Lightning whistler waves in the high‐latitude magnetosphere

Abstract

Whistler waves caused by lightning are known to penetrate the ionosphere with significant wave amplitudes. Recent rocket experiments have shown that lightning from sources as far as 1000 km from the ionospheric rocket subtrack are easily seen. The spectral energy density of lightning in the ionosphere often has significant power at frequencies near and below 1 kHz. Such low‐frequency whistler waves can propagate all the way to the magnetopause boundary layer if they begin in the cusp or polar cap. Lightning is common over high‐latitude continental land masses in the summer months which places this wave source function well within range of the cusp and polar cap. Ray tracing studies using a global three‐dimensional two‐fluid code are conducted to investigate the propagation of these whistler waves into the high latitude magnetosphere. The estimated, mapped lightning whistler wave amplitude is compared to wave intensity measurements from ISEE and AMPTE and supports the argument that falling tone whistler waves, seen by Geotail near the dayside magnetopause, may have been from intense lightning. It is found that the mapped whistler wave amplitude from lightning is comparable to the in situ wave amplitudes measured in the outer dayside magnetosphere and low latitude boundary layer.