A quantitative estimate of the ducted whistler power within the outer plasmasphere

Abstract

From a statistical study of ducted whistlers observed at Halley, Antarctica, in 1996, which had propagated on paths in the range L=2.5–4.5, we report mean occurrence rates, numbers of components per whistler, intensities, etc. for night and day conditions and in different seasons at solar minimum. We found an average whistler rate of 5 min −1 and 3 components per whistler. Received whistler amplitudes were measured as a function of frequency and were in the range 2–40 fT, typically 10 fT at 4 kHz. Combining these results with a propagation model, we estimate mean whistler duct output powers to be around 1–10 mW, (≃0.1–1 mJ per whistler in the 3–5 kHz band). Inferred typical equatorial wave fields for ducted whistlers of 0.3 pT led to estimated radiation belt lifetimes for 1–100 keV electrons due to gyroresonance with ducted whistlers of 2×10 6 days. This compares with published lifetimes due to plasmaspheric hiss of order 10 5 days or less, and we conclude that, on average, lightning which enters and propagates in magnetospheric ducts, although known to cause pitch angle scattering and precipitation of trapped electrons, does not significantly affect the radiation belt fluxes in a statistical sense. We have compared our results with those from a similar study by Burgess and Inan (J. Geophys. Res. 98 (1993) 15,643–15,665). In a separate investigation of multi-component whistlers received in winter at quiet times, using the same methodology, we have found that the duct output power generally decreases with increasing L. This is consistent with previous theoretical work and parallels a similar experimental conclusion with respect to higher-frequency whistler-mode signals from VLF transmitters.