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The Physical Nature and Structure of Oceanic Fronts

The Physical Nature and Structure of Oceanic Fronts

K. N. Fedorov

ISBN: 978-1-118-66926-6

Jul 2013, American Geophysical Union

333 pages

Select type: O-Book

Description

Published by the American Geophysical Union as part of the Lecture Notes on Coastal and Estuarine Studies Series, Volume 19.

During the past several years, research into the frontal divisions of the ocean has been particularly intensive. The significance of this lies not only in the fact that, in the five years from 1976 to 1980, more than 500 papers on this question were published in various journals throughout the world and at least three major international discussions were held (see p. 17). The newness of the discussion of the topic steins from the qualitative reinterpretation of the physical essence of the phenomenon and its role in the ocean, particularly in the processes of mixing and structure formation.

While in the past the conventional view of fronts as boundaries between large-scale water masses of the ocean only led to the recognition of convenient classification limits created by nature itself, there is now a tendency to study oceanic fronts as integral elements of the dynamics of oceanic waters. As we understand it, fronts are being associated more and more with the dynamic and kinematic features which arise when kinetic energy and enstrophy are transmitted through a cascade of scales characterizing various forms of motion of a stratified medium in laterally confined oceanic basins. We are beginning to get a better understanding of the role synoptic-scale oceanic eddies play in the process of frontogenesis in the ocean. We are beginning to perceive the laws that govern the creation and destruction of fronts due to sudden disruption of the normal processes which match the response of the ocean to the fluxes of heat and buoyancy across the ocean/atmosphere boundary. We can no longer ignore the role of the Earth's rotation in the formation, maintenance and evolution of fronts, as well as in the development of instability at these fronts. Finally, we are turning to fronts as the most likely, and possibly the most effective mechanism for mixing and the transfer of heat and salt through the hydrostatically stable pycnocline. We no longer doubt that the link between the vertical finestructure of the ocean and mesoscale horizontal inhomogeneities inevitably involves fronts.

INTRODUCTION 1

Chapter 1. THE SUBJECT AND METHODS OF RESEARCH

1.1. Historical summary of the development of ideas regarding oceanic fronts 7

1.2. Definitions, terminology and criteria 18

1.3. Classification of frontal zones and fronts of the World Ocean 23

1.4. Modern methods of frontal research 34

Chapter 2. GENERAL PHYSICAL DESCRIPTION OF THE PHENOMENON

2.1. How frequently are fronts encountered in the ocean? 41

2.2. General background of spatial variability in temperature and salinity near the surface of the ocean 59

2.2.1. Composite spectrum of spatial variability of the temperature field in the ocean 61

2.2.2. Spatial variability of salinity 68

2.3. Main physical parameters of frontal zones and interfaces 73

2.4. On the conditions of frontogenesis in the ocean and in the atmosphere 80

2.5. The concepts of deformation field and frontogenesis 92

2.6. On numerical modelling of oceanic frontogenesis 97

2.7. Problems of general frontal dynamics 116

2.8. Factors controlling the evolution of fronts 132

2.8.1. The effect of wind on near-surface fronts 133

2.8.2. Wave-like instability at fronts 135

2.9. On the two important functions of Ekman boundary layers 142

Chapter 3. CHARACTERISTIC FEATURES OF OCEANIC FRONTS

3.1. Eddies and fronts in the ocean 146

3.1.1. Frontogenesis in synoptic eddies 149

3.1.2. Eddy generation at fronts 155

3.1.3. Frontal systems of Gulf Stream rings 163

3.2. Peculiarities of coastal upwelling fronts 188

3.3. Salinity fronts originating from river discharge into coastal areas of the ocean 201

3.3.1. Open-sea discharge fronts 203

3.3.2. Estuarine fronts 220

3.4. Coastal fronts with tidal mixing 227

3.5. Surface phenomena of a frontal nature 230

Chapter 4. FRONTS AND THE STRUCTURE OF THE OCEAN

4.1. On the multifrontal structure of frontal zones 245

4.2. Thermohaline finestructure near oceanic fronts 254

4.2.1. Characteristics of the thermohaline finestructure of frontal zones. 256

4.2.2. The formation, evolution and destruction of frontal intrusions 266

4.3. Characteristic features of the three-dimensional spatial structure of frontal zones (as in the example of the Gulf Stream) 274

4.4. Cross-frontal transfer 286

4.4.1. Estimates of double-diffusive heat and salt transport 287

4.4.2. Role of the density increase due to mixing 290

Chapter 5. PROBLEMS FOR FUTURE RESEARCH AND THE CONCERNS OF ASSOCIATED DISCIPLINES

5.1. Some generalizations 296

5.2. Research on the physics of frontal phenomena in the ocean and associated problems of other disciplines 299

5.3. Future research tasks 303

REFERENCES 309

SUBJECT INDEX 327