Whistler propagation in nonsymmetrical density channels

We present results from a study of whistler propagation in plasma density channels extended along Earth's geomagnetic field and localized across it. Our study is focused on whistler guiding by channels with a nonsymmetrical density profile across the channel. Such profiles are typical for density inhomogeneities observed on/near the plasmapause formed in the Earth's magnetosphere during strong geomagnetic storms/substorms. Considering these density channels as a combination of high‐density and low‐density ducts, we analyze leakage of the electromagnetic energy from these ducts depending on various parameters of the system. Our results indicate that a whistler with a frequency less than half of the local electron gyrofrequency can propagate along a nonsymmetrical duct with a homogeneous central part, without any leakage, when the width of the duct is equal to an integral multiple of each of the two internal perpendicular wavelengths. We also show that a homogeneous ducting region is not necessary; a low‐frequency whistler can be guided along a region of appropriate density within a monotonic density gradient. This finding makes our results particularly relevant for the interpretation of intense whistler dynamics recorded in a number of satellite observations near/on the plasmapause where strong transverse density gradients are observed.