The influence of ENSO on the equatorial Atlantic precipitation through the Walker circulation in a CGCM
The link between El Niño/Southern Oscillation (ENSO) and the equatorial Atlantic precipitation during boreal spring (March–April–May) is explored using a coupled general circulation model (CGCM). Interannual variability of the equatorial Atlantic sea surface temperature (SST) in the CGCM is excluded by nudging the modeled SST toward the climatological monthly mean of observed SST in the equatorial Atlantic, but full air–sea coupling is allowed elsewhere. It is found that the equatorial Atlantic precipitation is reduced (increased) during El Niño (La Niña) in the case where the interannual variability of the equatorial Atlantic SST is disabled. The precipitation anomalies in the equatorial Atlantic during ENSO are not strongly associated with the meridional migration of the Atlantic inter-tropical convergence zone. We find the reduced precipitation in the equatorial Atlantic during El Niño is associated with an enhanced Atlantic Walker circulation characterized by strengthened low-level easterlies and anomalous dry, downward winds over the equatorial Atlantic, while the Pacific Walker circulation is weakened. The upper-level anomalous westerlies over the equatorial Atlantic are consistent with a Matsuno–Gill-type response to heating in the eastern equatorial Pacific. Our results of the CGCM experiments suggest that changes to the Walker circulation induced by ENSO contribute significantly to changes in precipitation over the equatorial Atlantic.
KeywordsITCZ ENSO Equatorial Atlantic Coupled general circulation model
All model experiments were performed on the Earth Simulator 2. We would like to thank two anonymous reviewers and the editor whose comments have led to a much improved manuscript.
- Roeckner E et al (2003) The atmospheric general circulation model ECHAM5, part I: model description, Max-Planck-Institut für Meteorologie Report 349Google Scholar
- Chiang JCH, Kushnir Y, Giannini A (2002) Deconstructing Atlantic intertropical convergence zone variability: influence of the local cross-equatorial sea surface temperature gradient and remote forcing from the eastern equatorial Pacific. J Geophys Res 107(D1). doi: 10.1029/2000JD000307 CrossRefGoogle Scholar
- Huang B, Schopf P, Pan Z (2002) The ENSO effect on the tropical Atlantic variability: a regionally coupled model study. Geophys Res Lett 29(21). doi: 10.1029/2002GL014872
- Levitus S (1982) Climatological Atlas of the World Ocean. NOAA Professional Paper, 13Google Scholar
- Madec G (2008) “NEMO ocean engine”. Note du Pole de modélisation, Institut Pierre-Simon Laplace (IPSL), France, No 27, ISSN No 1288-1619Google Scholar
- Matsuno T (1966) Quasi-geostrophic motions in the equatorial area. J Meteorol Soc Jpn 44:25–43Google Scholar
- Rodríguez-Fonseca B, Polo I, García-Serrano J, Losada T, Mohino E, Mechoso CR, Kucharski F (2009) Are Atlantic Niños enhancing Pacific ENSO events in recent decades? Geophys Res Lett 36:L20705. doi: 10.1029/2009GL040048
- Sasaki W, Doi T, Richards KJ, Masumoto Y (2014) Impact of the equatorial Atlantic sea surface temperature on the tropical Pacific in a CGCM. Clim Dyn. doi: 10.1007/s00382-014-2072-1
- Valcke S, Caubel A, Vogelsang R, Declat D (2004) OASIS3 ocean atmosphere sea ice soil user’s guide. Technical report TR/CMGC/04/68 CERFACS Toulouse FranceGoogle Scholar
- Wang C (2006) An overlooked feature of tropical climate: Inter-Pacific-Atlantic variability. Geophys Res Lett 33(12):L12702. doi: 10.1029/2006GL026324