Fluctuations in the ∼27-day sequences in the solar index F10 during solar cycles 22–23

A study of the daily values of the 10.7 cm ( 2800 MHz , F10) solar radio flux revealed fluctuations with peak spacings in a very wide range (∼13–40 days). There can be multiple reasons for such a wide range. Amongst these, there is a possibility that the dominant radiance within an active region may move rapidly forward or backward with respect to the solar surface, to give spacings different from ∼27 days (solar rotation period). This needs to be checked with an actual image analysis. An earlier conclusion by Pap et al. (Solar Phys. (1990) 165) that 27-day solar rotation is more pronounced in the declining phase of a solar cycle, seems to be true for cycles 22–23 also. However, during any year, the magnitudes of the 27-day oscillation can vary by more than a factor of two from one oscillation to another.