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Impacts of TC and MJO on El Nino Evolution: Revisiting the Formation Mechanism of 1986/87-1987/88 Two-Year El Nino
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DOI：10.1175/JCLI-D-25-0264.1.png)
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Abstract
En 中文
Canonical El Ni & ntilde;o (EN) events typically peak in boreal winter and then rapidly decay in the ensuing months, transitioning to a La Ni & ntilde;a (LN) event or a neutral condition by the following winter. Strikingly, an EN event that peaked in the 1986/87 boreal winter unexpectedly persisted into the following year, generating a rare 2-yr consecutive EN event. However, the 1986/87-1987/88 2-yr EN event receives little attention. This study reveals that this 2-yr EN event encompasses some critical yet commonly overlooked processes for the formation and development of an EN event. Specifi-cally, the high-frequency (HF) westerly wind anomalies, induced by the tropical cyclones (TCs) and Madden-Julian oscillation (MJO) events, were the pivotal drivers of the unexpected reignition in the second year. During the 1986/87 winter, the unexpected emergence of four TCs induced vigorous westerly wind anomalies over the western equatorial Pacific (WEP), disrupting the anomalous anticyclone circulation over the western North Pacific anticyclone (WNPAC) and the associated easterly wind anomalies over the WEP that were anticipated during the 1986/87 winter. Such unexpected westerly wind anomalies helped maintain the EN warming through December 1986-February 1987. Subsequently, a series of HF westerly wind anomalies, induced by TCs and MJO events in April, May, and July 1987, reinvigorated the waning warming, pulling it back into a fledged EN event by the end of 1987. Gaining insights into the formation mechanism behind this unique 2-yr EN event can deepen our understanding of El Ni & ntilde;o-Southern Oscillation (ENSO) dynamics and provide implications for enhancing the accuracy of EN prediction.
Keywords:
Atmosphere-ocean interaction
El Ni & ntilde
o
Wind stress
ENSO
Madden-Julian oscillation
Tropical cyclones
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4
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1.4W
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5.9W
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