Duct propagation of hydromagnetic waves in the upper ionosphere, 2, Dispersion characteristics and loss mechanism

<jats:p>Ducted propagation of short‐period hydromagnetic waves in the upper ionosphere are studied based on a layered model including a ducting upper ionospheric layer and an anisotropic conducting sheet (<jats:italic>E</jats:italic> layer) under vertical, uniform ambient magnetic fields. Energy of the ducted wave is dissipated by the ionospheric Joule loss, the Poynting loss due to the shear Alfvén wave converted from the fast magnetosonic wave and the Joule loss in the conducting Earth. The ionospheric Joule loss mainly contributes to energy dissipation of the ducted wave as far as the Pedersen conductivity is not much smaller than the Hall conductivity. Spatial attenuation of a ducted wave is obtained by total energy loss divided by horizontal transportation of the ducted wave energy. Thus when the wave frequency is near to the lower cutoff, the minimum attenuation is taking place, particularly, for the fundamental ducted wave because horizontal energy transportation is enhanced by an evanescent boundary wave in the magnetosphere. Electric field intensity of the vertically standing fast magnetosonic wave at the conducting layer is essential to the energy loss. As far as using the simplified ionosphere model, when the frequency increases the ducted wave is less attenuated owing to a decrease in the ionospheric Joule loss because the electric field disturbance tends to have a node at the ionosphere. There appears a quasi‐sinusoidal variation in the frequency dependence of the attenuation when the Hall conductivity is larger than the Pedersen conductivity. This variation is caused by the modulation of the mode conversion from the fast magnetosonic wave to the Alfvén wave associated with the standing wave pattern of the Alfvén wave in the ducting layer.</jats:p>