Abstract
The processes that determine the seasonality of precipitation in the Congo Basin are examined using the atmospheric column moisture budget. Studying the fundamental determinants of Congo Basin precipitation seasonality supports process-based studies of variations on all time scales, including those associated with greenhouse gas-induced global warming. Precipitation distributions produced by the ERA5 reanalysis provide sufficient accuracy for this analysis, which requires a consistent dataset to relate the atmospheric dynamics and moisture distribution to the precipitation field. The Northern and Southern Hemisphere regions of the Congo Basin are examined separately to avoid the misconception that Congo Basin rainfall is primarily bimodal. While evapotranspiration is indispensable for providing moisture to the atmospheric column to support precipitation in the Congo Basin, its seasonal variations are small and it does not drive precipitation seasonality. During the equinoctial seasons, precipitation is primarily supported by meridional wind convergence in the moist environment in the 800–500 hPa layer where moist air flows into the equatorial trough. Boreal fall rains are stronger than boreal spring rains in both hemispheres because low-level moisture divergence develops in boreal spring in association with the developing Saharan thermal low. The moisture convergence term also dominates the moisture budget during the summer season in both hemispheres, with meridional convergence in the 850–500 hPa layer as cross-equatorial flow interacts with the cyclonic flow about the Angola and Sahara thermal lows. Winter precipitation is low because of dry air advection from the winter hemisphere subtropical highs over the continent.
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Availability of data and material
The ERA5 reanalysis data is freely available at https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era5.
Code availability
Figures for the analysis were produced using the GRaDs software freely available at http://cola.gmu.edu/grads/gadoc/gadoc.php.
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Acknowledgements
Support for this work through NSF Award #1939880 is gratefully acknowledged. We also greatly appreciate the efforts of the ERA5 team at the ECMWF, which made this analysis possible.
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The research was supported by the U.S. National Science Foundation Award #1939880.
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Cook, K.H., Vizy, E.K. Hydrodynamics of regional and seasonal variations in Congo Basin precipitation. Clim Dyn 59, 1775–1797 (2022). https://doi.org/10.1007/s00382-021-06066-3
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DOI: https://doi.org/10.1007/s00382-021-06066-3