Elements of Physical Oceanography

A derivative of the Encyclopedia of Ocean Sciences
1. Auflage 2009
ISBN: 978-0-12-375721-0
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 647 Seiten

Elements of Physical Oceanography is a derivative of the Encyclopedia of Ocean Sciences, 2nd Edition and serves as an important reference on current physical oceanography knowledge and expertise in one convenient and accessible source. Its selection of articles-all written by experts in their field-focuses on ocean physics, air-sea transfers, waves, mixing, ice, and the processes of transfer of properties such as heat, salinity, momentum and dissolved gases, within and into the ocean. Elements of Physical Oceanography serves as an ideal reference for topical research.
References related articles in physical oceanography to facilitate further researchRichly illustrated with figures and tables that aid in understanding key conceptsIncludes an introductory overview and then explores each topic in detail, making it useful to experts and graduate-level researchersTopical arrangement makes it the perfect desk reference

Autoren/Hrsg.

Inhaltsverzeichnis

1;Front cover
;1
2;Encylopedia of Ocean Sciences: Elements of Physical Oceanography
;4
3;Copyright page
;5
4;Contents
;6
5;Elements of Physical Oceanography: Introduction;10
5.1;Editorial Advisory Board Members who helped in the production of this volume;11
5.2;References
;11
6;Surface Waves, Tides, and Sea level
;12
6.1;Surface Gravity and Capillary Waves;14
6.1.1;Introduction;14
6.1.2;Basic Formulations;14
6.1.3;Linear Waves;15
6.1.4;The Group Velocity;17
6.1.5;Second Order Quantities;17
6.1.6;Waves on Currents: Action Conservation;18
6.1.7;Nonlinear Effects;19
6.1.8;Resonant Interactions;19
6.1.9;Parasitic Capillary Waves;20
6.1.10;Wave Breaking;21
6.1.11;Further Reading;21
6.2;Wave Generation by Wind;23
6.2.1;Introduction;23
6.2.2;Theories of Wave Growth;23
6.2.3;Experiments and Observations;25
6.2.4;Numerical Modeling of the Wind Input;27
6.2.5;Conclusions;27
6.2.6;Further Reading;27
6.2.7;Relevant Website;28
6.3;Rogue Waves;29
6.3.1;Introduction;29
6.3.2;Surface Gravity Waves;30
6.3.3;Physical Mechanisms;31
6.3.4;Statistics of Large Waves;32
6.3.5;Experiments and Observations;35
6.3.6;Numerical Simulations;37
6.3.7;Conclusions;37
6.3.8;Further Reading;38
6.4;Waves on Beaches;40
6.4.1;Introduction;40
6.4.2;The Dynamics of Incident Waves;41
6.4.3;Radiation Stress: the Forcing of Mean Flows and Set-up;42
6.4.4;Nonlinear Incident Waves;43
6.4.5;Vertically Dependent Processes;43
6.4.6;2HD Flows - Circulation;43
6.4.7;Infragravity Waves and Edge Waves;44
6.4.8;Shear Waves;45
6.4.9;Conclusions;46
6.5;Wave Energy;48
6.5.1;Introduction;48
6.5.2;Wave Power: Resource and Exploitation;49
6.5.3;Economics of Wave Power Conversion;50
6.5.4;Concluding remarks;51
6.5.5;Further Reading;51
6.6;Whitecaps and Foam
;52
6.6.1;Introduction;52
6.6.2;Spilling Wave Crests: Stage A Whitecaps;52
6.6.3;Decaying Foam Patches: Stage B Whitecaps;53
6.6.4;Wind-Dependence of Oceanic Whitecap Coverage;55
6.6.5;Stabilized Sea Foam;55
6.6.6;Global Implications;57
6.6.7;Further Reading;57
6.7;Breaking Waves and Near-Surface Turbulence;58
6.7.1;Introduction;58
6.7.2;Breaking Waves;58
6.7.3;Turbulence beneath Breaking Waves;60
6.7.4;Conclusion;63
6.7.5;Further Reading;64
6.8;Seiches;66
6.8.1;Introduction;66
6.8.2;History;66
6.8.3;Dynamics;67
6.8.4;Generating Mechanisms and Observations;69
6.8.5;Further Reading;72
6.9;Tsunami;73
6.9.1;Introduction;73
6.9.2;Historical and Recent Tsunamis;74
