Statistical analysis of outflow ionospheric O+ on the declining phase of solar cycle 23 using Fast observations

• Outflow rates for high and low energy O+ were separately calculated to analyze the intensity gap.
• The rates were on different scales between the two energy level oxygen ions.
• Outflow rates during storms significantly exceeded these during quiet times.
• The rates were approximately correlated to the intensity of solar activities.

Based on the Fast/TEAMS observations in southern hemisphere from 2000 to 2005 on the declining phase of the solar activity cycle 23, the following questions were comparatively discussed during magnetically quiet times (Kp≤2+Kp≤2+) and storms (Kp≥3+Kp≥3+). One was the hemispheric distribution characteristics of O+ outflow rates and net outflow differential fluxes, and the other one was the characteristics of outflow ions, which were yielded in terms of correlations with the altitude, year and magnetic local time (MLT). Results showed that the outflow events during storms were mainly scattered on magnetic invariant latitude (ILAT) from 50° to 70° which was lower than that from 60° to 70° ILAT during quiet times. The high occurrence areas turned up on the auroral oval area at 00:00–07:00 MLT before dawn and 16:00–24:00 MLT before midnight. There were remarkable low energy outflow O+ (<1keV) on the dayside polar cusp during quiet times, while the high energy outflow O+ (≥1keV) rarely happened on the polar cusp. Specifically, we found that the outflow rates of high and low energy ions during storms exceeded those during quiet times by a factor of ~2.294 and ~1.572, respectively. As a result, the proportion of high and low energy outflow O+ increased during magnetic storms. Our results also suggested that the O+ outflow intensity increased from 2000 to 4200 km and had a positive correlation with the solar activities.