Evolution of spatial patterns of subdecadal signals in annual rainfall in Southern South America and Southern and Central North America

Abstract

Spatial patterns at different timescales of anomaly of annual rainfall in southern South America and southern and central North America are composed of quasi-standing wavelike signals. Emphasis in this research is on subdecadal timescales, short-subdecadal (3 to 6 years) and long-subdecadal (6 to 10 years). Indications were found of the existence in most cases of a slow long-term evolution of spatial patterns superimposed on the within-cycle evolution. There are different types of spatial patterns or regimes. These regimes last several quasi-cycles. The change of regime is abrupt. Spatial patterns of anomaly of annual rainfall volume (ARV) in short-subdecadal timescales (average quasi-period is approximately 4 years) are under the influence of the short-subdecadal component of the Southern Oscillation. Correlation coefficient, although statistically significant, is not large. Long-subdecadal spatial patterns of anomaly of annual rainfall volume are strongly correlated with the long-subdecadal component of the Southern Oscillation Index (SOI). Average quasi-period of long-subdecadal fluctuations is 8 years. Finally, it was analyzed the partial contribution of fluctuations in different timescales to the total anomaly of annual rainfall during the 10 wettest years and the 10 driest years. Findings indicate that in southern South America and in southern and central North America, the contributions are in the order of decreasing magnitude: [<3 years), [3 to 6 years) and [>10 years), and [6 to 10 years).