Investigation of scale-dependent dynamic alignment in the solar wind using WIND data

In 2005, Boldyrev proposed a phenomenological model of scale-dependent dynamic alignment (SDDA) to resolve the discrepancies between the -3/2 scaling of the energy spectrum observed in simulations and the -5/3 spectrum predicted by MHD turbulence models. Predictions from this SDDA model have been extensively tested in numerical simulations, and the results provide convincing evidence that SDDA may be a fundamental property of MHD turbulence. In comparison, studies using observational data are less numerous and have been unable to provide evidence of SDDA in the solar wind. For instance, Podesta et al. (2009) addressed SDDA in solar wind turbulence and found partial but inconclusive evidence of SDDA in the inertial range, which they argued it could be due to instrument uncertainties or to the presence of compressible fluctuations. In this work we investigate SDDA in the solar wind using a large statistical analysis of 23 years of WIND data. The data is conditioned using various parameters to isolate intervals dominated by non-compressive Alfvénic fluctuations, which best represents where SDDA would be present. Our analysis shows evidence of SDDA in the inertial range, with a power law scaling that is consistent with the measured spectral index of the power spectrum expected from the SDDA model.