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Global Three-Dimensional Atmospheric Structure of the Atlantic Multidecadal Oscillation As Revealed by Two Reanalyses

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Global Three-Dimensional Atmospheric Structure of the Atlantic Multidecadal Oscillation As Revealed by Two Reanalyses Global Three-Dimensional Atmospheric Structure of the Atlantic Multidecadal Oscillation as Revealed by Two Reanalyses DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the Graduate School of The Ohio State University By Scott Seele Stuckman Graduate Program in Environmental Science The Ohio State University 2016 Dissertation Committee: Jialin Lin, Advisor Desheng Liu Bryan G. Mark Jeffrey C. Rogers Copyright by Scott Stuckman 2016 Abstract The Atlantic Multidecadal Oscillation (AMO) is one of the dominant multidecadal modes of the global climate system, shaping global and regional climate and extreme events through interactions with other climate modes operating on similar timescales. These include the Interdecadal Pacific Oscillation (IPO), which appears to have some intriguing connections with the AMO, and anthropogenic global warming (AGW), the detection and attribution of which can be confounded by the AMO. The relatively short observational record limits confident characterization of the AMO structure, contributing to the difficulty of climate models to more realistically simulate the AMO and compromising the accuracy of climate change projections on multidecadal timescales. Analyses of the AMO have been restricted primarily to the surface or certain regions exclusively during the extreme (warm and cool) phases, despite the existence of transition (cool-to-warm and warm-to-cool) phases for years to a decade or more. Extending the AMO characterization to the upper air and to the transition phases provides a more comprehensive assessment of the AMO life cycle important for understanding AMO dynamics and global teleconnections, separating the AMO-AGW signals, and providing a baseline for evaluating climate model simulations of the AMO. ii This study is a first documentation of the structure of the entire AMO life cycle, including extreme and transition phases, throughout the global troposphere. The extreme phase climate signature is constructed based on the strongest and most robust patterns identified by two methods (linear correlation and composite analyses), two reanalysis datasets (the National Centers for Environmental Prediction/National Center for Atmospheric Research and Twentieth Century Reanalysis, supplemented with precipitation data from the University of Delaware dataset) and data from two consecutive AMO cycles. The first characterization of the AMO transition phases uses a transition index based on the time derivative of AMO index. When trying to compare the zonal mean structure of AMO with the El Niño-Southern Oscillation (ENSO), a literature search showed the zonal mean structure of ENSO remained unpublished, despite the otherwise generally well-characterized horizontal structures. Therefore this study includes a seasonal analysis of the ENSO zonal mean structure during boreal winter (DJF) and summer (JJA). The AMO extreme phase is characterized by a blend of low and middle latitude centers of action, with the associated tilt of geopotential height anomaly patterns consistent with off-equatorial heating patterns generated by the Held idealized model. The surface climate signature is connected to the upper air with baroclinic vertical structure over the North Atlantic but barotropic structures elsewhere. The associated zonal mean circulation features three circulation cells globally with strong inter- hemispheric mixing that suggests the traditional view of the AMO involving a Northern- Southern Hemisphere asymmetry is accurate only near the surface. iii The AMO transition phase features a more equatorial-based climate signature and associated geopotential height anomaly patterns consistent with the Matsuno-Gill idealized model. The zonal mean circulation of the transition phases features six, rather than three, circulation cells globally. The only baroclinic structure, over North America, and several barotropic structures are positioned west of corresponding similar structures during the AMO extreme phase, suggesting an eastward evolution of climate anomalies as the AMO progresses from a cool-to-warm transition phase to warm phase. The Pacific- based climate signature resembles the IPO warm phase and it is proposed the AMO and IPO are different basin-wide expressions of a single multidecadal oscillation. The identification of an AMO transition phase climate signature distinct from the extreme phase suggests transition phases are not neutral and may provide an additional source of information for characterizing climate cycles. iv Dedication Dedicated to My Families and Friends, especially Mengling v Acknowledgements I would like to acknowledge my sincere gratitude and respect to my advisor, Dr. Jialin Lin, and committee members Dr. Desheng Liu, Dr. Bryan Mark and Dr. Jeffrey Rogers. vi Vita 1994....…………………...………………B.S. Microbiology and Psychology, B.A. English, The Ohio State University 2007 to present…………………………Graduate Fellow, Graduate Teaching Assistant, Instructor at OSU-Lima, Department of Geography, The Ohio State University Fields of Study Major Fields: Environmental Science vii Table of Contents Abstract .......................................................................................................................... ii Dedication .......................................................................................................................v Acknowledgements ....................................................................................................... vi Vita .............................................................................................................................. vii Table of Contents ........................................................................................................ viii List of Tables............................................................................................................... xiii List of Figures ..............................................................................................................xiv CHAPTER 1: LITERATURE REVIEW OF THE ATLANTIC MULTIDECADAL OSCILLATION (AMO) ..................................................................................................1 A. IDENTIFICATION AND DESCRIPTION .................................................................1 B. CLIMATE IMPACTS .................................................................................................7 C. OCEANIC STRUCTURE ......................................................................................... 10 D. ATMOSPHERIC STRUCTURE ............................................................................... 13 E. EXISTING THEORIES AND PACIFIC CONNECTION ......................................... 14 CHAPTER 2: DATA AND METHODS ........................................................................ 20 A. DATASETS AND VARIABLES .............................................................................. 20 viii B. METHODS ............................................................................................................... 24 B.1. AMO Index, Extreme Phase ........................................................................................... 24 B.2. AMO Index, Transition Phase ........................................................................................ 25 B.3. ENSO Index .................................................................................................................. 26 B.4. Data analysis ................................................................................................................. 27 B.4.a. Linear Correlation ................................................................................................... 27 B.4.b. Composite Analysis ................................................................................................ 28 C. PLOTS AND SCHEMATICS ................................................................................... 28 CHAPTER 3: AMO EXTREME PHASE NCEP/NCAR-LC RESULTS ........................ 33 A. HORIZONTAL MAPS ............................................................................................. 33 B. ZONAL MEAN CROSS-SECTION PLOTS ............................................................. 37 CHAPTER 4: AMO EXTREME PHASE COMPARISON OF METHODS ................... 53 NCEP/NCAR Linear Correlation and NCEP/NCAR Composite Analyses ..................... 53 A. HORIZONTAL PLOTS: NCEP/NCAR-LC and NCEP/NCAR-Comp ...................... 54 A.1. Sea Surface Temperature Anomalies (SSTAs), annual mean and seasonal...................... 54 Annual Mean .................................................................................................................... 54 Seasonal ............................................................................................................................ 55 NCEP/NCAR-LC, JJA and DJF ........................................................................................ 55 NCEP/NCAR-Comp, JJA and DJF .................................................................................... 55 Seasonal Summary ............................................................................................................ 56 A.2.Geopotential Height Anomalies 1000 mb, annual mean and seasonal .............................. 57 Annual Mean .................................................................................................................... 57 Seasonal ...........................................................................................................................
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