Temporal variations of the Nimbus 7 measurements of solar UV flux, important for their stratospheric effects, are compared with ground-based measurements of the solar infrared He ¿i absorption line at 1083 nm. The close similarity of their temporal characteristics shows that the 1083-nm line is a better estimator of the UV flux than the classical indices of solar activity, the 10.7-cm radio flux and the sunspot number, for short time scales (days, weeks). The power spectrum of the He i line intensity matches that of the Nimbus 7 205-nm flux at the 27-day period peak but is weaker at the peak near 13 to 14 days period. The 27-day peak is caused by the combination of solar rotation of active regions with one major concentration in their solar longitude distribution, and the 13-day case involves two concentrations with solar longitude roughly 180¿ apart. The 13-day periodicity is not simply a second harmonic of the 27-day periodicity, because some episodes of activity are dominated by the 13-day periodicity with very weak 27-day periodicity while other episodes are dominated by 27-day periodicity with weak 13-day periods. These episodes of activity, which last typically 4 to 8 months, are caused mainly by groups of strong active regions that dominate the solar-rotational variations for several months. In addition to the enhanced short-term modulation during these episodes, the valleys in the solar-rotational modulation also slowly rise and decay. F10 and R tend to rise more steeply and peak earlier during these episodes than the UV flux and the He i line.