Ion upflow enhanced by drifting F-region plasma structure along the nightside polar cap boundary

Abstract

Conjugate observations by the incoherent scatter radar at Sondrestrom, Greenland, and the Wideband Imaging Camera (WIC) on the IMAGE satellite have been used to establish a causal relationship between drifting F-region plasma structure in the polar ionosphere and upward ion number flux near the poleward edge of the auroral oval. A longitudinally extended patch of enhanced F-region density was observed as it advected equatorward across the open-closed field line boundary and into a region of discrete auroral rays and strong ion upflow (Vi > 800 m/s at 900 km altitude). Upward velocities within the upflow region remained constant during the patch transit, such that the upflowing number flux was directly controlled by F-region density (both increased by a factor of 2 within the patch). Because polar cap patches and ion upflows are both longitudinally extended, quasi-stable features of the nightside polar cap boundary, the observed interaction can produce a global-scale increase in plasma density at higher attitudes where suprathermal outflows are initiated.