Dynamics of the Tropical Atmosphere and Oceans: (Advancing Weather and Climate Science)

This book presents a unique and comprehensive view of the fundamental dynamical and thermodynamic principles underlying the large circulations of the coupled ocean-atmosphere system Dynamics of The Tropical Atmosphere and Oceans provides a detailed description of macroscale tropical circulation systems such as the monsoon, the Hadley and Walker Circulations, El Niño, and the tropical ocean warm pool. These macroscale circulations interact with a myriad of higher frequency systems, ranging from convective cloud systems to migrating equatorial waves that attend the low-frequency background flow. Towards understanding and predicting these circulation systems. A comprehensive overview of the dynamics and thermodynamics of large-scale tropical atmosphere and oceans is presented using both a “reductionist” and “holistic” perspectives of the coupled tropical system. The reductionist perspective provides a detailed description of the individual elements of the ocean and atmospheric circulations. The physical nature of each component of the tropical circulation such as the Hadley and Walker circulations, the monsoon, the incursion of extratropical phenomena into the tropics, precipitation distributions, equatorial waves and disturbances described in detail. The holistic perspective provides a physical description of how the collection of the individual components produces the observed tropical weather and climate. How the collective tropical processes determine the tropical circulation and their role in global weather and climate is provided in a series of overlapping theoretical and modelling constructs. The structure of the book follows a graduated framework. Following a detailed description of tropical phenomenology, the reader is introduced to dynamical and thermodynamical constraints that guide the planetary climate and establish a critical role for the tropics. Equatorial wave theory is developed for simple and complex background flows, including the critical role played by moist processes. The manner in which the tropics and the extratropics interact is then described, followed by a discussion of the physics behind the subtropical and near-equatorial precipitation including arid regions. The El Niño phenomena and the monsoon circulations are discussed, including their covariance and predictability. Finally, the changing structure of the tropics is discussed in terms of the extent of the tropical ocean warm pool and its relationship to the intensity of global convection and climate change. Dynamics of the Tropical Atmosphere and Oceans is aimed at advanced undergraduate and early career graduate students. It also serves as an excellent general reference book for scientists interested in tropical circulations and their relationship with the broader climate system.

