ALBERT

Description: Clouds and seasonal variations are key parameters that play a crucial role in the albedo dynamics of forest canopies that ultimately impact the surface radiation budget and long-term climate trends. Additionally, the occurrence of natural extreme events such as prolonged dry spells or floods may further alter the feedback loop between the forest canopy and the Earth’s energy radiation budget. Limitations such as low spatio-temporal resolution in case of satellite-based analyses and lack of continuous in-situ observations hinder efforts to quantify the local effects of forest-cloud dynamics on climatic trends. To this effect, we have established a long-term autonomous measurement system on a crane within the Leipzig floodplain area, Leipzig, Germany, operational since June 2, 2021. We present a comparative analysis of the spectral forest canopy albedo as a function of cloud fraction for two consecutive years with different climatic conditions: year 2021 with conditions close to the climatological mean and year 2022 with a close to eight weeks long dry spell during summer months. The spectral irradiance is recorded daily between 12 Noon and 1 P.M. local time and the cloud fraction is obtained from the Tropomi sensor onboard the Sentinel-5P satellite. The results indicate a substantial dependence of the spectral canopy albedo on the cloud fraction and an overall increased canopy albedo for the year 2022 compared to the year 2021, which shows the biophysical impact of clouds on forests and the feedback mechanism of forest-cloud dynamics following an extreme event.