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    The State of Self-Organized Criticality of the Sun During the Last 3 Solar Cycles. I. Observations

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    We analyze the occurrence frequency distributions of peak fluxes PP, total fluxes EE, and durations TT of solar flares over the last three solar cycles (during 1980--2010) from hard X-ray data of HXRBS/SMM, BATSE/CGRO, and RHESSI. From the synthesized data we find powerlaw slopes with mean values of αP=1.72±0.08\alpha_P=1.72\pm0.08 for the peak flux, αE=1.60±0.14\alpha_E=1.60\pm0.14 for the total flux, and αT=1.98±0.35\alpha_T=1.98\pm0.35 for flare durations. We find a systematic anti-correlation of the powerlaw slope of peak fluxes as a function of the solar cycle, varying with an approximate sinusoidal variation αP(t)=α0+Δαcos[2π(tt0)/Tcycle]\alpha_P(t)=\alpha_0+\Delta \alpha \cos{[2\pi (t-t_0)/T_{cycle}]}, with a mean of α0=1.73\alpha_0=1.73, a variation of Δα=0.14\Delta \alpha =0.14, a solar cycle period Tcycle=12.6T_{cycle}=12.6 yrs, and a cycle minimum time t0=1984.1t_0=1984.1. The powerlaw slope is flattest during the maximum of a solar cycle, which indicates a higher magnetic complexity of the solar corona that leads to an overproportional rate of powerful flares.Comment: subm. to Solar Physic
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