ELDONET—A Decade of Monitoring Solar Radiation on Five Continents (original) (raw)
Related papers
Photochem. Photobiol. …, 2009
are compiled and the trends and correlation analyses with yearly and monthly average amounts of columnar ozone are presented. Mean yearly doses at 10 northern and 6 southern hemisphere sites exhibited exponential latitudinal gradients with similar slopes indicating a doubling of the dose with the decline of about 14 degrees. Among 12 sites where continual data for more than 6 years were available, increasing trends in yearly UV doses were observed at 11 sites. At one European (Brussels), two tropical Asian (Padang and Denpasar), and two South American (São Martinho and Punta Arenas) sites, decreasing trends of ozone amounts were noted, whereas at the remaining 6 sites (five sites in Japan and Thessaloniki), increasing trends of the UV doses were observed without notable changes, or with an increase at one site (Kiyotake), of the average ozone amounts. At one site (Taipei), the UV doses and the ozone amounts stayed constant. In the monsoon areas, climatic variations and changes, particularly in the extent of cloudiness and frequency of rainfall in summer months, might have been largely responsible for the trends of the UV doses. However, even at these sites, the decreases in the ozone amounts in summer months were frequently observed and might have contributed to the increasing trends of the UV doses. Since each region and locality is unique in climatic and atmospheric conditions, it is not easy to generalize the global trends. However, at many sites involved in this monitoring project, the increases in the biological UV doses during this period seemed to be linked to the decreases in the ozone amounts.
The European Light Dosimeter Network: four years of measurements
Journal of Photochemistry and Photobiology B: Biology, 2002
The European Light Dosimeter Network (ELDONET) has now been functional for more than four years. The network is based on dosimeters which measure radiation in three biologically relevant wavelength bands (UV-B, 280-315 nm; UV-A, 315-400 nm; and Photosynthetic Active Radiation, PAR, 400-700 nm). The ELDONET network is currently based on 33 stations with 40 instruments. The distribution of the instruments all over Europe allows measurement of the latitudinal and longitudinal light climate distribution. In addition, several instruments are active in South America, New Zealand, India, Africa and Japan. With some exceptions, the measured yearly doses depend on the latitude. While the maximal daily doses are almost comparable from station to station, seasonal changes and the different maximal solar zenith angles account for the differences in total yearly doses. Ratioing between UV-B and PAR allows the detection of subtle changes in the local light climate, due, for example, to mini-ozone holes encountered in northern Europe during spring. Comparison of satellite ozone data with terrestrial ELDONET measurements revealed an overall weak correlation between these data sets. However, local weather conditions, solar zenith angle and latitude as well as reflectivity (i.e. clouds and aerosol; satellite data) show a much stronger correlation to the doses received. The close relationship between the spectral sensitivity of the UV-B sensor used in the ELDONET dosimeter and the CIE erythemal action spectrum allows determination of the erythemal dose on the basis of the dosimeter readings.
Variability of UV Irradiance in Europe
Photochemistry and Photobiology, 2007
The diurnal and annual variability of solar UV radiation in Europe is described for different latitudes, seasons and different biologic weighting functions. For the description of this variability under cloudless skies the widely used onedimensional version of the radiative transfer model UVSPEC is used. We reconfirm that the major factor influencing the diurnal and annual variability of UV irradiance is solar elevation. While ozone is a strong absorber of UV radiation its effect is relatively constant when compared with the temporal variability of clouds. We show the significant role that clouds play in modifying the UV climate by analyzing erythemal irradiance measurements from 28 stations in Europe in summer. On average, the daily erythemal dose under cloudless skies varies between 2.2 kJ m )2 at 70°N and 5.2 kJ m )2 at 35°N, whereas these values are reduced to 1.5-4.5 kJ m )2 if clouds are included. Thus clouds significantly reduce the monthly UV irradiation, with the smallest reductions, on average, at lower latitudes, which corresponds to the fact that it is often cloudless in the Mediterranean area in summer.
