Frank Forcella USDA-ARS North Central Soil Conservation Research Laboratory, 803 Iowa Avenue, Morris, MN 56267 Two major properties that determine weed seed germination are soil temperature and moisture content. Incident radiation is the primary variable controlling energy input to the soil system and thereby influences both moisture and temperature profiles. However, many agricultural field si...

In order to evaluate satellite and cloud cover models, it is useful to understand the short-term variability of solar radiation. This article examines at the variability of beam and global solar radiation over short time intervals. First, 5-minute data are compare with data collected 5 and 15 minutes later. Second, data collected during the middle 5minute period of an hour are compared to hourl...

This paper reviews the main factors influencing the synthesis of vitamin D, with particular focus on ultraviolet radiation exposure. On the global level, the main source of vitamin D is the sun. The effect of solar radiation on vitamin D synthesis depends to some extent on the initial vitamin D levels. At moderate to high latitudes, diet becomes an increasingly important source of vitamin D due...

Terrestrial life is dependent on radiant energy from the sun. Solar radiation is largely optical radiation [radiant energy within a broad region of the electromagnetic spectrum that includes ultraviolet (UV), visible (light) and infrared radiation], although both shorter wavelength (ionizing) and longer wavelength (microwaves and radiofrequency) radiation is present. The wavelength of UV radiat...

Terrestrial life is dependent on radiant energy from the sun. Solar radiation is largely optical radiation [radiant energy within a broad region of the electromagnetic spectrum that includes ultraviolet (UV), visible (light) and infrared radiation], although both shorter wavelength (ionizing) and longer wavelength (microwaves and radiofrequency) radiation is present. The wavelength of UV radiat...

Solar radiation models for predicting the average daily and hourly global radiation, beam radiation and diffuse radiation are reviewed in this paper. Seven models using the Ångström– Prescott equation to predict the average daily global radiation with hours of sunshine are considered. The average daily global radiation for Hong Kong (22.3 N latitude, 114.3 E longitude) is predicted. Estimations...

The solar UV exposure to the eyes of humans is due to the direct and diffuse components of solar radiation. The direct ocular UV exposures to the eyes are reduced due to the natural aversion of the majority of people from looking directly at the sun. The diffuse UV is incident from all directions and as a result, it is more difficult to minimise the ocular exposure to this component of the sola...

Solar energy is expected to contribute major shares of the future global energy supply. Due to its fluctuating nature an efficient use will require reliable forecast information of its availability in various time and spatial scales depending on the application. The current status of forecasting solar irradiance for energy generation purposes is briefly reviewed with respect to very short-term ...