Effects of Ozone Column and Ozone Profiles on Global Spectral Ultraviolet Irradiance at the South Pole

Global solar UV measurements performed with a high-resolution spectroradiometer located at the South Pole are compared with results of the radiative transfer model UVSPEC/libRadtran. The UV spectroradiometer is part of the National Science Foundation's Office of Polar Programs (NSF/OPP) UV monitoring network. The South Pole is an unique place for this investigation because of stable meteorological conditions, negligible aerosol influence, frequent cloud-less days, constant high surface albedo, virtually constant solar zenith angle during one day, and high altitude.

A recent intercomparison between Version 7 column ozone data from the Total Ozone Mapping Spectroradiometer onboard Earth Probe satellite (TOMS/EP) and ground based Dobson ozone measurements indicates that TOMS/EP overestimates ozone column by over 5% at latitudes higher than 65°S [Piacentini et al., 2000]. The difference at the South Pole has been reported to be 6.4%. In order to study this discrepancy further, the comparison of measured and modeled NSF/OPP UV data is used in validating ozone data from different sources (TOMS/EP, TOVS, GOME, Dobson). The results confirm the finding by Piacentini et al. [2000] that TOMS/EP measures high. The results also reveal that ozone and temperature profiles have an important impact on the agreement between measurement and model. This is confirmed by comparing the UV measurements with model calculations using either standard profiles or actual profiles, which were measured by ozone sondes launched at the South Pole. When using Dobson ozone measurements and actual ozone profiles, and correcting NSF/OPP UV measurements for the cosine error of the entrance optics, measurement and model agree to within ±5% for solar elevations greater than 5°.