Variations of erythemal ultraviolet irradiance and dose at Tartu/Tõravere, Estonia
Climate Research
The variations of erythemally weighted ultraviolet (UV) irradiance and its relationships with atmospheric characteristics during 3 annual cycles (1998)(1999)(2000) at 1 site (Tõravere, Estonia; 58.3°N, 26.5°E; 70 m above sea level) were studied, with the further aim to estimate the erythemal doses for past years. In clear sky conditions the daily erythemal dose and noon irradiance exhibit total-ozone-related asymmetry in the annual cycle, with 27% lower values at spring equinox than at autumnal equinox. The clear sky ratio of erythemally weighted to broadband (300 to 3000 nm) irradiance increases from (0.5 ± 0.25) × 10 -4 to (2 ± 0.1) × 10 -4 with an increase in solar elevation from 10°t o 55°. In overcast low cloudiness conditions this ratio is higher. A simple empirical method to estimate the summer half-year erythemal dose for past years is proposed, and the doses were calculated for 1967-2000. A sharp drop in summer half-year sunshine duration and erythemal dose was found around 1975, with a following quasi-linear recovery to the values met in [1967][1968][1969][1970][1971][1972][1973][1974][1975]. A comparison with the measured and Total Ozone Mapping Spectrometer (TOMS)-derived data is provided for 1998-2000. In the fine summer of 1999 and the 'normal' one of 2000, the measured, estimated and TOMS-derived half-year doses agreed to within 0.7%. In the extremely cloudy summer of 1998, the difference between the measured and estimated values was 1.7% and between the measured and TOMS-derived values 6%.
Variability of UV-B at four stations in Europe
Geophysical Research Letters, 1997
The variability of solar irradiance in the UV-B spectral region is studied at four stations operating wellcalibrated spectroradiometers during the period 1991-96. It is confirmed that total ozone is the controlling factor in long-term changes of solar irradiance below 320 nm received at the ground. This result is supported by the similar long-term variability under clear sky and all sky conditions during the past five years. The study includes estimates of the amplitude of the annual cycle and estimates of long-term changes. An important result of this note is, that calculated changes in solar irradiance depend on the length of the observational period and that any speculations on its future changes should be treated always with caution. It is estimated that a 2.7% change per year in solar irradiance at 305 nm at Thessaloniki is a rate that could possibly continue in view of the expected continuation of the ozone decline resulting to an increase of 27% per decade, which is comparable to the amplitude of the annual cycle at that station. the atmosphere. Therefore changes in any or all of these factors may reduce, cancel, or even reverse the ex[, •cted UV-B amplification caused by the ozone decline. Blumthaler and Ambach [1990], found the erythemal dose increasing, at Jungfraujoch, a 3.6 km high mountain site in Switzerland, by about 1% per year in the 80' s. An increase was also reported in the 90's from spectrophotometric observations in Toronto [Kerr and McElroy, 1993] and at Thessaloniki under practically cloudless skies and constant zenith angle [Zerefos et al., 1995]. The opposition between short and long-term changes in total ozone and associated changes in the UV-B at the ground is well documented, particularly during periods of extreme ozone deficiencies, such as the case for 1992 and 1993, years of very low ozone [Seckmeyer et al., 1994]. In this paper we discuss the European extent of updated spectral UV-B changes over 4 European stations in the 90's, which are well maintained and calibrated [Bais et al., 1997], coveting a wide range of latitudinal and enviromnental exposure conditions.
