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Title: Dynamics of tropical climate and high-latitude teleconnections during the Pliocene
Author: Bonham, Sarah
ISNI:       0000 0004 2717 975X
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2011
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The El Nino-Southern Oscillation (EN SO) in the tropical Pacific, is the most dominant mode of inter-annual variability in the climate system, with significant global impacts. It is therefore vital to understand how this phenomenon may respond to long-term changes in global mean temperature. One way to test this is to examine past warm climates such as the mid-Pliocene Warm Period (mPWP; ea. 3.26 to 3.0 Ma), when global mean temperature and atmospheric CO2 were higher than today, at levels similar to predictions for the late 21 st Century. MPWP proxy data suggest that the tropical Pacific was characterised by a reduced sea surface temperature (SST) gradient and permanent El Nino-like condition, which has implications for how ENSO may respond to anthropogenic forcing of the climate. ENSO dynamics during the mPWP were assessed through a series of model experiments using the Hadley Centre Coupled Climate Model. Tropical Pacific SST in the mPWP Control experiment was significantly warmer than the pre-industrial control with a low east-to-west gradient. Initial results showed that ENSO variability continued despite an El Nino-like mean state, with increased frequency and amplitude although fewer extreme events. The propagation of SST anomalies shifted towards the T-mode, similar to the pattern seen in the last 30 years of the instrumental record. Sensitivity experiments showed that the strongest contributors to changes in ENSO were lower orography over North and South America and higher CO2. In the extratropics, the presence of 'modern' teleconnection patterns in the mPWP simulation can be attributed to changes in boundary conditions, with large differences between modern and mPWP teleconnections. Finally, extending the control simulations by ~1,000 years, showed that these changes remain in the mid- Pliocene simulation, with reduced centennial variability compared to the pre-industrial control.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available