A quasi-decadal cycle in Caribbean climate

Climatic variables in the period from 1951 to 2000 are analyzed across the tropics from the East Pacific to Africa. A quasi-decadal mode is isolated using singular value decomposition (SVD) applied to monthly smoothed and detrended rainfall, sea surface temperature (SST), sea level pressure (SLP), and 200 hPa zonal (U) wind anomalies. Seven-to 10-year cycles in Caribbean rainfall are revealed as the dominant mode (50% variance) and are found to be related to a mode of tropical variability that is distinct from previously known global signals. Sources of this signal include east Atlantic SST and the northern subtropical ridge, which modulate upwelling off Venezuela. SVD analysis of daily rainfall suggests interaction between annual and quasi-decadal signals, with northern summer convection as a driver. The second mode of Caribbean rainfall variability derives from the east Pacific El Nino Southern Oscillation (ENSO, 21% variance) that is expressed as an east-west dipole of convection across the Caribbean. Composite analysis of rainfall for high and low phases of the quasi-decadal cycle reveals a corresponding signal that extends from the eastern Pacific Ocean across the Caribbean and West Africa to India. The southern Hadley cell spins up during wet phase, and the ITCZ migrates northward. This hemispheric-scale anomaly brings pulses of convection to the Caribbean. Impacts of the quasi-decadal cycle on socioeconomic resources are investigated.