Estimation of UV-B irradiation from total global solar meteorological data in central Spain
Journal of Geophysical Research, 2011
Measurements of solar ultraviolet-B (UV-B) in the range (280-315 nm) and total global solar irradiation (G) for the period 2002-2006 in a continental Mediterranean environment have been analyzed. UV-B and G data have been recorded at the Low Atmosphere Research Laboratory, Valladolid, Spain, using a YES UVB-1 pyranometer and a Kipp&Zonen CM-6 radiometer, respectively. According to the cloud conditions, the time data series shows that the highest UV-B values are obtained in June and the lowest ones are obtained in December. A comparison of monthly UV-B values reveals that some summer months show more dispersion than winter ones. An empirical relationship between UV-B and G was established to estimate the daily UV-B irradiation from commonly measured daily total global solar irradiation. The annual cycle effects of the solar zenith angle and the ozone total column have been taken into account. A correction factor that depends on the daily total ozone column has been included in the relationship between UV-B and total global solar irradiation. The performance of this relationship has been evaluated comparing estimated and measured UV-B values in three different stations. Scatterplot, root-mean-square error (RMSE), mean bias error (MBE), and linear regression correlation coefficient have been used to compare measured and estimated values. The results of this comparison show that the correlation coefficients were similar to 1 while the RMSE ranges between 2.10 kJ m À2 and 1.94 k Jm À2 and, in percentage, 9.18% and 7.64%, respectively. According to these results, it can be concluded that total global solar irradiation is an appropriate variable to obtain UV-B daily values in places where ultraviolet radiation is not measured or to extend the existing data set back in time.
Comparative investigation of erythemal ultraviolet radiation in the tropics and mid-latitudes
2010
Ultraviolet (UV) radiation has several effects on human health as well as other biological and chemical systems. The radiation can be weighted with the erythemal action spectrum and then converted to the dimensionless UV Index, which is designed to indicate the detrimental ?sunburning power? of the radiation for public heath purposes. A global view of the erythemally weighted irradiance from the Ozone Monitoring Instrument (OMI) on board the Aura spacecraft has been available since July, 2004. However, ground-based validation and correction of the satellite data are still required. In this thesis, the erythemal dose rates at local solar noon taken from the satellite were compared to ground-based data measured by spectroradiometers or broadband radiometers in two different climate areas: the Tropics and midlatitudes. This seeks to redress the lack of data and satellite validation for the Tropics, and also allows comparison with previous work in midlatitudes. The validation results sh...
Annales Geophysicae, 2001
This study examines three UV-B data sets: groundbased long-term spectral records at Thessaloniki, Greece (40.5 • N, 22.9 • E) and San Diego, California, USA (32.7 • N, 117.2 • W) as well as a global data set of daily erythemal dose obtained from the Total Ozone Mapping Spectrometer (TOMS) onboard the Nimbus-7 satellite. Both ground-based stations have long enough records of spectral UV-B measurements to allow independent time series analyses. For 63 • solar zenith angle (SZA) and clear sky conditions the quasi biennial oscillation (QBO) effect in solar irradiance at 305nm E 305 is about 32% of the annual cycle for both San Diego and Thessaloniki. The effect slightly increases with cloud cover of up to 4/8, and decreases thereafter for cloud cover greater than 4/8. The data reveal that cloudiness cannot offset interannual signals in UV-B records. The observations at San Diego provide an independent confirmation of the widespread nature of the QBO in UV-B, which about coincides in amplitude at the two station studies, both located in the latitude zone 30 •-40 • N. The peak-to-peak amplitude of the QBO in erythemal dose derived from TOMS/Nimbus-7 data is 6.5% at Thessaloniki. This is similar to the values calculated from ground-based measurements from this station. Based on satellite data, we find that the amplitude of the QBO in the erythemal dose is almost 40% of the amplitude of the annual cycle only in the tropics. The ratio of the amplitudes of the QBO over the annual cycle in erythemal dose decreases towards the extratropics, becoming less than 5% over middle latitudes.
