Saturation effects of the lower ionosphere based on two‐dimensional HF heating model

This paper presents a two-dimensional (2-D) theoretical model of the lower ionospheric heating by high-frequency (HF) electromagnetic waves. Compared with the traditional one-dimensional model, we develop the half-power width of the heating beam into the theoretical formulations, which dictates the 2-D distribution characteristics of electron temperature and density perturbations; we also introduce the Sodankyla Ion Chemistry (SIC) model. Based on this numerical model, the saturation effect of ionospheric electron temperature and density is investigated, and simulation is performed by heating at a wave frequency of 6MHz. Results show that because of energy absorption, the electron temperature peaks at 74km, and the relative increment of electron density peaks at 94km in the height direction. Conversely, both the maximum perturbations of electron temperature and density appear on the beam center in the horizontal direction. Second, the saturation time of electron temperature initially increases slowly and then rapidly with increased height. Meanwhile, the saturation time of electron density decreases with increased height. In the horizontal aspect, both the saturation time of electron temperature and density are symmetrical at approximately the position of the beam center owing to the initial Gaussian distribution. Electron temperature far from the beam center results in a long saturation time. Conversely, with increased distance from the beam center, the saturation time of electron density decreases.