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

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,...

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Autor principal: Livadiotis, George
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2018
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7512360/
https://www.ncbi.nlm.nih.gov/pubmed/33265886
http://dx.doi.org/10.3390/e20100799
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author Livadiotis, George
author_facet Livadiotis, George
author_sort Livadiotis, George
collection PubMed
description 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.
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spelling pubmed-75123602020-11-09 Long-Term Independence of Solar Wind Polytropic Index on Plasma Flow Speed Livadiotis, George Entropy (Basel) Article 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. MDPI 2018-10-17 /pmc/articles/PMC7512360/ /pubmed/33265886 http://dx.doi.org/10.3390/e20100799 Text en © 2018 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Livadiotis, George
Long-Term Independence of Solar Wind Polytropic Index on Plasma Flow Speed
title Long-Term Independence of Solar Wind Polytropic Index on Plasma Flow Speed
title_full Long-Term Independence of Solar Wind Polytropic Index on Plasma Flow Speed
title_fullStr Long-Term Independence of Solar Wind Polytropic Index on Plasma Flow Speed
title_full_unstemmed Long-Term Independence of Solar Wind Polytropic Index on Plasma Flow Speed
title_short Long-Term Independence of Solar Wind Polytropic Index on Plasma Flow Speed
title_sort long-term independence of solar wind polytropic index on plasma flow speed
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7512360/
https://www.ncbi.nlm.nih.gov/pubmed/33265886
http://dx.doi.org/10.3390/e20100799
work_keys_str_mv AT livadiotisgeorge longtermindependenceofsolarwindpolytropicindexonplasmaflowspeed