Annales Geophysicae, 2001
This study examines three UV-B data sets: groundbased long-term spectral records at Thessaloniki, Greece (40.5 • N, 22.9 • E) and San Diego, California, USA (32.7 • N, 117.2 • W) as well as a global data set of daily erythemal dose obtained from the Total Ozone Mapping Spectrometer (TOMS) onboard the Nimbus-7 satellite. Both ground-based stations have long enough records of spectral UV-B measurements to allow independent time series analyses. For 63 • solar zenith angle (SZA) and clear sky conditions the quasi biennial oscillation (QBO) effect in solar irradiance at 305nm E 305 is about 32% of the annual cycle for both San Diego and Thessaloniki. The effect slightly increases with cloud cover of up to 4/8, and decreases thereafter for cloud cover greater than 4/8. The data reveal that cloudiness cannot offset interannual signals in UV-B records. The observations at San Diego provide an independent confirmation of the widespread nature of the QBO in UV-B, which about coincides in amplitude at the two station studies, both located in the latitude zone 30 •-40 • N. The peak-to-peak amplitude of the QBO in erythemal dose derived from TOMS/Nimbus-7 data is 6.5% at Thessaloniki. This is similar to the values calculated from ground-based measurements from this station. Based on satellite data, we find that the amplitude of the QBO in the erythemal dose is almost 40% of the amplitude of the annual cycle only in the tropics. The ratio of the amplitudes of the QBO over the annual cycle in erythemal dose decreases towards the extratropics, becoming less than 5% over middle latitudes.
Journal of Geophysical Research, 2005
1] The variability and long-term changes in the ultraviolet (UV) climate in the Netherlands have been studied in relation to ozone and clouds, by analyzing modeled and measured values for daily, monthly, and yearly integrated erythemally weighted UV doses. At Bilthoven, Netherlands (longitude 5.19°E, latitude 52.12°N), UV irradiance measurements for the 1994-2003 period yielded a mean annual dose of 447 ± 29 kJ/m 2 and a mean daily dose of 2.5 ± 0.5 kJ/m 2 for June and July. On average, the maximum UV index exceeded 6.5 (i.e., 0.1625 W/m 2 erythemally weighted) on 10 days per year (21 days in 2003). The mean value of measured-to-modeled ratios of erythemal UV irradiances was 1.00 with a standard deviation of 0.06 for days when the measured global solar radiation agrees within 5% with the cloudless sky value. Three previously introduced approaches to model cloud effects on UV doses were shown to have limitations when applied for low Sun and/or optically thick clouds, while a new approach provided the most consistent results with an average ratio of the measured-to-modeled daily doses of 1.02 and a standard deviation of 0.09, for all seasons and weather conditions for the period 1994-2002. Further analysis also revealed a wavelength dependency of the correlation between global solar radiation and UV radiation. Clouds, on average, reduced the daily dose of erythemal UV to 68% of the clear-sky value, whereas for global solar radiation this was 57%. The modeled annual erythemal UV dose was 622 kJ/m 2 (402 kJ/m 2 ) averaged over the years 1979-1982, while the years 2000-2003 yield 662 kJ/m 2 (448 kJ/m 2 ) for cloudless (cloudy) conditions. In the past 25 years the highest annual doses were received in 1995 (485 kJ/m 2 ) and 2003 (488 kJ/m 2 ): in 1995 as a result of extremely low ozone values and moderate cloud reduction and in 2003 as a result of extremely low cloud reduction combined with moderately low ozone values. As an indication of the changes over time, a linear regression is performed showing that the annual UV dose received at the ground for all weather conditions increased with 5.5 ± 2% per decade for erythemal UV over the 1979 period. Citation: den Outer, P. N., H. Slaper, and R. B. Tax (2005, UV radiation in the Netherlands: Assessing long-term variability and trends in relation to ozone and clouds, J. Geophys. Res., 110, D02203, doi:10.1029/2004JD004824. exist but do not translate directly to the past and present UV climate. Apart from the total ozone column, clouds, aerosols, ground albedo and altitude influence the groundlevel UV radiation as well. Clouds especially play a dominant role in the variability of UV doses. On a yearly basis, the reduction by clouds of the cloud-free UV dose ranges from 0 -10% for the south of Europe to 30-50% for the middle and north of Europe [Kelfkens et al., 2001]. Extreme observations, on a daily basis, show reductions of JOURNAL