Coronal Electron Temperature from the Solar Wind Scaling Law throughout the Space Age


Recent in situ observations of the solar wind show that charge states (e.g., the O7 +/O6 + and C6 +/C5 + abundance ratios) and α-particle composition evolved through the extended, deep solar minimum between solar cycles 23 and 24 (i.e., from 2006 to 2009). Prior investigations have found that both particle flux and magnetic field strength gradually decreased over this period of time. In this study, we find that (for a given solar wind speed) the coronal electron temperature (as derived from O7 +/O6 + and C6 +/C5 + measurements from ACE) likewise decreased during this minimum. We use the Schwadron & McComas solar wind scaling law to show that cooler coronal electron temperatures are naturally associated with lower particle fluxes because downward heat conduction must be reduced to keep the average energy loss per particle fixed. The results of the scaling law should apply to all solar wind models and suggest that the evolution of the solar wind is linked to the solar dynamo, which caused the coronal magnetic field strength to decrease in the deep, extended minimum. We utilize the scaling law to project coronal electron temperatures backward in time throughout the space age and find that these temperatures have been decreasing in successive temperature maxima since 1987 but were increasing in successive temperature maxima from 1969 to 1987. Thus, we show how the solar wind scaling law relates solar wind properties observed at 1 AU back to coronal electron temperatures throughout the space age.



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The Astrophysical Journal


American Astronomical Society

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