European Space Weather Week 2025

Spectral Splitting of Long-Lasting Whistler Echo Trains Propagating in a Dual Ducting Structure

Oct 30, 2025, 3:45 PM

15m

Studion

Oral SWR3 - Inner Magnetospheric Dynamics and Coupling Processes SWR3 – Inner Magnetospheric Dynamics and Coupling Processes

Speaker

Ivana Kolmasova (Institute of Atmospheric Physics of the Czech Academy of Sciences, Prague, Czechia)

Description

We report an observation of long-lasting echo trains of lightning-generated whistlers recorded by the WBD instruments on the Cluster spacecraft near the plasmapause on 23 April 2002 during an interval of quasiperiodic emissions. The whistler traces exhibit spectral discontinuities, which split each of them into two branches around 3.6 kHz, with lower-frequency components being stronger and arriving about 2 seconds later than higher-frequency ones. This highly unusual structure is not seen in similar whistler trains recorded just 25 minutes earlier. Ray tracing analysis suggests that this spectral splitting arises from propagation through two discrete field-aligned ducts separated by about 1.5 Earth radii. The intensification of the lower-frequency part is attributed to wave-particle interactions at the equator. These findings provide indirect evidence of fine-scale ducting structures near the plasmapause boundary.