Electron scattering by whistler‐mode ELF hiss in plasmaspheric plumes

Abstract

[1] Nonadiabatic loss processes of radiation belt energetic electrons include precipitation loss to the atmosphere due to pitch-angle scattering by various magnetospheric plasma wave modes. Here we consider electron precipitation loss due to pitch-angle scattering by whistler-mode ELF hiss in plasmaspheric plumes. Using wave observations and inferred plasma densities from the Plasma Wave Experiment on the Combined Release and Radiation Effects Satellite (CRRES), we analyze plume intervals for which welldetermined hiss spectral intensities are available. We then select 14 representative plumes for detailed study, comprising 10 duskside plumes and 4 nonduskside plumes, with local hiss amplitudes ranging from maximum values of above 300 pT to minimum values of less than 1 pT. We estimate the electron loss timescale t loss due to pitch-angle scattering by hiss in each chosen plume as a function of L-shell and electron energy; t loss is calculated from quasi-linear theory as the inverse of the bounce-averaged diffusion rate evaluated at the equatorial loss cone angle. We find that pitch-angle scattering by hiss in plumes can be efficient for inducing precipitation loss of outer-zone electrons with energies throughout the range 100 keV to 1 MeV, though the magnitude of t loss can be highly dependent on wave power, L-shell, and electron energy. For 100-to 200-keV electrons, typically t loss $ 1 day while the minimum loss timescale (t loss ) min $ hours. For 500-keV to 1-MeV electrons, typically (t loss ) min $ days, while (t loss ) min < 1 day in the case of large wave amplitude ($100's pT). Apart from inducing direct precipitation loss of MeV electrons, scattering by hiss in plumes may reduce the generation of MeV electrons by depleting the lower energy electron seed population. Models of the dynamical variation of the outer-zone electron flux should incorporate electron precipitation loss induced by ELF hiss scattering in plasmaspheric plumes.

Plasmaspheric Density Structures and Dynamics: Properties Observed by the CLUSTER and IMAGE Missions

“…Those structures are now known as "plasmaspheric plumes" (e.g., Elphic et al 1996;Ober et al 1997;. Plumes have commonly been detected in the past by in situ measurements on satellites such as OGO 4 (Taylor et al 1971), OGO 5 (Chappell et al 1970a), ISEE-1 (Carpenter and Anderson 1992), CRRES (Moldwin et al 2004;Summers et al 2008), and several at geosynchronous orbit (Moldwin et al 1995;Borovsky et al 1998), but also by ground-based instruments (Carpenter et al 1993;Su et al 2001). Plumes were predicted on the basis of various theoretical models.…”

The story of plumes: the development of a new conceptual framework for understanding magnetosphere and ionosphere coupling

“…What is now clear is that plumes connect the equatorial F region ionosphere to the dayside magnetopause and the nightside magnetotail plasma sheet (e.g., Su et al, 2001a, b;Horvath and Lovell, 2011;Walsh et al, 2014a, b;Foster et al, 2014). Through the formation and evolution of the different plumes, they impact wave generation and wave-particle interactions (e.g., Summers et al, 2008;Chen et al, 2012;Halford et al, 2015), particle precipitation (Spasojević and Fuselier, 2009;Yuan et al, 2011Yuan et al, , 2013, ion outflow (e.g., Zeng and Horowitz, 2008;Tu et al, 2007), local-time asymmetries in ULF wave field-line resonance (FLR) signatures (e.g., Archer et al, 2015;Ellington et al, 2016), satellite communication and navigation systems (Ledvina et al, 2004;Basu et al, 2005;Datta-Barua et al, 2014), and even the coupling efficiency of the solar wind to the magnetosphere (Borovsky and Denton, 2006;Borovsky et al, 2013;Ouellette et al, 2016;Fuselier et al, 2016). Though we now have a new appreciation and understanding of plumes, there are still many unanswered questions on their formation (e.g., Kelley et al, 2004;Horvath and Lovell, 2011;Zou et al, 2013Zou et al, , 2014Borovsky et al, 2014) and impact on global magnetospheric dynamics McFadden et al 2008;Walsh et al, 2014Walsh et al, , 2015.…”

Radial diffusion simulations of the 20 September 2007 radiation belt dropout

“…5, but the modeled lifetimes increase with energy while the observed lifetimes decrease with energy. Also, compared to the empirical values of Lam et al (2007) and Summers et al (2008), the assumed hiss amplitude of 100 pT seems rather high. …”

“…Li et al (2007) provided a simple, convenient model which was originally presented for a 2-D study at L = 4.5, but which was quickly adopted for all L (e.g., Shprits et al, 2009). A study by Summers et al (2008) of CRRES wave data restricted to plumes found considerably smaller wave amplitudes, but it may be argued that the plume crossings, mostly on the night side, were not favorably located.…”