6.9.3;Tsunami Generation Mechanisms;75
6.9.4;Modeling of Tsunami Generation, Propagation, and Coastal Inundation;79
6.9.5;Tsunami Hazard Mitigation;84
6.9.6;Acknowledgment;85
6.9.7;Further Reading;85
6.10;Storm Surges;87
6.10.1;Introduction and Definitions;87
6.10.2;Storm Surge Equations;87
6.10.3;Generation and Dynamics of Storm Surges;88
6.10.4;Areas Affected by Storm Surges;89
6.10.5;Storm Surge Prediction;92
6.10.6;Interactions with Wind Waves;94
6.10.7;Data Assimilation;95
6.10.8;Related Issues;96
6.10.9;Further Reading;96
6.11;Coastal Trapped Waves;98
6.11.1;Introduction;98
6.11.2;Formulation;98
6.11.3;Straight Unstratified Shelf;98
6.11.4;Other Geometry;99
6.11.5;Stratification;100
6.11.6;Friction;101
6.11.7;Mean Flows;102
6.11.8;Non-linear Effects;102
6.11.9;Alongshore Variations;103
6.11.10;Generation and Role of Coastal-trapped Waves;103
6.11.11;Summary;104
6.11.12;Further Reading;105
6.12;Tides;106
6.12.1;Introduction;106
6.12.2;Tidal Patterns;106
6.12.3;Gravitational Potential;106
6.12.4;The Equilibrium Tide;108
6.12.5;Tidal Analysis;108
6.12.6;Tidal Dynamics;109
6.12.7;Ocean Tides;111
6.12.8;Energy Fluxes and Budgets;112
6.12.9;Further Reading;113
6.13;Tidal Energy;114
6.13.1;Introduction;114
6.13.2;Energy of Tides;114
6.13.3;Extracting Tidal Energy: Traditional Approach;115
6.13.4;Extracting Tidal Energy: Non-traditional Approach;117
6.13.5;Utilizing Electric Energy from Tidal Power Plants;118
6.13.6;Conclusion;118
6.13.7;Further Reading;119
6.14;Sea Level Change
;120
6.14.1;Introduction;120
6.14.2;Sea-Level Changes Since the Last Glacial Maximum;120
6.14.3;Observed Recent Sea-Level Change;120
6.14.4;Processes Determining Present Rates of Sea-Level Change;122
6.14.5;Projected Sea-Level Changes for the Twenty-first Century;124
6.14.6;Regional Sea-Level Change;124
6.14.7;Longer-term Changes;124
6.14.8;Summary;125
6.14.9;Further Reading;125
6.15;Sea Level Variations Over Geological Time;126
6.15.1;Introduction;126
6.15.2;Sea Level Change due to Volume of Water in the Ocean Basin;126
6.15.3;Sea Level Change due to Changing Volume of the Ocean Basin;128
6.15.4;Sea Level Change Estimated from Observations on the Continents;130
6.15.5;Summary;134
6.15.6;Further Reading;134
7;The Air-Sea Interface
;136
7.1;Heat and Momentum Fluxes at the Sea Surface;138
7.1.1;Introduction;138
7.1.2;Measuring the Fluxes;138
7.1.3;Sources of Flux Data;140
7.1.4;Regional and Seasonal Variation of the Momentum Flux;141
7.1.5;Regional and Seasonal Variation of the Heat Fluxes;143
7.1.6;Accuracy of Flux Estimates;143
7.1.7;Further Reading;145
7.2;Sea Surface Exchanges of Momentum, Heat, and Fresh Water Determined by Satellite;146
7.2.1;Introduction;146
7.2.2;Flux Estimation Using Satellite Observations;146
7.2.3;Summary and Applications;152
7.2.4;Further Reading;154
7.2.5;Relevant Websites;155
7.3;Evaporation and Humidity;156
7.3.1;Introduction;156
7.3.2;History/Definitions and Nomenclature;156
7.3.3;Clausius-Clapeyron Equation;159
7.3.4;Tropical Conditions of Humidity;159
7.3.5;Latitudinal and Regional Variations;160
7.3.6;Vertical Structure of Humidity;160
7.3.7;Sublimation-Deposition;160
7.3.8;Sources of Data;160
7.3.9;Estimation of Evaporation by Satellite Data;161
7.3.10;Future Directions and Conclusions;161
7.3.11;Further Reading;162
7.4;Freshwater Transport And Climate;163
7.4.1;Introduction;163
7.4.2;Methods of Fresh Water Flux and Transport Estimation;165
7.4.3;Basin Balances;166
7.4.4;Interbasin Exchange;167
7.4.5;Global Budgets;169
7.4.6;Future Directions;169
7.4.7;Further Reading;170
