Livadiotis George
Division of Space Science and Engineering, Southwest Research Institute, San Antonio, TX 78238, USA.
Entropy (Basel). 2018 Oct 17;20(10):799. doi: 10.3390/e20100799.
The paper derives the polytropic indices over the last two solar cycles (years 1995-2017) for the solar wind proton plasma near Earth (~1 AU). We use ~92-s datasets of proton plasma moments (speed, density, and temperature), measured from the Solar Wind Experiment instrument onboard Wind spacecraft, to estimate the moving averages of the polytropic index, as well as their weighted means and standard errors as a function of the solar wind speed and the year of measurements. The derived long-term behavior of the polytropic index agrees with the results of other previous methods. In particular, we find that the polytropic index remains quasi-constant with respect to the plasma flow speed, in agreement with earlier analyses of solar wind plasma. It is shown that most of the fluctuations of the polytropic index appear in the fast solar wind. The polytropic index remains quasi-constant, despite the frequent entropic variations. Therefore, on an annual basis, the polytropic index of the solar wind proton plasma near ~1 AU can be considered independent of the plasma flow speed. The estimated all-year weighted mean and its standard error is = 1.86 ± 0.09.
本文推导了近地（约1天文单位）太阳风质子等离子体在过去两个太阳活动周期（1995 - 2017年）内的多方指数。我们使用从“风”号航天器上搭载的太阳风实验仪器测量得到的约92秒质子等离子体矩（速度、密度和温度）数据集，来估计多方指数的移动平均值，以及它们作为太阳风速和测量年份函数的加权平均值和标准误差。推导得到的多方指数长期行为与其他先前方法的结果一致。特别是，我们发现多方指数相对于等离子体流速保持准恒定，这与早期对太阳风等离子体的分析一致。结果表明，多方指数的大部分波动出现在快速太阳风中。尽管熵频繁变化，但多方指数仍保持准恒定。因此，以年为基础，约1天文单位附近太阳风质子等离子体的多方指数可被视为与等离子体流速无关。估计的全年加权平均值及其标准误差为 = 1.86 ± 0.09。
