Maximum UV-B Research Articles

STUDY OF ULTRAVIOLET SOLAR RADIATION IN DUHOK CITY UNDER CLEAR SKY CONDITIONS

This work focused on the UV solar radiation measurements under clear sky conditions for typical days in months (April to July) when the UV radiation is expected to have the highest values in Duhok city. Two types of UV, (UVA and UVB) were measured from April to July under clear sky conditions. The maximum UVA (wavelength 315-400 nm) irradiance (38 and 37) W/m2 was measured at noon in June and July, respectively. The minimum UVA of 30 W/m2 was recorded at April noon. In July, the hourly UVA ranged between 2.6 W/m2 at 6:00 pm to 37 W/m2 at 12:00 pm; maximum UVB (wavelength 280-315 nm) irradiance of 1.9 W/m2 was measured in July noon’s, and a minimum of 1.4 W/m2 at April noon. The effect of the atmosphere (solar zenith angle) on the UVB clearness index was investigated and a functional relationship between them was developed. Finally, the time required for UVB minimum erythemal dose was estimated.

New continuous total ozone, UV, VIS and PAR measurements at Marambio, 64° S, Antarctica

Abstract. A ground-based ultraviolet (GUV) multi-filter radiometer was set up at Marambio, 64∘ S, 56∘ W, Antarctica, in 2017. The instrument continuously measures ultraviolet (UV) radiation, visible (VIS) radiation and photosynthetically active radiation (PAR). The measurements are designed for providing high-quality long-term time series that can be used to assess the impact of global climate change in the Antarctic region. The quality assurance includes regular absolute calibrations and solar comparisons performed at Marambio and at Sodankylä, Finland. The measurements continue observations at Marambio that were performed with (Norwegian Institute for Air Re-search UV Radiometer (NILU-UV) radiometers between 2000 and 2010 as part of the Antarctic NILU-UV network. These measurements are ideally suited for assessing the effects of the ongoing stratospheric ozone recovery on the ecosystem, as the data products include information on radiation at various wavelengths ranging from UV to VIS so that changes on biologically effective radiation due to ozone can be separated from those due to other factors. Data products include total ozone, photosynthetically active radiation (PAR), visible (VIS) radiation at 555 nm, UV index, UV irradiance at 5 channels, UVB and UVA dose rate and daily dose, and biologically weighted UV dose rate and daily dose, calculated with 10 different action spectra. The data from the last 5 d and the daily maximum UV index time series are plotted and updated daily on the following web page: http://fmiarc.fmi.fi/sub_sites/GUVant/ (last access: 17 April 2020). The first 2 years of UV measurements were very different in terms of the results: for October, November and December the monthly average of daily maximum UVB dose rates were clearly higher in 2018 than in 2017. The largest difference was observed in October, when the average of daily maximum UVB dose rates was 76 and 102 µW cm−2 in 2017 and 2018, respectively. Monthly averages of the 3 months were similar in 2018, while in 2017 the monthly average of October was lower than those of November and December. The VIS and PAR time series show that daily maxima in 2018–2019 exceed those in 2017–2018 during late spring and summer (mid-November–January). The studied dataset, including daily maximum irradiances at five UV channels and one VIS channel; daily maximum UVB, UVA, and PAR dose rates; noon UVB, UVA, and PAR dose rates; noon total column ozone; and UVB and UVA daily doses, is freely accessible at https://doi.org/10.5281/zenodo.3688700 (Lakkala et al., 2019).

Ground-based measurements and modeling of solar UV-B radiation in Lhasa, Tibet

We present results from measurements by a NILU-UV Irradiance Meter of solar UV-B radiation in Lhasa, Tibet for the period from 7 July 1999 to 17 November 2002. The measured maximum UV-B dose rate was 1.50 W/m 2 during the winter, and 3.96 W/m 2, during the summer. The clear-sky values were below 3.00 W/m 2. Comparisons between measured and calculated UV-B dose rates on clear-sky days in Lhasa show good agreement. Comparisons of UV-B radiation levels in Lhasa (Tibet), Oslo (Norway), and Dar-Es-Salaam (Tanzania) show that the UV-B dose rates during the summer in Lhasa are higher than the maximum value in Dar-Es-Salaam, which is at the sea level in the equatorial region, and 60% higher than in Oslo, which is at the sea level but 60 degrees North. We conclude that the UV-B dose rates during the summer on the Tibetan plateau are among the highest levels in habituated regions of the world. Maximum measured daily-integrated UV-B doses in Lhasa range from about 10 kJ/m 2 in the winter to about 65 kJ/m 2 in the summer.