7.5;Air-Sea Gas Exchange;171
7.5.1;Introduction;171
7.5.2;Theory;171
7.5.3;Experimental Techniques and Results;177
7.5.4;Outlook;180
7.5.5;Further Reading;180
7.5.6;Relevant Websites;180
7.6;Air-Sea Transfer: Dimethyl Sulfide, COS, CS2, NH4, Non-methane Hydrocarbons, Organo-halogens;181
7.6.1;Dimethylsulfide;182
7.6.2;Carbonyl Sulfide;183
7.6.3;Carbon Disulfide;183
7.6.4;Nonmethane Hydrocarbons;184
7.6.5;Ammonia;184
7.6.6;Organohalogens;185
7.6.7;Conclusions;186
7.6.8;Further Reading;186
7.7;Air-Sea Transfer: N2O, NO, CH4, CO;187
7.7.1;Introduction;187
7.7.2;Nitrous Oxide (N2O);187
7.7.3;Nitric Oxide (NO);189
7.7.4;Methane (CH4);190
7.7.5;Carbon Monoxide (CO);191
7.7.6;Air-Sea Exchange of Trace Gases;193
7.7.7;Further Reading;194
7.8;Gas Exchange in Estuaries;195
7.8.1;Introduction;195
7.8.2;Gas Solubility;195
7.8.3;Gas Exchange (Flux) Across the Air/Water Interface;195
7.8.4;Models of Gas Exchange;195
7.8.5;Direct Gas Exchange Measurements;196
7.8.6;Individual Gases;197
7.8.7;Conclusions;200
7.8.8;Further Reading;201
7.9;Penetrating Shortwave Radiation;203
7.9.1;Introduction;203
7.9.2;Albedo;203
7.9.3;Spectrum of Downward Irradiance;204
7.9.4;Modeled Irradiance;205
7.9.5;Parameterized Irradiance versus Depth;206
7.9.6;Further Reading;207
7.10;Radiative Transfer in the Ocean;209
7.10.1;Introduction;209
7.10.2;Terminology;209
7.10.3;Radiometric Quantities;209
7.10.4;Inherent Optical Properties;211
7.10.5;The Radiative Transfer Equation;213
7.10.6;Apparent Optical Properties;213
7.10.7;Optical Constituents of Seawater;214
7.10.8;Examples of Underwater Light Fields;215
7.10.9;Further Reading;218
7.11;Atmospheric Transport and Deposition of Particulate Material to the Oceans;219
7.11.1;Introduction;219
7.11.2;Aerosol Sources, Composition, and Concentrations;219
7.11.3;Aerosol Removal Mechanisms;221
7.11.4;Deposition of Aerosols to the Oceans;223
7.11.5;Conclusions;228
7.11.6;Further Reading;228
7.12;Surface Films;229
7.12.1;Introduction;229
7.12.2;Orgin of Surface Films;229
7.12.3;Modifications of Air-Sea Interaction by Surface Films;230
7.12.4;Further Reading;231
7.13;Bubbles;232
7.13.1;Introduction;232
7.13.2;Sources of Bubbles;232
7.13.3;Dispersion and Development;233
7.13.4;Surfacing and Bursting;235
7.13.5;Acoustical and Optical Properties;236
7.13.6;Summary of Bubble Distribution;236
7.13.7;Further Reading;237
8;Boundary Layers: The Upper Ocean Boundary Layer
;238
8.1;Upper Ocean Vertical Structure;240
8.1.1;Introduction;240
8.1.2;Major Features of the Upper Ocean Vertical Structure;240
8.1.3;Definitions;242
8.1.4;Variability in Upper Ocean Vertical Structure;244
8.1.5;Other Properties That Define the Upper Ocean Vertical Structure;247
8.1.6;Conclusions;247
8.1.7;Further Reading;247
8.2;Wind- and Buoyancy-Forced Upper Ocean;248
8.2.1;Introduction;248
8.2.2;Air-Sea Interaction;248
8.2.3;The Seasonal Cycle;253
8.2.4;Conclusion;255
8.2.5;Further Reading;256
8.3;Upper Ocean Space And Time Variability;257
8.3.1;Introduction;257
8.3.2;Turbulence and Mixing;257
8.3.3;Langmuir Circulation and Convection;257
8.3.4;Internal Waves;258
8.3.5;Fronts and Eddies;259
8.3.6;Wind-Forced Currents;260
8.3.7;Seasonal Cycles;261
8.3.8;Climatic Signals;261
8.3.9;Conclusion;262
8.3.10;Further Reading;262
8.4;Upper Ocean Mean Horizontal Structure;263
8.4.1;Introduction;263
8.4.2;Horizontal Property Fields;263
8.4.3;The Mixed Layer and Seasonal Thermocline;266
8.4.4;The Barrier Layer;268
8.4.5;The Subtropical Gyres and the Permanent Thermocline;269
8.4.6;The Equatorial Region;270
8.4.7;The Polar Regions;271
