Se p 20 09 Physics of the Solar Cycle : New Views

With the recent overwhelming evidences that solar cycle and activity phenomena strongly influence the earth’s environment and climate (Hiremath 2009a and references there in), it is necessary to understand physics of the solar cycle and activity phenomena. Genesis of the solar cycle and activity phenomena-one of the major unsolved problem in solar physicsremains elusive to the solar community. Presently there are two schools of thoughts viz., turbulent dynamo and MHD oscillation mechanisms that explain the solar cycle and activity phenomena. Both the mechanisms are critically examined and fundamental difficulties are presented. By keeping in mind the more advantages of having MHD oscillation mechanism, compared to the turbulent dynamo mechanism, following new ideas on the genesis of the solar cycle and activity phenomena are presented. Inevitability of most likely existence of a combined steady poloidal and toroidal magnetic field structure in the solar interior. Owing to suitable steady poloidal field structure, Alfven wave perturbations of long periods (∼ 22 yrs) that excite in the solar core travel first to the poles in both the hemispheres and later reach the equator. While traveling towards the surface, Alfven wave perturbations along the weak poloidal field structure in turn perturb the embedded strong toroidal field structure producing sunspots, especially in the convective envelope, that travel to the surface due to buoyancy along isorotational contours. With realistic density structure of the solar interior, computation of Alfven wave travel times along different field lines of the poloidal field structure (Hiremath and Gokhale 1995) yields almost similar periods (∼ 22 yr) explaining the constancy of 22 yr period of the odd degree modes obtained from the Spherical Harmonic Fourier analysis of the surface magnetic field. The observed quasi-periodicities of solar activity indices in the range of 1-5 years are explained due to perturbation of the strong toroidal field structure and, variation of very long period solar cycle and activity phenomena such as the Maunder and grand minima is explained to be due to coupling of long period poloidal and toroidal MHD oscillations.