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Climatology of easterly wave disturbances over the tropical South Atlantic

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Abstract

A 21-year climatology of Easterly Waves Disturbances (EWDs) over the tropical South Atlantic (TSA) has been examined using data from the European Centers for Medium-Range Weather Forecasting interim reanalysis (ERAI) and satellite data. This includes the frequency distribution of EWDs and their interannual variability. The large-scale environment associated with EWDs has been investigated for the coastal region of Northeast Brazil (NEB) for the rainy (April–August) season using a composite analysis. EWDs were first identified in ERAI, resulting in 518 observed cases. These were found to show notable interannual variability with around 16–40 episodes each year and with an average lifetime of 4–6 days. Of the identified EWDs, 97% reached the coast of NEB, of which 64% were convective in nature and 14% moved across the NEB region and reached the Amazon. The annual occurrence of EWDs seems to be lower (higher) during El Niño (La Niña). The monthly occurrence of EWDs shows higher activity in the rainy season. EWDs originate in association with four types of system: cold fronts, convective clusters from the west coast of Africa, Intertropical Convergence Zone and Tropical Upper Tropospheric Cyclonic Vortices. The composite analysis indicates strong relative vorticity and divergence anomalies at low levels, as well as in the vertical profiles of relative humidity and vertical velocity (omega). The precipitation composites show that the EWDs propagate between the TSA and NEB and contribute at least 60% of the total rainfall over the east coast of NEB throughout the rainy season.

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Acknowledgements

This study was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico, CNPq (Grant nos. 143207/2009-1, 304298/2014-0 and 405664/2018-4) and Fundação de Amparo à Pesquisa do Estado de São Paulo, FAPESP, Brazil (Grant no. 08/58101-9). Pedro L. Silva Dias acknowledges the CNPq support through Grant no. 309395/2013-5. TA was also supported by the National Institute of Science and Technology for Climate Change Phase 2 under CNPq Grant 465501/2014-1, FAPESP Grant 2014/50848-9, and the National Coordination for High Level Education and Training (CAPES) Grant 16/2014. We thank the two reviewers for their very helpful comments which encouraged us to improve the analysis and present a comparison between subjective and objective tracking.

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Authors and Affiliations

  1. Institute of Atmospheric Sciences, Federal University of Alagoas, Maceió, Brazil

    Helber B. Gomes, Maria Cristina L. Silva & Heliofábio B. Gomes

  2. Department of Atmospheric Sciences, University of Sao Paulo, São Paulo, Brazil

    Tércio Ambrizzi & Pedro L. Silva Dias

  3. Capixaba Institute of Research, Technical Assistance and Rural Extension, Vitoria, Brazil

    Bruce F. Pontes da Silva

  4. Department of Meteorology, University of Reading, Reading, UK

    Kevin Hodges

  5. National Institute for Space Research, Cachoeira Paulista, Brazil

    Dirceu L. Herdies

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  1. Helber B. Gomes
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  2. Tércio Ambrizzi
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  3. Bruce F. Pontes da Silva
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  8. Heliofábio B. Gomes
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Correspondence to Helber B. Gomes.

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Gomes, H.B., Ambrizzi, T., Pontes da Silva, B.F. et al. Climatology of easterly wave disturbances over the tropical South Atlantic. Clim Dyn 53, 1393–1411 (2019). https://doi.org/10.1007/s00382-019-04667-7

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