Since 1980, a new type of ENSO, i.e., central Pacific (CP) ENSO, where sea surface temperature anomalies (SSTAs) are mainly located in the equatorial central Pacific, has been frequently observed. Several studies have documented and predicted a higher occurrence ratio of CP ENSO to eastern Pacific (EP) ENSO, where SSTAs mainly occur in the equatorial eastern Pacific, in a warming climate. Most studies centered on the difference between CP and EP ENSO have used traditional analysis methods, such as PCA/EOF analysis and regression, to define or differentiate the aforementioned two types of ENSO. However, the results obtained using these methods can only reveal accumulated spatial information which contributed most to the variance of the data, which is the usually the spatial information during the mature (peak) stage of ENSO; this spatial information is a static pattern and is not able to reveal sequential development of ENSO, which should be crucial for physical interpretations. In addition, although this spatial information in generally true for the entire temporal span, it is not necessarily true for any subperiods and thus not able to reveal any potential characteristic change of ENSO over time. In this study, an alternative Niño 3.4 index is defined to reflect only the interannual variability of equatorial Pacific SSTAs. Using this alternative index, we identify 28 El Niño events and 31 La Niña events. Then, we employ a newly developed analysis method, i.e., fast multidimensional ensemble empirical mode decomposition (FMEEMD), to extract the interannual spatiotemporal evolution of SSTAs to examine the developments of the identified ENSO events. All events are classified into four types of ENSO based on the interannual evolutions of SSTAs early in the development stage: (1) EP ENSO, (2) eastern-central Pacific (ECP) ENSO, (3) western-central Pacific (WCP) ENSO, and (4) mixed (MIX) ENSO. We apply the same method to analyze surface horizontal wind and thermocline depth data, and phase composite analyses on SSTAs, surface wind anomalies and thermocline depth anomalies are performed for each type of El Niño events. The results show four distinctive evolution patterns; it is found that La Niña events also have similar variation in the evolution patterns. The lower-frequency variability and change (decadal and longer time scales, including secular trend trend) in SSTAs, surface wind anomalies and thermocline depth anomalies are also examined. The secular trends show weak surface cooling over the central Pacific between 140°W and 160°W near the Equator, consistent with the anomalous wind divergence and thermocline shoaling in the same region. In response to decadal and lower-frequency oscillatory wind forcing, the background state of the thermocline is modified in a way that when western-central Pacific is dominated by shoaling (deepening), the eastern Pacific is dominated by deepening (shoaling). The combined effect of the secular trends and lower-frequency oscillatory variability is that for some decade(s), the thermocline depth is anomalously shallower (deeper) in the western-central Pacific region, while the thermocline depth is anomalously deeper (shallower) in the east. We suggest that this "seesaw" pattern in the depth anomalies across the Equator determines the evolving patterns of ENSO by hinder/facilitating the communication between ocean surface and subsurface, and thus modifying the effect of wave-associated thermocline displacements on SST change over the western-central Pacific. Additionally, for WCP and some of the MIX ENSO events, a potential SSTA precursor from Baja California/northeastern Pacific might be instrumental to the subsequent development, possibly by inducing zonal wind anomalies in the western Pacific. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the Doctor of Philosophy. / Spring Semester, 2015. / April 6, 2015. / ENSO, FMEEMD, SST / Includes bibliographical references. / Zhaohua Wu, Professor Directing Dissertation; Ming Ye, University Representative; Allan Clarke, Committee Member; Guosheng Liu, Committee Member; Philip Sura, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_252953 |
| Contributors | Feng, Jiaxin (authoraut), Wu, Zhaohua (professor directing dissertation), Ye, Ming (university representative), Clarke, Allan J. (committee member), Liu, Guosheng (committee member), Sura, Philip (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Earth, Ocean, and Atmospheric Science (degree granting department) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource (131 pages), computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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