Interaction of the Monsoon and Pacific Trade Wind System at Interannual Time Scales. Part II: The Tropical Band

T. P. Barnett Climate Research Group, Scripps Jnslitul ion of Oceanography, University of California. San Diego, La Jolla, CA 92093

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Abstract

This is the second of three papers describing the interaction between the Monsoon System and the Pacific Trade Wind fields. The current study concentrates on the tropical band within ±30° of the equator, an earlier study (Part I) concentrated on the region ±10° of the equator.

The results of the current study show that the two wind systems are strongly coupled across the tropical latitudes at interannual time scales with coherent variations apparent in the surface wind field from Africa to South America. It appears that the equatorial regions are coupled most strongly to the Southern Hemisphere. The couplings and interaction between the two systems are dependent on the phase of the annual cycle. The apparent temporal bimodality observed in Part I in the near-equatorial band is no longer seen when the full tropical band is analyzed. There is only a slight preference in the wind system for anomalous convergence over Indonesia. The eastward propagation of anomalous zonal wind in the equatorial region is still evident in this analysis.

The results suggest that the atmosphere changes its state in a way that is only broadly related to changes in the sea surface temperature (SST) in the central Pacific, Thus it appears that mechanisms other than those associated with the Pacific SST may be required to explain much of the variability described in this paper. It also appears that the climatic signal being described here is but part of an even larger mode of climatic variability.

Abstract

This is the second of three papers describing the interaction between the Monsoon System and the Pacific Trade Wind fields. The current study concentrates on the tropical band within ±30° of the equator, an earlier study (Part I) concentrated on the region ±10° of the equator.

The results of the current study show that the two wind systems are strongly coupled across the tropical latitudes at interannual time scales with coherent variations apparent in the surface wind field from Africa to South America. It appears that the equatorial regions are coupled most strongly to the Southern Hemisphere. The couplings and interaction between the two systems are dependent on the phase of the annual cycle. The apparent temporal bimodality observed in Part I in the near-equatorial band is no longer seen when the full tropical band is analyzed. There is only a slight preference in the wind system for anomalous convergence over Indonesia. The eastward propagation of anomalous zonal wind in the equatorial region is still evident in this analysis.

The results suggest that the atmosphere changes its state in a way that is only broadly related to changes in the sea surface temperature (SST) in the central Pacific, Thus it appears that mechanisms other than those associated with the Pacific SST may be required to explain much of the variability described in this paper. It also appears that the climatic signal being described here is but part of an even larger mode of climatic variability.

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