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  • 1. Bais, A F
    et al.
    Gardiner, B G
    Slaper, H
    Blumthaler, M
    Bernhard, G
    McKenzie, R
    Webb, A R
    Seckmeyer, G
    Kjeldstad, B
    Koskela, T
    Kirsch, P J
    Grobner, J
    Kerr, J B
    Kazadzis, S
    Leszczynski, K
    Wardle, D
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Brogniez, C
    Gillotay, D
    Reinen, H
    Weihs, P
    Svenoe, T
    Eriksen, P
    Kuik, F
    Redondas, A
    SUSPEN intercomparison of ultraviolet spectroradiometers2001In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 106, no D12, p. 12509-12525Article in journal (Refereed)
    Abstract [en]

    Results from an intercomparison campaign of ultraviolet spectroradiometers that was organized at Nea Michaniona, Greece July, 1-13 1997, are presented. Nineteen instrument systems from 15 different countries took part and provided spectra of global solar UV irradiance for two consecutive days from sunrise to sunset every half hour. No data exchange was allowed between participants in order to achieve absolutely independent results among the instruments. The data analysis procedure included the determination of wavelength shifts and the application of suitable corrections to the measured spectra, their standardization to common spectral resolution of 1 nm full width at half maximum and the application of cosine corrections. Reference spectra were calculated for each observational time, derived for a set of instruments which were objectively selected and used as comparison norms for the assessment of the relative agreement among the various instruments. With regard to the absolute irradiance measurements, the range of the deviations from the reference for all spectra was within +/- 20%. About half of the instruments agreed to within +/-5%, while only three fell outside the +/- 10% agreement limit. As for the accuracy of the wavelength registration of the recorded spectra, for most of the spectroradiometers (14) the calculated wavelength shifts were smaller than 0.2 nm. The overall outcome of the campaign was very encouraging, as it was proven that the agreement among the majority of the instruments was good and comparable to the commonly accepted uncertainties of spectral UV measurements. In addition, many of the instruments provided consistent results relative to at least the previous two intercomparison campaigns, held in 1995 in Ispra, Italy and in 1993 in Garmisch-Partenkirchen, Germany. As a result of this series of intercomparison campaigns, several of the currently operating spectroradiometers operating may be regarded as a core group Of instruments, which with the employment of proper operational procedures are capable of providing quality spectral solar UV measurements.

  • 2.
    Carlund, Thomas
    et al.
    SMHI, Core Services.
    Landelius, Tomas
    SMHI, Research Department, Atmospheric remote sensing.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Comparison and uncertainty of aerosol optical depth estimates derived from spectral and broadband measurements2003In: Journal of applied meteorology (1988), ISSN 0894-8763, E-ISSN 1520-0450, Vol. 42, no 11, p. 1598-1610Article in journal (Refereed)
    Abstract [en]

    An experimental comparison of spectral aerosol optical depth tau(a,lambda) derived from measurements by two spectral radiometers [a LI-COR, Inc., LI-1800 spectroradiometer and a Centre Suisse d'Electronique et de Microtechnique (CSEM) SPM2000 sun photometer] and a broadband field pyrheliometer has been made. The study was limited to three wavelengths ( 368, 500, and 778 nm), using operational calibration and optical depth calculation procedures. For measurements taken on 32 days spread over 1 yr, the rms difference in tau(a,lambda) derived from the two spectral radiometers was less than 0.01 at 500 and 778 nm. For wavelengths shorter than 500 nm and longer than 950 nm, the performance of the LI-1800 in its current configuration did not permit accurate determinations of tau(a,lambda). Estimates of spectral aerosol optical depth from broadband pyrheliometer measurements using two models of the Angstromngstrom turbidity coefficient were examined. For the broadband method that was closest to the sun photometer results, the mean (rms) differences in tau(a,lambda) were 0.014 (0.028), 0.014 (0.019), and 0.013 ( 0.014) at 368, 500, and 778 nm. The mean differences are just above the average uncertainties of the sun photometer tau(a,lambda) values (0.012, 0.011, and 0.011) for the same wavelengths, as determined through a detailed uncertainty analysis. The amount of atmospheric water vapor is a necessary input to the broadband methods. If upper-air sounding data are not available, water vapor from a meteorological forecast model yields significantly better turbidity results than does using estimates from surface measurements of air temperature and relative humidity.

