Testing the expanding‐contracting polar cap paradigm

Abstract

AbstractThe expanding‐contracting polar cap (ECPC) paradigm is tested. Under the ECPC paradigm ionospheric convection in the polar cap is driven by the combined effects of magnetic field dayside merging and nightside reconnection, as opposed to being mapped down from higher altitudes. The ECPC paradigm is tested by separately examining the cross polar cap potential when the polar cap is expanding versus contracting. The open magnetic flux is estimated from Super Dual Auroral Radar Network (SuperDARN) observations of the convection reversal boundary (CRB) made simultaneously at different local times. Sotirelis et al. (2005) established the CRB as a proxy for the open‐closed boundary. The correlation of the ionospheric convection potential, determined from SuperDARN, with solar wind/interplanetary magnetic field (IMF) driving is indeed found to depend on whether the polar cap is expanding or contracting. Specifically, when the polar cap is expanding, ionospheric convection potential correlates best (0.86) with the most recent 10 min of solar wind/IMF driving (versus 0.57 for contracting). When contracting, convection potential correlates best (0.87) with 90 min averages of solar wind/IMF driving (versus 0.51 for expanding). This result is consistent with the expectations of the ECPC paradigm.