Influence of the curvature of geomagnetic field lines on the trapping criterion for low-frequency electromagnetic waves entrapped into wave ducts with increased electron density in the Earth's magnetosphere

The influence of the curvature of geomagnetic ducts on the trapping conditions of the waves with very low frequencies (VLFs) is analyzed via geometric-optics methods. It is shown that consideration for this curvature results in formation of a special oscillation mode in the duct. Estimates of the corrections to the trapping criterion for the VLF waves entrapped into geomagnetic ducts are obtained.