Different triggering mechanisms for solar flares and coronal mass ejections

Context. Experimental observations indicate that flares and CMEs are often associated, even if the precise relationship between the two phenomena is a still hot and open question. Aims. We present a study of the statistical properties of solar flare and CME temporal organisation, in order to enlighten differences in the mechanisms at the basis of their occurrence. Methods. We analyse experimental catalogs and compare the occurrence rate of flares and CME with the sunspot number. We also perform numerical simulations of simple stochastic models to be compared with experimental data. Results. We find that the CME and flare occurrence rates are related, respectively, linearly and quadratically to the level of solar activity. Conclusions. This behaviour could be understood in terms of correlations among flares: the occurrence of a flare, by perturbing the magnetic configuration, may eventually trigger further flares. This interpretation is supported by the existence of Omori sequences of after-flares following more energetic flares.