Comparison of Models Used for UV Index Calculations

Koepke, Peter; Bais, Alkiviadis; Balis, D.; Buchwitz, Michael; Backer, H. De; Cabo, Xavier; Eckert, P.; Eriksen, P.; Gillotay, D.; Heikkilä, Anu; Koskela, Tapani; Lapeta, Bozena; Lityńska, Z.; Lorente, J.; Mayer, Bernhard; Renaud, Anne; Ruggaber, A.; Schauberger, Günther; Seckmeyer, Günther; Seifert, Péter; Schmalwieser, Alois W.; Schwander, Harry; Vanicek, K.; Weber, Mark

doi:10.1111/j.1751-1097.1998.tb09470.x

Cited by 36 publications

(46 citation statements)

References 13 publications

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“…We have to be careful when we interpret UVI at high latitude stations, as the magnitude of UVI is quite small most of the time due to large solar zenith angles. Nonetheless, at low and mid-latitudes the UVI differences observed are fully compatible with the errors attached with the measurements and models (Koepke et al, 1998).…”

Section: Model Validationsupporting

confidence: 83%

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Response to referee 2

LAMY¹

2018

Preprint

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We have derived values of the Ultraviolet Index (UVI) at solar noon from the Tropospheric Ultraviolet Model (TUV) driven by ozone, temperature and aerosol fields from the first phase of the Chemistry-Climate Model Initiative (CCMI-1). Since clouds remain one of the largest uncertainties in climate projections, we simulated only clear-sky UVI. We compared the UVI climatologies obtained from CCMI and TUV against present-day climatological values of UVI derived from satellite data (the OMI-Aura OMUVBd product) and ground-based measurements (from the NDACC network). Depending on the region, relative differences between the UVI obtained from CCMI and TUV and ground based measurements ranged between-4% and 11%. We calculated the UVI evolution throughout the 21st century for the four Representative Concentration Pathways (RCPs 2.6, 4.5, 6.0 and 8.5). Compared to 1960s values, we found an average increase in UVI in 2100 (of 2-4%) in the tropical belt (30°N-30°S). For the mid-latitudes, we observed a 1.8 to 3.4 % increase in the Southern Hemisphere for RCP 2.6, 4.5 and 6.0, and found a 2.3% decrease in RCP 8.5. Higher UV indices are projected in the Northern Hemisphere except for RCP 8.5. At high latitudes, ozone recovery is well identified and induces a complete return of mean UVI levels to 1960 values for RCP 8.5 in the Southern Hemisphere. In the Northern Hemisphere, UVI levels in 2100 are higher by 0.5 to 5.5% for RCP 2.6, 4.5 and 6.0 and they are lower by 7.9% for RCP 8.5. We analysed the impacts of greenhouse gases (GHGs) and ozone-depleting substances (ODSs) on UVI from 1960 by comparing CCMI sensitivity simulations (1960-2100) with fixed GHGs or ODSs at their respective 1960 levels. As expected with ODS fixed at their 1960 levels, there is no large decrease in ozone levels and consequently no sudden increase in UVI levels. With fixed GHG, we observed a delayed return of ozone to 1960 values, the same signal is observed on UVI, and looking at the UVI difference between 2090s values and 1960s values, we found an 8 % increase in the tropical belt during the summer of each hemisphere. Finally we show that, while in the Southern Hemisphere UVI is mainly driven by total ozone column, in the Northern Hemisphere both total ozone column and aerosol optical depth drive UVI levels, with aerosol optical depth having twice as much influence on UVI as total column does.

