The variance of solar soft X-ray fluxes
Abstract
Abstract The timeseries of GOES soft X-ray data contains clues about the nature of the heating mechanism(s) of the solar corona. This paper focuses on a basic statistical analysis: the correlation of the mean flux S and its variance var(S). Using Taylor's law var(S) = aSb, we can distinguish different degrees of coherence in the variability via the fitted value of the exponent; b = 1 implies Poisson statistics. For the GOES 1-8 A timeseries we find b to be substantially greater than unity for the entire dynamic range of the observations, which cover an eight-year period embracing both quiet times and flare-active times. A single value of b = 3.06 +- 0.05 characterizes the whole data set, 2018-2025, with no evidence for variability in time or any dependence on the base-level flux. This indicates that flares dominate the statistics to well below GOES A-class levels. The fact that the same correlation applies to quiet times as well as active times suggests that there is no need for a different physics to explain the heating of the quiescent corona. This finding does not exclude episodic heating mechanisms, but the heating events do not occur randomly.
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