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Über dieses Buch

The phenomenon of evaporation in the natural environment is of interest in various diverse disciplines. This book is an attempt to present a coherent and organized introduction to theoretical concepts and relationships useful in analyzing this phe­ nomenon, and to give an outline of their history and their application. The main objective is to provide a better understanding of evaporation, and to connect some of the approaches and paradigms, that have been developed in different disciplines concerned with this phenomenon. The book is intended for professional scientists and engineers, who are active in hydrology, meteorology, agronomy, oceanography, climatology and related environ­ mental fields, and who wish to study prevailing concepts on evaporation. At the same time, I hope that the book will be useful to workers in fluid dynamics, who want to become acquainted with applications to an important and interesting natural phenomenon. As suggested in its subtitle, the book consists of three major parts. The first, consisting of Chapters I and 2, gives a general ouline of the problem and a history of the theories of evaporation from ancient times through the end of the nineteenth century. This history is far from exhaustive, but it sket~hes the background and the ideas that led directly to the scientific revolution in Europe and, ultimately, to our present-day knowledge.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
The main concern of this book is the evaporation of water in the natural environment. In general, evaporation is the phenomenon by which a substance is converted from the liquid or solid state into vapor. In the case of a solid substance, the phenomenon is often referred to as sublimation. The vaporization of water through the stomata of living plants is called transpiration. Over land transpiration from vegetation and direct evaporation from the soil and small water surfaces are difficult to separate in computations; therefore these two terms are often combined in the term evapotranspiration. All these distinctions are useful at times; however, the term evaporation is usually adequate to cover all processes of vaporization, unless specified otherwise.
Wilfried Brutsaert

Chapter 2. History of the Theories of Evaporation — A Chronological Sketch

Abstract
Since time immemorial human beings have observed evaporation of water in their surroundings, and they undoubtedly have speculated on the nature of this phenomenon. For a better understanding of the discovery of our present knowledge, it is appropriate to review briefly some of the concepts of the past and their evolution.
Wilfried Brutsaert

Chapter 3. The Lower Atmosphere

Abstract
For many practical purposes, the air of the lower atmosphere can be considered as a mixture of perfect gases; in the present context these may conveniently be assumed to be dry air of constant composition and water vapor.
Wilfried Brutsaert

Chapter 4. Mean Profiles and Similarity in a Stationary and Horizontally-Uniform ABL

Abstract
In this chapter the so-called flux-profile relationships are presented for specific humidity, and other relevant quantities such as wind speed and temperature in the different sublayers of the ABL. Because of the above-mentioned difficulties of closure, these relationships are not derived by the solution of the transport equations; rather they are arrived at by invoking similarity, through the application of dimensional analysis. Thus, after the relevant physical quantities are identified from the governing equations or simply by inspection, they are organized into a reduced number of dimensionless quantities. Dimensional analysis only establishes the possible existence of a functional relationship between these dimensionless quantities; however, the function itself must usually be determined by experiment. Still, in some cases the functional form of the relationship may be inferred theoretically by means of a conceptual transport model or by applying a plausible closure assumption to the transport equations, and only some unknown constants need be determined experimentally. Especially in recent years numerous similarity models for the ABL have been proposed in the literature. This chapter does not present an exhaustive review but only the more important schemes that appear applicable in the determination of water vapor transport.
Wilfried Brutsaert

Chapter 5. The Surface Roughness Parameterization

Abstract
The momentum roughness, z 0 m , is an important parameter, not only for the wind profile, but it is also essential in the calculation of z 0 υ , for water vapor, z0 h for heat and the roughness parameters for other scalars.
Wilfried Brutsaert

Chapter 6. Energy Fluxes at the Earth’s Surface

Abstract
Evaporation and sensible heat flux into the atmosphere require the availability of some form of energy at the earth-atmosphere interface. This question can be treated quantitatively by considering the equation for the energy budget for a layer of surface material. Depending on the nature of the surface, this layer may consist of water, or of some other substrate like soil, canopy or snow; although this layer can be taken to be infinitesimally thin, it may sometimes even comprise a lake or a vegetational canopy over its entire depth.
Wilfried Brutsaert

Chapter 7. Advection Effects Near Changes in Surface Conditions

Abstract
The concepts reviewed up to this point are applicable to study local evaporation from surfaces, which are sufficiently uniform and large, so that edge effects involving horizontal advection by the mean wind are relatively unimportant. The assumption of a horizontally homogeneous and steady boundary layer allows a one-dimensional treatment of the transport phenomena near the surface. However, under natural conditions, this assumption is often invalid. In the case of evaporation from surfaces of limited extent, such as finite-size lakes or irrigated areas surrounded by arid land, the horizontal inhomogeneity can be very important.
Wilfried Brutsaert

Chapter 8. Methods Based on Turbulence Measurements

Abstract
Equations for the means, such as (3.44), (3.62) and (3.67) constitute the basis for the eddy-correlation method. This method consists of determining the turbulent fluxes of water vapor, momentum, sensible heat, or any other admixture from covariances. Hence, over a uniform surface under steady conditions, the surface fluxes E, H and u * can be obtained from (3.74), (3.75) and (3.76), respectively. In practice, the flux E is determined by measuring the fluctuations w′ and q′ and then computing the cross-correlation over a suitable averaging period, and similarly for u * and H. Equations (3.74) and (3.75) for scalars were first applied by Dyer (1961) and Swinbank (1951), respectively.
Wilfried Brutsaert

Chapter 9. Methods Based on Measurements of Mean Profiles

Abstract
Over a uniform surface with an adequate fetch, these methods are based directly on the similarity theories for the atmospheric boundary layer treated in Chapter 4. In the present chapter, first, a brief account is given of the application of profile expressions; second, a summary is given of different forms and applications of some related bulk transfer coefficients.
Wilfried Brutsaert

Chapter 10. Energy Budget and Related Methods

Abstract
These methods involve either the direct application, or some approximation of the equation for the energy budget. One form of this equation is given in (6.1) but in many practical situations it can be simplified considerably. A common characteristic of most energy budget methods is that they require the determination of the net radiation, R n . In general, the energy budget method allows the determination of one of the terms of (6.1), or a simplified form of it, when all the remaining terms can be determined by some independent method.
Wilfried Brutsaert

Chapter 11. Mass Budget Methods

Abstract
Mass budget methods are based on the principle of conservation of mass applied to some part of the hydrological cycle. Conservation of mass, formulated as a mass budget equation, requires that, in general, for any given control volume, the inflow rate minus the outflow rate equal the rate of change of the water stored. Accordingly, evaporation can be determined as the only unknown rest term in the budget equation if all the other terms can be determined independently. Although, from the conceptual point of view, mass budget methods are by far the simplest, their application is often difficult and impractical. Therefore, they are less commonly used than aerodynamic or energy budget methods. Nevertheless, their conceptual simplicity is an appealing feature and, in certain situations, a mass budget approach can be quite appropriate. In this chapter a brief description is given of several ways in which the mass budget can be applied in practice.
Wilfried Brutsaert

Backmatter

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