8.4.8;Further Reading;272
8.5;Upper Ocean Structure: Responses to Strong Atmospheric Forcing Events
;273
8.5.1;Introduction;273
8.5.2;Atmospheric Forcing;274
8.5.3;Air-Sea Parameters;275
8.5.4;Gulf of Mexico Basin;278
8.5.5;Oceanic Response;280
8.5.6;Summary;287
8.5.7;Acknowledgments;290
8.5.8;Further Reading;290
8.5.9;Relevant Website;291
8.6;Upper Ocean Mixing Processes;292
8.6.1;Introduction;292
8.6.2;Convection;294
8.6.3;Wind Forcing;295
8.6.4;Effects of Precipitation;297
8.6.5;Ice on the Upper Ocean;297
8.6.6;Parameterizations of Upper Ocean Mixing;298
8.6.7;Further Reading;298
8.7;Langmuir Circulation and Instability;299
8.7.1;Introduction;299
8.7.2;Description of Langmuir Circulation;299
8.7.3;Theory;301
8.7.4;Field Observations;305
8.7.5;Further Reading;307
8.8;Upper Ocean Heat and Freshwater Budgets;308
8.8.1;Introduction;308
8.8.2;Governing Processes;308
8.8.3;Measurements;310
8.8.4;Distributions;311
8.8.5;Severe Storms;316
8.8.6;Reactions to Climate Change;317
8.8.7;Future Developments;318
8.8.8;Further Reading;318
8.8.9;Relevant Websites;318
9;Boundary Layers: The Benthic Boundary Layer
;320
9.1;Turbulence In The Benthic Boundary Layer;322
9.1.1;Introduction;322
9.1.2;The Ekman Layer;322
9.1.3;Viscous Sublayer;324
9.1.4;The Wall Layer;324
9.1.5;Observations;325
9.1.6;Discussion;327
9.1.7;Further Reading;327
9.2;Benthic Boundary Layer Effects;328
9.2.1;Introduction;328
9.2.2;Organisms of the Benthic Boundary Layer;328
9.2.3;BBL Flow Adaptations;330
9.2.4;Life History Adaptations;330
9.2.5;Suspension-feeding Adaptations;331
9.2.6;Adaptations to Resist Shear Stress;332
9.2.7;Aggregation as an Adaptation;333
9.2.8;Conclusions;334
9.2.9;Further Reading;335
10;Boundary Laers: Under-Ice Boundary Layer
;336
10.1;Under-ice Boundary Layer;338
10.1.1;Introduction;338
10.1.2;History and Basic Concepts;338
10.1.3;Turbulence in the Under-ice Boundary Layer;340
10.1.4;Outstanding Problems;344
10.1.5;Further Reading;345
10.2;Ice-ocean Interaction;346
10.2.1;Introduction;346
10.2.2;Drag and Characteristic Regions of the Under-ice Boundary Layer;346
10.2.3;Heat and Mass Balance at the Ice-Ocean Interface: Wintertime Convection;349
10.2.4;Effects of Horizontal Inhomogeneity: Wintertime Buoyancy Flux;351
10.2.5;Effects of Horizontal Inhomogeneity: Summertime Buoyancy Flux;353
10.2.6;Internal Waves and Their Interaction with the Ice Cover;355
10.2.7;Outstanding Issues;356
10.2.8;Further Reading;356
11;Internal Waves
;358
11.1;Internal Waves;360
11.1.1;Introduction;360
11.1.2;Interfacial Waves;360
11.1.3;Internal Waves;362
11.1.4;Other Aspects;366
11.1.5;Conclusions;366
11.1.6;Further Reading;367
11.2;Internal Tides;368
11.2.1;Introduction;368
11.2.2;Modes and Beams;368
11.2.3;Observations;371
11.2.4;Implications for Energetics and Mixing;374
11.2.5;Further Reading;375
12;Processes of Diapycnal Mixing
;376
12.1;Three-dimensional (3d) Turbulence;378
12.1.1;Introduction;378
12.1.2;The Mechanics of Turbulence;378
12.1.3;Stationary, Homogeneous, Isotropic Turbulence;379
12.1.4;Turbulence in Geophysical Flows;382
12.1.5;Length Scales of Ocean Turbulence;383
12.1.6;Further Reading;385
12.2;Laboratory Studies of Turbulent Mixing;386
12.2.1;Introduction;386
12.2.2;Experiments;386
12.2.3;Continuous Stratification;389
12.2.4;Summary;391
12.2.5;Further Reading;391
12.3;Internal Tidal Mixing;392
12.3.1;Introduction;392
12.3.2;Stirring and Mixing;392
12.3.3;The Battle for Spatial Resolution;392
12.3.4;Maintaining the Stratification;393
12.3.5;Tidal Dissipation: The Astronomic Evidence;393
