S. Gonzalez

Average vertical and zonal F region plasma drifts over Jicamarca

The seasonal averages of the equatorial F region vertical and zonal plasma drifts are determined using extensive incoherent scatter radar observations from Jicamarca during 1968-1988. The late afternoon and nighttime vertical and zonal drifts are strongly dependent on the 10.7-cm solar flux. The authors show that the evening prereversal enhancement of vertical drifts increases linearly with solar flux during equinox but tends to saturate for large fluxes during southern hemisphere winter. They examine in detail, for the first time, the seasonal variation of the zonal plasma drifts and their dependence on solar flux and magnetic activity. The seasonal effects on the zonal drifts are most pronounced in the midnight-morning sector. The nighttime eastward drifts increase with solar flux for all seasons but decrease slightly with magnetic activity. The daytime westward drifts are essentially independent of season, solar cycle, and magnetic activity.

Comparison of the He+ layer observed over Arecibo during solar maximum and solar minimum with CTIP model results

[1]xa0Light ion concentration observations from the Arecibo incoherent scatter radar have shown regions of He+ layering in the topside ionosphere in the postmidnight hours. The He+ layering phenomenon has been observed during both solar maximum and solar minimum conditions. During solar maximum the layer is well defined, giving maximum relative abundances of over 50%. The observational results also show regions of He+ dominance in the topside ionosphere during solar maximum in the height range 750–1200 km. During solar minimum the magnitude of the layer is less, giving a maximum relative abundance of only ∼20%; however, the layer is still a well-defined feature. The coupled thermosphere-ionosphere-plasmasphere (CTIP) model is shown to model accurately the He+ layer and the regions of He+ dominance, provided that the modeled temperature profiles are normalized to the observed values. This study serves to further highlight the importance of helium ions in the topside ionosphere, particularly during solar maximum nighttime conditions.