How are rainforest photosynthesis and turbulent fluxes influenced by clouds? To what extent are clouds affected by local processes driven by rainforest energy, water and carbon fluxes? These interrelated questions were the main drivers of the intensive field experiment CloudRoots-Amazon22 which took place at the ATTO/Campina supersites in the Amazon rainforest during the dry season, in August 2022. CloudRoots-Amazon22 collected observational data to derive causal-effect relationships between processes occurring at the leaf-level up to canopy scales in relation to the diurnal evolution of the clear-to-cloudy transition. First, we studied the impact of cloud and canopy radiation perturbations on the sub-diurnal variability of stomatal aperture. We found an asymmetry modulated by clouds that favors photosynthesis in the morning. Second, we combined 1 Hz-frequency measurements of the stable isotopologues of carbon dioxide and water vapor with measurements of turbulence to determine carbon dioxide and water vapor sources and sinks within the canopy. Using scintillometer observations, we inferred 1-minute sensible heat flux that responded within minutes to the cloud passages. Third, collocated profiles of state variables and greenhouse gases enabled us to determine the role of clouds in vertical transport. We then inferred the area fraction of cloud cover and cloud mass flux to probe the need of collecting a comprehensive data set to establish causality between canopy and cloud processes and improve the representations in weather and climate models. These studies will be used to constrain numerical experiments carried out with large-eddy simulations to compare present and future scenarios influenced by warming and enhance carbon dioxide concentrations. Our findings contribute to advance our process knowledge of the coupling between cloudy boundary layers and primary carbon productivity of the Amazon rainforest.

J. Vilà-Guerau de Arellano
Meteorology and Air Quality Section
Wageningen University
The Netherlands
e-mail: Jordi.vila@wur.nl

This study investigates how moisture, clouds, and rainfall influence surface processes and ecosystems in the Atacama and Namib deserts—among Earth’s driest regions—by examining their atmospheric water cycles and contrasting topographies using advanced reanalysis, satellite data, and high-resolution simulations. Despite extreme aridity, both deserts receive moisture via fog, sporadic rainfall, and distinct transport mechanisms, such as the newly identified "Moist Northerlies" in the Atacama, which reveals Pacific-sourced moisture as a key driver, challenging prior assumptions of dominant Amazonian influences. These insights enhance our understanding of present-day desert climates, provide clues to past environmental conditions, and indicate how human-induced climate change may already be reshaping these hyperarid landscapes.

José M. Vicencio Veloso
PhD student @ University of Cologne
Institute of Geophysics and Meteorology
E-Mail: jvicenc1uni-koeln.de

This study examines nitrate deposits in the Atacama Desert, classified based on their geological context into alluvial fan deposits, vein deposits in massive rocks, vein deposits in alluvial fans, neptunic dykes, and lacustrine salt flat (salar) deposits. Isotope analysis confirms atmospheric nitrate deposition, with variations in their isotope composition values. The goal is to refine the current depositional model for these diverse nitrate deposits.

Camila Riffo Contreras
PhD student @ University of Cologne
Institute of Geology and Mineralogy
E-mail: criffocouni-koeln.de