Ion transport in the topside ionosphere at Arecibo

Incoherent scatter measurements at Arecibo can determine the separate vector drift velocities of O+ and H+ ions in regions where the two species are mixed. At times the field-aligned drifts are actually in opposite directions in regions where the H+-O and O+-H charge exchange reactons are important. Here we present observations of the structure and dynamics of the topside ionosphere for 2 days, one in summer and one in winter. Measurements on August 15--16, 1976, showed upward daytime fluxes of both species totaling about 2--4 x 108 cm-2 s-1. During the night the net flux was generally downward, averaging about 1 x 108 cm-2 s-1. On January 15--16, 1977, the net upward daytime flux was smaller (approx.1 x 108 cm-2 s-1), with the proton flux remaining slightly downward. During the night of January 15--16 the average downward flux was again about 1 x 108 cm-2 s-1. The total upward flux through 754 km integrated from 0800 to 1600 LT on August 15--16 was approx.8.6 x 1012 cnm-2, which was roughly 60% of the estimated total protonospheric content at 1500 LT. The total downward nighttime-integrated flux in theAugust observations was about 4 x 1012 cm-2. The August data thus suggest a net (24 hour) upward flux. The January data are less complete but suggest a possible net downward flux. If these 2 days caN be taken as being typical, they imply some interhemispheric transport from summer to winter