Consolini Giuseppe, Alberti Tommaso, Carbone Vincenzo
INAF-Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, 00133 Roma, Italy.
Dipartimento di Fisica, Università della Calabria, Ponte P. Bucci, 87036 Rende, Italy.
Entropy (Basel). 2020 Dec 15;22(12):1419. doi: 10.3390/e22121419.
In the past decades, there has been an increasing literature on the presence of an inertial energy cascade in interplanetary space plasma, being interpreted as the signature of Magnetohydrodynamic turbulence (MHD) for both fields and passive scalars. Here, we investigate the passive scalar nature of the solar wind proton density and temperature by looking for scaling features in the mixed-scalar third-order structure functions using measurements on-board the Ulysses spacecraft during two different periods, i.e., an equatorial slow solar wind and a high-latitude fast solar wind, respectively. We find a linear scaling of the mixed third-order structure function as predicted by Yaglom's law for passive scalars in the case of slow solar wind, while the results for fast solar wind suggest that the mixed fourth-order structure function displays a linear scaling. A simple empirical explanation of the observed difference is proposed and discussed.
在过去几十年里，关于行星际空间等离子体中存在惯性能量级串的文献越来越多，这被解释为磁场和被动标量的磁流体动力学湍流（MHD）特征。在此，我们通过利用尤利西斯号航天器在两个不同时期（即分别为赤道慢太阳风时期和高纬度快太阳风时期）的测量数据，寻找混合标量三阶结构函数中的标度特征，来研究太阳风质子密度和温度的被动标量性质。我们发现，在慢太阳风情况下，混合三阶结构函数呈现出如亚格洛姆定律所预测的被动标量的线性标度，而快太阳风的结果表明混合四阶结构函数呈现线性标度。我们提出并讨论了对观测到的差异的一个简单经验解释。
