Temporal evolution of FI_SXR, sunspot number, sunspot area, F10.7, and FI_Hα (from top to bottom panels) during solar cycles 21, 22, and 23. Different plots represent values of corresponding solar activity parameter averaged over a Carrington rotation (CR). The X-axis is labeled in the units of Carrington rotation as well as calendar year. The vertical dashed lines indicate the minimum phase of solar cycles. The smoothed curve in each plot indicates the 13-point running averages.