The temporal evolution of El Niño and La Niña varies greatly from event to event. To understand the dynamical processes controlling the duration of El Niño and La Niña events, a suite of observational data and a long control simulation of the Community Earth System Model, version 1, are analyzed. Both observational and model analyses show that the duration of El Niño is strongly affected by the timing of onset. El Niño events that develop early tend to terminate quickly after the mature phase because of the early arrival of delayed negative oceanic feedback and fast adjustments of the tropical Atlantic and Indian Oceans to the tropical Pacific Ocean warming. The duration of La Niña events is, on the other hand, strongly influenced by the amplitude of preceding warm events. La Niña events preceded by a strong warm event tend to persist into the second year because of large initial discharge of the equatorial oceanic heat content and delayed adjustments of the tropical Atlantic and Indian Oceans to the tropical Pacific cooling. For both El Niño and La Niña, the interbasin sea surface temperature (SST) adjustments reduce the anomalous SST gradient toward the tropical Pacific and weaken surface wind anomalies over the western equatorial Pacific, hastening the event termination. Other factors external to the dynamics of El Niño–Southern Oscillation, such as coupled variability in the tropical Atlantic and Indian Oceans and atmospheric variability over the North Pacific, also contribute to the diversity of event duration.
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Long Island Sound temperature variability and its associations with the ridge–trough dipole and tropical modes of sea surface temperature variability
Abstract. Possible mechanisms behind the longevity of intense Long IslandSound (LIS) water temperature events are examined using an event-basedapproach. By decomposing an LIS surface water temperature time series intonegative and positive events, it is revealed that the most intense LIS watertemperature event in the 1979–2013 period occurred around 2012, coincidingwith the 2012 ocean heat wave across the Mid-Atlantic Bight. The LIS eventsare related to a ridge–trough dipole pattern whose strength and evolution canbe determined using a dipole index. The dipole index was shown to be stronglycorrelated with LIS water temperature anomalies, explaining close to 64 %of cool-season LIS water temperature variability. Consistently, a majordipole pattern event coincided with the intense 2012 LIS warm event. Acomposite analysis revealed that long-lived intense LIS water temperatureevents are associated with tropical sea surface temperature (SST) patterns.The onset and mature phases of LIS cold events were shown to coincide withcentral Pacific El Niño events, whereas the termination of LIS coldevents was shown to possibly coincide with canonical El Niño events or ElNiño events that are a mixture of eastern and central Pacific El Niñoflavors. The mature phase of LIS warm events was shown to be associated withnegative SST anomalies across the central equatorial Pacific, though theresults were not found to be robust. The dipole pattern was also shown to berelated to tropical SST patterns, and fluctuations in central Pacific SSTanomalies were shown to evolve coherently with the dipole pattern and thestrongly related East Pacific–North Pacific pattern on decadal timescales.The results from this study have important implications for seasonal anddecadal prediction of the LIS thermal system.
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- Award ID(s):
- 1822015
- NSF-PAR ID:
- 10164903
- Date Published:
- Journal Name:
- Ocean Science
- Volume:
- 15
- Issue:
- 1
- ISSN:
- 1812-0792
- Page Range / eLocation ID:
- 161 to 178
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/os-15-161-2019
