Abstract
Abstract. Chorus-type whistler waves are one of the most intense electromagnetic waves generated naturally in the magnetosphere. These waves have a substantial impact on the radiation belt dynamics as they are thought to contribute to electron acceleration and losses into the ionosphere through resonant wave–particle interaction. Our study is devoted to the determination of chorus wave power distribution on frequency in a wide range of magnetic latitudes, from 0 to 40°. We use 10 years of magnetic and electric field wave power measured by STAFF-SA onboard Cluster spacecraft to model the initial (equatorial) chorus wave spectral power, as well as PEACE and RAPID measurements to model the properties of energetic electrons (~ 0.1–100 keV) in the outer radiation belt. The dependence of this distribution upon latitude obtained from Cluster STAFF-SA is then consistently reproduced along a certain L-shell range (4 ≤ L ≤ 6.5), employing WHAMP-based ray tracing simulations in hot plasma within a realistic inner magnetospheric model. We show here that, as latitude increases, the chorus peak frequency is globally shifted towards lower frequencies. Making use of our simulations, the peak frequency variations can be explained mostly in terms of wave damping and amplification, but also cross-L propagation. These results are in good agreement with previous studies of chorus wave spectral extent using data from different spacecraft (Cluster, POLAR and THEMIS). The chorus peak frequency variations are then employed to calculate the pitch angle and energy diffusion rates, resulting in more effective pitch angle electron scattering (electron lifetime is halved) but less effective acceleration. These peak frequency parameters can thus be used to improve the accuracy of diffusion coefficient calculations.
Highlights
The assessment of radiation belt dynamics is one of the most important objectives of space weather programmes (Baker, 2002), because of the impact of energetic particles on technology (e.g. Wrenn et al, 2002; Daglis et al, 2004; Iucci et al, 2005) and Earth’s environment (e.g. Thorne, 1977; Lanzerotti, 2012)
In which resonant wave–particle interactions are described in terms of particle pitch angle and energy diffusion (Kennel and Petschek, 1966; Trakhtengertz, 1966; Lyons and Williams, 1984), it has been shown that chorus-type whistler waves play a major role in both the loss and local acceleration of radiation belt electrons
The parameters obtained from Cluster statistics shown above, that can be used to calculate diffusion rates, are presented in Sect. 4, and we present the distribution obtained from numerical simulations in the dayside
Summary
The assessment of radiation belt dynamics is one of the most important objectives of space weather programmes (Baker, 2002), because of the impact of energetic particles on technology (e.g. Wrenn et al, 2002; Daglis et al, 2004; Iucci et al, 2005) and Earth’s environment (e.g. Thorne, 1977; Lanzerotti, 2012). Breuillard et al.: Field-aligned chorus power spectrum models (Bourdarie et al, 1996; Li et al, 2001; Glauert and Horne, 2005; Summers et al, 2007; Fok et al, 2008; Mourenas et al, 2012a, b, 2014), that are based on the quasi-linear theory Using this approach, in which resonant wave–particle interactions are described in terms of particle pitch angle and energy diffusion (Kennel and Petschek, 1966; Trakhtengertz, 1966; Lyons and Williams, 1984), it has been shown that chorus-type whistler waves play a major role in both the loss and local acceleration of radiation belt electrons In the Appendices the data set and analysis are described, as well as the numerical model employed in this study, in particular the energetic electron distributions used to reproduce wave growth/damping in the inner magnetosphere
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