Solar illumination control of ion upflow above the polar cap

Abstract:

This paper explores the solar illumination effects on ion upflow above the polar cap by applying an auto-identification method. Using plasma data from DMSP, we discuss the relevance between ion upflow and solar illumination(indicated by solar height angle SHA and F10.7 flux), convection velocity. The statistical result shows a significant relevance: as SHA increases, the vertical ion flow has more opportunity turns upward and shows a clear reversal boundary, and SHA of this boundary will increase if F10.7 flux or convection flow enhanced. The flow density shows a positive correlation with SHA and F10.7, without considering the convection flow; and flows density exhibits different characters at different convection flow speeds: when convection flow is quiet, density increases with SHA, if convection flow turns burst, density increases with SHA before 15 degree, after 15 degree the density decreases. All above suggests photoionization has strong effects on ion upflow, and shows different behaviors in different convections.