Dynamics of the Tropical Atmosphere and Oceans

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

• Preface xviiAcknowledgments xixAbbreviations xxiii1 Climatology of the Tropical Atmosphere and Upper Ocean 11.1 The Growth of Tropical Meteorology 11.2 Seasonal Characteristics 41.3 Macro-Scale Circulations 161.4 A Myriad of Variability 24Notes 342 Hydrological and Heat Exchange Processes 372.1 Water on Earth 382.2 Thermodynamics of Water and Earth’s Climate 392.3 Water and the Tropical System 432.4 Buoyancy, Differential Buoyancy, and the Generation of Horizontal Body Forces 502.5 Integrated Column Heating 532.6 Buoyancy in the Tropical Ocean 572.8 Convection–SST Relationships and the Vertical Scale of Tropical Motions 682.9 Coupled Global Ocean–Atmosphere Synergies 702.10 Synthesis 73Notes 733 Fundamental Processes 773.1 Some Fundamentals of Low-Latitude Atmospheric Dynamics 793.2 Dynamics of the Low-Latitude Upper Ocean 91Notes 1044 Kinematics of Equatorial Waves 1074.1 Phase and Group Velocities, and Energy Propagation 1074.2 Dispersive and Non-dispersive Waves 1114.3 Overview 112Notes 1135 Fundamental Prototypes of Tropical Systems 1155.1 The Laplace Shallow Fluid System 1155.2 Upper Ocean 1185.3 A Stratified Atmospheric Model 1195.4 Forced and Free Solutions and the Choice of H 1215.5 Some Remarks 123Notes 1236 Equatorial Waves in Simple Flows 1256.1 Atmospheric Modes in a Constant Basic State: Constant U 1256.2 Atmospheric Waves in Latitudinal Shear Flow: Ū = Ū(y) 1446.3 Physics of Equatorial Trapping 1466.4 Large-Scale Low-Latitude Ocean Modes 1516.5 Overview 157Notes 1587 Waves in Longitudinally and Vertically Varying Flows 1597.1 Horizontal and Vertical Coupling of Equatorial Modes 1607.2 Coupled Free and Forced Solutions of the Vertical Structure Equation 1637.3 Wave Characteristics in a Zonally Varying Basic State Ū = Ū(x) 1697.4 Numerical Substantiation of the Analytic Ray-Tracing Results 1767.5 Zonally Varying Basic State and the “Longwave Approximation” 1817.6 Vertical Trapping, Accumulation, and Lateral Emanation 1827.7 Quasi-Biennial Oscillation (QBO) 183Notes 1848 Moist Processes and Large-Scale Tropical Dynamics 1858.1 Convection and Large-Scale Budgets 1868.2 Emerging Perspective on Tropical Convection 1888.3 Comparison of Observed Waves and Waves from Theory 1908.4 Dry and Moist Modes in the Tropics 1918.5 Processes 1938.6 Synthesis 201Notes 2039 Extratropical Influence on the Tropics 2059.1 Lateral Wave Propagation in a Zonally Symmetric Basic State 2059.2 Equatorial Wave Propagation in a Zonally Varying Basic State 2089.3 Equatorward Wave Propagation in a Three-Dimensional Basic State 2149.4 Overview 221Notes 22110 Tropical Influence on the Extratropics: A Zonally Averaged Perspective 22310.1 Axisymmetric Meridional Circulation Models 22310.2 Zonally Averaged Perspective of Meridional Circulations 22510.3 Perspective 230Notes 23011 A Tropical–Extratropical Synergy 23111.1 Mean and Transient Potential Vorticity on the 370 K Isentrope 23111.2 Impermeability 23411.3 Shallow Fluid Experiments 23711.4 Recursively Breaking Rossby Waves 24011.5 Conclusions 241Notes 24312 Arid and Desert Climates 24512.1 Dynamics of Deserts 24512.2 Radiative and Surface Fluxes 24812.3 Diurnal Cycle of Divergence 25012.4 Tropospheric Energy Balance 25112.5 Nocturnal Stabilization of the Boundary Layer 25112.6 Desert–Monsoon Relationships 255Notes 25613 Near-Equatorial Precipitation 25713.1 Near-Equatorial Distributions of Precipitation 25813.2 Dynamic Instabilities Associated with a Cross-Equatorial Pressure Gradient 26213.3 Transient States of the Intertropical Convergence Zone 28013.4 The Great Cloud Bands 29013.5 Some Conclusions 298Notes 29914 Large-Scale, Low-Frequency Coupled Ocean–Atmosphere Systems 30114.1 The Walker Circulation 30214.2 The Southern Oscillation, El Niño and La Niña 30514.3 Indian Ocean Interannual Oscillations 332Notes 34215 Intraseasonal Variability in the Tropical Atmosphere 34515.1 Introduction 34515.2 Structure of the Austral Summer ISV 34515.3 Variability of Austral Summer ISVs 34815.4 Mechanisms 35115.5 Conclusions 358Notes 35816 Dynamics of the Large-Scale Monsoon 36116.1 Overview 36116.2 Theories of the Monsoon and Its Variability 36416.3 Macroscale Structure of the Summer Monsoon 37416.4 Macroscale Structure of the Winter Monsoon 38816.5 Subseasonal Summer Monsoon Variability 39116.6 Higher-Frequency Monsoon Variability 40016.7 Some Comments 405Notes 40517 The Coupled Monsoon System 40717.1 Coupled Characteristics of the Indian Ocean Region 40717.2 Processes Determining the Indian Ocean SST 41117.3 Do Ocean Heat Fluxes Regulate the Annual Cycle of the Monsoon? 41517.4 Variability Within the Coupled Monsoon System 41617.5 An Holistic View of the Monsoon System 421Notes 42818 The Changing Tropics 42918.1 Tropical Warm Pool 42918.2 Circulation Changes 43818.3 Summary and Conclusions 442Notes 44419 Some Concluding Remarks 445Notes 447Appendix A Thermal Wind Relationship 449Appendix B Stokes’ Theorem 451Appendix C Dry and Moist Thermodynamical Stability 453Appendix D Derivation of the Wave Equation (5.11) 455Appendix E Conservation of Potential Vorticity of Shallow Water System 457Appendix F Solutions to the Vertical Structure Equation for a Constant Lapse Rate Atmosphere 459Appendix G Nonlinear Numerical Model 461Appendix H Derivation of the Potential Vorticity Equation on an Extratropical β-Plane 463Appendix I Derivation of the Barotropic Potential Vorticity Equation (13.25) with Friction and Heating 465Appendix J Steady State Model of the Tropics 467Appendix K Intermediate Ocean Model 469References 471Index 493