LARGE-SCALE DYNAMICAL PHENOMENA DURING SOLAR-ACTIVITY CYCLES

The long-term behaviour of several solar-activity parameters (spots, f lares, radio and X-ray fluxes) was investigated to identify essential characteristics of the 11-year cycle maximum. We confirm past findings suggesting that activity maxima occur at least twice during a cycle: first, near the end of the rising activity phase and then in the early years of the declining phase. However, we show that the double peak i s more distinct when intense and/or long-lasting events are considered , because low-energy and short-duration events tend to follow a single -peaked 11-year cycle. Moreover, structured activity maxima are detect ed in all the solar atmospheric layers (photosphere, chromosphere and corona) up to interplanetary space, where several indices display a cl ear trace of the dual-peak maximum. Results based on some activity ind ices for cycle 21 support the effectiveness of the heliomagnetic cycle in producing the structured shape of the maximum phase of solar activ ity cycles.