Enhanced spectral UV irradiance: a 1 year preliminary study

The ultraviolet (UV) spectra on cloudy days were compared to those on cloud free days to determine which part of the UV spectrum has the greatest enhancement due to the cloud compared to both corresponding measured clear sky spectra as well as other enhanced spectra. In this preliminary study, cloud enhanced UV spectra selected for maximum UVA enhancement compared to a clear sky UV spectrum at similar solar zenith angle (SZA) and ozone values, showed that the ratio of the two sets of spectral irradiances was approximately wavelength independent (approximately 1.1) above the cut-off wavelength of approximately 306 nm. Similarly, above 306 nm the average ratio of the spectral irradiances of a maximum UVB enhanced UV spectrum compared to a clear sky spectrum was 1.2 with maximum values generally above this average between 316 and 344 nm and generally below 1.2 above the wavelength of 344 nm. The UVA and UVB enhanced spectra were separated into five SZA ranges and the irradiance at each wavelength averaged for each range and compared to clear sky spectra in each of the ranges. Above approximately 306 nm, the ratios are wavelength independent for all SZA. However, with the exception of the SZA range centred on 20°, there is an increasing dependency with shorter wavelengths below the 306 nm. Also there appears to be two distinct groupings of the average irradiance ratios, corresponding to the SZA range centred on 20°, 37° and 49° (ratio of 1.2) and 32° and 42° (ratio 1.0), the latter cases suggesting that on average there is no enhancement for these SZA, except for wavelengths less than 306 nm.

Effects of clouds on the surface erythemal UV-B irradiance at northern midlatitudes: estimation from the observations taken at Belsk, Poland (1999–2001)

Results of 2-year measurements at Belsk, Poland, have been analyzed to investigate the effects of clouds on ultraviolet (UV) radiation. Data were collected using a Solar Light UV-biometer 501A (erythemally weighed UV irradiances), Kipp&Zonnen CM11 pyranometer (total solar radiation), and SCI-TEC Brewer Spectrophotometer (total ozone, aerosol and thin cloud optical depth). Hourly reports on total cloud cover and cloud type were also used in this study. It is found that overcast conditions prevail over central Poland and the sky is covered mainly by low-level clouds. The averaged cloud properties derived from visual observations correspond with those estimated from satellite measurements. An empirical relationship has been postulated for the cloud reduction factor of the erythemally weighted UV radiation as a function of the cloud reduction factor for total solar radiation. The relation may be used to reconstruct the past UV-time series. It is established that information of cloud amount and type to estimate the UV-B attenuation provides a substantial uncertainty. Stronger attenuation of the UV radiation by real clouds was found than that estimated by a radiative transfer model when examining results of the cloud optical depth at 320 nm and the cloud attenuation of the UV radiation measurements. The reduction of the erythemally weighted UV irradiance by thin clouds seems to be independent of the cloud type. It is reported that 1.4% of UV-B irradiance measurements were cloud enhanced in the snowless period of the year. The maximum UV-B enhancement of ∼20% greater than an equivalent clear-sky value was found. Numerous enhancements occurred when high-, mid-, and low- (broken Cu) clouds appeared simultaneously. Similar range of the observed enhancements and cloud composition as in previous cloud enhancement studies (over low latitudinal regions) suggest that common mechanisms may govern this phenomenon in low- and mid-latitudinal regions.

Characteristics of UV-B Irradiance at Syowa Station, Antarctica: Analyses of the Measurements and Comparison with Numerical Simulations

The characteristics of UV-B (λ= 290-315 nm) irradiance at Syowa Station (69°00’S, 39°35’E) in Antarctica were investigated by the numerical simulations with the multiple scattering radiative transfer model for the atmosphere-snow system, and the analyses of measured UV-B irradiance in 1996. By the numerical simulations a study has been made on the sensitivity of UV-B irradiance to the snow grain size, surface condition, cloud cover, Antarctic aerosol, solar zenith angle and total ozone amount. On the snow surface it was found that the effect of multiple reflection between atmosphere (or cloud) and snow surface of high albedo is important for the characteristics of UV-B irradiance. By the analyses of measured UV-B irradiance it was found that the occurrence of the maximum UV-B irradiance was not in December at maximum solar elevation, but in November when the low total ozone amount was observed. This shows that the time in a year reaching the minimum total ozone amount is important for determining the annual trend of UV-B irradiance. It was also found that the values of UV-B irradiance would be enhanced by the occurrence of cloud for the cloud amount of 9/10-10¯/10 due to the effect of multiple reflection between cloud layers and snow surface. As a whole, theoretically calculated values of spectral and spectrally integrated UV-B irradiance agree well with the measured ones, however, at the low solar elevation or low energy level of UV-B irradiance, the measured values of UV-B irradiance were larger than the calculated ones due to the less sensitivity of the instrument to the weak irradiance.

