SuperDARN Observations of the Two Component Model of Ionospheric Convection

We use a 20 years database of Super Dual Auroral Radar Network (SuperDARN) observations to investigate the two component model of ionospheric convection. A convection pattern is included in the database if it is derived from at least 250 radar vectors and has a distribution of electric potential consistent with Dungey‐cycle twin vortex flow (a negative potential peak in the dusk cell and a positive potential peak in the dawn cell). We extract the locations of the foci of the convection cells from the SuperDARN convection patterns, and compare their dependencies on the north‐south component of the interplanetary magnetic field, IMF BZ, and the SuperMAG auroral electrojet index, SML. We use these parameters to define intervals of expected dayside or nightside dominated reconnection. Our results show that, under conditions favorable for dominant dayside reconnection, the dawn and dusk foci are shifted toward the dayside and that, under conditions favorable for dominant nightside reconnection, the dawn and dusk foci are shifted toward the nightside. Plain Language Summary The Earth's upper atmosphere is coupled to the near‐Earth space environment—the magnetosphere—via the planet's magnetic field. This magnetic coupling drives a circulation of plasma—the electrically charged component of the atmosphere, called the ionosphere—from day to night across the poles and back again at lower latitudes. This circulation of plasma is a key component of the energy transport in the magnetosphere‐ionosphere system. The circulation is not steady, instead changing in strength whilst expanding and contracting due to the time‐dependence of the driving mechanisms. To understand these mechanisms we can model the ionospheric circulation and test the models with observations. In this paper we use a 20 years database of ionospheric radar observations of the plasma flow to test one such model—the expanding‐contracting polar cap model—and find evidence to support its predictions of separate dayside and nightside components of the flow. Key Points The separation of the dawn and dusk ionospheric convection cell foci is found to vary from 4 to 22 hr of magnetic local time When the interplanetary magnetic field (IMF) is southwards and the auroral westward electrojet weak, the foci move to the dayside When the IMF is strongly northwards and the auroral electrojet modestly active, the foci move toward the nightside