Evaluated UVA Irradiances over a Twelve-year Period at a Subtropical Site from Ozone Monitoring Instrument Data Including the Influence of Cloud.

Abstract

This research investigated the influence of cloud on the broadband UVA solar noon irradiances evaluated from the solar noon satellite-based OMI spectral UV data that were compared to the irradiances of a ground-based radiometer from 1 October 2004 to 31 December 2016. The correlation between ground-based radiometer data and the evaluated OMI broadband UVA data evaluated with a model were dependent on whether or not the solar disk was obscured by the presence of cloud and the total sky cloud fraction. For conditions when the sun was not obscured by cloud, the evaluated satellite and the ground-based UVA irradiance correlation was best for cloud cover between 0 and 2 octa (R2 =0.77) and the worst for high cloud cover of >4-8 octa (R2 between 0.3 and 0.4). The R2 reduced with increasing cloud amount and showed significantly weaker correlation when the sun was obscured. The correlation between the evaluated satellite broadband UVA and the ground-based measurements over the twelve years for total cloud cover conditions of 4 or less octa confirmed that the broadband UVA satellite evaluation model for the OMI spectral data is valid for approximately 71% of the days at the Southern Hemisphere subtropical study site.