Whistler-mode waves play a critical role in shaping the behavior of high-energy particles in Earth’s radiation belts. These interactions can influence space weather and impact satellite operations. The way whistler-mode waves propagate depends heavily on the surrounding space environment, particularly variations in plasma density and magnetic field strength, called density and magnetic ducts.

Our observations reveal that complex ducting structures, including compound low-high magnetic ducts, aka magnetic-double duct, and compound low-high density ducts, named density-double ducts, can form in the Earth's magnetosphere. We observed direct interactions between whistler-mode waves and such compound ducts, showing that these structures can trap and guide multiple wave modes simultaneously. This confirms the physical existence and functionality of these intricate, field-aligned structures, and highlights their importance in enabling long-distance wave propagation.

We conducted theoretical analysis and numerical simulation to study wave behavior within each double-duct. We identified plasma and magnetic field conditions necessary for efficient wave trapping and guidance. While both magnetic and density double ducts effectively guide whistler-mode waves, they differ in how waves are confined and where wave leakage occurs. This research improves our understanding of wave dynamics in near-Earth space and contributes to ongoing efforts in space weather forecasting and satellite protection.