  • 3. Cheymol, Anne
    et al.
    De Backer, Hugo
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Stuebi, Rene
    Comparison and validation of the aerosol optical depth obtained with the Langley plot method in the UV-B from Brewer Ozone Spectrophotometer measurements2006In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 111, no D16, article id D16202Article in journal (Refereed)
    Abstract [en]

    [ 1] The Aerosol Optical Depths (AODs) retrieved from Brewer Ozone Spectrophotometer measurements with a method previously developed (Cheymol and De Backer, 2003) are now validated by comparisons between AODs from six Brewer spectrophotometers and two CSEM SPM2000 sunphotometers: two Brewer spectrophotometers 016 and 178 at Uccle in Belgium; one Brewer spectrophotometer 128 and one sunphotometer CSEM SPM2000 at Norrkoping in Sweden; and three Brewer instruments 040, 072, 156 at Arosa and one CSEM SPM2000 sunphotometer at Davos in Switzerland. The comparison between AODs from Brewer spectrophotometer 128 at 320.1 nm and sunphotometer SPM2000 at 368 nm at Norrkoping shows that the AODs obtained from the Brewer measurements with the Langley Plot Method (LPM) are very accurate if the neutral density filter spectral transmittances are well known: with the measured values of these filters, the correlation coefficient, the slope, and the intercept of the regression line are 0.98, 0.85 +/- 0.004, and 0.02 +/- 0.0014, respectively. The bias observed is mainly owing to the wavelength difference between the two instruments. The comparison between AODs from different Brewer spectrophotometers confirm that AODs will be in very good agreement if they are measured with several Brewer instruments at the same place: At Uccle, the correlation coefficient, slope, and intercept of the regression line are 0.98, 1.02 +/- 0.003, and 0.06 +/- 0.001, respectively; at Arosa, the comparisons between the AODs from three Brewer spectrophotometers 040, 072, and 156 give a correlation coefficient, a slope, and an intercept of the regression line above 0.94, 0.98 and below 0.04, respectively.

  • 4. den Outer, P. N.
    et al.
    Slaper, H.
    Kaurola, J.
    Lindfors, A.
    Kazantzidis, A.
    Bais, A. F.
    Feister, U.
    Junk, J.
    Janouch, M.
    Josefsson, Weine
    SMHI, Core Services.
    Reconstructing of erythemal ultraviolet radiation levels in Europe for the past 4 decades2010In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 115, article id D10102Article in journal (Refereed)
    Abstract [en]

    This paper is based on a comparative study on ultraviolet radiation (UV) measurements and UV reconstruction models for eight sites in Europe. Reconstruction models include neural network techniques and radiative transfer modeling combined with empirical relationships. The models have been validated against quality-controlled ground-based measurements, 8 to 20 years, on time scales ranging from daily to yearly UV sums. The standard deviations in the ratios of modeled to measured daily sums vary between 10 and 15%. The yearly sums agree within a 5% range. Depending on the availability of ancillary measurements, reconstructions have been carried out to the early 1960s. A method has been set up to educe one best estimate of the historical UV levels that takes into account the long-term stability and underlying agreement of the models, and the agreement with actual UV measurements. Using this best estimate, the yearly sums of erythemally weighted UV irradiance showed a range of 300 kJ/m(2) at 67 degrees N to 750 kJ/m(2) at 40 degrees N. The year-to-year variability was lowest at 40 degrees N with a relative variation of 4.3%; for central and northern European latitudes this year-to-year variation was 5.2 to 6.5%. With regard to the period 1980 to 2006, first-order trend lines range from 0.3 +/- 0.1 to 0.6 +/- 0.2% per year, approximately two thirds of which can be attributed to the diminishing of cloudiness and one third to ozone decline.

  • 5. den Outer, P. N.
    et al.
    van Dijk, A.
    Slaper, H.
    Lindfors, A. V.
    De Backer, H.
    Bais, A. F.
    Feister, U.
    Koskela, T.
    Josefsson, Weine
    SMHI, Core Services.
    Applying spaceborne reflectivity measurements for calculation of the solar ultraviolet radiation at ground level2012In: ATMOSPHERIC MEASUREMENT TECHNIQUES, ISSN 1867-1381, Vol. 5, no 12, p. 3041-3054Article in journal (Refereed)
    Abstract [en]

    Long-term analysis of cloud effects on ultraviolet (UV) radiation on the ground using spaceborne observations requires the use of instruments that have operated consecutively. The longest data record can be built from the reflectivity measurements produced by the instruments Total Ozone Mapping Spectrometers (TOMS) flown on Nimbus 7 from 1979 to 1992, TOMS on Earth Probe from 1996 to 2005, and the Ozone Monitoring Instrument (OMI) flown on EOS Aura since 2004. The reflectivity data produced by TOMS on Earth Probe is only included until 2002. A comparison is made with cloud effects inferred from ground-based pyranometer measurements at over 83 World Radiation Data Centre stations. Modelled UV irradiances utilizing the standard reflectivity are compared with measurements of UV irradiances at eight European low-elevation stations. The reflectivity data of the two TOMS instruments shows a consistent agreement, and the required corrections are of low percentage, i.e. 2-3%. In contrast, the reflectivity product of OMI requires correction of 7-10%, and a solar angle dependency therein is more pronounced. These corrections were inferred from a comparison with pyranometer data, and tested using the UV measurements. The average reduction of UV radiation due to clouds for all sites together indicates a small trend: a diminishing cloudiness, in line with ground-based UV observations. Uncorrected implementation of the reflectivity data would have indicated the opposite. An optimal area was established for reflectivity data for the calculation of daily sums of UV radiation. It measures approximately 1.25 degrees in latitudinal direction for square-shaped areas overhead the ground-based UV stations. Such an area can be traversed within 5 to 7 h at the average wind speeds found for the West European continent.

