Ancient Analogs of ENSO-Like Moisture Anomaly Patterns Across North America
Tuesday, 16 December 2014: 9:15 AM
A tripole-like structure tends to develop in the latitudinal distribution of seasonal drought and wetness across North America during El Nino and La Nina extremes. Composite maps of instrumental and tree-ring reconstructed moisture indices during El Nino extremes nearly mirror the teleconnected moisture patterns during La Nina extremes, but the signs of the regional anomalies are reversed. During El Nino events wetness tends to prevail over the southwestern U.S. and northern Mexico, simultaneously with drought over Central America and the Pacific Northwest. Map congruence analysis was used to measure the similarity between the composite moisture anomaly map during 10 El Nino extremes and the continent-wide pattern of tree-ring reconstructed moisture during each year from 1400 to 2005. Map congruence was also computed using the composite moisture anomalies during La Nina extremes as the target (ENSO extremes defined using the extended Multivariate ENSO Index). The two congruence time series (El Nino vs La Nina-like) are far from the perfect inverse of one another (r = -0.36; p < 0.001; 1400-1979), but sub-decadal smoothing reveals interesting episodes of continental scale structure in the moisture field that may have arisen from multi-year cool and warm ENSO extremes over the past 600-years.