Study of Sun's rotation and solar activity

Abstract

In my thesis I have presented many interesting properties of Sun's rotation and magnetic activity derived from extensive analysis of over 100 year photoheliographic data on sunspot activity and 26 year's data on photospheric motions from Mt Wilson, and supporting data from GONG and SOHO. Some important results are : 1. The rate of emergence of toroidal magnetic flux above Sun's surface can be expressed as the superposition of at least four 'global' MHD oscillations. Frequency of the dominant mode is ~ 1/21.4 yr-l. 2. There exis~s a '" 22 year periodicity in the differential rotation. Thus, the above-mentioned oscillations may be ''torsional MHD oscillations" . 3. (i) The magnetic structures which yield spot groups with life spans 10- 12 days are initially anchored near the base of the convective envelope; (li) in latitudes 100 - 200 these structures rise at a rate rv 21 Mm per day, as the spot group ages; and (iii) the magnetic structures of spot groups which live successively shorter by 1 day are initially anchored in layers successively shallower by "" 21 Mm. 4. (i) Magnetic structures with magnetic flux iP ~ 1022 Mx might be generated around the base of the convection zone, (li) many of the magnetic structures may be fragmenting (or branching) into smaller structures while rising through the solar convection zone, and (iii) magnetic structures with iP < 1022 Mx might be the fragmented (or branched) parts of the larger magnetic structures. 5. The mean rotation frequencies of the long-lived young groups, the longlived old groups and the short-lived spot groups suggeSt that the periodicities .. e-mail:jj@iiap.emet.in 606 J. Javaraiah '" 21 yr and '" 11 yr in the differential rotation are dominant in the rotational perturbations of the Sun's deeper layers (r ,..... 0.73%) and shallower layers ('" r > 0.95%). 6. The solar meridional flow seems to be strong and poleward during declining ends of the solar cycles. There exists a reasonable correlation between the solar cycle variations of the average meridional motion and the differential rotation, suggesting existence of a coupling in the latitudinal and longitudinal motions somewhere in the convection zone.