  • 6. Feister, U.
    et al.
    Junk, J.
    Woldt, M.
    Bais, A.
    Helbig, A.
    Janouch, M.
    Josefsson, Weine
    SMHI, Core Services.
    Kazantzidis, A.
    Lindfors, A.
    den Outer, P. N.
    Slaper, H.
    Long-term solar UV radiation reconstructed by ANN modelling with emphasis on spatial characteristics of input data2008In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 8, no 12, p. 3107-3118Article in journal (Refereed)
    Abstract [en]

    Artificial Neural Networks (ANN) are efficient tools to derive solar UV radiation from measured meteorological parameters such as global radiation, aerosol optical depths and atmospheric column ozone. The ANN model has been tested with different combinations of data from the two sites Potsdam and Lindenberg, and used to reconstruct solar UV radiation at eight European sites by more than 100 years into the past. Special emphasis will be given to the discussion of small-scale characteristics of input data to the ANN model. Annual totals of UV radiation derived from reconstructed daily UV values reflect interannual variations and long-term patterns that are compatible with variabilities and changes of measured input data, in particular global dimming by about 1980/1990, subsequent global brightening, volcanic eruption effects such as that of Mt. Pinatubo, and the long-term ozone decline since the 1970s. Patterns of annual erythemal UV radiation are very similar at sites located at latitudes close to each other, but different patterns occur between UV radiation at sites in different latitude regions.

  • 7. Grobner, J
    et al.
    Rembges, D
    Bais, A F
    Blumthaler, M
    Cabot, T
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Koskela, T
    Thorseth, T M
    Webb, A R
    Wester, U
    Quality assurance of reference standards from nine European solar-ultraviolet monitoring laboratories2002In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 41, no 21, p. 4278-4282Article in journal (Refereed)
    Abstract [en]

    A program for quality assurance of reference standards has been initiated among nine solar-UV monitoring laboratories. By means of a traveling lamp package that comprises several 1000-W ANSI code DXW-type quartz-halogen lamps, a 0.1-Omega shunt, and a 6-1/2 digit voltmeter, the irradiance scales used by the nine laboratories were compared with one another; a relative uncertainty of 1.2% was found. The comparison of 15 reference standards yielded differences of as much as 9%; the average difference was less than 3%. (C) 2002 Optical Society of America.

  • 8.
    Jansson, Anna
    et al.
    SMHI, Core Services.
    Josefsson, Weine
    SMHI, Core Services.
    Modelling of surface global radiation and CIE-weighted UV-radiation for the period 1980-20002007Report (Other academic)
    Abstract [en]

    This report presents the procedure for creation of surface global radiation and CIE-weighted UVradiation for the years 1980-2000. The work was ordered by the Swedish Radiation Protection Authority (SSI) on behalf of “Miljömålsrådet”. The created data covers a large geographical areaover northwest Europe with a fine spatial (22x22 km) and temporal resolution (1 hour).The input data are selected from the new version of the Rossby Centre regional atmospheric climate model (RCA3), ERA-40 (www.ecmwf.int/research/era) and observations.For the creation of CIE-weighted UV-radiation, a clear sky model was first used and then a cloud modification model that reduces the clear sky radiation dependent on the cloud amount from theRCA3 model.The report also includes a validation of the modelled CIE-weighted UV-radiation against independent observations. The root mean square deviation is for daily values about 38%, for monthly values, 13% and for yearly values 7%. Also a small bias toward higher modelled UVcompared to observations exists in the data set.For the creation of global radiation, the data has been selected from the RCA3 model with a correction made depended on the sun height. Also for the global radiation the validation results are presented in the report. The root mean square deviation is in the same order as for the modelledCIE-weighted UV-radiation, also here a small bias toward higher modelled values exist, but smaller then for the modelled CIE-weighted UV-radiation.All CIE-weighted UV-radiation and global radiation created in this project are freely available for non-commercial usage at the web-interface, www.smhi.se/strang/omna. Here charts, fields and time series can be selected for hourly, daily, monthly and yearly values.

