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The response of the polar ionosphere–thermosphere (I-T) system toelectromagnetic (EM) energy input is fundamentally different to thatfrom particle precipitation. To understand the I-T response topolar energy input one must know the intensities and spatialdistributions of both EM and precipitation energy deposition.Moreover, since individual events typically display behaviordifferent from statistical models, it is important to observe theglobal system state for specific events. We present an analysis ofan event in Northern Hemisphere winter for sustained southwardinterplanetary magnetic field (IMF), 10 January 2002, 10:00–12:00 UT,for which excellent observations are available from theconstellation 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 particleprecipitation energy fluxes to the Northern Hemisphere poleward of60° MLAT and examine their spatial distributions andintensities. The accuracy of the global estimates are assessedquantitatively using comparisons with in-situ observationsby DMSP along two orbit planes. While the location of EM power inputevaluated from Iridium and SuperDARN data is in good agreement withDMSP, the magnitude estimated from DMSP observations isapproximately 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 energyflux with DMSP plasma data indicates that the IMAGE FUV resultssimilarly locate the precipitation accurately while underestimatingthe precipitation input somewhat. The total particle input isestimated to be 20 GW, nearly a factor of ten lower than the EMinput. We therefore expect the thermosphere response to bedetermined primarily by the EM input even under winter conditions,and accurate assessment of the EM energy input is therefore key toachieving a comprehensive understanding of the I-T system,particularly during active times when the energy input increasesmarkedly and expands well equatorward of nominal auroral latitudes

Global observations of electromagnetic and particle energy flux for an event during northern winter with southward interplanetary magnetic field