A parametric study on how lightning-generated whistler waves propagate up into the magnetosphere

Lightning-generated whistler (LGW) waves leaking into the magnetosphere can efficiently scatter electrons into the atmosphere and produce a diffuse aurora. Here, we investigate the propagation of LGW waves by utilizing a numerical ray tracing model. The simulations indicate that the spatial distribution of an LGW wave exhibits two peaks: one in the ionosphere and the other within L ~ 2–3 in the magnetosphere. The ionospheric peak is due to the waves trapped in the ionosphere as they are emitted at low latitudes (λ < ~15°) or as their initial normal angles are ~90°. The magnetospheric peak is due to the waves propagating into the magnetosphere under the conditions of enhanced geomagnetic activity or at higher emission latitudes (λ > ~35°). Moreover, the LGW waves propagating into the magnetosphere are finally confined to specific magnetic shells because the wave normal angle increases to the Gendrin angle near the reflection point, subsequently leading to field-aligned propagation. These findings refine current characterization of the propagation and distribution of LGW waves in the magnetosphere, contributing to quantifying the precipitation losses of electrons.