Study of Meridional Flow Using Ca-K Line Profiles during Solar Cycles 22 and 23

Abstract

The analysis of Ca-K line spectra as a function of solar latitude and integrated over longitudes taken during the period of 1989-2011 indicates that the K1 width attains maximum amplitude at various latitude belts at different phases of the solar cycle. The FWHM of the K1 distribution at different latitudes shows that its width varies by about 30% for the equatorial belt (<30°) and 11% for the polar region (>70°) latitudes. Interestingly, the K1 width varies by ~6% only in the 40-60° latitude belts during the solar cycle. The analysis of cross-correlation coefficients of the K1 width between the 35° latitude and other latitude belts as a function of phase differences indicates that the activity representing toroidal field shifted at a uniform rate of about 5.1 m s–1 in the northern hemisphere from mid-latitudes toward the equator. In the southern hemisphere, activity shifted at a faster rate, ~14 m s–1, in the beginning of the cycle and the speed decreased with time, yielding an average speed of 7.5 m s–1 toward the equator. The shift of activity in the higher latitude belts showed complex behavior, indicating poleward and equatorward migration. These findings, especially the fewer variations in mid-latitude belts as compared to polar regions, asymmetry in the speed of the shift in the activity in both hemispheres, and complex variation in the direction of the shift in the activity representing poloidal fields in mid-latitude belts, will have an important implication on the modeling of the solar dynamo.