Observations and Dynamics of Circulations in the North Indian Ocean

Description

The book is the first to focus on the physical oceanography of the North Indian Ocean (NIO), a special region of the global ocean that exhibits a distinct seasonality due to the impact of the South Asian Monsoon (SAM). It is written as a textbook about the NIO for graduate students, lecturers, and researchers in physical oceanography. It will also be useful for courses on the interior, coastal, and equatorial dynamics in any other ocean. It helps readers, particularly new entrants to the field, to gain a comprehensive understanding of tropical-ocean dynamics by: developing from first principles the equation set for the linear continuously stratified (LCS) model, which has long been used to study tropical oceans; and then obtaining solutions that explore different aspects of the dynamics. Part 1 of the book provides an overview of observed ocean circulations and forcing functions in the NIO that are linked to the SAM. Part 2 develops the equations of motion for the LCS model. Part 3 (Free Waves) and Part 4 (Forced Solutions) derive and discuss analytic solutions to the LCS model that illustrate basic processes in the interior (unbounded), coastal, and equatorial regions of the ocean. The last two chapters of Part 4 consider more complicated processes and phenomena that build upon the simpler solutions previously found: vertical propagation of coastal and equatorial waves, and the Indian Ocean's shallow overturning circulations. Each analytic solution is illustrated (and extended) by a suite of numerical LCS solutions presented as video clips, providing a powerful means for visualizing complex processes. Preface Contents 1 Introduction 1.1 Observational Background 1.2 Theoretical Background 1.3 Book Overview Part I Observations: Atmospheric Forcing and Ocean Response 2 Atmospheric Circulation 2.1 Monsoons and the ITCZ 2.1.1 General Properties 2.1.2 South Asian ITCZ 2.2 South-Asian Summer Monsoon 2.2.1 Precipitation and Orography 2.2.2 Monsoon Winds 2.2.3 SST and Ocean Processes 2.2.4 Non-orographic Rainfall 2.2.5 Summary 2.3 Interannual Variability 2.3.1 ENSO 2.3.2 IOD 2.4 Sub-annual Variability 2.4.1 Madden-Julian Oscillations 2.4.2 Quasi-biweekly Mode 2.4.3 Sub-weekly Oscillations 2.4.4 Diurnal Variability 3 Ocean Forcing and the Surface Mixed Layer 3.1 Ocean Forcing 3.1.1 Definitions 3.1.2 Climatological Fluxes 3.2 Surface Mixed Layer 3.2.1 Mixed-layer Processes 3.2.2 Mixed-layer Models 3.2.3 Basin-wide Properties 3.2.4 Arabian Sea and Bay of Bengal 4 Ocean Circulations 4.1 Thermohaline Structure 4.1.1 Overview 4.1.2 Bottom Layer 4.1.3 Deep Layer 4.1.4 Intermediate Layer 4.1.5 Upper Layer 4.2 Climatological Surface Currents and Sea Level 4.2.1 Currents 4.2.2 Sea Level and Geostrophic Velocity 4.3 Southern-Hemisphere Circulations 4.3.1 South Equatorial Thermocline Ridge 4.3.2 South Equatorial Current 4.3.3 South Equatorial Countercurrent 4.3.4 East Africa Coastal Current 4.4 Equatorial Region 4.4.1 Wyrtki Jets 4.4.2 Upwelling Events 4.4.3 Equatorial Undercurrents and Deeper Flows 4.4.4 Intraseasonal Oscillations 4.5 Sumatra/Java Coast 4.5.1 Mean Currents 4.5.2 Semiannual and Annual Cycles 4.5.3 Intraseasonal Variability 4.5.4 Dynamics 4.6 Andaman Sea 4.6.1 Background Properties 4.6.2 Annual Cycle 4.6.3 Intraseasonal Variability 4.6.4 Dynamics 4.7 Bay of Bengal 4.7.1 Interior Circulation 4.7.2 Intraseasonal Variability and Eddies 4.7.3 East India Coastal Current 4.7.4 Western-Boundary Gyres 4.7.5 Salt Balance 4.8 Monsoon Currents 4.8.1 Summer Monsoon Current 4.8.2 Winter Monsoon Current 4.8.3 Dynamics 4.9 Arabian Sea 4.9.1 Lakshadweep High and Low 4.9.2 West India Coastal Current 4.9.3 Pakistan Coastal Current 4.9.4 Interior Circulation 4.9.5 East Arabia Coastal Current 4.9.6 Somali Current 4.9.7 Salt Balance 4.10 Marginal Seas 4.10.1 Persian Gulf 4.10.2 Gulf of Oman 4.10.3 Red Sea 4.10.4 Gulf of Aden Part II Models 5 Ocean Models 5.1 Ocean General Circulation Models 5.1.1 Equations 5.1.2 Mixing 5.1.3 Boundary Conditions 5.1.4 Coordinate Systems 5.2 Linear, Continuously Stratified Model 5.2.1 Equations of Motion 5.2.2 