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Open AccessArticle

Long-Term Independence of Solar Wind Polytropic Index on Plasma Flow Speed

Division of Space Science and Engineering, Southwest Research Institute, San Antonio, TX 78238, USA
Entropy 2018, 20(10), 799; https://doi.org/10.3390/e20100799
Received: 1 October 2018 / Revised: 12 October 2018 / Accepted: 16 October 2018 / Published: 17 October 2018
(This article belongs to the Section Statistical Physics)
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 γ = 1.86 ± 0.09. View Full-Text
Keywords: polytropic index; solar wind; entropy; space plasmas polytropic index; solar wind; entropy; space plasmas
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MDPI and ACS Style

Livadiotis, G. Long-Term Independence of Solar Wind Polytropic Index on Plasma Flow Speed. Entropy 2018, 20, 799. https://doi.org/10.3390/e20100799

AMA Style

Livadiotis G. Long-Term Independence of Solar Wind Polytropic Index on Plasma Flow Speed. Entropy. 2018; 20(10):799. https://doi.org/10.3390/e20100799

Chicago/Turabian Style

Livadiotis, George. 2018. "Long-Term Independence of Solar Wind Polytropic Index on Plasma Flow Speed" Entropy 20, no. 10: 799. https://doi.org/10.3390/e20100799

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