A survey of 25 years’ transpolar voltage data from the SuperDARN radar network and the Expanding-Contracting Polar Cap model
Lockwood, M.
It is advisable to refer to the publisher's version if you intend to cite from this work. See Guidance on citing. To link to this item DOI: 10.1029/2021JA029554 Abstract/SummaryWe use 214410 hourly observations of transpolar voltage, {\Phi}_{PC}, from 25 years’ observations by the SuperDARN radars to confirm the central tenet of the Expanding-Contracting Polar Cap model of ionospheric convection that {\Phi}_{PC} responds to both dayside and nightside reconnection voltages ({\Phi}_{D} and {\Phi}_{N}). We show {\Phi}_{PC} increases at a fixed level of the nightside auroral electrojet AL index with increasingly southward IMF (identifying the well-known effect of {\Phi}_{D} on {\Phi}_{PC}) but also with increasingly negative AL at a fixed southward IMF (identifying a distinct effect of {\Phi}_{N} on {\Phi}_{PC}). We also study the variation of {\Phi}_{PC} with time elapsed {\Delta}t since the IMF last pointed southward and show low/large values occur when (-AL) is small/large. Lower numbers of radar echoes, n_{e}, mean that the “map-potential” re-analysis technique used to derive {\Phi}_{PC} is influenced by the model used: we present a sensitivity study of the effect of the threshold of n_{e} required to avoid this. We show that for any threshold n_{e}, {\Phi}_{PC} falls to about 15 kV for {\Delta}t greater than about 15 hours, indicating any viscous-like voltage {\Phi}_{V} is considerably smaller than this. It is shown that both {\Phi}_{PC} and (-AL) increase with increased solar wind dynamic pressure p_{SW}, but not as much as the mid-latitude geomagnetic index am. We conclude p_{SW} increases both {\Phi}_{D} and {\Phi}_{N} through increasing the magnetic shear across the relevant current sheet but has a larger effect on mid-latitude geomagnetic indices because of the effect of additional energy stored in the tail lobes.
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