Multiscale Nature of the Dissipation Range in Gyrokinetic Simulations of Alfvénic Turbulence

Nonlinear energy transfer and dissipation in Alfvén wave turbulence are analyzed in the first gyrokinetic simulation spanning all scales from the tail of the MHD range to the electron gyroradius scale. For typical solar wind parameters at 1 AU, about 30% of the nonlinear energy transfer close to the electron gyroradius scale is mediated by modes in the tail of the MHD cascade. Collisional dissipation occurs across the entire kinetic range $k_{\perp }{\rho }_i\gtrsim 1$. Both mechanisms thus act on multiple coupled scales, which have to be retained for a comprehensive picture of the dissipation range in Alfvénic turbulence.

Figure 1

Normalized field energy spectra. Power law exponents obtained from the $B_{\perp }$ energy spectra within the dotted sections are printed into the plot.

Figure 2

Nonlinear shell-to-shell transfer function for electrons, normalized to the maximum absolute value of each wave number scale.

Figure 3

Infrared locality functions for several shells $k_c$, normalized to the total nonlinear energy transfer through $k_c$, versus the probe wave number $k_p{\rho }_i$. For the curves with $k_c{\rho }_i\gtrsim 5$, a change in slope is apparent when the probe $k_p$ crosses the ion gyroradius scale.

Figure 4

Normalized, short-time averaged collisional dissipation rate for electrons, ions, and its total value. Curves are multiplied by $k_{\perp }$ so the area under the curve is proportional to the energy dissipation rate.