Prediction of the Wave Normal Angle of Proton‐Band EMIC Waves Near Geosynchronous Orbit

Abstract We investigate how the wave normal angle (WNA) and polarization of proton‐band electromagnetic ion cyclotron (EMIC) waves change as they travel from their source to Earth. This paper marks a significant milestone as the first full‐wave simulation of proton‐band EMIC waves reflecting from the ionosphere. Our findings show that the WNA can change rapidly during propagation, primarily due to plasma inhomogeneities, such as variations in the Alfvén speed. The wave polarization is strongly related to the WNA, consistent with theory. Newly generated EMIC waves near the equator propagate with a WNA of 0, then the WNA gradually shifts to 90 as they move toward Earth. In contrast, reflecting waves having 90 of WNA at Earth maintain a relatively larger WNA even near the magnetic equator. As a result, only the newly generated waves close to the source, where the magnetic latitude is less than approximately 20, show left‐handed polarization, while linear polarization remains dominant throughout the rest of the propagation.