Solar Radiation

Photosynthetically active solar radiation (PAR, 400 - 700 nm), atmospheric vapor pressure, and wind speed are also recorded at each of the weather stations. Between 1982 and 1990, mean daily total PAR values have exceeded 40 mol m^-2d^-1 (Figure 8), which is typical for mid-latitude sites having only moderate cloud cover and little summer precipitation. This number is quite useful not only in estimating the available photon flux for photosynthesis, but also in providing an estimate of the extent of solar heating of the surface, which ultimately affects air temperatures. Elevation has a limited impact on the PAR values within Red Butte Canyon, since the difference in elevation is relatively small. However, we suspect there may be relatively large differences in PAR between Red Butte Canyon and Salt Lake City because of increased air pollutants within the city that tend to reflect the sunlight before it strikes the earth's surface. Most notably we would see this as haze or smog within the valley that is lacking once in the canyon.

Fig. 8. Mean monthly air temperature, vapor pressure, and photosynthetically active solar radiation (400-700 nm) measured at Red Butte #2 between 1982 and 1990.