Statistical characterisation of full-disk EUV/XUV solar irradiance and correlation with solar activity

摘要

We investigate the distribution of fluctuations in solar irradiance whenintegrated over the full disk, obtained using extreme ultraviolet/soft X-rayobservations from the SOHO CELIAS/SEM instrument. This time series sums overboth the contributions of single distinguishable flares, and of many otherprocesses. By detrending we select events with timescales of less than a fewhours such as waves, slow flows, and CMEs. The statistics generated by thisrange of phenomena can be characterised by power-law-tailed distributions. Weshow that (i) during the high-activity period 2000 Jan-June the tail exponenta(T)=1.5 +/- 0.1; (ii) during the low-activity period 1996 Jan-June a(T)=3.0+/- 0.2; and (iii) in general a(T) decreases with increasing activity.