The Impacts of Inter-El Nino Variability on the Tropical Atlantic and Northeast Brazil Climate

Author(s)

Rodrigues, Regina R. ^[1] ; Haarsma, Reindert J. ^[2] ; Campos, Edmo J. D. ^[1] ; Ambrizzi, Tercio ^[3]

Affiliation

^[1] Univ Sao Paulo, Oceanog Inst, Sao Paulo - Brazil

^[2] Royal Netherlands Meteorol Inst, NL-3730 AE De Bilt - Netherlands

^[3] Univ Sao Paulo, Dept Atmospher Sci, Sao Paulo - Brazil

• Document type: Journal article
• Source: Journal of Climate; v. 24, n. 13, p. 3402-3422, JUL 2011.
• Web of Science Citations: 48

Abstract

In this study, observations and numerical simulations are used to investigate how different El Nino events affect the development of SST anomalies in the Atlantic and how this relates to the Brazilian northeast (NE) precipitation. The results show that different types of El Nino have different impacts on the SST anomalies of the equatorial and tropical South Atlantic but a similar SST response in the tropical North Atlantic. Strong and long (weak and short) El Ninos with the main heating source located in the eastern (central) Pacific generate cold (warm) anomalies in the cold tongue and Benguela upwelling regions during boreal winter and spring. When the SST anomalies in the eastern equatorial and tropical South Atlantic are cold (warm), the meridional SST gradient across the equator is positive (negative) and the ITCZ is not allowed (allowed) to move southward during the boreal spring; as a consequence, the precipitation is below (above) the average over the NE. Thus, strong and long (weak and short) El Ninos are followed by dry (wet) conditions in the NE. During strong and long El Ninos, changes in the Walker circulation over the Atlantic and in the Pacific-South Atlantic (PSA) wave train cause easterly wind anomalies in the western equatorial Atlantic, which in turn activate the Bjerknes mechanism, establishing the cold tongue in boreal spring and summer. These easterly anomalies are also responsible for the Benguela upwelling. During short and weak El Ninos, westerly wind anomalies are present in the western equatorial Atlantic accompanied by warm anomalies in the eastern equatorial and tropical South Atlantic; a positive phase of the South Atlantic dipole develops during boreal winter. The simulations highlight the importance of ocean dynamics in establishing the correct slope of the equatorial thermocline and SST anomalies, which in turn determine the correct rainfall response over the NE. (AU)

• FAPESP's process: 07/03279-5 - The role of variability in the Tropical and South Atlantic in the climate of the Northeast of Brazil in El Niño years
• Grantee: Regina Rodrigues Rodrigues
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 08/01565-3 - The role of the tropical and south Atlantic variability on the northeast Brazil climate in El Niño
• Grantee: Regina Rodrigues Rodrigues
• Support Opportunities: Scholarships abroad - Research