The State of Self-Organized Criticality of the Sun During the Last 3 Solar Cycles. I. Observations
Markus J. Aschwanden Submitted: 2010-06-24 12:55
We analyze the occurrence-frequency distributions of peak fluxes P,
total fluxes E, and durations T of solar flares over the last
three solar cycles (during 1980-2010) from HXRBS/SMM, BATSE/CGRO,
and RHESSI hard X-ray data. From the synthesized data
we find powerlaw slopes with mean values of
α _P=1.73pm0.07 for the peak flux,
α _E=1.62pm0.12 for the total flux, and
α _T=1.99pm0.35 for flare durations.
We find a tendency of an anti-correlation of the powerlaw slope of peak fluxes
with the flare rate or sunspot number as a function of the solar cycle.
The occurrence powerlaw slope is always steeper by Delta α approx
0.1 during a solar-cycle minimum compared with the previous solar-cycle
maximum, but the relative amplitude varies for each cycle or instrument.
Since each solar cycle has been observed with a different instrument,
part of the variation could be attributed to instrumental characteristics
and different event selection criteria used in generating the event catalogs.
The relatively flatter powerlaw slopes during solar maxima could
indicate more energetic flares with harder electron energy spectra,
probably due to a higher magnetic complexity of the solar corona.
This would imply a non-stationarity (or solar-cycle
dependence) of the coronal state of self-organized criticality.
Authors: Markus J. Aschwanden
Publication Status: Solar Physics, WIH Topical Issue, March 2011, (in press)
Last Modified: 2011-03-14 09:28