  • 9.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Computed global radiation using interpolated, gridded cloudiness from the MESA-BETA analysis compared to measured global radiation1989Report (Other academic)
  • 10.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Five years of solar UV-radiation monitoring in Sweden1996Report (Other academic)
  • 11.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    FOCUSED SUN OBSERVATIONS USING A BREWER OZONE SPECTROPHOTOMETER1992In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 97, no D14, p. 15813-15817Article in journal (Refereed)
    Abstract [en]

    Accurate measurements of total ozone at high latitudes during winter have become increasingly important for studies of polar ozone depletion. The direct Sun measurements are the most direct and physically well defined type of measurement of total ozone with Dobson and Brewer spectrophotometers along with the focused Sun measurements. The direct Sun and focused Sun method are influenced by many sources of error at low solar elevations. A large error arises from the addition of radiation scattered from air along the path of the solar beam. A method to correct for this error using the Brewer instrument is described. The method gives reasonably accurate values down to solar elevations of 5-degrees compared to 10-degrees-20-degrees without corrections. This is especially important for high-latitude stations, where the low solar elevations are a limiting factor for accurate measurements of the total ozone particularly during the winter.

  • 12.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Measurements of total ozone 1997 - 19992000Report (Other academic)
  • 13.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Normalvärden för perioden 1961-90 av globalstrålning och solskenstid i Sverige1993Report (Other academic)
  • 14.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Quality of total ozone measured by the focused sun method using a Brewer spectrophotometer2003In: Journal of applied meteorology (1988), ISSN 0894-8763, E-ISSN 1520-0450, Vol. 42, no 1, p. 74-82Article in journal (Refereed)
    Abstract [en]

    Strong ozone depletions and large natural variations in total ozone have been observed at high latitudes. Accurate measurements of total ozone are important so as not to misinterpret the involved processes and to track correctly the variations. The primary basis for ground-based monitoring of total ozone is the network of Dobson and Brewer ozone spectrophotometers. However, these instruments have limitations. At high latitudes, the fundamental direct sun observation used by these instruments is not possible during large parts of the year. In particular, the low sun and the resulting weak signals present a challenge. The focused sun observation method can extend the possible range of measurements using the Brewer instrument. Here, this method is discussed from the point of accuracy. Direct (synchronized) validation against the fundamental direct sun method is not possible with the current instrument configuration. Alternative methods to overcome the obstacle of nonsynchronous observations are applied. An estimate of the uncertainty of the validation is provided. The results show that the focused sun method gives data that are in line with the estimated uncertainty of the validation. No major additional uncertainty is needed to explain the observed scatter. The main conclusion is that the focused sun observation method can have an uncertainty close to the fundamental direct sun method and thus can be used to extend the possible range of observation for the Brewer ozone spectrophotometer.

  • 15.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Solar ultraviolet radiation in Sweden1986Report (Other academic)
  • 16.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Solar UV-radiation monitoring 19961996Report (Other academic)
  • 17.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    UV-radiation 1983-2003 measured at Norrkoping, Sweden2006In: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 83, no 1-4, p. 59-76Article in journal (Refereed)
    Abstract [en]

    Total ozone has been monitored with high accuracy at many sites for a relative long period of time. This is not the case for UV. The main reason is that UV is difficult to measure accurately. Extensive monitoring started first during the 1990s. However, there are some data series still in operation that were initiated at earlier dates. This paper will discuss one such series from Norrkoping, Sweden that began in March 1983. The instruments used to measure UV radiation have some characteristics producing an output signal that is not directly related to the UV. Here, these problems are discussed and corrections are applied. The goal is to produce a homogenous and an accurate set of UV data as is possible. An analysis of the various sources of uncertainty is done and summarised as total uncertainty. This was found to be about 6% for the yearly values of CIE weighted UV. However, the precision is much better at about 0.6%. Finally, some results are shown for yearly and seasonal UV. The trends for the full period 1983-2003 are tested for significance. The spring, summer, autumn and yearly data showed a significant increase in UV of respectively 0.8, 0.3, 0.8 and 0.5% per year. To get some indication of the cause of the variation of global radiation (indicator of cloudiness) and total ozone measured at the same site were also processed. A small, but insignificant, decrease of total ozone was found, whilst global radiation showed an increase. It seems that cloudiness is the major factor for the observed variation in UV for this period. The data are available on the internet.

  • 18.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    UV-radiation measured in Norrköping 1983-20032004Report (Other academic)
    Abstract [en]

    The purpose of this work is to homogenise a number of different data sets of daily values of UV-radiation to enable studies of the temporal variation of UV-radiation and atmospheric processes. Efforts are concentrated on the longest series measured using a Robertson-Berger and a Solar Light Model 501 radiometer. The lack of practical and reliable calibration standards have made measurements of UV uncertain. There are also several sources of uncertainty inherited in the designs of the instruments as well as uncertainties in the input data to the models used for corrections and for filling gaps of missing data.The primary goal is to achieve a homogenous data set. The second goal is to mimic a true CIE-weighted irradiation, McKinley and Diffey (1987). The third goal is to be as close as possible to an absolute irradiance scale.There are some factors that will prevent the achievement of these goals. These factors will introduce uncertainty in various fashions and affect the data differently. The applied corrections are assumed to remove systematic differences in a statistical sense. However, as will be discussed below, large differences may still remain in the hourly data.For those not familiar with measurements in the UV spectral range it may seem surprising that UV data recorded by different instruments differ so much. This is partly due to the very large change (several orders of magnitude) in the solar spectrum combined with small differences in the spectral responsivity of the instruments in this range. Apparently small differences in spectral responsivity will produce relatively large variable differences in the output only by changing the solar elevation during the day or during the year. The yearly effect will be seen in the results below.