12.3.6;Boundary Layer Dissipation Versus Scatter;393
12.3.7;Satellite Altimetry to The Rescue;394
12.3.8;Discussion;395
12.3.9;Further Reading;395
12.4;Estimates of Mixing;396
12.4.1;Introduction;396
12.4.2;Approaches to Quantifying Mixing;397
12.4.3;Large-Scale Estimates;398
12.4.4;Fine- and Microscale Estimates;399
12.4.5;Summary;405
12.4.6;Further Reading;406
12.5;Energetics of Ocean Mixing;407
12.5.1;Introduction;407
12.5.2;The Global Ocean’s Energy Budget;408
12.5.3;The Traditional Paradigm of Ocean Mixing: The Abyssal Ocean;409
12.5.4;An Alternative Paradigm of Ocean Mixing: The Permanent Pycnocline;413
12.5.5;Conclusion;415
12.5.6;Further Reading;416
12.6;Fossil Turbulence;417
12.6.1;Introduction;417
12.6.2;History of Fossil Turbulence;419
12.6.3;Intermittency of Oceanic Turbulence and Mixing;421
12.6.4;Turbulence and Fossil Turbulence Definitions;422
12.6.5;Formation and Detection of Stratified Fossil Turbulence;423
12.6.6;Quantitative Methods;423
12.6.7;Further Reading;424
12.7;Open Ocean Convection;425
12.7.1;Introduction;425
12.7.2;Phenomenology;425
12.7.3;Penetrative Convection;427
12.7.4;Relative Contributions of Convection and Shear Stress to Turbulence;427
12.7.5;Convection and Molecular Sublayers;429
12.7.6;Diurnal and Seasonal Cycles of Convection;430
12.7.7;Conclusions;431
12.7.8;Further Reading;432
12.8;Deep Convection;433
12.8.1;Introduction;433
12.8.2;Plumes - the Mixing Agent;435
12.8.3;Temperature and Salinity Variability;436
12.8.4;Restratification;437
12.8.5;Discussion;439
12.8.6;Further Reading;441
12.9;Double-Diffusive Convection;442
12.9.1;Introduction;442
12.9.2;Salt Fingers;442
12.9.3;Diffusive Convection;446
12.9.4;Intrusions;448
12.9.5;Global Importance;448
12.9.6;Further Reading;450
12.10;Differential Diffusion;451
12.10.1;Introduction;451
12.10.2;What Is Differential Diffusion?;451
12.10.3;Laboratory Evidence for Differential Diffusion;452
12.10.4;Numerical Simulation of Differential Diffusion;452
12.10.5;Oceanic Values of Diffusivity Ratio;454
12.10.6;Other Observational Evidence for Differential Diffusion?;455
12.10.7;Does Differential Diffusion Matter?;456
12.10.8;Further Reading;458
12.11;Dispersion and Diffusion in the Deep Ocean;459
12.11.1;Introduction;459
12.11.2;The Thermohaline Circulation;459
12.11.3;Deep-sea Observations of Mixing;459
12.11.4;Summary;465
12.11.5;Further Reading;466
13;Horizontal Dispersion, transport, and Ocean Properties
;468
13.1;Vortical Modes;470
13.1.1;Introduction;470
13.1.2;Potential Vorticity;470
13.1.3;Basin Scales;471
13.1.4;Mesoscale;472
13.1.5;Fine-scale;472
13.1.6;Generation Mechanisms;472
13.1.7;Observational Challenge;473
13.1.8;Conclusions;474
13.1.9;Further Reading;474
13.2;Intrusions;475
13.2.1;Introduction;475
13.2.2;Observational Studies;477
13.2.3;Theoretical Studies;478
13.2.4;Summary;479
13.2.5;Further Reading;479
13.3;Dispersion in Shallow Seas;480
13.3.1;Introduction;480
13.3.2;Fundamentals - The Fluid Mechanics of Dispersion;480
13.3.3;Dispersion Phenomena;483
13.3.4;Further Reading;485
13.4;Dispersion From Hydrothermal Vents;486
13.4.1;Introduction;486
13.4.2;The Rising Plume;486
13.4.3;Mesoscale Flow and Vortices;488
13.4.4;Large-scale flow;490
13.4.5;Discussion;492
13.4.6;Further Reading;494
13.5;Nepheloid Layers;495
13.5.1;Introduction;495
13.5.2;Optics of Nephelometers: What They ’See’;495
13.5.3;Nepheloid Layer Features;498
13.5.4;Separated Mixed-Layer Model;499
13.5.5;Decay of Concentration: Aging of Particulate Populations;499
13.5.6;Chemical Scavenging by Particles in Nepheloid Layers;500
