Climatology and trends of downward shortwave radiation over Brazil

The solar downward shortwave radiation (DSWR) is the primary source of energy to Earth and a driving forcing for sensible/latent heat and water vapor fluxes over the terrestrial ecosystems and the atmosphere. Evaluation of the DSWR spatiotemporal patterns and trends is crucial to the understanding of weather and climate variability. In this study, DSWR is investigated over Brazil between 1980 and 2016 from contemporary state-of-the-art high resolution gridded datasets (observations, reanalyses and merged products). The results show an increase in both annual and seasonal DSWR for all regions of Brazil, with large changes over the northern, west central, and southeastern parts of the country. The European Centre for Medium-Range Weather Forecast (ERA5) reanalysis proves to be an excellent option for investigating DSWR across Brazil, matching the observed climatology trends well. The best results are identified for the northeastern and southeastern regions during the months of March April-May, and the poorest results for the center-west region during September-October-November. Changes in cloud cover (CC) are linked to changes in DSWR. Decadal fluctuations in CC are highly correlated with DSWR trends, with the strongest correlation (r = -0.89) in the southeast region, and weakest correlation (r = -0.37) in the north. We conclude that CC is a primary modulating factor of brightening across Brazil between 1980 and 2016. In a global context, our results agree with observations from other regions over the globe. Our results may indicate changes in the rainy seasons across Brazil, especially in the northeast. Future studies may use these results to further understand the impacts of brightening over Brazil on solar energy production and agriculture.

Automated summary

The study investigates the solar downward shortwave radiation (DSWR) over Brazil between 1980 and 2016, showing an increase in both annual and seasonal DSWR across all regions, particularly in the northern, west central, and southeastern parts. Changes in cloud cover (CC) are linked to DSWR changes and are considered a primary modulating factor for brightening in Brazil. The European Centre for Medium-Range Weather Forecast (ERA5) reanalysis is found to be a reliable option for investigating DSWR trends across Brazil.