Variability of cloud cover and cloud genera and its effects on shortwave solar radiation at J.G. Mendel station, northern Antarctic Peninsula

Cloud cover has the strongest influence on the variability of shortwave radiation flux (SR) among atmospheric factors. Depending on cloud genera, its properties, and its position relative to the Sun, SR intensity generally decreases due to absorption within cloud cover. However, certain cloud genera, mainly cirrus clouds, can enhance reflection, increasing the diffuse component of SR and, in some cases, leading to higher SR compared to clear-sky conditions. The effect of cloud cover on SR intensity was investigated at the Czech J. G. Mendel station, located in the northeastern part of the Antarctic Peninsula. This region is characterized by high cloud cover variability due to its position within the circumpolar trough of mean sea level pressure. Despite this, cloud and SR observations in Antarctica remain relatively limited. To fill this gap, summer experiment based on ground-based instrumentation and observation techniques was conducted between February and March 2026. All-sky images were obtained by Wx Labs camera every 5 minutes in HDR and automatic, long and short exposure to estimate cloud cover properties. The total cloud cover, layer cloud amount and cloud genera were also observed manually every hour from 7:00 to 21:00 local time. SR intensity was measured by Kipp‌&Zonen CMP-11 pyranometer at 10-min interval while clear-sky SR was estimated using Bird and Hulstrom radiative transfer model. To analyse effects of cloud cover and different cloud genera on SR variability, cloud modification factor (CMF) and cloud radiative effect (CRE) were calculated. Mean observed cloud cover was 60 %. Cloud genera with the most typical occurrence included cirrus, altocumulus, stratus and stratocumulus. The strongest attenuation of SR was associated with stratus clouds with typical CMF values between 0.1 and 0.5 and CRE values between -500 and -100 W.m^-2. In contrast, cirrus and cirrostratus clouds had the weakest impact on SR intensity and occasionally led to its enhancement. CMF values typically ranged from 0.8 to 1.1, while CRE values predominantly fell between -200 and 100 W.m^-2.