Boundary Conditions 5.2.3 Vertical Normal Modes 5.2.4 Barotropic and Baroclinic Modes 5.2.5 Modal Equations 5.2.6 Convergence 5.3 Layer Models 5.3.1 Overview 5.3.2 Nonlinear 112-layer Model 5.3.3 Linear 112-layer Model 5.3.4 Multi-layer Models 5.4 Potential Vorticity Part III Free Waves 6 Overview 6.1 Wave Structure 6.1.1 Plane Wave 6.1.2 General Wave 6.1.3 Other Waves 6.2 Dispersion Relation 6.3 Wave Groups in a Uniform Medium 6.4 Impact of a Slowly-varying Medium 6.5 Impact of Mixing 7 Midlatitude Waves 7.1 Gravity and Rossby Waves 7.1.1 Dispersion Relation 7.1.2 Phase and Group Velocities 7.1.3 Extension to Variable f 7.1.4 Critical Latitudes 7.1.5 Videos 7.2 Kelvin Waves 7.2.1 Zonal Coasts 7.2.2 Meridional Coasts 7.3 Boundary-Generated Rossby Waves 7.3.1 Solution 7.3.2 Videos 7.3.3 Meridional Energy Propagation 7.4 Waves Along a Slanted Coast 7.4.1 Kelvin Waves 7.4.2 Rossby-Wave Pathways 7.5 Observations 7.5.1 Critical Latitude 7.5.2 Meridional Energy Propagation 7.5.3 Zero-Group-Velocity Resonance 8 Equatorial Waves 8.1 Hermite Functions 8.2 Equatorial Gravity and Rossby Waves 8.2.1 Dispersion Relation 8.2.2 Phase and Group Velocities 8.2.3 Videos 8.3 Mixed Rossby-Gravity Wave 8.4 Equatorial Kelvin Wave 8.5 Relationship to Midlatitude Waves 8.6 Observations Part IV Forced Solutions 9 Overview 9.1 Common Aspects 9.1.1 Approximations 9.1.2 Basin and Boundary Conditions 9.1.3 Radiation and Initial Conditions 9.1.4 Wind-stress Forcing 9.2 Dirac δ-function 9.3 Transform Methods 9.3.1 Fourier Transforms 9.3.2 Laplace Transforms 9.4 Examples 9.4.1 Switched-on Forcing 9.4.2 Periodic Forcing 10 Ekman Drift and Inertial Oscillations 10.1 Midlatitude Ocean 10.1.1 Constant f 10.1.2 Variable f 10.1.3 Observations 10.2 Equatorial Ocean 10.2.1 Single-mode Response 10.2.2 Solutions with z-dependence 10.2.3 Observations 10.3 Review 11 Sverdrup Flow and Boundary Currents 11.1 Interior Circulation 11.1.1 Solution 11.1.2 Videos 11.1.3 Pycnocline Response 11.1.4 Observations 11.2 Boundary Currents 11.2.1 Western Boundary 11.2.2 Other Boundaries 11.2.3 Observations 12 Interior Ocean 12.1 Simplified Model Equations 12.2 Constant-f Solutions 12.2.1 Switched-On Forcing 12.2.2 Periodic Forcing 12.2.3 Observations 12.3 Variable-f Solutions 12.3.1 Switched-On Forcing 12.3.2 Periodic Forcing 12.3.3 Observations 13 Coastal Ocean 13.1 Simplified Model Equations 13.2 Switched-On Forcing 13.2.1 Two-Dimensional Response 13.2.2 Three-Dimensional Response, β=0 13.2.3 Three-Dimensional Response, β=0 13.3 Periodic Forcing 13.3.1 Solution 13.3.2 Dynamics 13.3.3 Videos 13.3.4 Solutions for a Slanted Boundary 13.4 Observations 13.5 River-Driven Circulations 14 Equatorial Ocean: Switched-On Forcing 14.1 Simplified Model Equations 14.2 Interior Solution 14.2.1 Small-Time Response 14.2.2 Long-Time Solution 14.3 Reflections from a Single Boundary 14.3.1 East-Coast Reflections 14.3.2 West-coast Reflections 14.4 Reflections from Both Boundaries 14.5 Observations 15 Equatorial Ocean: Periodic Forcing 15.1 Interior Solution 15.1.1 v Field 15.1.2 u Field 15.1.3 p Field 15.1.4 Dynamics 15.1.5 Videos 15.2 Reflections from a Single Boundary 15.2.1 Eastern Boundary 15.2.2 Western Boundary 15.2.3 Meridional Energy Propagation 15.2.4 Reflections from a Slanted Boundary 15.3 Observations 15.4 Equatorial Resonances 15.4.1 Equatorial Basin Resonance 15.4.2 Zero-Group-Velocity Resonance 16 Beams and Undercurrents 16.1 Beams 16.1.1 Properties 16.1.2 Videos 16.1.3 Observations 16.2 Undercurrents 16.2.1 Conceptual Explanations 16.2.2 Dynamics 16.2.3 Videos 16.2.4 Observations 17 Cross-Equatorial and Subtropical Cells 17.1 Overview 17.2 Structure 17.2.1 Two-Dimensional Overturning 17.2.2 Three-dimensional Pathways 17.2.3 Transports 17.2.4 Observations 17.3 Dynamics 17.3.1 Model Overview 17.3.2 STC Dynamics 17.3.3 CEC Dynamics 17.3.4 Cross-Equatorial Flow 17.3.5 Equatorial Roll Appendix A List of Acronyms Appendix B Simplified LCS Equations B.1 Non-dimensional Parameters B.2 Parameter Choices B.2.1 General Scalings B.2.2 Interior-Ocean Scaling B.2.3 Coastal-Ocean Scaling B.2.4 Equatorial-Ocean Scaling Appendix C Video Overview Appendix References Index