| Summary: | As multi-year (MY) ENSO events become increasingly frequent in the 21st century, our traditional understanding of ENSO climate impacts is no longer sufficient. This dissertation investigates global climate impacts and associated mechanisms induced by MY and single-year (SY) ENSOs using a 2,200-year CESM1 pre-industrial simulation, forced Atmospheric General Circulation Model (AGCM) experiments, and observational datasets. The study finds that the most distinct impacts produced by MY ENSO compared to SY ENSO occurred on Antarctic sea ice concentration (SIC) during austral winter and on surface air temperature (SAT) over middle-to-high latitude continents during boreal winter. Therefore, the first three chapters of the dissertation focus on these two particular regions to provide a comprehensive understanding of the distinct impacts and the teleconnection mechanisms that enable these effects. Furthermore, this dissertation study observes that the distinct climate impacts of MY ENSO extend beyond the surface to affect soil moisture variations over four specific land areas of the world. The differential soil moisture responses between MY and SY ENSO events are documented, and the associated impact mechanisms are identified in the fourth chapter of the dissertation.In the Southern Hemisphere during austral winter, MY La Niñas induce a zonal shift in the tri-polar SIC anomaly pattern typically induced by the SY La Niñas (Chapter 2). This shift arises from the unique pre-onset conditions associated with MY La Niñas that interact with the Indian Ocean and subsequently trigger atmospheric circulation modes that affect the Antarctic SIC anomaly pattern. The dissertation further explores the Antarctic SIC response to MY El Niños and finds that MY El Niño's impacts on Antarctic SIC are not symmetric to MY La Niña's impacts on Antarctic SIC (Chapter 3). The asymmetry arises from the different pre-onset conditions between the El Niño and La Niña phases of MY ENSO events, which enable MY La Niña to only produce unique Indian ...
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