Abstract
Longitudinal and Latitudinal characteristics of the O+-H+ ion transition height in the topside ionosphere at the low latitudes during the sunspot minimum period (1975-76) were observed by a retarding potential analyzer aboard TAIYO.
The results indicate that:
1) A semi-empirical formula of the ion transition height (H in km) is expressed as a function of the solar zenith angle (χ in deg.) and the geomagnetic dip angle (I in deg.); H=591-87.1sin2 I, (χ≥90°), and H=591-87.1sin2 I+(217+473sin2 I) cos0.331χ, (χ≤90°).
2) The ion transition heights around the South Atlantic geomagnetic anomaly are rather variable than those at another region in the nighttime. The region with variable ion transition height roughly coincides with that of anomalous intense count observed with a high energy measuring instrument (SXR) aboard TAIYO in the ionosphere.
3) Discussions and comparisons with other experiments are given. The remarkable asymmetry of the ion transition heights between the southern and northern hemispheres is explained by the semi-empirical formula to some extent.