  • 19.
    Josefsson, Weine
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Karlsson, Jan-Erik
    Measurements of total ozone 1994-19961997Report (Other academic)
  • 20.
    Josefsson, Weine
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Landelius, Tomas
    SMHI, Research Department, Atmospheric remote sensing.
    Effect of clouds on UV irradiance: As estimated from cloud amount, cloud type, precipitation, global radiation and sunshine duration2000In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 105, no D4, p. 4927-4935Article in journal (Refereed)
    Abstract [en]

    Ten years of measurements of UV irradiance, monitored by the Robertson-Berger (RB) meter in Norrkoping, 58.58 degrees N, 16.15 degrees E, Sweden, have been combined with concurrent synoptic cloud observations, measurements of sunshine duration, and global radiation to establish the relative influence of clouds on UV irradiance. It is shown that the cloud effect for UV wavelengths is less than for the whole solar spectrum (global radiation). Relations retrieved for global radiation may be used by correcting for the differences. High-level clouds are more transparent than low- and medium-level clouds. As expected, it was found that precipitating clouds in general are more opaque than nonprecipitating clouds. If there is any solar elevation dependency in the effect of clouds, it is small. Using only total cloud amount as parameter to model, the cloud effect on UV irradiance will give a substantial uncertainty, which can be decreased considerably using cloud type and/or information on precipitation conditions. It has also been shown that sunshine duration can be used in a similar way as cloud covet.

  • 21.
    Josefsson, Weine
    et al.
    SMHI, Core Services.
    Ottosson Löfvenius, Mikaell
    SMHI.
    Measurements of total ozone 2006-20082009Report (Other academic)
    Abstract [en]

    This report summarises the quality control, quality assurance and measurements of total ozone at Norrköping and Vindeln for the period 2006-2008. Significant incidents affecting the measurements are noted. Daily data are listed and plotted.

  • 22.
    Josefsson, Weine
    et al.
    SMHI, Core Services.
    Ottosson Löfvenius, Mikaell
    SMHI.
    Total ozone from zenith radiance measurements: An empirical model approach2008Report (Other academic)
    Abstract [en]

    At Vindeln monitoring of the total ozone has been done using the Dobson spectrophotometer #30 since 1991. The fundamental observation is done by observing the direct solar radiance. However, when clouds cover the sun an observation of the zenith radiance is collected. This type of measurement is called a zenith observation and by using an empirical relation one can deduce the total ozone. Up to now an old empirical relation based on data from Boulder USA has been applied. In this report we present the development and testing of a site specific empirical relation.

  • 23.
    Josefsson, Weine
    et al.
    SMHI, Core Services.
    Ottosson Löfvenius, Mikaell
    Perrnilla, Löfvenius
    Measurements of total ozone 2012-20152016Report (Other academic)
    Abstract [en]

    This report summarises the quality control, quality assurance and measurements of total

    ozone at Norrköping and Vindeln for the period 2012-2015. Significant incidents affecting the

    measurements are documented. Daily data are listed and plotted.

    This work was supported by the Swedish Environmental Protection Agency.

  • 24. Kaurola, J.
    et al.
    Lindfors, A.
    Lakkala, K.
    Hansen, G.
    Josefsson, Weine
    SMHI, Core Services.
    Vuilleumier, L.
    Feister, U.
    Slaper, H.
    On the usability of the ERA-40 reanalysis in the estimation of past surface UV radiation over Europe2010In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 115, article id D24107Article in journal (Refereed)
    Abstract [en]

    Erythemal daily UV doses have been calculated using input data from the ERA-40 reanalysis for years 1958-2002. The quality of input parameters for UV calculations has been validated with available ground based total ozone data and estimates of Cloud Modification Factor (CMF), and the results have been compared with existing UV data. Owing to limited availability of validation data especially during 1960s and 1970s the analysis focused on sites located in central and northern Europe. The current work is the first step in deriving reliable long-term UV time series from the ERA-40 reanalysis. Total ozone from the ERA-40 reanalysis is affected by significant biases, especially before satellite ozone measurements were available for assimilation. Estimations of the effect of clouds on surface UV were made using global radiation (300-3000 nm) budgets at the surface because available ERA-40 cloud data do not allow good estimates of surface daily UV doses. There are some problems with ERA-40 solar radiation budgets which cause systematic biases in calculated daily UV doses. Comparison of calculated daily erythemal UV doses against ground-based UV data indicate that ERA-40 UV doses are typically overestimated by 6-18% in central and northern Europe and underestimated by 9-17% at Davos, Switzerland. Root-mean-square errors of the calculated daily UV doses are usually in the range of 30-40%. Trends of UV doses were calculated for the concurrent period of the TOMS satellite UV data (1979-2002). The trends of zonally averaged ERA-40 and TOMS UV agree well and are mostly of the same sign and magnitude.

