we studied how whistler-mode waves, electromagnetic waves that travel through Earth’s magnetosphere, can be guided by changes in plasma density and magnetic field inhomogeneities. These guiding structures, called ducts, form when the plasma or magnetic field increases or decreases in specific ways. They help the waves travel long distances with little energy loss, something confirmed in recent satellite observations.

In our work, we focused on how one type of whistler-mode wave can switch to from a less oblique wave to more oblique one with respect to the field lines across the duct. We found that this switching happens when certain critical values of plasma density and magnetic field are reached in a narrow region. We developed equations to describe this process and backed them up with simulations. We also explored how the size of this transition region affects the mode switching.

Our results show that both density and magnetic field ducts control wave behavior in similar and different ways, based on key thresholds that depend on the wave properties and the surrounding plasma.