et al, 1995;Deng et al, 2008]. Upward Poynting fluxes are generally weaker but exist especially during a larger southward IMF [Gary et al, 1995], indicating presence of escaping electromagnetic energy associated with large-scale electric fields from the ionosphere toward the magnetosphere.…”

Ionosphere-thermosphere (IT) response to solar wind forcing during magnetic storms

“…Poynting fluxes have been calculated for the ionosphere for some time (Kelley et al 1991;Wilder et al 2012;Cosgrove et al 2014). DMSP routinely measures the ion drifts from which the convective electric field (E) can be extracted, as well as magnetic perturbations (dB) about the Earth's magnetic field.…”