Variation of Chromospheric Features as a Function of Latitude and Time Using Ca-K Spectroheliograms for Solar Cycles 15 – 23: Implications for Meridional Flow

Abstract

We have analysed the Ca-K images obtained at Kodaikanal Observatory as a function of latitude and time for the period of 1913 - 2004 covering the Solar Cycle 15 to 23. We have classified the chromospheric activity into plage, Enhanced Network (EN), Active Network (AN), and Quiet Network (QN) areas to differentiate between large strong active and small weak active regions. The strong active regions represent toroidal and weak active regions poloidal component of the magnetic field. We find that plages areas mostly up to 50 deg latitude belt vary with about 11-year Solar Cycle. We also find that weak activity represented by EN, AN and QN varies with about 11-year with significant amplitude up to about 50 deg latitude in both the hemispheres. The amplitude of variation is minimum around 50 deg latitude and again increases by small amount in the polar region. In addition, the plots of plages, EN, AN and QN as a function of time indicate the maximum of activity at different latitude occur at different epoch. To determine the phase difference for the different latitude belts, we have computed the cross-correlation coefficients of other latitude belts with 35 deg latitude belt. We find that activity shifts from mid-latitude belts towards equatorial belts at fast speed at the beginning of Solar Cycle and at slower speed as the cycle progresses. The speed of shift varies between approximately 19 and 3 m/s considering all the data for the observed period. This speed can be linked with speed of meridional flows those believed to occur between convection zone and the surface of the Sun.