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Measurements of the basic meteorological parameters and ultraviolet (UV) erythemalradiation (UVER) were performed in Didcot, England, on 6 and 7 April 2017. The UVERdata was collected by dosimeters, which consist of two sensors (named UVA and UVBC)collecting the erythemally weighted UV-A (320 - 400 nm) and UVBC (UV-B and UV-C, 250- 320 nm) radiation parts, respectively. Both measurement days were characterized by clearconditions during the morning and afternoon hours. Around noon of both days,however, development of shallow stratocumulus clouds (SSC) occurred. In addition, alow-ozone event (ozone mini-hole) took place on 7 April being characterized bya 34 DU (Dobson Unit) drop in total stratospheric ozone content. Compared to6 April, the UVER increase as a result of the low-ozone event amounts to 2.67standard erythema dose (SED) for diffuse and 4.32 SED for global radiation. Thecorresponding radiation amplification factors (RAF) amount to 1.62 and 1.52 fordiffuse and global UVER, respectively. The SSC coverage caused reductions forthe total global UVER doses amounting to 2.33 SED (6 April) and 2.81 SED(7 April). As innovation, we present a decomposition of the RAF into two parts, called cloud ozonefactor (COF) and radiation amplification factor based on measured data (RAFm). The goalof this decomposition is to quantify the low-ozone event’s effect and the SSC influence inindependently modifying the UVER doses. Hereby the newly introduced COFexpresses the weight of each of these two effects acting during the same low-ozoneevent. For the case presented, the COF values range between -0.13 and -0.11 fordiffuse UVER and -0.03 to -0.07 for the global UV and UV-B parts. A positive COFvalue (0.18) results for the global UV-A range. Negative (positive) COF valuescorrespond to a decreased (increased) cloud influence on the second of both referencedays. [ABSTRACT FROM AUTHOR]

The stratocumulus deck over the South Atlantic is regularly advected into the hyper-arid Namib where it appears as fog when it intercepts with the ascending terrain. This fog is a major source of water for plants and animals. The project Namib Fog Life Cycle Analysis (NaFoLiCA) aims at improving the knowledge about the vertical and spatial patterns of this fog through three subprojects using field measurements, remote sensing and numerical modelling.For this purpose, an intensive operation period (IOP) was conducted between 10th September and 5th October 2017 in the central Namib. The measurements were linked to the FogNet network with main activities taking place at the Gobabeb research and training centre. During the IOP, micrometeorological data including cloud base height, fog deposition, liquid water path and vertical profiles of wind speed and direction were measured continuously. Additionally, profiles of temperature and relative humidity were sampled during five selected nights with stratus/fog using tethered balloon soundings, drone profiling and radiosondes. Measurements took place at both coastal and inland sites as well as on different elevation levels in order to gather data on the spatial dynamics of the fog events. Fog droplet distribution was measured with a cloud droplet probe and liquid water content/liquid water flux estimated with a co-located sonic anemometer. The fog events exhibited considerable spatial and temporal variation between single events and within the network. Selected results from the IOP will be presented with the focus on the development of one fog event. [ABSTRACT FROM AUTHOR]