Teleconnection of ENSO extreme events and precipitation variability over the United States

This study describes a comprehensive investigation of the contiguous United States precipitation patterns in relation to the warm and cold phases of El Nin similar to o/southern Oscillation (ENSO) using a set of empirical and statistical analyses, such as harmonic analysis, annual cycle composites, and cross-correlation analysis. Monthly precipitation composites for the first harmonic, covering 24-month ENSO events, are formed for all climate divisions over the United States spanning up to 29 ENSO episodes. From the harmonic vectorial maps plotted on the study area, each vector reveals both intensity and temporal phase of the ENSO-related precipitation teleconnection, and the corresponding candidate and core regions are determined using a machine learning technique of Gaussian Mixture Model (GMM) based on magnitude and temporal phase of climate signal, and Ko center dot ppen climate classification. As a result of vectorial mapping, five core regions were designated as North-West region (NW), South-West region (SW), Middle-Inland region (MI), South-East region (SE), and North-East region (NE). During fall (0) to spring (+) seasons, the results of this analysis show below (above) normal precipitation response to the El Nin similar to o events at the NW region (SW, MI, SE, and NE regions), while the opposite patterns are detected for the cold phase of ENSO. The temporal consistency values were 0.72 to 0.86 (0.77 to 0.82), and spatial coherence values ranged from 0.96 to 0.99 (0.94 to 0.99) for the warm (cold) events. Comparative analyses of precipitation responses to both El Nin similar to o and La Nin similar to a events reveal the high significance level of the ENSO-related precipitation signals with an opposite tendency in monthly precipitation anomalies. Positive precipitation anomalies during the El Nin similar to o thermal forcing are more significant than negative precipitation departures during the La Nin similar to a events. Consequently, middle latitude precipitation responses to the El Nin similar to o/La Nin similar to a phenomena are detectable over the contiguous United States.