Information Cascade in Solar Wind Density Fluctuations

Solar wind density fluctuations show typical features of a turbulent energy cascade, including power-law spectra and intermittency. An alternative description in terms of an information cascade and the study of the transition to complexity of the scale-dependent dynamics can provide complementary information on the nonlinear processes governing turbulence. High-resolution proton density measurements from the Spektr-R spacecraft are analyzed using empirical mode decomposition in intrinsic mode functions. The transfer of information and coupling strength between different scales is quantitatively assessed using transfer entropy and mutual information operators. The possible role of intermittency in preventing information from vanishing at proton scales is discussed. In particular, it is demonstrated that in the inertial range it promotes efficient information exchange/coupling, while its absence at kinetic scales constrains the causal transfer to local interactions, only between immediately adjacent scales. The analysis, quantified by the asymmetric flux ratio, confirms that the forward (direct) cascade is the overall dominant causal mechanism across the inertial range. However, the inverse flow becomes locally dominant at kinetic scales.