Impact of ENSO‐like tropical Pacific decadal variability on the relative frequency of El Niño and La Niña events
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Impact of ENSO‐like tropical Pacific decadal variability on the relative frequency of El Niño and La Niña events

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  • Journal Title:
    Geophysical Research Letters
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    Observational and modeling studies show that the relative frequency of El Nino and La Nina varies in association with El Nino-Southern Oscillation (ENSO)-like tropical Pacific decadal variability (TPDV), but the causality of the linkage remains unclear. This study presents evidence that ENSO-like TPDV affects the frequency of ENSO events, particularly of El Nino, through a set of climate model experiments. During the positive phase of TPDV, tropical Pacific warming relative to the Indian and Atlantic Oceans increases the occurrence of anomalous westerly winds over the western equatorial Pacific in late boreal winter-spring, triggering more El Nino and fewer La Nina events. The opposite happens for the negative TPDV phase. The La Nina frequency is also influenced by oceanic adjustments following El Nino, which tends to counteract the effect of wind changes. The mean state control of ENSO offers a potential opportunity for decadal predictions of climate extremes. Plain Language Summary Previous research shows that El Nino occurs more frequently than La Nina during decades when the tropical Pacific becomes warmer across the basin, and vice versa. However, it is not clear whether changes in the baseline conditions of the tropical Pacific are the cause or the effect of changes in the frequency of El Nino and La Nina. Using a set of climate model experiments, this study presents the evidence for the former case. In particular, basin-wide warming and cooling of the tropical Pacific are shown to strongly affect the frequency of El Nino by modulating surface winds over the western equatorial Pacific, which play an important role in triggering El Nino. The baseline conditions have less impact on the frequency of La Nina, for which slow oceanic processes are also important. These results may help to predict long-term changes in climate extremes over the regions strongly affected by El Nino and La Nina.
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  • Source:
    Geophysical Research Letters,47,e2019GL085832.
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    Submitted
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