Structure of interannualto-decadal climate variability in the tropical Atlantic.

• Main Authors: Alfredo Ruiz-Barradas, AND James A Carton, Sumant Nigam
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2000
• Subjects: North Atlantic; North Atlantic oscillation
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1081.6493; http://users.clas.ufl.edu/prwaylen/Mweru/ruiz%20barradas%202003.pdf

ABSTRACT A search for coupled modes of atmosphere-ocean interaction in the tropical Atlantic sector is presented. Previous studies have provided conflicting indications of the existence of coupled modes in this region. The subject is revisited through a rotated principal component analysis performed on datasets spanning the 36-yr period 1958-93. The analysis includes four variables, sea surface temperature, oceanic heat content, wind stress, and atmospheric diabatic heating. The authors find that the first rotated principal component is associated with fluctuations in the subtropical wind system and correlates with the North Atlantic oscillation (NAO), while the second and third modes, which are the focus of interest, are related to tropical variability. The second mode is the Atlantic Niño mode with anomalous sea surface temperature and anomalous heat content in the eastern equatorial basin. Wind stress weakens to the west of anomalously warm water, while convection is shifted south and eastward. Surface and upper-level wind anomalies of this mode resemble those of El Niño-Southern Oscillation (ENSO) events. When the analysis is limited to boreal summer, the season of maximum amplitude, the Atlantic Niño mode explains 7.5% of the variance of the five variables. Thermodynamic air-sea interactions do not seem to play a role for this mode. The third mode is associated with an interhemispheric gradient of anomalous sea surface temperature and a dipole pattern of atmospheric heating. In its positive phase anomalous heating occurs over the warmer Northern Hemisphere with divergence aloft shifting convection to the north and west of the equator and intensifying the subtropical jet stream, while descending motion occurs on the western side of the Southern Hemisphere. Surface and subsurface structures in the ocean are controlled by surface winds. This interhemispheric mode is strongest in boreal spring when it explains 9.1% of the combined variance of the five variables. Thermodynamic air-sea interactions do seem to ...