Pacific Teleconnections Dynamics in a Changing Climate: Theories, Observations, and Models

By: 
Youngji Joh
Time: 
Thursday, September 3, 2020 - 1:00pm
Place: 
https://bit.ly/3gmJFAB
Committee: 
Dr. Emanuele Di Lorenzo (Advisor), Dr. Taka Ito, Dr. Jie He, Dr. Antonietta Capotondi (NOAA/ESRL/PSD/CIRES), and Dr. Benjamin Kirtman (U. Miami)
Summary: 

Pacific climate and weather extreme events such as heatwaves, drought, and hydrological extremes are dynamically linked large-scale climate variability. This work aims at improving the current understanding of the role of climate coupling within the Pacific system and investigating their changes to anthropogenic forcing. Using observational reanalyses and global climate model ensemble, we show that prolonged multi-year marine heatwaves are linked to the dynamics of the two dominant modes of winter sea surface temperature variability in the North Pacific, the Pacific Decadal Oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO). Specifically, we find a significant correlation between winter NPGO anomalies and the following winter PDO arising from extratropical/tropical teleconnections. Our work reports that marine heatwaves in the North Pacific are becoming stronger in amplitude with a larger area as well as more persistent under anthropogenic forcing. We next propose that a preferred decadal timescale in the Kuroshio Extension (KE) may arise from the interaction between the KE and the extratropical/tropical Pacific variability. We show that changes in the KE states apply a persistent downstream atmospheric response that projects on the atmospheric forcing of the Pacific Meridional Modes (PMM) over 9 months timescales. Subsequently, the PMM energizes the central Pacific El Niño Southern Oscillation (CP-ENSO), which in turn excites oceanic Rossby waves in the central North Pacific that propagate westward changing the KE (~3 years). We provide a cross-correlation function between the KE and the PMM/CPENSO indices exhibiting a significant sinusoidal shape corresponding to a preferred spectral power at decadal timescales (~10 years). Finally, through combining observations, numerical simulations, and empirical dynamical models, we confirm that KE and the tropical Pacific are dynamically linked, especially during the recent decades. The statistical differences between the KE properties before and after the mid-1980 suggest nonstationary decadal KE variability. Moreover, the KE interaction with the CP-ENSO has been increasing in a changing climate. We discuss the link of the enhanced extratropical-tropical coupled KE system with the potential impact of anthropogenic forcing and changes in the KE downstream response with stronger subtropical wind forcing and subsequent favorable conditions for Pacific Meridional modes and CP-ENSO.