| Table of Contents |
| | Mathematical Notations | |
| 1. | Introduction | 1 |
| 1.1. | The Ocean Near-Surface Layer in the Ocean--Atmosphere System | 1 |
| 1.2. | Basic Equations of Fluid Mechanics and Useful Approximations | 4 |
| 1.2.1. | Mathematical Notation and Governing Equations | 4 |
| 1.2.2. | Boundary-Layer Approximation | 6 |
| 1.2.3. | Low Rossby Number Approximation | 8 |
| 1.2.4. | Turbulence and Turbulent Kinetic Energy Budget | 8 |
| 1.3. | Boundary Conditions | 10 |
| 1.3.1. | Types of Surface Boundary Conditions | 11 |
| 1.3.2. | Bulk-Flux Formulation | 13 |
| 1.4. | Radiative Forcing | 19 |
| 1.4.1. | Definitions | 19 |
| 1.4.2. | Solar Constant and Insolation | 20 |
| 1.4.3. | Insolation Under Clear Skies | 22 |
| 1.4.4. | Insolation Under Cloudy Skies | 23 |
| 1.4.5. | Albedo of the Sea Surface | 25 |
| 1.4.6. | Attenuation of Solar Radiation in the Ocean | 28 |
| 1.4.7. | Longwave Radiation | 32 |
| 1.5. | Rain Forcing | 32 |
| 1.5.1. | Dynamics of Raindrops at the Air--Sea Interface | 32 |
| 1.5.2. | Partition Between Surface and Submerged Fractions of Freshwater Due to Rain | 34 |
| 1.5.3. | Volume Source of Freshwater Due to Rain | 35 |
| 1.5.4. | Rain-Induced Heat Flux | 37 |
| 1.5.5. | Surface Stress Due to Rain | 38 |
| 1.6. | Surface Waves | 39 |
| 1.6.1. | Potential Approximation | 39 |
| 1.6.2. | Linear Waves | 42 |
| 1.6.3. | Nonlinear Waves | 43 |
| 1.6.4. | Wave Breaking | 44 |
| 1.6.5. | Statistical Description of Surface Waves | 46 |
| 1.6.6. | Wave form Stress and Kinetic Energy Flux to Waves from Wind | 49 |
| 1.7. | Planetary Boundary Layers | 51 |
| 1.7.1. | Ekman Boundary Layer | 52 |
| 1.7.2. | Monin--Oboukhov Similarity Theory | 56 |
| 1.7.3. | Surface Mixed Layer | 58 |
| 1.7.4. | Barrier Layer and Compensated Layer | 60 |
| 1.7.5. | Modeling Mixing in the Upper Ocean | 60 |
| | References | 63 |
| 2. | Sea Surface Microlayer | 71 |
| 2.1. | Introduction | 71 |
| 2.2. | Phenomenology | 74 |
| 2.2.1. | Viscous Sublayer | 74 |
| 2.2.2. | Thermal Sublayer | 75 |
| 2.2.3. | Diffusion Sublayer | 77 |
| 2.2.4. | Sea Surface Microlayer Ecosystem | 77 |
| 2.2.5. | Surfactants and Surface Films | 78 |
| 2.3. | Physics of Aqueous Molecular Sublayers | 81 |
| 2.3.1. | Convective and Shear Instability | 82 |
| 2.3.2. | Microscale Wave Breaking | 86 |
| 2.3.3. | Wave Breaking and Whitecapping | 87 |
| 2.3.4. | Capillary Wave Effects | 88 |
| 2.3.5. | Chemical and Photochemical Reactions in the Sea Surface Microlayer | 90 |
| 2.3.6. | Natural and Anthropogenic Influences | 90 |
| 2.3.7. | Effects of Surface Films | 91 |
| 2.4. | Parameterization of Molecular Sublayers During Nighttime Conditions | 98 |
| 2.4.1. | Dimensional Analysis | 98 |
| 2.4.2. | Renewal Model | 101 |
| 2.4.3. | Boundary-Layer Model | 112 |
| 2.5. | Effect of Penetrating Solar Radiation | 116 |
| 2.5.1. | Model Equations | 116 |
| 2.5.2. | Renewal Time | 120 |
| 2.5.3. | Convective Instability of the Cool Skin During Daytime | 120 |
| 2.5.4. | Model Calculations | 121 |
| 2.5.5. | Comparison with Daytime and Nighttime Cool-Skin Field Data | 123 |
| 2.6. | Cool and Freshwater Skin of the Ocean during Rainfall | 127 |
