The Solar Spectrum in the Atacama Desert

The Atacama Desert has been pointed out as one of the places on earth where the highest surface irradiance may occur. This area is characterized by its high altitude, prevalent cloudless conditions and relatively low columns of ozone and water vapor. Aimed at the characterization of the solar spectrum in the Atacama Desert, we carried out in February-March 2015 ground-based measurements of the spectral irradiance (from the ultraviolet to the near infrared) at seven locations that ranged from the city of Antofagasta (on the southern pacific coastline) to the Chajnantor Plateau (5,100 m altitude). Our spectral measurements allowed us to retrieve the total ozone column, the precipitable water, and the aerosol properties at each location. We found that changes in these parameters, as well as the shorter optical path length at high-altitude locations, lead to significant increases in the surface irradiance with the altitude. Our measurements show that, in the range 0?5100 m altitude, surface irradiance increases with the altitude by about 27% in the infrared range, 6% in the visible range, and 20% in the ultraviolet range. Spectral measurements carried out at the Iza?a Observatory (Tenerife, Spain), in Hannover (Germany) and in Santiago (Chile), were used for further comparisons

Effective surface albedo due to snow cover of the surrounding area

Albedo inversion techniques are investigated in this work. Several methods are applied to spectral irradiance data from a measurement campaign held in the German Alps during the spring of 1999. One first method is based on the comparison of measurements of absolute levels of UV irradiance with model calculations. The second method takes advantage of changes in the spectral slope of spectral UV irradiance, which is a function of the surface albedo. In the third method, the surrounding area is partitioned into snow-covered and snow-free regions, and the effective albedo estimated by applying a higher or lower reflectivity to each facet before integrating over the surroundings. We present sensitivity analysis, the differences and the correlations between the various methods as well as the results for the different locations

Effects of UV-B radiation on the structural and physiological diversity of bacterioneuston and bacterioplankton

The effects of UV radiation (UVR) on estuarine bacterioneuston and bacterioplankton were assessed in microcosm experiments. Bacterial abundance and DNA synthesis were more affected in bacterioplankton. Protein synthesis was more inhibited in bacterioneuston. Community analysis indicated that UVR has the potential to select resistant bacteria (e.g., Gammaproteobacteria), particularly abundant in bacterioneuston

Measurements of Spectral Snow Albedo at Neumayer, Antarctica

Spectral albedo in high resolution, from 290 to 1050 nm, has been measured at Neumayer, Antarctica, (70°39' S, 8°15' W) during the austral summer 2003/2004. At 500 nm, the spectral albedo nearly reaches unity, with slightly lower values below and above 500 nm. Above 600 nm, the spectral albedo decreases to values between 0.45 and 0.75 at 1000 nm. For one cloudless case an albedo up to 1.01 at 500 nm could be determined. This can be explained by the larger directional component of the snow reflectivity for direct incidence, combined with a slightly mislevelled sensor and the snow surface not being perfectly horizontal. A possible explanation for an observed decline in albedo is an increase in snow grain size. The theoretically predicted increase in albedo with increasing solar zenith angle (SZA) could not be observed. This is explained by the small range of SZA during albedo measurements, combined with the effect of changing snow conditions outweighing the effect of changing SZA. The measured spectral albedo serves as input for radiative transfer models, describing radiation conditions in Antarctica

A new sunlight simulator for ecological research on plants.

A new sunlight simulator was designed and built which meets the spectral and energetic requirements of experimental ecological plant research. Its radiation is generated by a combination of four commercially available lamp types: metal halide, quartz-halogen, blue and UVB fluorescent lamps. IR radiation is filtered by a layer (20 mm) of circulating water. The plant-damaging, short-wave UV radiation is eliminated by 13 mm of borosilicate glass. The total input power of the system is 40 kW. The net illuminated space for plants is 1.2 m×1.2 m×0.25 m (length×width×height). The geometric arrangement of 184 lamps, located in specially designed aluminium reflectors, and the high reflection coefficient of the aluminium walls result in diffuse incident light. Irradiances reach more than 1000 W m-2, but less than 10-7 W m-2 below 280 nm; the measured illuminance is 102 klx; the photosynthetically active radiation (PAR, 400-700 nm) is 2200 μmol m-2 s-1. The spatial homogeneity and the temporal variation of the irradiance are satisfactory. The spectral distribution is much more similar to natural global radiation than any other simulator known. By using highly efficient and commercially available lamp types, the running costs remain low. Hence, for the first time, a simulator in the square metre range has been developed, which provides the irradiance and the temporal, spatial and spectral distribution of global radiation at an economically reasonable scale