Ionospheric Outflows and Geomagnetic and Solar Activity

We present studies of long-term variations of ionospheric outflows over 11-year solar cycle between 1996 and 2008. Using measurements of cold ions of Polar/TIDE instrument, we calculated monthly averages of the fluxes of the ionospheric outflows at altitudes of 0.8-3 Re for dayside and nightside polar cap regions and correlated with solar EUV F10.7 index, sunspot numbers and geomagnetic Dst index. We found a good correlation between the Solar EUV or sunspot numbers and the flux of ionospheric outflows in the dayside polar cap region over the solar cycle. The correlation coefficients are ~0.6 for the dayside polar cap region compared with ~0.4 in the nightside. The changes in the monthly average fluxes of the outflows are about a factor of 10 from solar minimum to solar maximum. On the other hand, ionospheric outflows are not correlated well with the Dst index over the 11-year solar cycle. Although the Dst index is somewhat more variables during the periods of the solar maximum, the correlation between the outflows and Dst was reduced in the monthly-average data set. This indicates that the periodicities of the variations the Dst mostly occur in a time scale smaller than a month. Spectral analysis of the ionospheric outflows indicates annual and seasonal variations on top of the 11-year solar cycle trend. The amplitudes of these variations are comparable or even larger than the minimum-to-maximum value of the solar cycle trend. This indicates the importance of the influence of solar wind-magnetosphere-ionosphere interaction on the ionospheric outflows at short time scales in addition to the 11-year solar cycle trend caused by the more direct energization of the ionospheric ions by the solar EUV flux.