Monofractality in the solar wind at electron scales

Abstract

Solar wind turbulence at electron scale is generally thought to be governed primarily by kinetic Alfvén waves (KAW), but the monofractal behavior observed is a puzzling problem that contradicts the standard properties of intermittency. We investigate this long-standing problem using direct numerical simulations (DNS) of three-dimensional electron reduced magnetohydrodynamics (ERMHD). Both weak and strong KAW turbulence regimes are studied in the balanced case. After recovering the expected theoretical predictions for the magnetic spectra, a higher-order multiscale statistical analysis is performed. This study reveals a striking difference between the two regimes, with the emergence of monofractality only in weak turbulence, whereas strong turbulence is multifractal. This result, combined with recent studies, shows the relevance of collisionless weak KAW turbulence to describe the solar wind at electron scale.