Quantifying the effects of a low-ozone event and shallow stratocumulus clouds on ultraviolet erythemal radiation exposure

Meteorological and dosimetric ultraviolet (UV) erythemal radiation (UVER) measurements were performed in Didcot, England, on 6 and 7 April 2017. Both days were characterized by clear-sky conditions in the morning and the afternoon with development of shallow stratocumulus clouds (SSC) around noon. In addition, a low-ozone event occurred on 7 April characterized by a 34 DU (Dobson Unit) drop in total stratospheric ozone content. Compared to 6 April, the ozone mini-hole caused UVER increases of 2.67 standard erythema dose (SED) for diffuse and 4.32 SED for global radiation characterized by radiation amplification factors (RAF) of 1.62 and 1.52, respectively. The total global UVER dose reductions due to SSC coverage amount to 2.33 SED (6 April) and 2.81 SED (7 April). As innovation the RAF is decomposed into two parts, named cloud ozone factor (COF) and radiation amplification factor based on measured data (RAF_m), to quantify the low-ozone event's effect and the SSC influence in independently modifying the UVER doses. Hereby, the weight of each of these two effects acting during the same low-ozone event is expressed by the new COF. In this case, the COF values range between -0.13 and -0.11 for diffuse UVER and -0.03 to -0.07 for the global UV and UV-B parts. A positive COF value (0.18) results for the global UV-A range.

Analysis of a low ozone episode over Extremadura (Spain) in January 2006 and its influence on UV radiation

Abstract. The main objectives of this work are to analyze, firstly, the detail of the causes of a low ozone event which occurred in January 2006 and, secondly, the related effects of this anomalous episode on ultraviolet (UV) radiation measured at three locations in Extremadura (South-Western Spain). On 19 January 2006, the OMI total ozone column (TOC) was 16–20% below the January mean value of TOMS/NASA TOC (period 1996–2005). The back trajectories analysis with the HYSplit model indicates that the notable decrease of TOC could be attributed to a fast rise of the isentropic trajectories height. Concomitantly, UV erythemal radiation greatly increases (between 23% and 37%) on 19 January 2006 respect to UV erythemal radiation measured on 19 January 2005. This notable increase in winter UV solar radiation may involve harmful effects for organisms adapted to receive less radiation during that season (e.g. early developmental stages of terrestrial plants and phytoplankton).