Statistical study of ion upflow associated with subauroral polarization streams (SAPS) at substorm time

We present a statistical study of the ion upflow associated with subauroral polarization streams (SAPS) in the ionospheric subauroral region at different substorm times using three Defense Meteorological Satellite Program satellite (F16-F18) data for five years (2010-2014) in the Northern Hemisphere. The results show similarities between SAPS and the ion upflow at different intensity of substorms both in occurrence rate distribution and velocity distribution. In comparison to SAPS, the distribution of the ion upflow shows the smaller occurrence region and lower velocity. We also find that frictional heating plays an important role in ion upflow from the SAPS region. The intense substorms can trigger strong SAPS channels, enhanced frictional heating, and large ion upflow. In addition, there is a moderate linear correlation between SAPS velocity and field-aligned velocity that is consistent with some previous findings. Our results also show that frictional heating can gradually dominate the ion upflow process in intense substorms, while it may not be the only factor to affect the whole upflow process.