High frequency (HF) radio waves can modify the electron density profile of the ionosphere in the upper hybrid resonance region (UHR). The spatial and temporal development of this modification was investigated using a multi-frequency Doppler diagnostic system at the TROMS¿ facility <Lobachevsky et al., 1992>. We present the results of the simulations of the density profile modification near the upper hybrid resonance height for the parameters relevant to the experiment and show that the spatio-temporal development of the density modification is quantitatively modelled by the mode conversion and the radio wave heating.