NUMERICAL SIMULATION OF IONOSPHERIC STRUCTURE BELOW F₂ PEAK

Taking account of the photo-chemical reactions and the transport processes induced by diffusion and neutral wind, a one-dimensional and time-dependent numerical model for the ionospheric profile is established, in which stable and metastable atomic ions [O⁺(⁴S), O⁺(²D) and O⁺(²P)]and molecular ions (O₂⁺, NO⁺ and N₂⁺) are involved. Based on the model, the ionospheric morphology and related processes at WUCHANG (30.5°N, 114.4°E) in the region below the F₂ peak, especially. within the E/F and F₁/F₂ valleys, are discussed, and the main results are summarized as follows:(1) With respect to atomic ions, the chemical reactions and the transport process for O⁺(⁴S) only are responsible for a shallow F₁/F₂ valley; the O⁺(²D)Patticipated reactions are more favourable to form a deep one conversely, O⁺(²P), when present, is an unfavourable factor for ie valley formation. As for molecular ions, the transport induced by neutral wind is also beneficial for a deep valley. (2) The atomic-molecular ions transit level is located at about 180-190 km with a larger value for morning and evening hours only above which the linear assumption of the loss rate is valid in the traditional continuity epuation with respect to electrons.(3) The widest F₁/F₂ valley occurs at ¹¹h (LT), and the deepest Due at local noon. The E/F valley width is generally about 20-30km for low solar activity and 25-45km for high one, and the morning and evening values are 10-20km larger. (4) O₂⁺ with a double-peak profile is the most important composition in for ining Eand F₁ ledges. Its low peak forms E-layer, while the upper one, in combination with NO⁺ contribution, makes up F₁-Layer.Good agreements are found between the simulated and the observational results as a whole. The present model exhibits great potentiality for the study of ionospheric profiles, such as its mathematical description, the ionogram inversion techniques. and also the morphological and related mechanical research for a particular geophysical event.