Abstract
Abstract. The response of the polar ionosphere–thermosphere (I-T) system to electromagnetic (EM) energy input is fundamentally different to that from particle precipitation. To understand the I-T response to polar energy input one must know the intensities and spatial distributions of both EM and precipitation energy deposition. Moreover, since individual events typically display behavior different from statistical models, it is important to observe the global system state for specific events. We present an analysis of an event in Northern Hemisphere winter for sustained southward interplanetary magnetic field (IMF), 10 January 2002, 10:00–12:00 UT, for which excellent observations are available from the constellation of Iridium satellites, the SuperDARN radar network, and the Far-Ultraviolet (FUV) instrument on the IMAGE satellite. Using data from these assets we determine the EM and particle precipitation energy fluxes to the Northern Hemisphere poleward of 60° MLAT and examine their spatial distributions and intensities. The accuracy of the global estimates are assessed quantitatively using comparisons with in-situ observations by DMSP along two orbit planes. While the location of EM power input evaluated from Iridium and SuperDARN data is in good agreement with DMSP, the magnitude estimated from DMSP observations is approximately four times larger. Corrected for this underestimate, the total EM power input to the Northern Hemisphere is 188 GW. Comparison of IMAGE FUV-derived distributions of the particle energy flux with DMSP plasma data indicates that the IMAGE FUV results similarly locate the precipitation accurately while underestimating the precipitation input somewhat. The total particle input is estimated to be 20 GW, nearly a factor of ten lower than the EM input. We therefore expect the thermosphere response to be determined primarily by the EM input even under winter conditions, and accurate assessment of the EM energy input is therefore key to achieving a comprehensive understanding of the I-T system, particularly during active times when the energy input increases markedly and expands well equatorward of nominal auroral latitudes.
Highlights
The interaction of the solar wind with the Earth’s magnetic environment in space gives rise to an electromagnetic dynamo that is coupled to the ionosphere–thermosphere (I-T) via electromagnetic fields, currents, and particle precipitation
The peak magnitudes of the boxcar-averaged magnetic perturbations and electric fields from DMSP are significantly lower than the observed maxima, but are still a factor of ∼2 larger than those evaluated from the Iridium and SuperDARN fits
The Poynting vector from Iridium and SuperDARN observations was compared to in-situ observations by two DMSP satellites and the locations of enhanced energy flux were found to be in good agreement
Summary
The interaction of the solar wind with the Earth’s magnetic environment in space gives rise to an electromagnetic dynamo that is coupled to the ionosphere–thermosphere (I-T) via electromagnetic fields, currents, and particle precipitation. The most reliable determinations use in-situ magnetic and electric field (or plasma drift) measurements from low-altitude satellites, which are combined to estimate the Poynting vector (Gary et al, 1994, 1995; Mishin et al, 2003) The advantage of this approach is that the measurements are sampled closely in both space and time so that the obtained Poynting vectors represent instantaneous observations. Because the engineering uses for the data only require coarse time resolution, the time interval between telemetered samples on an individual satellite is roughly three minutes For this reason, global distributions of the magnetic perturbations are obtained using observations accumulated over intervals one or two hours long (Anderson et al, 2000).
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