Variability Of Ultraviolet Radiation Research Articles

Solar Ultraviolet Radiation Temporal Variability Analysis from 2-Year of Continuous Observation in an Amazonian City of Brazil

Solar ultraviolet radiation (UVR) is a highly energetic component of the solar spectrum that needs to be monitored because of the effects on human health and on the ecosystems. In Brazil, few cities monitor UVR, especially in the Amazon region which is particularly poor in observation. This work is the first to address the short-term (2-year) time variability of UVR in Santarém (2°25′ S, 54°44′ W, 51 m) using ground-based measurements. The irradiance in the wavelength range of 250–400 nm was investigated on different time scales. Furthermore, to understand how the UVR varies without the influence of clouds, the hours corresponding to the clear sky condition were analyzed as well as the hours in all sky conditions. Regarding the averages, there is a slight variation over the year. In all sky and clear sky conditions, the dry season had a higher average than the rainy season, despite the slight difference. Also, both in all-sky and clear-sky conditions the maximums occurred around local solar noon, and reached a maximum of 87 W/m2 in the dry season under the clear sky condition. Further understanding of the radiative effects of the clouds in UVR time variability is considered essential for future research. This study can serve as a reference for UVR levels in this region where no other ground-based UVR measurements are made.

Long-term variability of UV radiation in the spectral range of 300–380 nm in Moscow

The seasonal and interannual variability of global ultraviolet (UV) radiation in the spectral range of 300-380 nm (0380) in Moscow in 1968-2014 is analyzed. The effect of cloudiness on the magnitude of 0380 is assessed. The smallest (-22...-26%) losses due to cloudiness are registered in May-August, and the highest ones (to -45%) are observed in October-November. According to the UV radiation reconstruction model and measurement data, the long-term deviations of 0380 from the average (for 1968-1997) due to clouds can reach + (11-12)%. The statistically significant positive linear trend in total annual 0380 is revealed from the data of both the reconstruction model and observations (about 1.5% per decade for 1968-2014 and 3% per decade for 1979-2014).

Aerosol optical depth determination in the UV using a four-channel precision filter radiometer

Abstract. The determination of aerosol properties, especially the aerosol optical depth (AOD) in the ultraviolet (UV) wavelength region, is of great importance for understanding the climatological variability of UV radiation. However, operational retrievals of AOD at the biologically most harmful wavelengths in the UVB are currently only made at very few places. This paper reports on the UVPFR (UV precision filter radiometer) sunphotometer, a stable and robust instrument that can be used for AOD retrievals at four UV wavelengths. Instrument characteristics and results of Langley calibrations at a high-altitude site were presented. It was shown that due to the relatively wide spectral response functions of the UVPFR, the calibration constants (V0) derived from Langley plot calibrations underestimate the true extraterrestrial signals. Accordingly, correction factors were introduced. In addition, the instrument's spectral response functions also result in an apparent air-mass-dependent decrease in ozone optical depth used in the AOD determinations. An adjusted formula for the calculation of AOD, with a correction term dependent on total column ozone amount and ozone air mass, was therefore introduced. Langley calibrations performed 13–14 months apart resulted in sensitivity changes of ≤ 1.1 %, indicating good instrument stability. Comparison with a high-accuracy standard precision filter radiometer, measuring AOD at 368–862 nm wavelengths, showed consistent results. Also, very good agreement was achieved by comparing the UVPFR with AOD at UVB wavelengths derived with a Brewer spectrophotometer, which was calibrated against the UVPFR at an earlier date. Mainly due to non-instrumental uncertainties connected with ozone optical depth, the total uncertainty of AOD in the UVB is higher than that reported from AOD instruments measuring in UVA and visible ranges. However, the precision can be high among instruments using harmonized algorithms for ozone and Rayleigh optical depth as well as for air mass terms. For 4 months of comparison measurements with the UVPFR and a Brewer, the root mean squared AOD differences were found < 0.01 at all the 306–320 nm Brewer wavelengths.

