[en] A numerical model for the ionosphere-plasmasphere system in the region of geomagnetic force tubes with L=1.5-7 is considered. The model consistently takes into account the photoelectron heating and permits computation of diurnal density and temperature variations of the O⁺, and H⁺ ions and electrons at altitudes above 200 km. The computations performed have shown that successive allowance for the increase with latitude of the volume of a geomagnetic force tube supported by the ionosphere allows one to explain the following peculiarities of the outer ionosphere structure: 1) the formation of the equatorial edge of the light ion trough (LIT) which is independent of the presence of the plasmapause: 2) manifestation of the LIT as the mid-latitude trough (MLT) at heights, where the H⁺ ion prevails; 3) an increase in electron temperature toward high latitudes during the nigh time. It is shown that under geomagnetically quiet conditions, both plasmasphere heating and the heat flux into the outer ionosphere are provided by the photoelectron energy deposition in the plasmasphere