Ionospheric convection signatures of the interchange cycle at small interplanetary magnetic field clock angles

The purpose of this paper is to show a "proof of the existence" of the ionospheric situation that is expected for the interchange cycle, during periods of favorable interplanetary magnetic field (IMF) and dipole tilt conditions. To do so, we present three case studies of dayside high-latitude ionospheric convection that is observed around the equinoxes (near-zero dipole tilt) and at small IMF clock angles (one θ_c ∼ -30° event and two θ_c ∼ 30° events, where θ_c Arg(B_Z + iB_Y)), using Super Dual Auroral Radar Network (SuperDARN)/Defense Meteorological Satellite Program (DMSP)/National Oceanic and Atmospheric Administration (NOAA) data in the Northern Hemisphere and, when available, DMSP data in the Southern Hemisphere. The convection pattern exhibits twin reverse cells in both hemispheres, but the constituents of each cell are different. In the Northern Hemisphere, for θ_c ∼ 30 (θ_c ∼ -30°), the center of the dawnside (duskside) cell is located poleward of the polar cap boundary, while the center of the duskside (dawnside) cell is located equatorward of the polar cap boundary. For θ_c ∼ 30°, we confirmed that the above-mentioned dawn-dusk relation reverses in the Southern Hemisphere. The north-south asymmetric behavior of the conjugate reverse cells, on the dawnside and duskside each, is consistent with two independent interchange cycles that result from the coupling of IMF-lobe reconnection in one hemisphere with lobe-closed reconnection in the opposite hemisphere.