Asymmetric variations of the coronal green line intensity

Abstract

The analysis of the daily measurements of the coronal green line intensity, which have been extensively tested for homogeneity and freedom of trends observed at the Pic-du-Midi observatory during the period 1944-1974, has revealed some characteristic asymmetric variations. A north-south asymmetry of the green line intensity is the main feature of the period 1949-1971 while a south-north one is obvious within 1972-1974 and the minor statistical significance span 1944-1948. On the other hand a significant W-E asymmetry has been confirmed in the whole period 1944-1974. It is noteworthy that the period 1949-1971, where the N-S asymmetry takes place consists a 22-yr solar cycle which starts from the epoch of the solar magnetic field inversion of the solar cycle No. 18 and terminates in the relevant epoch of the cycle No. 20. The combination of N-S and S-N asymmetry with a W-E one makes the NW solar-quarter to appear as the most active of all in the 22-yr cycle 1949-1971, while in the periods 1944-1948 and 1972-1974 the SW quarter is the most active. Finally, from the polar distribution of the green line intensity has been derived that the maximum values of the asymmetries occur in heliocentric sectors ± 10°-20° far from the solar equator on both sides of the central meridian. Physical mechanisms which could contribute to the creation of both N-S and E-W asymmetries of the solar activity and the green line intensity as an accompanied event, like different starting time of an 11-yr solar cycle in the two solar hemispheres, the motion of the Sun towards the Apex, and short-lived 'active' solar longitudes formed by temporal clustering of solar active centers, have been discussed. © 1988 Kluwer Academic Publishers