[1] In this study, evidence is presented from statistical analyses, numerical model experiments, and case studies to show that the impact on US winter temperatures is different for the different types of El Niño. While the conventional Eastern-Pacific El Niño affects winter temperatures primarily over the Great Lakes, Northeast, and Southwest US, the largest impact from Central-Pacific El Niño is on temperatures in the northwestern and southeastern US. The recent shift to a greater frequency of occurrence of the CentralPacific type has made the Northwest and Southeast regions of the US most influenced by El Niño. It is shown that the different impacts result from differing wave train responses in the atmosphere to the sea surface temperature anomalies associated with the two types of El Niño.
In what is arguably one of the most dramatic phenomena possibly associated with climate change or natural climate variability, the location of El Niño has shifted more to the central Pacific in recent decades. In this study, we use statistical analyses, numerical model experiments and case studies to show that the Central-Pacific El Niño enhances the drying effect, but weakens the wetting effect, typically produced by traditional Eastern-Pacific El Niño events on the US winter precipitation. As a result, the emerging Central-Pacific El Niño produces an overall drying effect on the US winter, particularly over the Ohio-Mississippi Valley, Pacific Northwest and Southeast. The enhanced drying effect is related to a more southward displacement of tropospheric jet streams that control the movements of winter storms. The results of this study imply that the emergence of the Central-Pacific El Niño in recent decades may be one factor contributing to the recent prevalence of extended droughts in the US.
Extreme precipitation events, commonly associated with “Atmospheric Rivers,” are projected to increase in frequency and severity in western North America; however, the intensity and landfall position are difficult to forecast accurately. As the isotopic signature of precipitation has been widely utilized as a tracer of the hydrologic cycle and could potentially provide information about key physical processes, we utilize both climate and precipitation isotope data to investigate these events in California from 2001 to 2011. Although individual events have extreme isotopic signatures linked to associated circulation anomalies, the composite across all events unexpectedly resembles the weighted mean for the entire study period, reflecting diverse moisture trajectories and associated teleconnection phases. We document that 90% of events reaching this location occurred during the negative Arctic Oscillation, suggesting a possible link with higher‐latitude warming. We also utilize precipitation data of extreme precipitation events across the entire western U.S. to investigate the relationships between key tropical and Arctic climate modes known to influence precipitation in this region. Results indicate that the wettest conditions occur when the negative Arctic Oscillation, negative Pacific/North American pattern, and positive Southern Oscillation are in sync and that precipitation has increased in the southwestern U.S. and decreased in the northwestern U.S. relative to this phase combination's 1979–2011 climatology. Furthermore, the type of El Niño–Southern Oscillation event, Central Pacific or Eastern Pacific, influences the occurrence, landfall location, and isotopic composition of precipitation.
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