Version 2 data of the National Science Foundation's Ultraviolet Radiation Monitoring Network: South Pole

Abstract

[1] Spectral ultraviolet (UV) and visible irradiance has been measured at the South Pole between 1991 and 2003 by a SUV-100 spectroradiometer, which is part of the U.S. National Science Foundation's UV Monitoring Network. Here we present a new data edition, labeled ''Version 2.'' The new version was corrected for wavelength shift errors and deviations of the spectroradiometer from the ideal cosine response. A comprehensive uncertainty budget of the new data set was established. Below 400 nm the expanded standard uncertainty (coverage factor 2) varies between 4.6 and 7.2%, depending on wavelength and sky condition. The uncertainty of biologically relevant UV irradiances is approximately 6%. Compared to the previously published data set, Version 2 UV data are higher by 5-14%, depending on wavelength, solar zenith angle (SZA), and year of observation. By comparing Version 2 data with results of a radiative transfer model, the good consistency and homogeneity of the new data set were confirmed. The data set is used to establish a UV climatology for the South Pole, focusing on the effects of aerosols, clouds, and total column ozone. Clouds are predominantly optically thin; 71% of all clouds have an optical depth between 0 and 1. The average attenuation of UV irradiance at 345 nm by clouds is less than 5% and no attenuations greater than 23% were observed. Attenuation by homogeneous clouds is generally larger in the visible than in the UV. The wavelength dependence of cloud attenuation is quantitatively explained with the wavelength-dependent radiance distribution on top of clouds and the incidence-angle dependence of cloud transmittance. Largest radiation levels occur in late November and early December when low stratospheric ozone amounts coincide with relatively small SZAs. Owing to the large effect of the ''ozone hole,'' short-and long-term variability of UV during the austral spring is very high. When the ozone hole disappears, DNA-damaging irradiance can decrease by more than a factor of two within 2 days. Typical summer UV index values range between 2 and 3.5 and vary by ±30% (±1s) between different years. Linear regression analyses did not indicate statistically significant UV trends owing to the large year-to-year variability and the fact that the network was established only after the first occurrence of the ozone hole. Current measurements therefore document variability on an elevated level.

Atmospheric Moisture and Cloud Cover Characteristics Forecast by AMPS*

“…Many problems complicate the ground-based visual cloud cover observations at South Pole station, including the very thin nature of clouds at all levels through which the sun/stars are often seen [these conditions tend to favor partly cloud observations instead of overcast conditions; Mahesh et al (2001); Bernhard et al (2004); Town et al (2007)], a 6-month period of complete darkness, making clouds difficult to observe, and extremely cold temperatures year round with especially strong inversion layers in the winter (Turner and Pendlebury 2007). Town et al (2005) further note the persistent presence of "diamond dust" or clear-sky precipitation during the winter, which may also add to errors in observed cloud fraction.…”

Total ozone and solar erythemal irradiance in southwestern Spain: Day‐to‐day variability and extreme episodes

“…The long-term variation in UV variation generally indicates an increase, mainly related to stratospheric ozone depletion. This decrease in ozone is particularly intense during the period of the ozone hole in spring [Bernhard et al, 2004], and during summertime at northern high latitudes, caused by chemical destruction and transport processes [Orsolini et al, 2003].…”

Retrieving vertical ozone profiles from measurements of global spectral irradiance

“…biospherical.com/Version2/Uncertainty_SUV150B.pdf. Data used in this paper are from the version 2 data edition (Bernhard et al, 2004) and are corrected for the cosine error of the instrument's entrance optics. The wavelength mapping was determined with a Fraunhofer-line correlation method and the wavelength uncertainty (k = 2) of processed data is 0.02 nm.…”

“…The model's results are spectra of global irradiance. Model input parameters include the extraterrestrial spectrum (as defined by Bernhard et al (2004) and available at http://uv.biospherical.com/Version2/Paper/ 2004JD004937-ETS_GUEYMARD.txt), surface albedo, at-mospheric pressure, and the ozone absorption cross section (Bass and Paur, 1985). While more accurate ozone absorption cross sections are now available (Gorshelev et al, 2014;Orphal et al, 2016), we used Bass and Paur (1985) data to facilitate validation with OMI total ozone column measurements, which are also based on Bass and Paur (1985).…”

“…Bernhard et al, 2004Bernhard et al, , 2008 and for a large range of conditions at other sites (e.g. Mayer and Kylling, 2005, and references therein).…”