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After the decrease of ozone-depleting substances (ODSs) as a consequence of the Montreal Protocol, it is still challenging to detect a recovery in the total column amount of ozone (total ozone) at northern high-latitudes. To assess regional total ozone changes in the "ozone-recovery"-period (2000-2020) at northern high-latitudes, this study investigates trends from ground-based total ozone measurements at three stations in Norway (Oslo, Andøya, and Ny-Ålesund). For this purpose, we combine measurements from Brewer spectrophotometers, ground-based UV filter radiometers (GUVs), and a SAOZ instrument. The Brewer measurements have been extended to work under cloudy conditions using the global irradiance (GI) technique, which is also presented in this study. We derive trends from the combined ground-based time series with the multiple linear regression model from the Long-term Ozone Trends and Uncertainties in the Stratosphere (LOTUS) project. We evaluate various predictors in the regression model and found that tropopause pressure and lower-stratospheric temperature contribute most to ozone variability at the three stations. We report significant positive trends at Andøya (0.9% per decade) and NyÅlesund (1.5% per decade) and no annual trends at Oslo, but significant positive trends in autumn at all stations. Finally we found positive but insignificant trends of around 3% per decade in March at all three stations, which may be an indication for Arctic spring-time ozone recovery. Our results contribute to a better understanding of regional total ozone trends at northern high-latitudes, which is essential to assess how Arctic ozone responds to changes in ODSs and to climate change. [ABSTRACT FROM AUTHOR]

A six-channel moderate-bandwidth filter instrument for measurement of UV and visible radiation has been developed. The characteristics of the instrument are described, including the spectral and the angular responses. Furthermore the calibration procedure is outlined. Combining information from several channels, one may determine the total ozone-column amount, various biological dose rates, a cloud transmission factor, and the effective cloud optical depth. The methods used to determine these parameters are presented, and the measured parameters are compared with similar ones obtained from other instruments. The total ozone as measured by the instrument agrees with measurements from a standard Brewer to -0.05% [+ or -] 2.04% over a two-year period. Two weeks of cloudless Commission Internationale de L'Eclairage dose rates agree with those from a Bentham double monochromator spectroradiometer to 0.99 [+ or -] 0.03. OCIS codes: 010.1280, 120.0120, 010.4950.

A method is described for deriving total ozone abundances from zenith-sky intensities measured by an UV-visible spectrometer, known as the System of Analysis of Observations at Zenith (SAOZ). Total ozone abundances are determined by comparison of intensity ratios measured at two wavelengths in the UV region with ratios computed with a radiative transfer model. The wavelength pair 320-307 nm was used in this study. Spectra recorded by the SAOZ spectrometer in Oslo (60 [degrees] N) from the beginning of May 1995 to the end of August 1995 were analyzed, and the results were compared with total ozone measured with a Brewer instrument. The relative difference in derived ozone abundances for the whole period, including days with thin and medium-thick cloud covers, is -0.18 [+ or -] 1.46%. We study the effects of clouds and varying ground albedo on the derived total ozone. Clouds result in an overestimation of the derived total ozone. The error increases with the optical depth of the cloud from approximately 2% for an optically thin cloud ([Tau] = 0.5) to approximately 10% for a thick cloud ([Tau] = 50). The ratio between measured intensities at 550 and 350 nm, the so-called color index, can be used as a measure of the cloud optical depth for thin and medium-thick clouds. The effects of thin and medium-thick clouds on the derived ozone abundances can be compensated for by use of an empirical relationship found between the measured color index and the error in the inferred ozone abundances caused by cloud scattering. We also study the influence of changes in the ground albedo and in the ozone profiles on derived total ozone values. Key words: Ozone, spectroscopy, UV-visible spectrometer, stratosphere.

I describe a method to derive biologically effective UV dose rates, total ozone abundances, and cloud optical depths from irradiance measurements with moderate bandwidth filter instruments that have only a few channels in the UV region. These quantities are determined when the measured irradiances are combined with radiative transfer calculations. The method was applied to a four-channel filter instrument with center wavelengths at 305, 320, 340, and 380 nm and bandwidths of 10 nm. I compared the instrument with a high-wavelength-resolution spectroradiometer during a 1-week period in San Diego, California, with variable cloudiness. The relative difference in Commission Internationale de l'Eclairage (CIE)-weighted UV dose rates for solar zenith angle's (SZA's) [less than] 80 [degrees] was 1.4 [+ or -] 3.2%. The relative difference for clear sky was 0.6 [+ or -] 1.5% for SZA's [less than] 80 [degrees]. The total ozone inferred from the irradiance measurements with the filter instrument is insensitive to clouds. The instrument was compared with a Dobson and a Brewer instrument in Oslo, Norway, 60 [degrees] N, for more than 1 year. The relative difference in derived ozone abundance for the entire period, including cloudy days, was 0.3 [+ or -] 2.9%. The standard deviation was reduced to 1.9% when only clear sky and SZA's [less than] 60 [degrees] were included. By using the total ozone and the cloud optical depth derived from the filter instrument as input to a radiative transfer model, one can compute a complete spectrum from 290 to 400 nm with 1-nm resolution. Such calculated spectra are in good agreement with spectra measured simultaneously with a high-wavelength-resolution spectroradiometer for clear as well as cloudy sky conditions and can be used to determine dose rates for any desired action spectrum. Only one UV-B channel and one UV-A channel are required to compute the spectra. Key words: UV radiation, UV doses, ozone, radiometer, cloud transmission.