Distribution of ionospheric O⁺ ion in synchronous altitude region

Based on satellite observation data, using dynamics equation, the ionospheric O⁺ ion's distribution in the synchronous altitude region for different geomagnetic activity index K_p is studied by theoretical modeling and numerical analyzing, and semi-empirical models for the O⁺ ion's density and flux versus longitude in the synchronous altitude region for different K_p are given. The main results show that in the synchronous altitude region: (i) The O⁺ ion's density and flux in dayside are larger than those in nightside. (ii) With longitude changing, the higher the geomagnetic activity index K_p is, the higher the O⁺ ion's density and flux, and their variation amplitude will be. The O⁺ ion's density and flux when K_p ≥ 6 will be about ten times as great as that when K_p = 0. (iii) When K_p = 0 or K_p ≥ 6, the O⁺ ion's density reaches maximum at longitudes 120° and 240° respectively, and minimum in the magnetotail. When K_p = 3-5, the O⁺ ion's density gets to maximum at longitude 0°, and minimum in the magnetotail. However, the O⁺ ion's flux reaches maximum at longitude 120° and 240° respectively, and minimum in the magnetotail for any K_p value.