High-latitude poynting flux from combined Iridium and SuperDARN data

Abstract

Field-aligned currents convey stress between the magnetosphere and ionosphere, and the associated low altitude magnetic and electric fields reflect the flow of electromagnetic energy to the polar ionosphere. We introduce a new technique to measure the global distribution of high latitude Poynting flux, S∥, by combining electric field estimates from the Super Dual Auroral Radar Network (Super-DARN) with magnetic perturbations derived using magnetometer data from the Iridium satellite constellation. Spherical harmonic methods are used to merge the data sets and calculate S∥ for any magnetic local time (MLT) from the pole to 60° magnetic latitude (MLAT). The effective spatial resolutions are 2° MLAT, 2h MLT, and the time resolution' is about one hour due to the telemetry rate of the Iridium magnetometer data. The technique allows for the assessment of high-latitude net S∥ and its spatial distribution on one hour time scales with two key advantages: (1) it yields the net S∥ including the contribution of neutral winds; and (2) the results are obtained without recourse to estimates of ionosphere conductivity. We present two examples, 23 November 1999, 14:00-15:00 UT, and 11 March 2000, 16:00-17:00 UT, to test the accuracy of the technique and to illustrate the distributions of S∥ that it gives. Comparisons with in-situ S∥ estimates from DMSP satellites show agreement to a few mW/m2 and in the locations of S∥ enhancements to within the technique's resolution. The total electromagnetic energy flux was 50GW for these events. At auroral latitudes, S∥ tends to maximize in the morning and afternoon in regions less than 5° in MLAT by two hours in MLT having S∥=10 to 20 mW/m2 and total power up to 10GW. The power poleward of the Region 1 currents is about one-third of the total power, indicating significant energy flux over the polar cap. © European Geosciences Union 2004.