(a) Map of the proxy ionosphere inferred from the observations of ionospheric oxygen ions in the XYMSO plane obtained from the ASPERA-3 data during almost 3 years of the observations. Strong asymmetry is caused by the fact that the dawn ionosphere was sampled at much higher altitudes than the ionosphere at the dusk side. (b, c) Maps of mean and maximum numbers of counts of low-energy oxygen ions in the X ZMSO plane. Strong asymmetry between the northern and southern ionospheres appears due to the crustal magnetic field. Note that the high fluxes measured in the solar wind are mainly due to the UV contamination.