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Section: Model Validationsupporting

confidence: 83%

“…According to Koepke et al (1998), the UVI modelling error is about 5 % for a coverage factor of 2 standard deviation.…”

Section: Model Validationmentioning

confidence: 99%

Response to referee 2

LAMY¹

2018

Preprint

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“…The MOM is described by Wendisch et al [2002]; it participated in ICRCCM‐III (InterComparison of Radiation Codes in Climate Models, Phase III) [ Barker et al , 2003] and was tested against measurements [ Wendisch et al , 2002]. LRM is a comprehensive radiative transfer model package (A. Kylling and B. Mayer, http://www.libradtran.org, 2002), which also has been validated by comparison with other models [ Koepke et al , 1998; van Weele et al , 2000] and radiation measurements [ Mayer et al , 1997].…”

Section: Radiative Transfer Modelsmentioning

confidence: 99%

Vertical distribution of spectral solar irradiance in the cloudless sky: A case study

Wendisch

Mayer

2003

Geophysical Research Letters

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[1] First airborne measurements of spectral solar downand upwelling irradiances with a high spectral resolution (2 -3 nm) are presented. The data were gathered in cloudless, hazy conditions over sea and land using a new instrument (called albedometer), which is equipped with a unique sensor head leveling technique. The downwelling irradiances and their spectral slope increase with altitude, illustrating the impact of Rayleigh scattering and boundary layer aerosols. The upwelling spectra reveal typical reflection features of the underlying surface (e.g., vegetation step around 700 nm). The measurements are compared with radiative transfer model results based on simultaneous airborne aerosol observations. The downwelling irradiances mostly agree to ±10% which is within the experimental and modeling uncertainties. The upwelling irradiances are highly sensitive to uncertainties in the spectral surface albedo. Reasonable agreement between measurements and simulations required us to determine the surface albedo from flights at low altitude, rather than adopting literature values.

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“…The lookup tables and the factors are calculated by applying STAR (Ruggaber et al, 1994) in its neural network version (Schwander et al, 2001). STAR is a one-dimensional multi-scattering model allowing a detailed description of the atmospheric parameters and has been tested with good results (Koepke et al, 1998). The albedo of the soil is low in the UV compared to that in the visible spectral range.…”

Section: Modelling Hourly Erythemally Effective Uvmentioning

confidence: 99%

Hourly resolved cloud modification factors in the ultraviolet

Staiger¹,

Outer²,

Bais³

et al. 2008

Preprint

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Abstract. Cloud impacts on the transfer of Ultraviolet (UV) radiation through the atmosphere can be assessed using a cloud modification factor (CMF). The total global solar irradiation has proven to be a solid basis to derive CMF's for the UV radiation (UV_CMF). Total global irradiance is frequently measured and forecasted by numerical weather prediction systems. Its advantage compared to for instance cloud cover is that measured solar global irradiance contains already the effect of multiple reflection between cloud layers, reflection between the sides of the clouds, as well as the distinct difference whether the solar disc is obscured by clouds or not. In the UV range clouds decrease the irradiance to a lesser extent than in the visible and infrared spectral range; Rayleigh scattering in the atmosphere yields a larger fraction of scatter radiation compared to that of light and infrared, hence, obscuring the solar disc will not totally block out the irradiation. Thus the relationship between CMF's for solar radiation and for UV-radiation is not straight forwards, but will depend on e.g. the solar zenith angle (SZA) and wavelength band or action spectrum in the UV considered. Den Outer et al. (2005) provide a UV_CMF algorithm on a daily base accounting for these influences. It requires as input a daily CMF in total global radiation (SOL_CMF) and the SZA at noon. The calculation of SOL-CMF uses the clear sky algorithm of the European Solar Radiation Atlas to account for varying turbidity impacts. The algorithm's capability to derive hourly UV_CMF's based on the SZA at the corresponding hour and its worldwide applicability is validated using hourly resolved observational data retrieved from the databases of the COST-Action 726 on "Long term changes and climatology of UV radiation over Europe" and the USDA UV-B Monitoring and Research Program. The model performance for hourly resolution is shown to be comparable in absolute and relative deviations from a measured mean smoothed dependent on SZA with the well performing daily models of the COST-726 model intercomparison (Koepke et al., 2006).

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Comparison of Models Used for UV Index Calculations

Cited by 36 publications

References 13 publications

Response to referee 2

Response to referee 2

Vertical distribution of spectral solar irradiance in the cloudless sky: A case study

Hourly resolved cloud modification factors in the ultraviolet

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