On the uncertainties and dynamics of Pacific interannual and decadal climate variability and climate change .

摘要

Tropical and extratropical Pacific decadal climate variability substantially impact physical and biological systems in the Pacific Ocean and strongly influence global climate through teleconnection patterns. Current understanding of Pacific decadal variability centers around three key modes of variability in the atmosphere and ocean: the El Nino-Southern Oscillation (ENSO), the Aleutian Low (AL), and the Pacific Decadal Oscillation (PDO). However, recent literature has highlighted the emerging roles of secondary modes of variability of the tropical and extratropical Pacific atmosphere and ocean that explain and drive other aspects of the climate system (i.e., the Central Pacific Warming (CPW) phenomenon, the North Pacific Oscillation (NPO), and the North Pacific Gyre Oscillation (NPGO)). This work analyzes the statistics and uncertainties behind Pacific interannual and decadal-scale climate variability in observations and models, and in particular, focuses on better understanding the importance of the roles of the CPW, NPO, and NPGO for predictability of global climate change.;The study begins by examining the dynamics of the NPO and its role in Pacific interannual and decadal climate variability. While the NPO is considered an intrinsic mode of atmospheric variability in the North Pacific, analyses demonstrate that the individual poles of the NPO behave differently. In particular, the subtropical node contains strong power at low frequencies (periods of 7-10 years), but not the northern pole. The source of this low-frequency variability in the southern node of the NPO is tropical Pacific sea surface temperature (SST) variability, as shown through a simple modeling experiment. NPO variability is further divided into: (a) a high-frequency component associated with stochastic forcing and the ENSO precursor signature; and (b) a low-frequency component directly connected with tropical Pacific SST forcing. The NPO-induced variability by the tropical Pacific SSTa is then integrated by the underlying ocean surface to form the decadal-scale NPGO signal. Thus, a new link between the CPW, the NPO, and the NPGO is formed, akin to the ENSO-AL-PDO framework.;The new framework of North Pacific decadal variability (NPDV) is then evaluated in 24 state-of-the-art coupled climate models used for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Results indicate that the PDO and NPGO do not exhibit significant changes in their spatial and temporal characteristics under projected greenhouse warming. However, the ability of the models to capture the dynamics associated with the PDO and NPGO is questionable. The temporal and spatial statistics of PDO and NPGO exhibit significant discrepancies from observations in their 20th century climate, especially for the NPGO. Furthermore, most models lack the proper connections between extratropical and tropical Pacific, for both the ENSO-AL-PDO and CPW-NPO-NPGO connections. In fact, the atmospheric teleconnections associated with the CPW phenomenon in some models have a significant projection on, and excite, the AL/PDO coupled mode instead.;The last part of the dissertation explores further the importance of the CPW mode by comparing and contrasting two popular paleoclimate SST anomaly reconstruction methods used for tropical Indo-Pacific SSTs. The first method exploits the high correlation between the canonical ENSO mode and tropical precipitation; the second method uses a multi-regression model that exploits the multiple modes of covariability between tropical precipitation and SSTs, including the CPW mode. The multi-regression approach demonstrates higher skill throughout the tropical Indo-Pacific than the first approach, illustrating the importance of including the CPW phenomenon in understanding past climates.