Dynamics, variability and bioclimatic effects of low clouds in western Central Africa

• Applicant: Professor Dr. Andreas Fink
• Subject Area: Atmospheric Science
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 431336378

Low-level clouds are key components of many regional climates but usually not well represented in numerical models and difficult to observe. Recently it has been shown that an extensive low-level cloud cover (LCC) develops during the June-September main dry season in western central Africa. Such a cloudy main dry season is unique in the moist tropics and likely explains the presence of the densest evergreen forests in this region. As paleoclimatic studies indicate a high instability, any reduction of the LCC due to climate change may represent a tipping-point for forest cover. Thus, there is an urgent need to better understand the presence, variability and bioclimatic effects of the LCC in western central Africa.To achieve these aims, an consortium composed of French, German and Gabonese partners has been built including meteorologists, climatologists, and experts in remote sensing and forests functioning. The meteorological processes controlling the LCC formation and dissolution at the diurnal scale will be studied along two ocean-land transects based on a synergistic analysis of historical in-situ data, a dedicated field campaign and atmospheric modelling activities. Results will be compared to a recently developed conceptual model for LCC over southern West Africa.The intraseasonal to interannual variability of LCC will be characterized from the analysis of long-term in-situ data and satellite estimates. Variations in the timing (seasonal onset and retreat, intraseasonal breaks) and in the inland extent of the LCC will be documented. Approaches based on weather types and equatorial waves will be used to understand intraseasonal variations of LCC. The impact of local to regional sea surface temperatures on the LCC development and its interannual variability will be assessed, coupling statistical analyses and dedicated sensitivity experiments with a regional climate model.Lastly the effect of low clouds on light and water availability on forest functioning will be explored based on in-situ measurements. Results will be compared with those obtained from pre-existing measurements in the northern Republic of Congo, where the dry season is sunny, and with outputs from a simple water balance model adapted to the region. Water balance analyses will reveal the compensation or amplification effects of rain vs. potential evapotranspiration, both modulated by the LCC, on the water deficit.Results from DYVALOCCA will lead to the first conceptual model for low-cloud formation and dissolution in western equatorial Africa and give direction for an evaluation of climate change simulations with a focus on the assessment of tipping-points for the evergreen forests in past and future climates.

• DFG Programme: Research Grants
• International Connection: France, Gabon
• Co-Investigator: Professor Dr. Peter Knippertz
• International Co-Applicant: Professor Dr. Jean-Damien Maloba Makanga
• Cooperation Partner: Dr. Nathalie Philippon