| 2.6.1. | Effects of Rain on the Cool Skin | 129 |
| 2.6.2. | Freshwater Skin of the Ocean | 131 |
| 2.6.3. | Surface Renewals Due to Rain Mixing | 133 |
| 2.6.4. | Buoyancy Effects in Molecular Sublayer Due to Rain | 136 |
| 2.6.5. | Rain Effects on Sea Surface Roughness | 137 |
| 2.6.6. | Flux of Kinetic Energy Carried by Rain | 140 |
| 2.6.7. | Combined Effect | 141 |
| 2.6.8. | Comparison with Data | 143 |
| 2.6.9. | Discussion | 145 |
| | References | 146 |
| 3. | Near-Surface Turbulence | 153 |
| 3.1. | Introduction | 153 |
| 3.2. | Free-Surface Turbulent Boundary Layer | 154 |
| 3.2.1. | Wave-Following Coordinate System | 154 |
| 3.2.2. | Wall-Layer Analogy | 155 |
| 3.2.3. | Deviations from the Wall-Layer Analogy in a Free-Surface Layer | 157 |
| 3.2.4. | Structure of the Upper Ocean Turbulent Boundary Layer Below Breaking Surface Waves | 159 |
| 3.3. | Observation of Near-Surface Turbulence | 161 |
| 3.3.1. | Observational Challenges | 161 |
| 3.3.2. | Wave-Following Versus Fixed Coordinate System | 162 |
| 3.3.3. | Disturbances from Surface Waves | 162 |
| 3.3.4. | Dynamics of a Free-Rising Instrument in the Near-Surface Layer of the Ocean | 164 |
| 3.3.5. | A Near-Surface Turbulence and Microstructure Sensor System | 167 |
| 3.4. | Wave-Enhanced Turbulence | 180 |
| 3.4.1. | Dimensional analysis | 180 |
| 3.4.2. | Craig and Banner (1994) Model of Wave-Enhanced Turbulence | 182 |
| 3.4.3. | Benilov and Ly (2002) Wave-Turbulent Model | 193 |
| 3.4.4. | Concluding Remarks on Wave-Enhanced Turbulence | 200 |
| 3.5. | Effects of Thermohaline Stratification | 202 |
| 3.5.1. | Formulation of the Monin-Oboukhov Theory for the Upper Ocean | 203 |
| 3.5.2. | Asymptotic regimes | 205 |
| 3.5.3. | Boundary-Layer Scaling of the Velocity and Dissipation Rate Profiles | 208 |
| 3.6. | Parameterization of Turbulent Mixing | 210 |
| 3.6.1. | Parameterization of Wave-Enhanced Mixing Coefficient | 210 |
| 3.6.2. | Richardson-Number Type Mixing Parameterization | 212 |
| 3.6.3. | Rotation Effects | 218 |
| 3.6.4. | Boundary-Layer Horizontal Pressure Gradients | 218 |
| | References | 219 |
| 4. | Fine Structure and Microstructure | 225 |
| 4.1. | Introduction | 225 |
| 4.2. | Near-Surface Thermohaline Structures | 226 |
| 4.2.1. | Diurnal Mixed Layer and Diurnal Thermocline | 226 |
| 4.2.2. | Examples of Near-Surface Structures Associated with Diurnal Cycle | 228 |
| 4.2.3. | Wave-Like Disturbances in the Diurnal Thermocline | 230 |
| 4.2.4. | Rain-Formed Mixed Layer and Halocline | 232 |
| 4.2.5. | Low-Salinity Patches Due to Convective Rains | 233 |
| 4.2.6. | Combined Effect of Diurnal and Freshwater Cycles on the Upper Ocean Structure | 235 |
| 4.3. | Surface-Intensified Jets | 241 |
| 4.3.1. | Slippery Near-Surface Layer of the Ocean Arising Due to Diurnal Warming | 241 |
| 4.3.2. | Self-Regulating State of the Diurnal Thermocline | 243 |
| 4.3.3. | Upper Velocity Limit for the Diurnal Jet | 249 |
| 4.3.4. | Upper Velocity Limit for the Rain-Formed Jet | 250 |
| 4.4. | Evolution of the Diurnal Mixed Layer and Diurnal Thermocline Under Low Wind Speed Conditions | 250 |