  • 25. Kaurola, J
    et al.
    Taalas, P
    Koskela, T
    Borkowski, J
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Long-term variations of UV-B doses at three stations in northern Europe2000In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 105, no D16, p. 20813-20820Article in journal (Refereed)
    Abstract [en]

    Recent analysis of the total ozone observations indicate a negative trend of about 4%/decade in the Northern Hemisphere midlatitudes during the last two decades [WMO, 1999]. The effect of this decline on surface UV levels is of interest to a variety of applications. In this work the long-term variation of UV radiation at three stations located in northern Europe (Belsk, Norrkoping, and Jokioinen) has been studied using data from (1) ground-based observations, (2) surface UV doses determined using TOMS satellite measurements, and (3) reconstructed UV doses using observations of global radiation, total ozone, and radiative transfer modeling. For each station the estimates of daily UV doses from various sources have been intercompared, and a trend analysis has been performed to reveal long-term changes in the UV radiation. Data sets, which start in the late 1970s or early 1980s, show a general positive trend in annual doses of UV radiation. Some of these upward trends are statistically significant. For Belsk the increases are in the range of 5-15% per decade during spring and summer. The largest increases, about 20%/decade, has been observed in Norrkoping during spring. At Jokioinen there has been a slight upward trend in UV throughout the year. The analysis of reconstructed Belsk data from 1966 onward shows that the positive trend since late 1970s was preceeded by a negative trend. The reason for such changes is probably not only related to the changes in the total ozone but also to changes in aerosol content and cloudiness. The agreement of the UV series based on different data sources is good. This was studied using a subset of data in which it was required that data from all possible sources were available. The different trend estimates were in very close agreement with each other. However, there were often differences in absolute values, which is probably related to problems in calibration and limitations of the models.

  • 26.
    Landelius, Tomas
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Methods for cosine correction of broadband UV data and their effect on the relation between UV irradiance and cloudiness2000In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 105, no D4, p. 4795-4802Article in journal (Refereed)
    Abstract [en]

    Irradiance measurements on a horizontal surface often deviate from theory where the irradiance is supposed to be proportional to the cosine of the angle of incidence. This discrepancy is known as the cosine error. In this paper, three different methods for cosine error correction are investigated. The simplest method is based on the assumption of an isotropic sky radiance distribution, regardless of sky conditions, and the irradiance is treated as a single component. In the second method the irradiance is divided into one direct solar and one diffuse sky component, where the latter is assumed to have an isotropic distribution. Finally, a third method also divides the irradiance into two components but under the assumption of an anisotropic sky radiance distribution. Irradiances under general sky conditions are found by interpolation between clear and overcast cases on the basis of sunshine duration or cloud cover. The three methods are applied to data from a Robertson-Berger sunburning meter located in Norrkoping, Sweden. Both methods, where the irradiance is divided into two components, produce acceptable and similar results, while the isotropic one-component method does not.

  • 27.
    Landelius, Tomas
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Persson, Thomas
    SMHI.
    A system for modelling solar radiation parameters with mesoscale spatial resolution2001Report (Other academic)
    Abstract [en]

    Today, modern analysis systems synthesise meteorological data from a number of sources, e.g.\ round based SYNOP, satellites, radar, etc., into field information which enable us to model radiation at the Earth’s surface on the mesoscale. At the Swedish Meteorological and Hydrological Institute (SMHI) we have set up a model system that produce hourly information in terms of field data with a resolution of about 22 ´ 22 km2 for a geographic area covering Scandinavia and the run off region of the Baltic sea.Presently, the model calculates fields of global-, photosynthetically active- (PAR), UV- and direct radiation based on output from a mesoscale analysis system, a high resolution limited area numerical weather prediction model (NWP), an ice model for the Baltic sea together with satellite measurements of total ozone. A spectral clear sky model lies at the heart of the model system. Its output is multiplied by a function which captures the influence of clouds and precipitation. Different cloud effect functions are applied to the different radiation components, with the exception of global- and PAR for which the same relation is assumed.Measurements from the radiation network of SMHI were used for estimation and validation purposes. A first evaluation of the model system suggests that the RMSE for hourly global radiation data is on the order of 28% and about 16% for daily values. These errors are comparable to those obtained for models purely based on synoptic observations (SYNOP) (29% and 13%) . For UV radiation the figures are similar but for the direct radiation component they are worse; 53% and 31% respectively compared to 25% and 15% for the SYNOP models. To some extent the larger errors for the direct component could be explained by its sensitivity to scale differences when model grid squares are validated against point measurements.

