Variable Cascade Dynamics and Intermittency in the Solar Wind at 1 AU

Abstract:

In recent studies by ourselves and others of third-moment expressions for the rate of energy cascade in the solar wind, it has been shown that relatively large volumes of data are needed to produce convergent averages. These averages are in good agreement with independently obtained estimates for the average heating rate for a solar wind plasma under those conditions. The unanswered question has been whether the convergence issue is the result of intermittent dynamics or simple measurement uncertainties. In other words, is the difficulty in obtaining a single result that characterizes many similarly prepared samples due to in situ dynamics that create physically real variations or simple statistics? There have been publications showing evidence of intermittent dynamics in the solar wind. Here we show that the third-moment expressions and the computed energy cascade for relatively small samples of data comparable to the correlation length are generally well-formed estimates of the local dynamics. This leads us to conclude that intermittency and not simple measurement uncertainties are responsible for the slow convergence to expected heating rates. We partially characterize the scale size of the intermittency to be comparable to or smaller than the correlation length of the turbulence and we attempt to rephrase the discussion of third moments in terms of intermittent dynamics.