| 4.5. | Large Diurnal Warming Events | 259 |
| 4.5.1. | In Situ Data | 259 |
| 4.5.2. | Global Distribution of Large Diurnal Warming Events | 261 |
| 4.5.3. | Physics of Large Diurnal Warming Events | 264 |
| 4.6. | Modeling Large Diurnal Warming Events | 266 |
| 4.6.1. | Radiative-Convective Mixed Layer | 266 |
| 4.6.2. | Transition from Radiative-Convective to Wind Mixing Regime | 272 |
| 4.6.3. | A Rapid Increase in the SST When the Air is Warmer Than the Water and Low Wind Speed Conditions Persist | 275 |
| 4.6.4. | Parameterizations for the Diurnal SST Range | 275 |
| 4.6.5. | One-Dimensional Numerical Simulation of Diurnal Cycle | 277 |
| 4.6.6. | Three-Dimensional Numerical Simulation of Diurnal Cycle | 280 |
| 4.7. | Fine Structure of the Near-Surface Layer in the Polar Seas | 282 |
| | References | 286 |
| 5. | Spatially-Varying and Coherent Structures | 291 |
| 5.1. | Introduction | 291 |
| 5.2. | Self-Organization in Two-Dimensional Turbulence | 293 |
| 5.3. | Horizontal Mixing as a Nonlinear Diffusion Process | 300 |
| 5.3.1. | Horizontal Wave Number Statistics | 301 |
| 5.3.2. | Nonlinear Advection--Diffusion Model | 302 |
| 5.3.3. | Buoyancy Flux Through the Bottom of the Mixed Layer | 303 |
| 5.3.4. | Atmospheric Buoyancy Forcing | 306 |
| 5.3.5. | Equilibrium Subrange | 307 |
| 5.3.6. | Numerical Diagnostics of Nonlinear Diffusion Equation | 309 |
| 5.3.7. | Relationship Between Vertical and Horizontal Mixing and Atmospheric Forcing Conditions | 312 |
| 5.3.8. | Implications for Horizontal Mixing Parameterization | 313 |
| 5.4. | Sharp Frontal Interfaces | 316 |
| 5.4.1. | Observations of Sharp Frontal Interfaces in the Western Pacific Warm Pool | 317 |
| 5.4.2. | Statistics of Sharp Frontal Interfaces in the Western Pacific Warm Pool | 329 |
| 5.4.3. | Internal Wave-Shear Flow Interaction as a Cause of Repeating Frontal Interfaces | 333 |
| 5.4.4. | Interaction of Sharp Fronts with Wind Stress | 336 |
| 5.4.5. | Parameterization for Cross-Frontal Exchange | 346 |
| 5.4.6. | Implications for the T--S Relationship in the Mixed Layer | 347 |
| 5.4.7. | Observations of Sharp Frontal Interfaces in Mid-Latitudes and High Latitudes | 347 |
| 5.5. | Internal Waves in the Near-Surface Pycnocline | 348 |
| 5.5.1. | Large-Amplitude Internal Waves | 348 |
| 5.5.2. | Surface--Internal Wave Resonant Interactions | 351 |
| 5.5.3. | Kelvin--Helmholtz Instability of a Sheared Stratified Flow | 353 |
| 5.6. | Ramp-Like Structures | 355 |
| 5.6.1. | Phenomenology of Ramp-like Coherent Structures | 355 |
| 5.6.2. | Observation of Ramp-like Coherent Structures with Bow-Mounted Sensors | 357 |
| 5.6.3. | Skewness of temperature derivative | 360 |
| 5.6.4. | Vertical Profiles | 362 |
| 5.6.5. | Townsend's Hypothesis and Ramp-Like Structures | 364 |
| 5.6.6. | Vorticity Waves in Shear Flows | 366 |
| 5.7. | Langmuir Circulations | 369 |
| 5.7.1. | Phenomenology | 369 |
| 5.7.2. | Concepts and Theories | 372 |
| 5.7.3. | Numerical Models of Langmuir Circulations | 378 |
| 5.7.4. | An Alternative Mechanism of Langmuir Circulation | 380 |
| 5.8. | Convection | 381 |
| 5.8.1. | Phenomenology | 382 |
