Conjugate features of daytime absorption associated with specific changes in the solar wind observed by inter-hemispheric high-latitude imaging riometers

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Imaging riometers at Ny-Alesund (NYA) and Danmarkshavn (DMH) in the Arctic and Zhongshan (ZHS) in Antarctica were used to examine conjugate features of daytime ionospheric absorption in the polar cusp/cleft for specific changes in solar wind plasma parameters and the interplanetary magnetic field (IMF). We observed absorption spikes in the afternoon (1300-1500 MLT) associated with a steep increase in the high solar wind dynamic pressure and a synchronized spike-type IMF excursion. Afternoon absorption was identified between the stations at NYA and ZHS. The absorption extended longitudinally over a few hundred km, in a narrow arc about 50 km wide in latitude. Magnetic field compression associated with the steep pressure increase may stimulate substorm electrons drifting eastward from the nightside magnetosphere through the inner edge of the LLBL. We also observed absorption spikes around noon that were associated with a sudden pressure increase and a synchronized IMF excursion after a prolonged quiet state. The noon absorption was identified simultaneously at the DMH and ZHS inter-hemispheric stations. It extended longitudinally for several hundred km, including a small gap of about 50 km, and for over 400 km wide in latitude. Magnetic field compression associated with the sudden pressure increase may stimulate a population of magnetospheric electrons located at the equatorward boundary of the cusp/cleft.
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