A statistical analysis is presented of the long-term variations of upflowing ionosphere ion (UFI) occurrence morphology in the high-altitude (8000-23,300 km) auroral and polar cap ionosphere, using data from the Dynamics Explorer 1 Energetic Ion Composition Spectrometer from 1981 to 1984. The study is based on over 100,000 data samples, each consisting of pitch angle distributions of H+ and O+ intensities at 0.001--1, 1--4, and 4--17 keV/e. The data samples were grouped into 91-day intervals (seasons). Within each interval they were sorted into altitude, invariant latitude, magnetic local time, and magnetic activity (Kp index) bins, and the occurrence frequency and intensity characteristics of H+ and O+ UFI in the respective bins were determined. The September 1981 to May 1984 period coincides with the declining phase of solar cycle 21, when the solar radio flux at 10.7 cm, F10.7, decreased from a high of 222 (¿10-22 W m-2 Hz-1) in September 1981 to a low of 93 in November 1983. The observed occurrence frequency, intensity, and angular characteristics of O+ UFI exhibited marked variations which correlate with variations in the solar radio flux (and which envelop those of magnetic activity and seasonal origins). In contrast, the H+ UFI morphology did not display any observable long-term variations. At both quiet (Kp≤2+) and active times (3-≤Kp≤5+) the solar maximum O+ data displayed (1) a factor of 2-3 increase in the occurrence frequency of intense UFI; (2) a similar increase in the occurrence frequency of transversely accelerated ions above 8000 km; and (3) an increase in conic abundance (fraction of ion conics in UFI).

Together, items (1) and (3) imply about a twofold increase of energetic O+ outflow to the magnetosphere at solar maximum; items (2) and (3) indicate an upward shift in the perpendicular ion acceleration region. The correlation of O+ UFI abundance and occurrence with variations of the solar radio flux, in the absence of magnetic and other geophysical variations, suggests solar activity variations related to the solar flux to be the causative factor in the long-term variations in observed UFI morphology. Seasonal variations in UFI occurrence were present in O+ and absent in H+. The O+ frequencies in the summer periods were found to be significantly higher than the values in winter periods of comparable solar activity. The observed solar activity and seasonal variations are interpreted in terms of increased ionospheric and atmospheric scale heights at solar maximum and summer solstice, which effectively shift the O+-H charge exchange altitude upward and facilitate O+ injection to higher altitudes. The observed variations are compared with solar cycle variations in the ring current density, and their magnetospheric implications are discussed.