The in situ storage of magnetic energy is studied in a linear force-free arcade sheared by a relative velocity between its footpoints. The photospheric velocity fields used in the analysis are related to sunspots proper motions and to the solar differential rotation pattern. As observations have shown, the flare productivity is enhanced in sites where anomalies in the solar differential rotation pattern are present, where with anomalies, rigidly rotating structures, like pivot points in long-lived filaments, and parasitic polarities are indicated. Aim of this work was to verify whether these anomalies may play a significative role in the pre-flare stage of magnetic energy storage. Moreover, as deduced from the analysis of 103 years of observations, 2 days old sunspot-groups have angular velocities 0.3 degrees/day higher than recurrent sunspots, and this difference decreases almost linearly with time as the sunspots evolve. Therefore an arcade interconnecting differently aged sunspots is subject to a shearing motion. We have calculated the amount of energies involved in the magnetic energy build-up phase using velocity fields reflecting the above mentioned characteristics and, for comparison, a velocity field characteristic of a proper motion. The results show that sunspots proper motions are the most efficient to build-up magnetic energy (approximately 2.7 10(33) erg after 100 hours with a velocity of 1.5 10(4) cm s-1), but that also the values of the stored magnetic energy in a region characterized by rigidly rotating structures coupled with new born sunspots (approximately 10(33) erg after 100 h), may be sufficient to allow flaring activity. Therefore we may conclude that the anomalies in the solar angular velocity pattern, as deduced by observations, may have an important role in the magnetic energy build-up.
|Titolo:||PECULIAR PHOTOSPHERIC VELOCITY-FIELDS AND MAGNETIC ENERGY BUILDUP|
|Data di pubblicazione:||1992|
|Appare nelle tipologie:||1.1 Articolo in rivista|