Night sky brightness at sites from DMSP-OLS satellite measurements

We apply the sky brightness modelling technique introduced and developed by Roy Garstang to high-resolution DMSP-OLS satellite measurements of upward artificial light flux and to GTOPO30 digital elevation data in order to predict the brightness distribution of the night sky at a given site in the primary astronomical photometric bands for a range of atmospheric aerosol contents. This method, based on global data and accounting for elevation, Earth curvature and mountain screening, allows the evaluation of sky glow conditions over the entire sky for any site in the World, to evaluate its evolution, to disentangle the contribution of individual sources in the surrounding territory, and to identify main contributing sources. Sky brightness, naked eye stellar visibility and telescope limiting magnitude are produced as 3-dimensional arrays whose axes are the position on the sky and the atmospheric clarity. We compared our results to available measurements.Comment: 14 pages, 12 figures, accepted for publication in MNRAS, 17 june 200

Effects of fire on certain physical properties of selected chaparral soils

Wildfires have burned through chaparral environments of southern California for at least 100,000 years. Surface temperatures of up to 800° c. have been recorded during such fires. Under these conditions, the physical properties of the soil may be altered, and soil characteristics such as porosity, permeability, stability, and susceptibility to erosion by water and wind may be effected. This study focuses on fire's effect on the inorganic particles present in certain chaparral soils, and the implications of this effect to the soil-water environment. Samples of two different soils from southern California chaparral areas were analyzed for color, pH, particle size distribution, and mineralogy. The samples were subjected to wildfire conditions in the laboratory, and changes in these soil properties were observed. Soil color was found to change from lighter to darker. The pH of each soil increased after heating; one soil was found to vary from pH 7.4 to pH 9.6 after heating to 800° c, and the other exhibited a variation from 6.3 to 8.3. The particle size distribution of each soil displayed a shift in frequency of grain sizes. (See more in text.)Includes bibliographical references (pages 49-51)California State University, Northridge. Department of Geography

Cloud Coverage Acts as an Amplifier for Ecological Light Pollution in Urban Ecosystems

The diurnal cycle of light and dark is one of the strongest environmental factors for life on Earth. Many species in both terrestrial and aquatic ecosystems use the level of ambient light to regulate their metabolism, growth, and behavior. The sky glow caused by artificial lighting from urban areas disrupts this natural cycle, and has been shown to impact the behavior of organisms, even many kilometers away from the light sources. It could be hypothesized that factors that increase the luminance of the sky amplify the degree of this “ecological light pollution”. We show that cloud coverage dramatically amplifies the sky luminance, by a factor of 10.1 for one location inside of Berlin and by a factor of 2.8 at 32 km from the city center. We also show that inside of the city overcast nights are brighter than clear rural moonlit nights, by a factor of 4.1. These results have important implications for choronobiological and chronoecological studies in urban areas, where this amplification effect has previously not been considered