On the Role of Field‐Aligned Density Ducts in Z‐to‐O Mode Conversion in the Ionosphere: A 2D Simulation Study

High‐frequency (HF) ordinary polarized (O)‐mode waves transmitted along the Earth's geomagnetic field can excite plasma modes on both the bottomside and topside of the ionosphere, a process attributed to O‐to‐Z mode conversion. This mechanism explains how electromagnetic wave energy penetrates beyond the resonance. However, a key question is whether Z‐mode waves interacting with the resonance remain confined or escape the ionosphere via Z‐to‐O conversion. While O‐to‐Z conversion is well studied, Z‐to‐O remains less explored, especially in the presence of field‐aligned irregularities. We use two‐dimensional finite‐difference time‐domain simulations to investigate Z‐mode interaction with the resonance, with and without field‐aligned density ducts, across a range of magnetic field angles. The results show that duct‐assisted Z‐to‐O conversion is highly angle‐dependent. We compare its efficiency with that of O‐to‐Z conversion, and discuss implications for the magnetic zenith effect.