U of S | Mailing List Archive | alt-photo-process-l | Re: Yellow tents and UV (was: outdoor gum demo)

Re: Yellow tents and UV (was: outdoor gum demo)

Okay, I keep looking and looking for data on UVA vs UVB; I want to see a graph of them together across days and years, but all I've found is little bits and pieces of data here and there...
I don't know if I have been more lucky than you, but I can add some information to yours (see below; the text after the citation is the abstract). I have not the full text, nor I have the opportunity to retrieve it in a few days.
Henriksen K., Claes S., Svenøe T. and Stamnes K. (1992) "Spectral UV and visible irradiance measurements in the Barents Sea and Svalbard" J. Atmos. Terrest. Phys. 54(9):1119-1127
Using a single monochromator, spectral measurements of solar irradiances of the UV and visible spectral ranges have been carried out during the midnight sun period in Arctic regions. Diurnal intensity variations are similar throughout the whole spectral region. Spectral ratios of the regions are obtained, and strong diurnal variations of the spectral ratios caused by the ozone layer are documented. The UVB region is mostly affected by the ozone layer. With UVB as the numerator in the spectral ratios the maxima of the spectral ratios occur at midday, because then the optical path of the UVB through the ozone layer is shortest. With UVA as the numerator hardly any diurnal variation between this range and visible blue occurs, mainly because of the small influence of ozone attenuation in these wavelength ranges. The influence of weather has much less influence on the spectral ratios than on the irradiances.
Henriksen K., Stamnes K, and Østensen P. (1989) "Measurements of solar u.v., visible and near i.r. irradiance at 78° N" Atmos. Environ. 23(7):1573-1579
Spectral measurements of solar radiation in the Arctic during the summer of 1987 were carried out with a double monochromator calibrated in absolute units. Integrated irradiances for parts of the UVB (2900Å–3150Å), UVA (3150Å–4000Å) and the whole measured spectral range (2900Å–8000Å) are tabulated. No irradiance is detected below 3050 Å. The measurements show that the diurnal variation in the UVB is a factor 7 stronger than in the UVA and a factor 6 stronger than for the total measured spectral range. We also find that in the ultraviolet part of the spectrum the diffuse radiation is the dominant component of global irradiance. Under clear sky conditions the measured spectral irradiances are closely reproduced by radiative transfer calculations.
Sabburg J.M., Parisi A.V. and M. G. Kimlin (2003) "Enhanced spectral UV irradiance: a 1 year preliminary study" Atmos. Research 66(4):261-272
The ultraviolet (UV) spectra on cloudy days were compared to those on cloud free days to determine which part of the UV spectrum has the greatest enhancement due to the cloud compared to both corresponding measured clear sky spectra as well as other enhanced spectra. In this preliminary study, cloud enhanced UV spectra selected for maximum UVA enhancement compared to a clear sky UV spectrum at similar solar zenith angle (SZA) and ozone values, showed that the ratio of the two sets of spectral irradiances was approximately wavelength independent (approximately 1.1) above the cut-off wavelength of approximately 306 nm. Similarly, above 306 nm the average ratio of the spectral irradiances of a maximum UVB enhanced UV spectrum compared to a clear sky spectrum was 1.2 with maximum values generally above this average between 316 and 344 nm and generally below 1.2 above the wavelength of 344 nm. The UVA and UVB enhanced spectra were separated into five SZA ranges and the irradiance at each wavelength averaged for each range and compared to clear sky spectra in each of the ranges. Above approximately 306 nm, the ratios are wavelength independent for all SZA. However, with the exception of the SZA range centred on 20°, there is an increasing dependency with shorter wavelengths below the 306 nm. Also there appears to be two distinct groupings of the average irradiance ratios, corresponding to the SZA range centred on 20°, 37° and 49° (ratio of 1.2) and 32° and 42° (ratio 1.0), the latter cases suggesting that on average there is no enhancement for these SZA, except for wavelengths less than 306 nm.

Sabburg J.M. and Parisi A.V. (2006) "Spectral dependency of cloud enhanced UV irradiance" Atmos. Research 81,3:206-214
This paper addresses two questions of primary importance to the solar UV community: 1) “Are cloud induced UV enhancements always wavelength dependent?” and 2) “Are the enhancements greatest in the UVA or UVB wavebands?” The answer to the first question is a definite no, with the conclusion to the second question that most of the enhancements found at this southern hemisphere measurement site are in the UVB waveband. This research is based on the results from a scanning UV spectroradiometer and a colour, all-sky camera over a 19-month period. In both the UVB and UVA wavebands there were cases that showed increasing, decreasing and no spectral dependence towards the shorter and longer wavelengths respectively. This research has found that cases of spectral dependence that decreased with wavelength tended to correspond to cloud fraction distributed in the outer field of view of the sky camera images for relatively low solar zenith angles. It is speculated that this is most likely due to an increase of scattered UV, compared to cases of increasing trends with wavelength, which would be accounted for by an increase in reflected UV from cloud surfaces in closer proximity to the sun. It also appears that wavelength dependency trends are related to the overall cloud fraction.