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Future characteristics of African Easterly Wave tracks

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Abstract

African Easterly Waves (AEWs) impact Sahel rainfall and tropical cyclones (TCs). Gaining a detailed understanding of AEW behavior within global climate models can yield higher confidence in Sahel rainfall and TC projected trends. This study uses a Hovmöller tracking technique to track AEWs at 850 hPa in three reanalysis products and simulations from the fifth phase of the Coupled Model Intercomparison Project (CMIP5). AEW track characteristics are compared between reanalysis and CMIP5 historical simulations to establish historical biases. The resolution of the models is found to be more important in reducing biases in northern track AEWs compared to southern track AEWs, but large biases exist in the genesis and dissipation of AEWs over land and ocean. The tracking technique was then applied to future simulations (Representative Concentration Pathway 8.5). Between 1980–2000 and 2080–2100, models project an average increase of 1.5 AEWs (range of − 5.0 to + 7.6 AEWs) in the northern track, including an increased frequency of higher intensity waves. Projections of southern track AEWs are more varied compared to the northern track, with a projected model mean decrease of 1.1 AEWs but with a range of − 11.5 to + 11.6 AEWs in individual models. There is an indication of a shift in seasonality of southern track AEWs towards the later summer months, which may impact the timing of the Atlantic TC season. No clear differences were found in projected changes between models characterized as having high or low biases in the historical period.

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Acknowledgements

The authors would like to thank two anonymous reviewers for insightful suggestions and comments that significantly enhanced this manuscript. We thank Alan Brammer for sharing the Hovmöller tracking algorithm and for his help in adjusting the settings for use within climate models. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP5, and thank the climate modeling groups for producing and making available their model output. For CMIP5, the U.S. Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. ERA-Interim data is provided courtesy of the European Centre for Medium-Range Weather Forecasts. The JRA-55 reanalysis data is contributed by the Japan Meteorological Agency. CFSR data is graciously supplied by the National Centers for Environmental Prediction.

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  1. School of Meteorology, University of Oklahoma, 120 David L. Boren Blvd., Norman, OK, 73072, USA

    Allison Lynn Brannan & Elinor R. Martin

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Correspondence to Allison Lynn Brannan.

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Brannan, A.L., Martin, E.R. Future characteristics of African Easterly Wave tracks. Clim Dyn 52, 5567–5584 (2019). https://doi.org/10.1007/s00382-018-4465-z

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