On the left column, is plotted against for solar cycles (a) 21, (b) 22 and (c) 23. On the right column, is plotted against for solar cycles (d) 21, (e) 22 and (f) 23. The linear fit for the complete solar cycle is shown in black. The ascending and descending phases of each solar cycle along with the corresponding linear fit are shown in blue and red, respectively. In the lower right corner of each plot, the corresponding correlation coefficients are shown.