13.5.7;The Turbidity Minimum;502
13.5.8;Concentration and Spreading in the Atlantic and Indian Oceans;503
13.5.9;Boundary Mixing, INLs, and Inversions;503
13.5.10;Trenches and Channels;504
13.5.11;Further Reading;504
13.6;Heat Transport and Climate;506
13.6.1;Introduction: The Global Heat Budget;506
13.6.2;Air-Sea Heat Exchange;508
13.6.3;Distribution of Ocean Heat Transport;508
13.6.4;Eddy Heat Transport;510
13.6.5;Future Developments;511
13.6.6;Further Reading;512
13.7;El Nintildeo Southern Oscillation (enso);513
13.7.1;Introduction;513
13.7.2;The Tropical Pacific Ocean-Atmosphere System;515
13.7.3;Mechanisms of ENSO;520
13.7.4;Interannual Variations in Climate;520
13.7.5;Impacts;523
13.7.6;ENSO and Seasonal Predictions;524
13.7.7;Further Reading;525
13.8;North Atlantic Oscillation (nao);526
13.8.1;Introduction;526
13.8.2;What is the NAO?;526
13.8.3;Impacts of the NAO;528
13.8.4;What are the Mechanisms that Govern NAO Variability?;532
13.8.5;Further Reading;533
13.9;Water Types And Water Masses;534
13.9.1;Introduction;534
13.9.2;What is a Water Mass?;534
13.9.3;Descriptive Tools: The TS Curve;534
13.9.4;Global Water Mass Distribution;536
13.9.5;Summary TS Relationships;540
13.9.6;Discussion and Conclusion;541
13.9.7;Further Reading;542
13.10;Neutral Surfaces and the Equation of State;543
13.10.1;Introduction;543
13.10.2;Requirements for a Neutral Surface to Exist;544
13.10.3;The Helical Nature of Neutral Trajectories;544
13.10.4;Neutral Density Surfaces Compared with Potential Density Surfaces;545
13.10.5;Equation of State;547
13.10.6;Summary;548
13.10.7;Further Reading;549
13.10.8;Relevant Website;549
14;Ice
;550
14.1;Sea Ice: Overview;552
14.1.1;Introduction;552
14.1.2;Extent;552
14.1.3;Geophysical Importance;552
14.1.4;Properties;554
14.1.5;Drift and Deformation;555
14.1.6;Trends;557
14.1.7;Further Reading;559
14.2;Sea Ice Dynamics;561
14.2.1;Introduction;561
14.2.2;Drift Ice Medium;561
14.2.3;Equation of Motion;566
14.2.4;Numerical Modeling;569
14.2.5;Concluding Words;569
14.2.6;Further Reading;570
14.2.7;Relevant Websites;571
14.3;Sea Ice;572
14.3.1;Introduction;572
14.3.2;Sea Ice Extent;572
14.3.3;Sea Ice Thickness;582
14.3.4;Further Reading;588
14.4;Polynyas;590
14.4.1;Introduction;590
14.4.2;Physical Processes within the Two Polynya Types;591
14.4.3;Remote Sensing Observations;593
14.4.4;Physical Importance;593
14.4.5;Biological Importance;594
14.4.6;Conclusions;595
14.4.7;Acknowledgments;595
14.4.8;Further Reading;595
15;Processes in Coastal and Shelf Seas
;596
15.1;Beaches, Physical Processes Affecting;598
15.1.1;Introduction;598
15.1.2;Beaches;598
15.1.3;Wave-dominated Beaches;598
15.1.4;Tide-modified Beaches;604
15.1.5;Tide-dominated Beach;606
15.1.6;Beach Modification;606
15.1.7;Further Reading;608
15.2;Shelf Sea and Slope Sea Fronts
;609
15.2.1;Introduction
;609
15.2.2;Freshwater Fronts in Shelf Seas
;609
15.2.3;Tidal Mixing Fronts in Shelf Seas
;610
15.2.4;Shelf Slope Fronts
;615
15.2.5;Summary
;617
15.2.6;Further Reading
;617
15.2.7;Relevant Websites
;618
16;Appendices
;620
16.1;Appendix 1. SI Units and Some Equivalences;622
16.2;Appendix 6. The Beaufort Wind Scale anD Seastate
;625
17;Index
;628

Leseproben

Surface Gravity and Capillary Waves
W.K. Melville    Scripps Institution of Oceanography, University of California, San Diego, La Jolla, USA Introduction