  • 28. Lindfors, Anders
    et al.
    Kaurola, Jussi
    Arola, Antti
    Koskela, Tapani
    Lakkala, Kaisa
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Olseth, Jan Asle
    Johnsen, Bjorn
    A method for reconstruction of past UV radiation based on radiative transfer modeling: Applied to four stations in northern Europe2007In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 112, no D23, article id D23201Article in journal (Refereed)
    Abstract [en]

    A method for reconstruction of past UV radiation has been developed. The idea of the method is to use measurements of global radiation (300 - 3000 nm) for determining the influence of clouds on UV radiation. In order to transfer the information contained in the global radiation data into a cloud effect in the UV range, a so-called cloud modification table was developed, which is based on physical relationships determined through radiative transfer calculations. The method was given as input the measured global radiation and total ozone column, the total water vapor column from the ERA-40 data set, the surface albedo as estimated from snow depth, and the altitude of the location. Using this method, erythemally weighted UV irradiances were reconstructed back to the early 1980s at four stations in northern Europe: Bergen in Norway, Norrkoping in Sweden, and Jokioinen and Sodankyla in Finland. The reconstructed daily UV doses are in good agreement with measurements. For the summer season, the systematic error was found to vary between 0% at Bergen and 4% at Jokioinen, and the correlation coefficient was 0.99 at all stations. The summer root-mean-square error was 5% at all stations except Jokioinen, where it was 9%. The method performs well also for spring and autumn, whereas for winter conditions of low Sun, a systematical underestimation was found. A large part of this underestimation was found to be due to the plane-parallel approximation used in the radiative transfer calculations. The time series of reconstructed UV exhibit a clear increase since the early 1980s at both Sodankyla " (4.1%/decade; statistically significant) and Norrkoping (3.3%/decade; not significant). At Jokioinen, a weak increase was found, while at Bergen there was no considerable overall change. At both Sodankyla and Norrkoping, the increase in the reconstructed UV radiation was primarily driven by an increase in the global radiation, that is, by decreased cloudiness. The method is general in the sense that it can be applied also to other stations.

  • 29. Lindfors, Anders
    et al.
    Tanskanen, Aapo
    Arola, Antti
    van der A, Ronald
    Bais, Alkiviadis
    Feister, Uwe
    Janouch, Michal
    Josefsson, Weine
    SMHI, Core Services.
    Koskela, Tapani
    Lakkala, Kaisa
    den Outer, Peter N.
    Smedley, Andrew R. D.
    Slaper, Harry
    Webb, Ann R.
    The PROMOTE UV Record: Toward a Global Satellite-Based Climatology of Surface Ultraviolet Irradiance2009In: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, ISSN 1939-1404, E-ISSN 2151-1535, Vol. 2, no 3, p. 207-212Article in journal (Refereed)
    Abstract [en]

    This paper describes the PROMOTE UV Record, which aims to provide a global long-term record of the surface UV radiation. The algorithm developed takes as input cloud information from the International Satellite Cloud Climatology Project (ISCCP) and a recently developed multisensor assimilated record of the total ozone column. Aerosols and surface albedo are based on climatologies. Here, first validation results of the PROMOTE UV Record are presented through comparison against ground-based measurements of daily erythemal UV doses at eight European stations. The validation shows that the method is working reasonably, although there is a clear tendency toward overestimation. Typically, the median bias as compared to measurements is 3%-10% and 56%-68% of the daily doses are within +/- 20% from the ground-based reference. The prototype version of the PROMOTE UV Record included in this paper covers the period from July 2002 to June 2005. The time series will later be extended to start in 1983.

  • 30. Meinander, O.
    et al.
    Kazadzis, S.
    Blumthaler, M.
    Ylianttila, L.
    Johnsen, B.
    Lakkala, K.
    Koskela, T.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Diurnal discrepancies in spectral solar UV radiation measurements2006In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 45, no 21, p. 5346-5357Article in journal (Refereed)
    Abstract [en]

    Unexpected diurnal discrepancies between high-quality spectroradiometers were observed during the 2000 Nordic Ozone Group Intercomparison campaign. The spectral ratios of the irradiances showed a diurnal variation of similar to 2-9%. This cannot be explained by the nonideal angular response of the instruments' input optics in one plane (cosine effect). Instead, by using a radiative transfer model, we show that differences in the angular response in four azimuth planes have the potential to bias the measured data by up to 4.4% (azimuth effect). Other relevant factors are also discussed and quantified and are shown to be significant when diurnal changes in radiation are explained by environmental factors, or when measured data are compared with model or satellite data. Again, intercomparison campaigns have the potential to reveal errors that would otherwise remain undetected. (c) 2006 Optical Society of America.

  • 31.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Josefsson, Weine
    SMHI, Core Services.
    Skyfallsuppdraget ett regeringsuppdrag till SMHI2015Report (Other academic)
    Abstract [en]

    Arbetet har sammanfattats i en rapport, som kan betraktas som en lägesrapport, inkluderar en omvärldsanalys; vad som gjorts i Sverige och i andra länder, delvis inhämtat vid en expertworkshop. Rapporten innehåller också en bearbetning av SMHIs nederbördsobservationer avseende korttidsnederbörd (skyfall) och en diskussion kring olika statistiska metoder att analysera dessa observationer. Dessutom har SMHIs nuvarande system för att prognosera skyfall uppgraderats och i rapporten diskuteras även vilka möjligheter som finns att ytterligare förbättra prognoserna i framtiden. Den pågående klimatförändringen påverkar vädret och därmed skyfallen. Rapporten tar upp de senaste rönen inom forskningen och även de negativa effekter som skyfall ger på samhället. Vilka behov finns i samhället och vad kan vi göra för att minimera de negativa effekterna var något som diskuterades vid en användarworkshop.

  • 32. Petkov, Boyan H.
    et al.
    Vitale, Vito
    Tomasi, Claudio
    Siani, Anna Maria
    Seckmeyer, Gunther
    Webb, Ann R.
    Smedley, Andrew R. D.
    Casale, Giuseppe Rocco
    Werner, Rolf
    Lanconelli, Christian
    Mazzola, Mauro
    Lupi, Angelo
    Busetto, Maurizio
    Diemoz, Henri
    Goutail, Florence
    Koehler, Ulf
    Mendeva, Bogdana D.
    Josefsson, Weine
    SMHI, Core Services.
    Moore, David
    Lopez Bartolome, Maria
    Moreta Gonzalez, Juan Ramon
    Misaga, Oliver
    Dahlback, Arne
    Toth, Zoltan
    Varghese, Saji
    De Backer, Hugo
    Stuebi, Rene
    Vanicek, Karel
    Response of the ozone column over Europe to the 2011 Arctic ozone depletion event according to ground-based observations and assessment of the consequent variations in surface UV irradiance2014In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 85, p. 169-178Article in journal (Refereed)
    Abstract [en]

    The strong ozone depletion event that occurred in Arctic during spring 2011 was found to cause appreciable reduction in the ozone column (OC) in Europe, even at lower latitudes. The features of this episode have been analysed using the data recorded at 34 ground-based stations located in the European area and compared with the similar events in 2000 and 2005. The results provided evidence that OC as far south as 40 degrees N latitude was considerably influenced by the Arctic ozone loss in spring 2011. The reduction of OC at the northernmost sites was about 40% with respect to the mean value calculated over the previous six-year period, while a similar decrease at the southern extreme ranged between 15 and 18%, and were delayed by nearly two weeks compared to the Arctic region. The ozone distributions reconstructed for the West Europe sector show that the decline of OC lasted from late March to late April 2011. The echo of the Arctic ozone depletion on mid-latitude UV irradiance has been analysed trough model computations that show an increase of the midday erythemal dose by 3-4 SED (1 SED = 100 J m(-2)) that was slightly higher than at polar regions. On the other hand it was assessed that the biosystems in the northernmost regions were a subject of about 4 times higher UV stress than those at mid-latitudes. Despite indications of an OC recovery, the event examined here shows that the issue of ozone depletion episodes cannot be belittled. (C) 2013 Elsevier Ltd. All rights reserved.

  • 33. Zerefos, Christos S.
    et al.
    Eleftheratos, Kostas
    Kapsomenakis, John
    Solomos, Stavros
    Inness, Antje
    Balis, Dimitris
    Redondas, Alberto
    Eskes, Henk
    Allaart, Marc
    Amiridis, Vassilis
    Dahlback, Arne
    De Bock, Veerle
    Diemoz, Henri
    Engelmann, Ronny
    Eriksen, Paul
    Fioletov, Vitali
    Grobner, Julian
    Heikkila, Anu
    Petropavlovskikh, Irina
    Jaroslawski, Janusz
    Josefsson, Weine
    SMHI, Core Services.
    Karppinen, Tomi
    Koehler, Ulf
    Meleti, Charoula
    Repapis, Christos
    Rimmer, John
    Savinykh, Vladimir
    Shirotov, Vadim
    Siani, Anna Maria
    Smedley, Andrew R. D.
    Stanek, Martin
    Stubi, Rene
    Detecting volcanic sulfur dioxide plumes in the Northern Hemisphere using the Brewer spectrophotometers, other networks, and satellite observations2017In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 17, no 1, p. 551-574Article in journal (Refereed)
1 - 33 of 33
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