Long-Term Variability of the Polytropic Index of Solar Wind Protons at 1 AU

G. Nicolaou, G. Livadiotis, X. Moussas

Research output: Contribution to journalArticlepeer-review

58 Scopus citations

Abstract

Spacecraft data from the OMNI database were used to calculate the value of the polytropic index of the solar wind by fitting the logarithms of proton density and temperature in selected time intervals from 1 January 1995 to 30 June 2012. Bernoulli's integral and the correlation coefficient were used to filter the results. An alternative method based on the maximization of the correlation coefficient was employed to confirm our results. The long-term behavior of the polytropic index we obtained is found to be virtually identical for both methods. We noticed a characteristic behavior of the estimated polytropic index values, particularly from 1995 to 2006, which tends to have a periodicity of about one year. The distribution of the polytropic index is best described by a κ-Gaussian distribution with mean ≈ 1.8 and standard deviation ≈ 2.4. We finally examined the possible correlation between the polytropic index values and solar activity.

Original languageEnglish (US)
Pages (from-to)1371-1378
Number of pages8
JournalSolar Physics
Volume289
Issue number4
DOIs
StatePublished - Apr 2014
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Polytropic index
  • Solar cycle
  • Thermodynamics
  • Variations

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