| 5.8.2. | Penetrative Convection | 384 |
| 5.8.3. | Diurnal and Seasonal Cycle of Convection | 386 |
| 5.9. | Conclusions | 388 |
| | References | 388 |
| 6. | High Wind Speed Regime | 397 |
| 6.1. | Introduction | 397 |
| 6.2. | Air Bubbles in the Near-Surface Turbulent Boundary Layer | 398 |
| 6.2.1. | Active and Passive Phases in Bubble Life | 398 |
| 6.2.2. | Bubble Rise Velocity | 398 |
| 6.2.3. | Bubble Size Distribution Function | 402 |
| 6.2.4. | Bubble Dispersion and Diffusion | 406 |
| 6.2.5. | Buoyancy Effects in Bubble Plumes | 409 |
| 6.3. | Sea Spray Aerosol Production | 411 |
| 6.3.1. | Introduction | 411 |
| 6.3.2. | Mechanisms of Sea Spray Production | 412 |
| 6.3.3. | Sea Spray Source Function | 414 |
| 6.3.4. | Primary Aerosol Number Distributions | 417 |
| 6.3.5. | Parameterization of Sea Spray Aerosol Production Flux | 418 |
| 6.4. | Air-sea Exchange During High Wind Speeds | 420 |
| 6.4.1. | Effect of Spray on Air-Sea Exchanges | 420 |
| 6.4.2. | Dynamics of Suspension Flow | 425 |
| 6.4.3. | The Air--Sea Interface Under Hurricane Conditions | 430 |
| 6.4.4. | Direct disruption of the air--sea interface | 431 |
| 6.4.5. | The Air--Sea Momentum Exchange in Very Strong Winds | 436 |
| 6.4.6. | Problem of Parameterization of the Air--Sea Drag Coefficient in Hurricane Conditions | 440 |
| | References | 445 |
| 7. | Applications | 451 |
| 7.1. | Introduction | 451 |
| 7.2. | Remote Sensing of the Ocean | 452 |
| 7.2.1. | Remote Sensing of Surface Winds | 452 |
| 7.2.2. | Sea Surface Temperature | 454 |
| 7.2.3. | Sea Surface Salinity | 457 |
| 7.2.4. | Surface Ocean Currents | 460 |
| 7.3. | High-Resolution Microwave Imagery of the Sea Surface | 461 |
| 7.3.1. | Surface Features of Natural Origin | 463 |
| 7.3.2. | Wakes of Ships | 466 |
| 7.3.3. | Atmospheric Influences | 475 |
| 7.3.4. | Numerical Simulation of Natural and Artificial Features in Radar Imagery | 476 |
| 7.4. | Remote Sensing of Oil Spills | 477 |
| 7.5. | Marine Optics | 484 |
| 7.5.1. | Monochromatic and Color Imagery | 484 |
| 7.5.2. | Remote Sensing of Ocean Color | 485 |
| 7.5.3. | Inherent Optical Characteristics of the Upper Ocean Water | 488 |
| 7.5.4. | Influence of Bubbles on Optical Scattering in the Upper Ocean | 489 |
| 7.6. | Marine Chemistry and Biology | 492 |
| 7.7. | Ocean Acoustics | 495 |
| 7.7.1. | Effects of Stratification | 496 |
| 7.7.2. | Biological Scattering Layers | 497 |
| 7.7.3. | Effects of Bubbles on Sound Propagation | 498 |
| 7.7.4. | Acoustic Technique for Measuring Bubble Size Distributions | 502 |
| 7.7.5. | Ambient Noise Produced by Bubbles | 503 |
| 7.7.6. | Ambient Noise Produced by Rain | 504 |
| 7.7.7. | Passive Acoustic Monitoring of Sea Surface Processes | 507 |
| 7.7.8. | Passive Acoustic Monitoring of Surface Waves from Seafloor Pressure Fluctuations in the Deep Ocean | 513 |
| 7.7.9. | 3D Sonar Technology for Near-Surface Studies | 515 |
| 7.8. | Ocean State Estimation, Climate Modeling, and Prediction | 517 |
| 7.8.1. | Air--Sea Fluxes | 519 |
| 7.8.2. | Interactions | 523 |
| 7.8.3. | Ocean State Estimation and Prediction | 524 |
| | References | 527 |
| | Index | 539 |