Ocean surface waves are the most common oceanographic phenomena that are known to the casual observer. They can at once be the source of inspiration and primal fear. It is remarkable that the complex, random wave field of a storm-lashed sea can be studied and modeled using well-developed theoretical concepts. Many of these concepts are based on linear or weakly nonlinear approximations to the full nonlinear dynamics of ocean waves. Early contributors to these theories included such luminaries as Cauchy, Poisson, Stokes, Lagrange, Airy, Kelvin and Rayleigh. Many of the current challenges in the study of ocean surface waves are related to nonlinear processes which are not yet well understood. These include dynamical coupling between the atmosphere and the ocean, wave–wave interactions, and wave breaking. For the purposes of this article, surface waves are considered to extend from low frequency swell from distant storms at periods of 10 s or more and wavelengths of hundreds of meters, to capillary waves with wavelengths of millimeters and frequencies of O(10) Hz. In between are wind waves with lengths of O(1–100) m and periods of O(1–10) s. Figure 1 shows a spectrum of surface waves measured from the Research Platform FLIP off the coast of Oregon. The spectrum, F, shows the distribution of energy in the wave field as a function of frequency. The wind wave peak at approximately 0.13 Hz is well separated from the swell peak at approximately 0.06 Hz. Figure 1 (A) Surface displacement spectrum measured with an electromechanical wave gauge from the Research Platform FLIP in 8 m s—1 winds off the coast of Oregon. Note the wind-wave peak at 0.13 Hz, the swell at 0.06 Hz and the heave and pitch and roll of FLIP at 0.04 and 0.02 Hz respectively. (B) An extension of (A) with logarithmic spectral scale, note that from the wind sea peak to approximately 1 Hz the spectrum has a slope like f—4, common in wind-wave spectra. (Reproduced with permission from Felizardo FC and Melville 1995. Correlations between ambient noise and the ocean surface wave field. Journal of Physical Oceanography 25: 513–532.) Ocean surface waves play an important role in air–sea interaction. Momentum from the wind goes into both surface waves and currents. Ultimately the waves are dissipated either by viscosity or breaking, giving up their momentum to currents. Surface waves affect upper-ocean mixing through both wave breaking and their role in the generation of Langmuir circulations. This breaking and mixing influences the temperature of the ocean surface and thus the thermodynamics of air–sea interaction. Surface waves impose significant structural loads on ships and other structures. Remote sensing of the ocean surface, from local to global scales, depends on the surface wave field. Basic Formulations
The dynamics and kinematics of surface waves are described by solutions of the Navier-Stokes equations for an incompressible viscous fluid, with appropriate boundary and initial conditions. Surface waves of the scale described here are usually generated by the wind, so the complete problem would include the dynamics of both the water and the air above. However, the density of the air is approximately 800 times smaller than that of the water, so many aspects of surface wave kinematics and dynamics may be considered without invoking dynamical coupling with the air above. The influence of viscosity is represented by the Reynolds number of the flow, Re = UL/µ, where U is a characteristic velocity, L a characteristic length scale, and v = µ/P is the kinematic viscosity, where µ is the viscosity and ? the density of the fluid. The Reynolds number is the ratio of inertial forces to viscous forces in the fluid and if Re>>1, the effects of viscosity are often confined to thin boundary layers, with the interior of the fluid remaining essentially inviscid (v = 0). (This assumes a homogeneous fluid. In contrast, internal waves in a continuously stratified fluid are rotational since they introduce baroclinic generation of vorticity in the interior of the fluid). Denoting the fluid velocity by u = (u, v, w), the vorticity of the flow is given by =?