Erythema UV-B exposure near the Antarctic Peninsula and comparison with an equatorial site

Observations of UV-B radiation in the area of the Antarctic Peninsula are described, with the objective to obtain an evaluation of the UV-B enhancements observed during ozone hole episodes, and compare these with equatorial values. The enhancements observed during Southern Hemisphere spring are described in terms of a specific case of enhancement, at the Antarctic peninsula, which has shown a maximum UV-B index of 8.7, in October 1998. The average enhancement between the autumn-unperturbed and spring-perturbed periods results in an UV-B index of 5.4, but with large fluctuations in which much larger indices are produced. These values are compared to indices normally observed in the equatorial region. For measurements obtained with the same kind of instrument at Natal (5.8°S, 35.2°W), the UV-B index varies between 7 and 14, which means that enhanced UV-B indices in the Antarctic Peninsula may become of the same order of magnitude of the lower limit equatorial values.

The effect of clouds on enhancing UVB irradiance at the Earth's surface: A one year study

The most extensive study of frequency, magnitude and sky properties associated with UVB enhancement is reported. The first integrated automatic sky camera and irradiance measurement system was used for simultaneous data collection over the solar zenith angle range of 4.2 to 64.3°. It is reported that 3% of UVB irradiance measurements collected at intervals of 6 minutes, over a one‐year period, were cloud enhanced. It was found that 85% of possible UVB enhancements occurred for solar zenith angles ranging from 40 to 63°. The study was undertaken during September 1997 to August 1998 at Toowoomba, Australia (27.6°S, 151.9°E). The maximum UVB enhancement was found to have an irradiance of 8% greater than that of an equivalent clear‐sky. A mechanism for UVB enhancement for cases of solar obstruction by cirrus cloud is postulated. Analysis showed that 86% of enhancement occurred under hazy/cirrus skies.

On the daily maximum UV-B doses during the significant ozone deficiencies in the transition seasons of 1992/93

The daily maximum UV-B dose rates during the significant ozone anomalies in October 1992 and March 1993 are calculated relative to the normal conditions of the period from 1979 to 1990. Gridded Total Ozone Mapping Spectrometer data have been used to determine the days with ozone deficiencies below the 2σ confidence level. For these days maps of maximum daily UV-B dose rates during these extreme ozone conditions show that UV-B dose rates increased from 10% to 50% at high latitudes. These changes compare well with observations at the Laboratory of Atmospheric Physics, of the Aristotle University of Thessaloniki, Greece and they provide an independent quality assurance and control of the accuracy of coarser model calculations under clear sky conditions. Our analysis shows that the largest increases in the UV-B dose rates during the extreme ozone deficiencies studied are confined to 10°N–40°N in March 1993 and to 10°S to 70°S in October 1992.

Environmental factors involved in colouration of flowers of Kangaroo Paw

Environmental regulation of flower colouration has been examined for Kangaroo Paw ( Anigozanthos spp.) grown in protected cultivation. Two commercial ‘Bush Gem’ hybrids were grown in controlled conditions at various temperatures, irradiances and levels of ultraviolet-B radiation (UV-B). Based on spectral reflectance differences between vividly coloured and faded flowers, their colour depends on pigment(s) absorbing over the 520–630 nm waveband which should involve flavonoids including anthocyanins. This anthocyanin-like pigment, localised in the epidermal hairs of the flowers, was extracted and quantified spectrophotometrically. Flower colour (OD 535 nm g −1 FW) was greatest for plants grown at low temperature and decreased linearly as the growth temperature increased from 13 up to 28 °C. Increasing the photosynthetic irradiance to 550 μmol m −2 s −1 gave strong flower colour as did the addition of UV-B. Although the maximum exposure to UV-B (0.5 mW m −2 at 302 nm) may not have been saturating, this was slightly higher than that of a clear summer day at a latitude matching those occurring where Anigozanthos grows naturally. The maximum UV-B exposure caused leaf and stem tissue damage reminiscent of ‘Ink Spot’ disease. Flower colour could be manipulated only during flower development but differences were evident within 1–3 weeks of transfers between cool and warm conditions or within 1–2 weeks of exposure to UV-B. The data obtained in this study provide the basis for developing ways to manipulate flower colour to give the most vivid display in commercial production systems.

Measurements of solar middle ultraviolet radiation in a desert environment.

Abstract— In this study measurements are reported that were carried out between August 1983 and December 1985 on the solar middle ultraviolet radiation (UVB‐280‐320 nm) in Kuwait (29.5°N). These measurements are based primarily on polysulfone film detectors. Comparative measurements were also made on a Robertson‐Berger meter and a spectroradiometer. The results reported include the daily variation of the solar UVB between 11:30 a.m. and 12:00 noon over the year, the diurnal variation, as well as the amount of UVB as a function of the receiving angle with the horizontal.Based on these data the polysulfone films were found to be reliable and inexpensive detectors, giving results similar to those of the R‐B meter. The diurnal variation of the solar UVB was found to vary as sin2q, where q is an angle that corresponds to the time since sunrise compared to the sunrise‐sunset interval times 180. An empirical equation is developed that gives the maximum UVB as a function of the time of day and day of year. A correlation is determined of the polysulfone readings with the spectroradiometric and the R‐B meter measurements. The solar insolation was found to be independent of the receiving angle with the horizontal in the winter months and develops into a cosine dependence in the summer months.