Impact of evolving turbulence on the diffusion coefficients for wave-particle interactions associated with whistler waves

ABSTRACT Wave-particle interactions driven by whistler waves significantly regulate suprathermal electron transport in the solar wind. However, previous numerical models based on simplified spectral assumptions fail to reproduce observational features of the radial evolution of suprathermal electrons. To resolve this, we generalize the Fokker–Planck diffusion coefficients by incorporating a magnetic energy spectral density for whistler wave, preserving its complete general form. Using a nearly-incompressible magnetohydrodynamic turbulence model and dimensional analysis, an analytical expression for the magnetic energy spectral density at the resonant wavenumber is obtained. The analytical spectral density is then substituted into the generalized diffusion coefficients, establishing a description that depends on the turbulence model. The radial evolution of the turbulence-modified diffusion coefficients is investigated and compared with previous power-law coefficients. Our analysis shows that turbulence-modified coefficients decrease more slowly with distance from 0.1 au and are about one order of magnitude stronger than power-law-based ones between $0.2\, {\rm and}\, 2$ au. This enhancement addresses the drawbacks in previous simulations of suprathermal electron transport. We further find that the spectral index of the dissipation range must exceed 2 to maintain physically consistent energy-dependent scattering. These findings advance our understanding of turbulence-regulated electron transport dynamics, with direct implications for improving solar wind heat flux predictions and elucidating the physical mechanisms governing the strahl-to-halo transition. The work underscores the essential role of realistic turbulence spectra in the kinetic modelling of heliospheric plasma processes.