×u If =0, the flow is said to be irrotational. From Kelvin’s circulation theorem, the irrotational flow of an incompressible (?.u = 0) inviscid fluid will remain irrotational as the flow evolves. The essential features of surface waves may be considered in the context of incompressible irrotational flows. For an irrotational flow, u = ?? where the scalar ? is a velocity potential. Then, by virtue of incompressibility, ? satisfies Laplace’s equation 2?=0   [1] We denote the surface by z =(x, y,t), where (x, y) are the horizontal coordinates and t is time. The kinematic condition at the impermeable bottom at z = -h, is one of no flow through the boundary: ??z=0atz=-h   [2] There are two boundary conditions at z = ?: ??t+u???x+????y=w   [3] ??t+12u2+g?=(pa-p)/?   [4] The first is a kinematic condition which is equivalent to imposing the condition that elements of fluid at the surface remain at the surface. The second is a dynamical condition, a Bernoulli equation, Which is equivalent to stating that the pressure p_ at z = ?_, an infinitesimal distance beneath the surface, is just a constant atmospheric pressure, pa, plus a contribution from surface tension. The effect of gravity is to impose a restoring force tending to bring the surface back to z = 0. The effect of surface tension is to reduce the curvature of the surface. Although this formulation of surface waves is considerably simplified already, there are profound difficulties in predicting the evolution of surface waves based on these equations. Although Laplace’s equation is linear, the surface boundary conditions are nonlinear and apply on a surface whose specification is a part of the solution. Our ability to accurately predict the evolution of nonlinear waves is limited and largely dependent on numerical techniques. The usual approach is to linearize the boundary conditions about z= 0. Linear Waves
Simple harmonic surface waves are characterized by an amplitude a, half the distance between the crests and the troughs, and a wavenumber vector k with |k|= k=2p/?, where ? is the wavelength. The surface displacement, (unless otherwise stated, the real part of complex expressions is taken) =aei(k.x-st)   [5] where s = 2p/T is the radian frequency and T is the wave period. Then ak is a measure of the slope of the waves, and if ak <<1, the surface boundary conditions can be linearized about z = 0. Following linearization, the boundary conditions become ??t=w   [6] ??t+g?=G?(?2??x2+?2??y2)atz=0   [7] where the linearized Laplace pressure is a-p_=G(?2??x2+?2??y2)   [8] where G is the surface tension coefficient. Substituting for ? and satisfying Laplace’s equation and the boundary conditions at z= 0 and -h gives =ig'acoshk(z+h)scoshkh   [9] Where 2=g'ktanhkh   [10] and '=g(1+Gk2/?)   [11] Equations relating the frequency and wavenumber, =s(k),are known as dispersion relations, and for linear waves provide a fundamental description of the wave kinematics. The phase speed, =s/k=(g'ktanhkh)1/2   [12] is the speed at which lines of constant phase (e.g., wave crests) move. For waves propagating in the x-direction, the velocity field...