Mean kinematic characteristics of synoptic easterly disturbances over the Atlantic

• Published in: Advances in Atmospheric Sciences
• Main Authors: Diedhiou, Arona, Machado, Luiz A. T., Laurent, Henri
• Other Authors: Laboratoire d'étude des transferts en hydrologie et environnement (LTHE), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut National Polytechnique de Grenoble (INPG)-Centre National de la Recherche Scientifique (CNRS), Center for Weather Forecasting and Climate Studies São Paulo (CPTEC), Instituto Nacional de Pesquisas Espaciais (INPE), the CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico, Brazil) / IRD (Institut de Recherche pour le Développement, France) cooperative project (Grant No. 910153/98-1); the FAPESP (Fundaçao de Amparo à Pesquisa do Estado de Sao Paulo) (Grant No.99/06045)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2010
• Subjects: synoptic activity; African easterly waves; tropical Atlantic; North Atlantic
• Online Access: https://insu.hal.science/insu-00412021; https://doi.org/10.1007/s00376-009-9092-5

International audience This study investigates the mean kinematic characteristics of the tropical Atlantic easterly disturbances in January–March (JFM), April–June (AMJ), July–September (JAS) and October–December (OND) from 1968–1998. For each season, the preferential tracks of these disturbances in the 3–10-day band periods were computed and spatialized, as well as their associated wavelength, velocity and main period, which lies between 3–5 days and between 6–9 days depending on the track and the season. Two main tracks are highlighted over the Atlantic Ocean. During OND and JFM these two tracks are well separated and located in each hemisphere around 15°S and 12.5°N. From AMJ to JAS these tracks migrate northward; in JAS, they merge into one over the northern tropical Atlantic along 17.5°N. The associated wavelength fields exhibit a meridional gradient, with large wavelengths (greater than 4000 km) around the equator, between 5°N and 5°S, and smaller wavelengths outside of this latitude band (between 2500–3500 km). The phase speed is also found to exhibit poleward decreasing values from 12–6 m s−1. Over the north Atlantic track, 6–9-day disturbances were found to occur from January to May and approximately from October to December. From June to September, the 3–5-day waves dominate the synoptic activity. Over the south Atlantic track, between May and August the synoptic variability is mainly explained by the 3–5-day disturbances but from January to April and from September to December both 3–5-day waves and 6–9-day waves can occur.