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.

Differences in the temporal behavior of the ultraviolet irradiance at 205 nm and the 10.7‐cm radio flux, the ultraviolet irradiance at 121.6 nm, model calculations of the 205‐nm irradiance derived from Ca II K plage emission, and the sunspot‐blocking function are examined during a 5‐year period near the maximum of solar cycle 21. Because of solar rotation the dominant variance in each of these time series occurs at 27 days, but real temporal differences arise because the five solar time series are each formed at different heights within the solar atmosphere and are associated with a variety of solar active region phenomena having different spatial and temporal characteristics on the solar disc. These differences may be important if the ground‐based solar activity time series are used instead of the measured UV irradiances in correlation studies of solar variability with atmospheric parameters such as ozone densities and temperature. Recognizing the presence of autocorrelation in the UV irradiance time series is also important in solar terrestrial correlation studies, since it complicates the use of classical statistical techniques for estimating the significance of the results.

The turbulent fluxes of ozone and latent and sensible heat are computed from fast‐response measurements made aboard a National Oceanic and Atmospheric Administration aircraft over downtown Philadelphia and the surrounding suburbs during the afternoon and evening of August 22, 1979. In the afternoon the ozone flux at a height of 200 m is downward throughout the region with the largest magnitude (−2 (ppb) m s−1) occurring over the urban center. During the afternoon at both 200 m and a few hundred meters below cloud base, the horizontal profile of mean ozone concentration peaks at 130 ppb over the urban core with values of the order of 90 ppb to the southeast and northwest. The urban ozone concentration at 200 m decreases to 35 ppb by early evening. The normalized variances and spectra of vertical velocity, temperature, and ozone show little change with height or location in the urban center and northwest suburbs during the afternoon in good agreement with normalized statistics obtained over rural terrain (Kaimal et al., 1976; Lenschow et al., 1980). Data from a cloud penetration by the aircraft is used to estimate a mean updraft velocity of 4 m s−1 and an updraft area of approximately 1 km2. The flux of ozone due to the mean motion in the updraft is 2 orders of magnitude larger than the turbulent eddy fluxes within the cloud.

The complex structure of the earth's surface influenced atmospheric parameters pertinent to modeling the diffusion process during the 1978 'STATE' field study. The Information Theory approach of statistics proved useful for analyzing the complex structures observed in the radiometric surface temperature signals as measured from an aircraft. Results show that regardless of their complexities, these temperature processes are well approximated as Gaussian processes. Turbulent kinetic energy is shown to increase as the surface temperature signals become more complex. The nature of these variations is examined for five different categories of agricultural land as defined by percent cultivation and percent forestation.