Investigating SAPS Channels and Related Phenomena Observed Under Weak Magnetic Conditions in the Midday Subauroral Geospace

Subauroral geospace is a dynamic region. Its various features include Subauroral Polarization Streams (SAPS), hot and cold zones, and storm enhanced densities (SED). Previous studies have covered the nightside, leaving the dayside largely unexplored and poorly understood. This study investigates the prenoon and midday sectors, based on multi-instrument, multipoint observations. In the inner magnetosphere, the observed dayside SAPS’ development was set off by solar-wind flow pressure increases compressing the dayside magnetosphere in the equatorial plane and triggering earthward-directed hot plasma surges or particle injections in the coupled Alfvenic solar wind and dayside magnetosphere. The dayside SAPS developed in an inner-magnetosphere voltage generator and appeared sometimes within the cold zone where the isotropic ion temperature (Ti‖ ≈ Ti⊥) minimized and sometimes within the hot zone fueled by whistler-mode chorus waves locally enhancing the field-aligned temperature anisotropy (T‖ > T⊥) and providing localized plasma heating both via Landau damping and implicitly. In the ionosphere, the observed dayside SAPS’ development was unfolding in a prenoon eastward auroral electrojet (AEJ) scenario on the dawnside and in a midday westward AEJ scenario on the duskside. The observed dayside SAPS mapped down to the noontime SED plume base depicted by the total electron content maps.