| Autor: |
Johnson, N. C., L'Heureux, M. L., Chang, C.‐H., Hu, Z.‐Z. |
| Předmět: |
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| Zdroj: |
Geophysical Research Letters; Oct2019, Vol. 46 Issue 20, p11416-11425, 10p |
| Abstrakt: |
The recent borderline El Niño events of 2014/2015 and 2018/2019 provided operational centers with unique challenges because of the apparent absence of typical coupling between the tropical atmosphere and ocean before onset. The mismatch between atmosphere and ocean raises questions about its causes and predictability. Here we analyze observational data since 1979 to show that a sea surface temperature pattern characterized by an anomalous gradient in the western and central equatorial Pacific played a critical role in inhibiting the expected onset of central tropical Pacific deep convection during these events. This sea surface temperature pattern, which produces an atmospheric response that opposes the response to elevated eastern Pacific sea surface temperatures, has become more prevalent over the past 40 years. Plain Language Summary: The El Niño–Southern Oscillation, a naturally occurring climate pattern that impacts most of the planet, develops through interactions between the tropical atmosphere and ocean. During the development of recent borderline El Niño episodes in 2014 and 2018, however, the tropical atmosphere failed to behave in a typical manner despite conducive oceanic conditions, providing forecasters with challenges in classifying the events and in forecasting their future development and global impacts. A key question is whether forecasters could have anticipated the atypical tropical atmospheric pattern or if it was the result of chaotic weather variability that could not have been forecast with much advance warning. Here we analyze 40 years of observational data and find that a sea surface temperature pattern in the western and central equatorial Pacific offsets the typical El Niño impacts during these events. This sea surface temperature pattern has become more prevalent over the past 40 years, which indicates a recent tendency for El Niño tropical atmospheric conditions to be weaker relative to past episodes. The identification of this characteristic sea surface temperature pattern provides hope that forecasters may be able to anticipate when it may reinforce or offset the atmospheric conditions associated with the El Niño–Southern Oscillation. Key Points: Tropical Pacific zonal sea surface temperature gradients modulate tropical atmospheric patterns traditionally associated with El NiñoAn anomalously strong tropical Pacific zonal sea surface temperature gradient delayed the occurrence of recent weak El Niño eventsThe zonal sea surface temperature gradient and associated atmospheric variables have strengthened significantly since 1979 [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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