Scale-dependent Kurtosis of magnetic field fluctuations in the solar wind: A multi-scale study with Cluster 2003-2015

The Cluster II mission was launched in 2000 to study three-dimensional space plasma processes. Over the past two decades, the Cluster spacecraft have collected data from various near-Earth space plasmas, including the solar wind. During the lifetime of the mission, the inter-spacecraft distances of Cluster in the solar wind have changed from the large scales (~ 10,000 km) where fluid physics dominates the turbulent fluctuations, down to the scales of protons (~ 200 km). More recently, as part of the Guest Investigator (GI) campaign, the mission achieved a novel formation where a pair of spacecraft were separated by ~7 km, close to electron scales. The small distances and the exceptional sensitivity of the search coil magnetometer provide an excellent data set for studying solar wind turbulence at electron scales. This study will investigate intermittency of the magnetic field fluctuations in the slow wind from fluid to kinetic scales, using both time-lagged increments from a single spacecraft and spatially lagged increments using multiple spacecraft. As the turbulent cascade proceeds to smaller scales in the inertial range, the deviation from Gaussian statistics is observed to increase in both temporal and spatial increments. At ion scales, there is a maximum of kurtosis, and at sub-ion scales, the fluctuations are only weakly non-Gaussian. The observations show differences in kurtosis of time and space increments, indicating its spatial anisotropy.