According to the analysis of the ISR observation data, the heating effects in polar winter ionospheric modification experiments carried out in January 2008 at Tromsø, Norway were studied. A clear disturbance effect is present under the O‐mode over‐dense heating conditions. The enhancement of the electron temperature is up to 60%~120%, extending from 150 km to 400 km. The disturbance of the electron density is not obvious, with a 12% maximum decrease. An 1~2 kHz increase at the acoustic frequency can be observed, and an enhancement in the peak‐to‐valley ratio of the ion line and sometimes its high‐order harmonics can be seen as well. The power of the ion line and plasma line has shown an overshoot effect, single‐humped, double‐humped and triple‐humped structures have appeared in the power profile of plasma line, and the enhancement in power amplitude of the plasma line decreases exponentially as the frequency increases.

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According to the well-performed ionospheric heating experiments at Arecibo in the low latitudes as well as at Tromsø in the high latitudes, the large-scale modification effects are simulated under an assumption of equivalent conditions, i.e., with the same effective radiative power and the same ratio of the heating frequency fHF to the critical frequency of ionospheric F region foF2. The findings are extensively exploited to verify the validation of our model by comparison to the experimental results. Further, a detailed study is carried out on the influences of the background electron density gradient as well as the ratio of fHF to foF2 on heating effects. Conclusions are drawn as follows: under certain conditions, a smaller electron density gradient of background ionospheric F region leads to a better ionospheric heating effect; during over-dense heating, the heating effects are enhanced if the ratio of fHF to foF2 increases, which is slightly limited by the resultant elevation of the reflection height. However, there might be a better ratio range with small values of the ratio of fHF to foF2, e.g., [0.5, 0.7] in the current study. Finally, we analyzed how to select heating parameters efficiently under adverse conditions so to obtain relatively effective results.

Based on the mechanisms of both electron cooling and heating in the ionosphere, a theoretical simulation model of under-dense heating by X-mode waves is constructed. And this model is verified by simulating the known experimental results. Using this model, we analyze the influences of heating parameters and the ambient ionosphere on the heating effects. The results show that in the under-dense heating ionosphere by powerful Xmode wave, the heating effects are enhanced when the effective radiated power (ERP) increases, and weakened as the heating frequency increases. The lower the electron temperature and the smaller the density, the stronger the heating effects are. Finally, some applications of under-dense heating by X-mode waves are analyzed.

Under the condition of ionosphere heating in the low region, the theoretical incoherent scatter model with the non-Maxwellian distribution in collisional plasma is presented, and the measured data in polar winter ionospheric modification experiments carried out in January 2008 at Tromsø are analyzed. The obvious electron temperature enhancement can be seen in this experiment, and the maximum percentage is up to 168.9%. The non-Maxwellian index is also given, and the heating electric field is deduced from the index, which has important meaning for numerical simulation of the artificial ionospheric modification.