Ozone and Aerosol Influence on Ultraviolet Radiation on the East Coast of the Brazilian Northeast

The purpose of this research is to determine the influence of Total Ozone and Aerosols about variability of Ultraviolet Radiation (UV) in the east coast of the Northeastern region of Brazil through measures from multispectral sensor GUV (Ground-based Ultraviolet Radiometer). The methodology consisted of descriptive study and cluster analyses using data of UV in channels UVB (305 nm) and UVA (320 nm, 340 nm and 380 nm) and data of UV index, Total Ozone, Aerosol, Global Solar Radiation, Cloudiness and Wind. The results for city of Natal indicated that an annual event occurs in September/October which stabilizes the UV or UV Index when Total Ozone levels reach their annual maximum. This event is influenced by marine Aerosol that is found on mainland at a higher concentration in September due to greater Wind intensity and their southeasterly direction (sea for land). The cluster analysis using the variables above allowed us to detect three different groups: the first group is formed by Natal, Recife and Jo?o Pessoa and so determined that this event occurs in these three cities; the second group is formed by Maceio, Aracaju and Salvador and the third group includes only Fortaleza and had different results.

Analysis of ultraviolet radiation in Central China from observation and estimation

Measurements of UV (ultraviolet) and global solar radiation in Central China during 2006–2012 were first reported to investigate the UV radiation variability in different time scales and its UV fraction under different sky conditions. Both UV irradiation and UV fraction showed similar features that peaked in values at noon during summer (July) and reached their lowest in winter (January) with annual mean values being about 0.49 MJ m−2 d−1 and 4.35%, respectively. It was also discovered that there were inverse relationships between UV fractions and clearness indexes at all sky conditions; clouds, water vapor and seasonality were main factors causing the daily variations of UV irradiations. The maximum UV irradiances decreased by 51.14% (33.49%) in overcast days when compared to clear days in summer (winter). By analyzing the dependence of UV irradiances on cosine of solar zenith angle and clearness index, an efficient all-sky model has been developed for estimating UV values in Central China, which has also been tested at Sanjiang and Lhasa and produced satisfied estimations. UV dataset from 1961 to 2011 in Central China was then reconstructed and annual mean daily UV irradiation was about 0.488 MJ m−2 d−1. There was a significant decreasing trend (−0.018 MJ m−2 d−1 per decade) during the last 50 years, the decreases were sharpest in summer (−0.027 MJ m−2 d−1 per decade) with smallest decreases being observed in autumn (−0.001 MJ m−2 d−1 per decade). Meanwhile, it was also revealed that UV energy began to increase since 1990s (0.003 MJ m−2 d−1 per year).

Monsoon variability of ultraviolet radiation (UVR) attenuation and bio-optical factors in the Asian tropical coral-reef waters

The East coast of Peninsular Malaysia is strongly influenced by the North-East (NE) monsoon, and may significantly influence the optical environment of coral-reef ecosystems. However, our knowledge of temporal variability, including episodic events, of environmental factors in Asian tropical regions is still limited. The objectives of this study were to (1) observe temporal variability in ultraviolet radiation (UVR) and photosynthetically active radiation (PAR) attenuation and (2) determine the bio-optical factors regulating the optical environment in shallow coral-reef waters. Downwelling UVR and PAR irradiance and in situ bio-optical factors were measured monthly near Bidong Island on the East coast of Peninsular Malaysia from June 2010 to June 2011. The NE monsoon was recognized between November 2010 and January 2011. The highest diffuse attenuation coefficient at 305 nm was 2.05 ± 0.03 m−1 in a coral-reef area on December 2010. The most significant bio-optical factor at 305, 380, 440 nm during the NE monsoon season was CDOM (89 ± 8% at 305 nm, 84 ± 9% at 380 nm and 49 ± 17% at 440 nm). All UVR attenuation coefficients showed significant correlations with the CDOM absorption coefficients (aCDOM). CDOM with relatively low S275-295 during the NE monsoon season (0.0177 ± 0.0020 nm−1) suggests terrestrial sources, which is also supported by the correlation between salinity and aCDOM(305). A significant correlation between S275-295 and the carbon specific absorbance coefficient (a*(305)) suggest the potential to measure DOC optically in these waters. The high CDOM during the NE monsoon season may have an important role to reduce harmful UVR exposure reaching benthic communities.

