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Abstract The duskside and dawnside subauroral polarization streams (SAPS) refer to high‐velocity westward and eastward plasma flows located equatorward of the auroral oval. While extensive research has focused on the duskside SAPS, the simultaneous evolution of both dawnside and duskside SAPS remains unreported. In this study, for the first time, we investigated the simultaneous evolution of duskside and dawnside SAPS using multiple Super Dual Auroral Radar Network radars during an intense storm. Observations indicate that the duskside SAPS exhibits a wider magnetic local time extension (∼7 MLT) and longer duration (∼1 hr) than the dawnside SAPS. Furthermore, the duskside SAPS resides within low‐density mid‐latitude troughs, whereas the dawnside SAPS is not located within the trough. The dawnside SAPS exhibits significantly higher electron density but comparable velocity to the duskside SAPS. These findings highlight the distinct evolution of dawnside and duskside SAPS, providing new insights into the electrodynamic processes of subauroral ionosphere and magnetosphere coupling. 

Abstract Strong Thermal Emission Velocity Enhancement (STEVE) is a latitudinally narrow, purple‐band emission observed at subauroral latitudes. Stable Auroral Red (SAR) arcs characterized by major red emission, and red/green arcs with both red and green emissions also occur at subauroral latitudes. Characteristics of magnetospheric source plasma and electromagnetic fields of these three types of arcs have not been fully understood because of the limited conjugate observations between magnetosphere and the ground. In this study, we report 11 conjugate observations (2 STEVEs, 7 SAR arcs, and 2 red/green arcs), using all‐sky images obtained at seven ground stations over more than four years from January 2017 to April 2021 and magnetospheric satellites (Arase and Van Allen Probes). We found that, in the inner magnetosphere, the source region of STEVEs and red/green arcs were located outside the plasmasphere, and that of the SAR arc was in the region of spatial overlap between the plasmasphere and ring current region. Electromagnetic waves at frequencies below 1 Hz were observed for STEVEs and red/green arcs. SuperDARN radar data showed a strong westward plasma flow in the ionosphere, especially during STEVE events, whereas the plasma flows associated with SAR arcs and red/green arcs were generally weaker and variable. The STEVE and SAR arc can appear simultaneously at slightly different latitudes and STEVEs and red/green arcs can transform into SAR arcs. These first comprehensive ground‐satellite measurements of three types of subauroral‐latitude auroras increase our understanding on similarlity, differences, and coupling of these auroras in the ionosphere and the magnetosphere.