Table of Contents:
Preface xvii Acknowledgments xix Abbreviations xxiii 1 Climatology of the Tropical Atmosphere and Upper Ocean 1 1.1 The Growth of Tropical Meteorology 1 1.2 Seasonal Characteristics 4 1.3 Macro-Scale Circulations 16 1.4 A Myriad of Variability 24 Notes 34 2 Hydrological and Heat Exchange Processes 37 2.1 Water on Earth 38 2.2 Thermodynamics of Water and Earth’s Climate 39 2.3 Water and the Tropical System 43 2.4 Buoyancy, Differential Buoyancy, and the Generation of Horizontal Body Forces 50 2.5 Integrated Column Heating 53 2.6 Buoyancy in the Tropical Ocean 57 2.8 Convection–SST Relationships and the Vertical Scale of Tropical Motions 68 2.9 Coupled Global Ocean–Atmosphere Synergies 70 2.10 Synthesis 73 Notes 73 3 Fundamental Processes 77 3.1 Some Fundamentals of Low-Latitude Atmospheric Dynamics 79 3.2 Dynamics of the Low-Latitude Upper Ocean 91 Notes 104 4 Kinematics of Equatorial Waves 107 4.1 Phase and Group Velocities, and Energy Propagation 107 4.2 Dispersive and Non-dispersive Waves 111 4.3 Overview 112 Notes 113 5 Fundamental Prototypes of Tropical Systems 115 5.1 The Laplace Shallow Fluid System 115 5.2 Upper Ocean 118 5.3 A Stratified Atmospheric Model 119 5.4 Forced and Free Solutions and the Choice of H 121 5.5 Some Remarks 123 Notes 123 6 Equatorial Waves in Simple Flows 125 6.1 Atmospheric Modes in a Constant Basic State: Constant U 125 6.2 Atmospheric Waves in Latitudinal Shear Flow: Ū = Ū(y) 144 6.3 Physics of Equatorial Trapping 146 6.4 Large-Scale Low-Latitude Ocean Modes 151 6.5 Overview 157 Notes 158 7 Waves in Longitudinally and Vertically Varying Flows 159 7.1 Horizontal and Vertical Coupling of Equatorial Modes 160 7.2 Coupled Free and Forced Solutions of the Vertical Structure Equation 163 7.3 Wave Characteristics in a Zonally Varying Basic State Ū = Ū(x) 169 7.4 Numerical Substantiation of the Analytic Ray-Tracing Results 176 7.5 Zonally Varying Basic State and the “Longwave Approximation” 181 7.6 Vertical Trapping, Accumulation, and Lateral Emanation 182 7.7 Quasi-Biennial Oscillation (QBO) 183 Notes 184 8 Moist Processes and Large-Scale Tropical Dynamics 185 8.1 Convection and Large-Scale Budgets 186 8.2 Emerging Perspective on Tropical Convection 188 8.3 Comparison of Observed Waves and Waves from Theory 190 8.4 Dry and Moist Modes in the Tropics 191 8.5 Processes 193 8.6 Synthesis 201 Notes 203 9 Extratropical Influence on the Tropics 205 9.1 Lateral Wave Propagation in a Zonally Symmetric Basic State 205 9.2 Equatorial Wave Propagation in a Zonally Varying Basic State 208 9.3 Equatorward Wave Propagation in a Three-Dimensional Basic State 214 9.4 Overview 221 Notes 221 10 Tropical Influence on the Extratropics: A Zonally Averaged Perspective 223 10.1 Axisymmetric Meridional Circulation Models 223 10.2 Zonally Averaged Perspective of Meridional Circulations 225 10.3 Perspective 230 Notes 230 11 A Tropical–Extratropical Synergy 231 11.1 Mean and Transient Potential Vorticity on the 370 K Isentrope 231 11.2 Impermeability 234 11.3 Shallow Fluid Experiments 237 11.4 Recursively Breaking Rossby Waves 240 11.5 Conclusions 241 Notes 243 12 Arid and Desert Climates 245 12.1 Dynamics of Deserts 245 12.2 Radiative and Surface Fluxes 248 12.3 Diurnal Cycle of Divergence 250 12.4 Tropospheric Energy Balance 251 12.5 Nocturnal Stabilization of the Boundary Layer 251 12.6 Desert–Monsoon Relationships 255 Notes 256 13 Near-Equatorial Precipitation 257 13.1 Near-Equatorial Distributions of Precipitation 258 13.2 Dynamic Instabilities Associated with a Cross-Equatorial Pressure Gradient 262 13.3 Transient States of the Intertropical Convergence Zone 280 13.4 The Great Cloud Bands 290 13.5 Some Conclusions 298 Notes 299 14 Large-Scale, Low-Frequency Coupled Ocean–Atmosphere Systems 301 14.1 The Walker Circulation 302 14.2 The Southern Oscillation, El Niño and La Niña 305 14.3 Indian Ocean Interannual Oscillations 332 Notes 342 15 Intraseasonal Variability in the Tropical Atmosphere 345 15.1 Introduction 345 15.2 Structure of the Austral Summer ISV 345 15.3 Variability of Austral Summer ISVs 348 15.4 Mechanisms 351 15.5 Conclusions 358 Notes 358 16 Dynamics of the Large-Scale Monsoon 361 16.1 Overview 361 16.2 Theories of the Monsoon and Its Variability 364 16.3 Macroscale Structure of the Summer Monsoon 374 16.4 Macroscale Structure of the Winter Monsoon 388 16.5 Subseasonal Summer Monsoon Variability 391 16.6 Higher-Frequency Monsoon Variability 400 16.7 Some Comments 405 Notes 405 17 The Coupled Monsoon System 407 17.1 Coupled Characteristics of the Indian Ocean Region 407 17.2 Processes Determining the Indian Ocean SST 411 17.3 Do Ocean Heat Fluxes Regulate the Annual Cycle of the Monsoon? 415 17.4 Variability Within the Coupled Monsoon System 416 17.5 An Holistic View of the Monsoon System 421 Notes 428 18 The Changing Tropics 429 18.1 Tropical Warm Pool 429 18.2 Circulation Changes 438 18.3 Summary and Conclusions 442 Notes 444 19 Some Concluding Remarks 445 Notes 447 Appendix A Thermal Wind Relationship 449 Appendix B Stokes’ Theorem 451 Appendix C Dry and Moist Thermodynamical Stability 453 Appendix D Derivation of the Wave Equation (5.11) 455 Appendix E Conservation of Potential Vorticity of Shallow Water System 457 Appendix F Solutions to the Vertical Structure Equation for a Constant Lapse Rate Atmosphere 459 Appendix G Nonlinear Numerical Model 461 Appendix H Derivation of the Potential Vorticity Equation on an Extratropical β-Plane 463 Appendix I Derivation of the Barotropic Potential Vorticity Equation (13.25) with Friction and Heating 465 Appendix J Steady State Model of the Tropics 467 Appendix K Intermediate Ocean Model 469 References 471 Index 493

About the Author :
Peter J. Webster, PhD, is Professor Emeritus in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology.