Ion transport in the topside ionosphere at Arecibo

Abstract

Incoherent scatter measurements at Arecibo can determine the separate vector drift velocitites 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 reactions 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 × 10 8 cm −2 s −1 . During the night the net flux was generally downward, averaging about 1 × 10 8 cm −2 s −1 . On January 15–16, 1977, the net upward daytime flux was smaller (∼1 × 10 8 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 × 10 8 cm −2 s −1 . The total upward flux through 754 km integrated from 0800 to 1600 LT on August 15–16 was ∼8.6 × 10 12 cm −2 , which was roughly 60% of the estimated total protonospheric content at 1500 LT. The total downward nighttime‐integrated flux in the August observations was about 4 × 10 12 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.