Influence of El Niño Southern Oscillation on Tropical Eastern Pacific Mean State and Annual Cycle

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dc.contributor.advisorLi, Tim TL
dc.contributor.authorXue, Manrui
dc.contributor.departmentAtmospheric Sciences
dc.date.accessioned2024-03-11T22:20:03Z
dc.date.available2024-03-11T22:20:03Z
dc.date.issued2023
dc.description.degreePh.D.
dc.identifier.urihttps://hdl.handle.net/10125/107990
dc.subjectAtmospheric sciences
dc.subjectAir-sea Interactions
dc.subjectEl Niño Southern Oscillation
dc.subjectTropical Climate State
dc.titleInfluence of El Niño Southern Oscillation on Tropical Eastern Pacific Mean State and Annual Cycle
dc.typeThesis
dcterms.abstractThis dissertation explores the role of El Niño Southern Oscillation (ENSO) in modulating the mean state and annual cycle in the tropical eastern Pacific. In the first part, characteristics of the tropical climate mean state, annual cycle, and ENSO along with their associated essential mechanisms are introduced. On the one hand, the tropical Pacific mean state is critical to determine the preferred location of maximum sea surface temperature (SST) variability associated with ENSO. The eastern equatorial Pacific (EEP) permits an effective air-sea coupling on the interannual timescale, leading to ENSO growth. On the other hand, the impact of the mean state on ENSO can also be inferred from its phase locking to the annual cycle. To understand the capability of ENSO in modulating the climate state over the tropical eastern Pacific, the second part with observational analysis reveals that the linear ODH associated with ENSO has a considerable amplitude. However, its impact on the long-term SST is small due to changing signs between El Niño and La Nina phases. The nonlinear oceanic dynamic heating (ODH) exhibits a consistent sign during warm and cold episodes, but its weak amplitude limits its cumulative effect on the mean SST. As for thermodynamic processes, surface heat flux shows weak effects, with downward longwave radiative heating offsetting the net shortwave radiative heating. In the third part, the OGCM numerical experiments confirm the observational findings, indicating a modest rectification effect of ENSO on the mean state. In the fourth part, the modulation effect of ENSO on the annual cycle is investigated in the equatorial eastern Pacific by applying the analytical heat budget model. The analysis reveals that ENSO primarily modulates the annual cycle through ODH processes, including anomalous temperature advection by the mean vertical and meridional currents, anomalous zonal advection associated with the geostrophic current, and anomalous upwelling induced vertical advection. Thermodynamic processes induced by ENSO also exert modulation effects, with downward longwave radiative flux reinforcing the ocean dynamic impact and surface latent heat flux offsetting it. These ENSO impacts on the EEP annual cycle persist from fall to winter and weaken during spring. Overall, the rectification effect of ENSO on the mean SST in the tropical eastern Pacific is found to be moderate. However, ENSO exhibits a significant impact on the annual cycle, primarily through ODH processes. The relationships between ENSO, mean state, and annual cycle are analyzed using a quantitative diagnostic methodology.
dcterms.extent137 pages
dcterms.languageen
dcterms.publisherUniversity of Hawai'i at Manoa
dcterms.rightsAll UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
dcterms.typeText
local.identifier.alturihttp://dissertations.umi.com/hawii:11867

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Ph.D. - Atmospheric Sciences