Source region for whistlers detected at Rothera, Antarctica

The accepted mechanism for whistler generation implicitly assumes that the causative lightning stroke occurs within reasonable proximity to the conjugate foot point of the guiding magnetic field line and that nighttime whistlers are prevalent because of low transionospheric attenuation. However, these assumptions are not necessarily valid. In this study we consider whistler observations from Rothera, a station on the Antarctic Peninsula, and contrast their occurrence with global lightning activity from the World Wide Lightning Location Network. The correlation of one-hop whistlers observed at Rothera with global lightning yields a few regions of significant positive correlation. The most probable source region was found over the Gulf Stream, displaced slightly equatorward from the conjugate point. The proximity of the source region to the conjugate point is in accord with the broadly accepted whistler production mechanism. However, there is an unexpected bias toward oceanic lightning rather than the nearby continental lightning. The relationship between the diurnal pattern of the Rothera whistlers and the conjugate lightning exhibits anomalous features which have yet to be resolved: the peak whistler rate occurs when it is daytime at both the source and the receiver and when source lightning activity is at its lowest. As a result, we propose that preferential whistler-wave amplification in the morning sector is a possible cause of the high whistler occurrence, although this does not account for the bias toward oceanic lightning.

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