Equatorial plasma bubbles at altitudes of the topside ionosphere

A consistent patter, indicating that subtroughs in the He⁺ density and plasma bubbles can be considered as phenomena of the same origin, has been obtained within the scope of the existent model of equatorial plasma bubbles. The study has been performed based on the measurements of the ISS-b satellite, which flew during the period of high solar activity. The conclusion has been made based on a comparative analysis of the characteristics of subtroughs with the parameters of the known equatorial phenomena. (1) The similarity of the LT variations in the latitude of the minimums of subtroughs in the He⁺ density has been revealed. (2) It has been displayed that the variations in the averaged depth of subtroughs change from season to season similarly to the LT variations in the average velocity of the equatorial vertical plasma drift. (3) Good correlation (R = 0.67) between the occurrence probability of subtroughs and equatorial spread F statistics, constructed as the functions of LT and month, has been obtained. (4) The obtained velocity of the possible rise of plasma irregularities (observed as regions depleted in He⁺) is in good agreement with the ionosonde, satellite, and radar measurements of the equatorial plasma bubble velocities of the same period. (5) It has been indicated that plasma irregularities, reaching the altitudes of the topside ionosphere in the low-latitude and midlatitude regions during high solar activity, are most observable as depleted regions (subtroughs) of He⁺ density.