Abstract:[1] The optical thickness of the atmosphere, t at , was deduced from measurements of narrowband direct solar UV-B (280 -320 nm) radiation. This is the radiation that is strongly absorbed in the stratosphere by ozone, especially near the lower limit wavelength of these measurements, 306.3 nm. Measurement campaigns were organized to obtain radiation data at different sites, for different kinds of aerosol, using the same methods and instruments, in order to deduce the atmospheric optical thickness for different a… Show more
“…Lower fluence on target corresponds to lower laser pulse energy required from the laser. Further, atmospheric attenuation at 355 nm is 0.3/km [13], so that transmission on a tangent path to Earth from space is only 2.5E-9, preventing eye injuries on the ground. This choice also gives low background illumination and dark, absorptive targets.…”
“…Lower fluence on target corresponds to lower laser pulse energy required from the laser. Further, atmospheric attenuation at 355 nm is 0.3/km [13], so that transmission on a tangent path to Earth from space is only 2.5E-9, preventing eye injuries on the ground. This choice also gives low background illumination and dark, absorptive targets.…”
“…Nonetheless, a was determined in the UV wavelength range by using AOD obtained from LPM at Ispra, Italy, and El Arenosillo, Huelva, Spain (de la Casinière et al 2005;Grö bner and Meleti 2004;Meleti and Cappellani 2000), with a positive a retrieval. In contrast, negative values of a have been observed by others (Cachorro et al 1989;Jacovides et al 2000;Kirchhoff et al 2002;Marenco et al 1997;Silva and Kirchhoff 2005). According to Mie scattering theory, a negative a would require a very large mean radius of aerosol particle and a large real part of the refractive index (Arola and Koskela 2004), which is not realistic for urban aerosol, implying that extracting a from the limited Brewer wavelength range is sometimes beyond the capabilities of the instrument and conditions.…”
Aerosols play an important role in attenuating solar radiation reaching the earth's surface and are thus important inputs to climate models. Aerosol optical depth is routinely measured in the visible range but little data in the ultraviolet (UV) are available. In the UV range it can be determined from Langley plots of directsun measurements from the Brewer spectrophotometer (where conditions allow) and can also be determined as the residual once the ozone and sulfur dioxide have been accounted for in the extinction observed during a normal Brewer direct-sun measurement. By comparing aerosol optical depth derived from Brewer directsun data in both the United Kingdom and Malaysia, two very different locations, it is determined that while most of the existing global Brewer network could contribute to aerosol optical depth data, further analysis, such as calculation of the Å ngströ m parameter, would be dependent on latitude and sky conditions.
“…In outer space, UV radiation accounts for only about 8% of the total solar radiation (e.g., Sabziparvar 2000), while at any location on the earth's surface, the UV radiation value depends on many factors. Absorption by ozone, atmospheric attenuation processes (e.g., aerosols and trace gases), UV surface albedo, the air mass traversed by the direct solar beam (which depends on the solar zenith angle), sun-earth distance, and the altitude of observational site are some of the factors that contribute to change in the surface UV under clear sky conditions (e.g., Kylling et al 2000;Kirchhoff et al 2002;Luccini et al 2003).…”
To establish a relation between biologically effective erythemal radiation (EER) and global solar radiation, the hourly and daily clear-sky broadband (310-2,800 nm) global solar radiation (G) and spectral ultraviolet radiation incident on a horizontal surface at Esfahan, Iran (32 degrees 37'N, 51 degrees 40'E) were measured during the period 2001-2005. Good correlations at statistically significant levels between the daily values of EER and the daily G were found. The seasonal variability of EER/G is also discussed and the correction factors are determined for inclusion of vertical column ozone and solar zenith angle (SZA) cycles. The comparison of the estimated daily EER against the independent observed EER revealed that under clear sky conditions the estimations are accurate to 10% or better over SZA of 10-60 degrees and column ozone of 250-350 Dobson. The comparison of the results with the similar works that have used shorter period of experimental data showed more accurate estimates. The deduced relations could be used to a rough estimate of the daily EER from G in arid climate regions, where there is no measured UV radiation or there are instrumental and other difficulties encountered in measuring UV radiation.
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