Future projections of surface UV-B in a changing climate

[1] Results of comprehensive long-term simulations of surface all-sky and clear-sky ultraviolet (UV) radiation through 1960–2100 are presented. A new earth system model, MIROC-ESM-CHEM, is used for the simulation, which considers key processes that change the surface UV radiation: atmospheric dynamics and chemistry affecting ozone in the stratosphere and troposphere, aerosols and clouds in the troposphere, and changes in surface albedo with sea ice and snow cover. In contrast to previous assessments considering only the effect of long-term change in stratospheric ozone, the simulated long-term behavior of UV radiation in this study is strongly affected by other processes. In one of two simulations, all-sky UV radiation in the northern midlatitudes is projected to increase in the 21st century despite the expected recovery of the stratospheric ozone layer. Reductions in aerosols and clouds are expected to overcompensate for the effect of ozone recovery. The results are sensitive to the future socioeconomic scenario, describing GHG concentrations and emissions of aerosol and ozone precursors in the troposphere. The interannual variability of UV radiation associated with the 11 year solar cycle and local processes is also discussed.

Incident Ultraviolet Radiation and Disappearance of the Aquatic Macrophyte Egeria densa in a Ramsar Wetlands Site

AbstractDuring mid 2004, abrupt environmental changes including a massive die off of the dominant macrophyte Egeria densa were observed within the wetlands of Río Cruces, a Ramsar site in southern Chile. One of the hypotheses presented to explain these changes was that increased ultraviolet radiation (UVR) may have been responsible. Since variation in UVR operates at regional scales, it is important to understand if the demise of E. densa also occurs at concurrent spatial and temporal scales. The current results demonstrate that monthly and annual variability of UVB was very stable during 1998 to 2006. Furthermore, in situ vertical profiles sampled across the wetlands and nearby rivers showed that UVR penetrates deeper into waters located outside the wetlands, where healthy stands of E. densa are commonly seen. The massive die off of E. densa within the Río Cruces wetlands cannot be explained by regional variability in UVR, and it is much more likely that the definitive reason is found locally within the wetlands rather than regionally.

Effects of clouds and stratospheric ozone depletion on ultraviolet radiation trends

ANTHROPOGENIC depletion of ozone in the lower stratosphere has been of global environmental concern for two decades, but the environmentally relevant quantity—the flux of solar ultraviolet radiation (UVR) reaching the Earth's surface—remains poorly quantified on a global basis. The three most important parameters governing surface UVR fluxes and trends are solar elevation, total vertically integrated ozone abundance and cloud opacity. Here we use global satellite measurements of total ozone abundance and cloud reflectance to examine how the trends in UVR resulting from established trends in total ozone abundance1,2 compare with the potentially large natural variability in UVR that results from variations in cloud opacity. We find that throughout many temperate regions—including large parts of continental Europe, North and South America, New Zealand, Australia and southern Africa—interannual variability in cloud opacity is sufficiently small that by the end of this century, trends in summer average local-noon UVR dose rates relevant to mammalian skin cancer or plant damage should be significant with respect to cloud variability.

Analysis of the Earth's ultraviolet radiation variability from satellite measurements and model calculations

More than 7000 spectrograms of nadir ultraviolet radiation measurements at λ = (0.28–0.34) μm from satellite “Meteor” in 1985–1987 over different regions are systematized according the sets of λ values and solar zenith angles θ. The factors of radiation variability at λ = 0.34 μm and θ = (15°–30°) are analysed. It is found from 1500 spectrograms that the maximum brightness exceeds the minimum in 6.5 times and the most frequently registered brightness is 2.5 times higher than the minimum. The brightness is calculated according to the atmosphere radiation in the 0 – 74 km height region at λ = 0.34 μm for the model of ozone absorption with different ozone content, molecular and aerosol scattering, different heights of the underlying surface H and the reflection coefficient K. The most frequently registered brightness corresponds to cloudiness with K = (0.3–0.4) in the presence of aerosols. The minimum levels of measured brightness correspond to calculated levels at H = 0 and K = (0.1–0.2); the maximum brightness is comparable with the model for nonaerosol atmosphere with K = 1.