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A survey of 25 years' transpolar voltage data from the SuperDARN radar network and the Expanding-Contracting Polar Cap model
  • Michael Lockwood,
  • Kathryn A McWilliams
Michael Lockwood
University of Reading, University of Reading

Corresponding Author:m.lockwood@reading.ac.uk

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Kathryn A McWilliams
University of Saskatchewan, University of Saskatchewan
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We use 214410 hourly observations of the transpolar voltage, ΦPC, from 25 years of observations by the SuperDARN radars, to confirm the central tenet of the Expanding-Contracting Polar Cap (ECPC) model of ionospheric convection that ΦPC responds to both dayside and nightside reconnection voltages (ΦD and ΦN). We show ΦPC increases at a fixed level of nightside auroral electrojet AL index with increasingly southward IMF (identifying the well-known effect of ΦD on ΦPC) but also with increasingly negative AL at a fixed southward IMF (identifying a distinct effect of ΦN on ΦPC ). We study the variation of ΦPC with time elapsed Δt since the IMF last pointed southward and show that low/large values occur when -AL is small/large. We have to allow for the fact that at lower numbers of radar echoes, ne , the matched potential re-analysis technique used to derive is influenced by the model used: this is done by a sensitivity study of the threshold of ne required. We show that for any threshold ΦPC falls to about 15kV for & Δt greater than about 15 hours giving an upper limit to the viscous-like voltage. It is shown that both ΦPC and -AL increase with increased solar wind dynamic pressure psw , but not as much as the mid-latitude geomagnetic range index am. We conclude psw increases both ΦD and ΦN through increasing the magnetic shear across the relevant current sheet but has a bigger effect on mid-latitude geomagnetic activity indices via the additional energy stored in the tail lobes.
Sep 2021Published in Journal of Geophysical Research: Space Physics volume 126 issue 9. 10.1029/2021JA029554