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Clear Sky Conditions (clear + sky_condition)

Distribution by Scientific Domains

Earth and Environmental Science	50%

Selected Abstracts

Solar power for an Antarctic rover

HYDROLOGICAL PROCESSES, Issue 4 2006
J. H. Lever
Abstract Sensors mounted on mobile robots could serve a variety of science missions in Antarctica. Although weather conditions can be harsh, Antarctic snowfields offer unique conditions to facilitate long-distance robot deployment: the absence of obstacles, firm snow with high albedo, and 24 h sunlight during the summer. We have developed a four-wheel-drive, solar-powered rover that capitalizes on these advantages. Analyses and field measurements confirm that solar power reflected from Antarctic snow contributes 30,40% of the power available to a robot consisting of a five-side box of solar panels. Mobility analyses indicate that the 80 kg rover can move at 0·8 m s,1 during clear sky conditions on firm snow into a 5 m s,1 headwind, twice the speed needed to achieve the design target of 500 km in 2 weeks. Local winter tests of the chassis demonstrated good grade-climbing ability and lower than predicted rolling resistance. Tests of the completed robot occurred in Greenland in 2005. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Snow disappearance in Eastern Siberia and its relationship to atmospheric influences

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2007
Yoshihiro Iijima
Abstract In the present study, we examine the climatological features and interannual variations in snow disappearance within the Lena River Basin, Eastern Siberia, during a recent 15-year period (1986,2000), and the relationship of snow disappearance to atmospheric conditions. According to the climatology of the day of the year on which snow disappears, the boundary of snow disappearance within the Lena River Basin migrates rapidly northward from mid-April until early June, with minimum interannual variation occurring in the middle part of the basin. In addition, the preceding snow disappearance is apparent in the central Lena River Basin. Melting of snow within the Lena River Basin commonly occurs within 30 days of complete snow disappearance under certain atmospheric conditions: daily mean air temperature in excess of , 10 °C, greater than 2 hPa of water vapor pressure, and, hence, more than 170 W m,2 of downward longwave radiation under clear sky conditions. Composite analysis using a reanalysis dataset demonstrates that the increase in air temperature and water vapor that accompanies snow melting is due to wet (and warm) air advection in conjunction with enhanced water vapor convergence over the central Lena River Basin during the 30-day period prior to snow disappearance. Copyright © 2006 Royal Meteorological Society. [source]

A simple device for the evaluation of the UV radiation index

METEOROLOGICAL APPLICATIONS, Issue 2 2003
Giuseppe Rocco Casale
The solar ultraviolet radiation (UV) flux density at the earth's surface depends on the incoming solar energy and the transmission properties of the atmosphere. UV radiation is strongly absorbed by ozone in the spectral range 200,310 nm, while the attenuation is increasingly weaker at longer wavelengths. Following the discovery of the Antarctic ozone hole in 1985, the risk of a possible UV increase at ground level, due to the observed stratospheric ozone depletion, has heightened the interest within the scientific community given the potentially harmful effects on terrestrial and aquatic ecosystems. Spectroradiometers, broad-band meters and dosimeters may be used for measurements of solar UV. In addition, radiation transfer models can be used to quantify UV irradiances at various times and locations, provided that the extraterrestrial solar radiation and the state of the atmosphere are known. Information about UV radiation at the earth's surface is given by the ultraviolet index ,UVI', which is defined as the effective integrated irradiance (280,400 nm) weighted by the erythemal action spectrum. The UV Index is widely used by many international weather services as an indicator of UV levels at the earth's surface providing public awareness of the effects of prolonged exposure to the sun's rays. The aim of this paper is to present a device capable of estimating the UV Index. This device is a compact disc, used as a sundial, and is based on modelled UV irradiances derived from the STAR radiative transfer model (System for Transfer of Atmospheric Radiation). The device was tested in an urban setting under clear sky conditions. Copyright © 2003 Royal Meteorological Society [source]

A Novel System for Spectral Analysis of Solar Radiation within a Mixed Beech-Spruce Stand

PLANT BIOLOGY, Issue 2 2002
H. Reitmayer
Abstract: A multi-sensor system is described, based on a 1024 channel diode array spectrometer, to measure spectral radiant flux density in the range of 380 nm to 850 nm, with a resolution of 0.8 nm in minimal 16 milliseconds integration time per sensor (noon, clear sky conditions). 264 space-integrating 4, sensors deployed in the canopies and 2 m above stand floor are sequentially connected to the spectrometer by means of 30-m long fibre optics. During low-level conditions (dawn, overcast sky) the system automatically lengthens the integration time of the spectrometer. About 3 sec per sensor, i.e., 13 min for the total of 264 sensors (worst case) are needed to collect spectral energy data, store them on hard disk and move the channel multiplexer to the next fibre optic position. The detection limit of quartz fibre sensors is 0.2 W/m2; precision and absolute error of radiant flux density are smaller than 3 % and 10 %, respectively. The system, operating since 1999, is derived from a 20-sensor pilot system developed for PAR measurements (PMMA fibre sensor, 400nm to 700 nm). Data achieved with the system serve to determine vertical profiles of wavelength dependent radiation extinction, with special respect to R/FR ratios and to develop a model of spectral radiation distribution in a mature forest stand, prerequisites for the computation of carbon gain of the stand and the evaluation of stand growth models. [source]