High-precision measurements of total solar irradiance, made by the active cavity radiometer irradiance monitor on the Solar Maximum Mission satellite, show the irradiance to have been variable throughout the first 153 days of observations. The corrected data resolve orbit-to-orbit variations with uncertainties as small as 0.001 percent. Irradiance fluctuations are typical of a band-limited noise spectrum with high-frequency cutoff near 0.15 day(-1) their amplitudes about the mean value of 1368.31 watts per square meter approach +/- 0.05 percent. Two large decreases in irrradiance of up to 0.2 percent lasting about 1 week are highly correlated with the development of sunspot groups. The magnitude and time scale of the irradiance variability suggest that considerable energy storage occurs within the convection zone in solar active regions.

The total irradiance of the Sun has been found to vary mostly because of changes in the areas of dark sunspots and bright faculae. Improved observations, such as those discussed in this paper, are needed to understand better the interplay between these two competing features. In this paper, faculae are determined by observations using a Ðlter centered at the Ca II K line (393.4 nm) with a bandpass of 0.9 nm. This Ðlter allows the detection of faculae across the entire solar disk rather than just at the limb, as is the case for white-light faculae. Sunspots are detected with a Ðlter at 672.3 nm with a bandpass of 9.7 nm. The mean ratio of facular to sunspot area was found to be 16.7^0.51 for a year period during 71 2 solar cycle 22 but showed a signiÐcant increase as the solar cycle progressed. This ratio suggests that the irradiance excess associated with faculae outweighs the irradiance deÐcit associated with sunspots by about 50%. The facular area also exhibited a quadratic dependence on sunspot area, as suggested by Foukal, but there is no clear evidence of a turnover in facular area at large sunspot areas. Lagged crosscorrelations between facular and sunspot areas showed a clear rotational modulation extending to lags of Ðve to six rotations when spots led faculae. Lags in the opposite direction, however, showed the rotational modulation falling abruptly after about two rotations.

Increased metal concentrations have been associated with freshwater acidification. Continuous-flow acute toxicity tests were conducted in soft water to determine the effect of pH on the toxicity of cadmium, copper, and zinc to small (1–6 g) steelhead trout (Salmo gairdneri). LC50 values were calculated for 96- and 168-h exposure periods in waters of pH 4.7, 5.7, and 7.0. Test fish were significantly more tolerant of the metals at the lowest pH value than at higher pH's. The 96-h LC50 values at pH 4.7, 5.7, and 7.0 were 671, 97, and 66 μg∙L−1 for zinc, 66.0, 4.2, and 2.8 μg∙L−1 for copper, and 28.0, 0.7, and < 0.5 μg∙L−1 for cadmium, respectively. The 168-h results were similar to the 96-h values. These results indicate that for the metals tested, toxicity is ameliorated in depressed pH waters over short exposure periods, such as may occur during snowmelt runoff. The possibility of hydrogen ion interference with metal uptake is postulated.

In this study, we have attempted to model the variations in total solar irradiance from two spacecraft. Specifically, we have modeled the Earth Radiation Budget on the Nimbus 7 spacecraft and the active cavity radiometer irradiance monitor (ACRIM‐I) on the Solar Maximum Mission (SMM) spacecraft using ground‐based photometry of sunspots and faculae from the San Fernando Observatory (SFO). Additionally, for some cases, solar backscatter ultraviolet/2 data on the Mg II core‐to‐wing ratio from the NOAA 9 spacecraft was used. We have found that most of the solar cycle variation in the total solar irradiance can be accounted for by sunspots and faculae/network. The unexplained variation is not greater than approximately 0.0022% (22 ppm) per year for most of solar cycle 22. Using Nimbus 7 data from March 2, 1985, to December 13, 1993 (1281 data points), as the dependent variable, with the SFO photometric sunspot index (PSI) and the NOAA 9 Mg II core‐to‐wing ratio for the faculae/network as independent variables (the best model for this interval), we obtained a multiple correlation coefficient squared (R2) of 0.848. The rms noise in the residuals is approximately 0.221 W m−2 (162 ppm). This rms noise appears to be dominated by noise in the spacecraft data. For the same model, but for the time interval from March 2, 1985, to July 14, 1989, we obtained an R2 of 0.838 for 718 data points. The same type of model for this same interval, substituting SMM/ACRIM‐I total irradiance for Nimbus 7, gave an R2 of 0.857 for 685 data points. Our best correlation, however, came from a three‐parameter model, fitting Nimbus 7 data to the SFO digital PSI, the SFO facular index PFIFA, and the NOAA 9 data for the interval May 30, 1988, to December 13, 1993, giving an R2 of 0.887 (745 data points). These strong correlations suggest that most of the variation in solar irradiance is associated with known solar magnetic features. Whether or not these magnetic features can explain all of the solar irradiance variability will require more stable and accurate long‐term measurements from space and the ground.

Continuous‐flow toxicity tests were conducted to determine the relative tolerances of newly hatched alevins, swim‐up alevins, parr, and smolts of chinook salmon (Oncorhynchus tshawytscha) and steelhead (Salmo gairdneri) to cadmium, copper, and zinc. Newly hatched alevins were much more tolerant to cadmium and, to a lesser extent, to zinc than were later juvenile forms. However, the later progression from swim‐up alevin, through parr, to smolt was accompanied by a slight increase in metal tolerance. The 96‐h LC50 values for all four life stages ranged from 1.0 to >27 μg Cd/liter, 17 to 38 μg Cu/liter, and 93 to 815 μg Zn/liter. Steelhead were consistently more sensitive to these metals than were chinook salmon. When a sensitive life stage for acute toxicity tests with metals is sought, the more resistant newly hatched alevins should be avoided. Although tolerance may increase with age, all later juvenile life stages are more sensitive and should give similar results.