. índice . Prefacio . Preface . . aguas . 1 . 2 . 3 . 4 . 5 . 6 . . contamina 1 . 2 . 3 . 4 . 5 . 6 . . holocausto 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . 10 . 11 . 12 . 13 . . lineas 1 . 2 . 3 . 4 . . hidrotermias 1 . 2 . 3 . 4 . 5 . 6 . . nuevas 1 . 2 . 3 . . Reconquista 1 . 2 . . hidrogeo 1 . 2 . 3 . 4 . 5 . 6 . . esbozos 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . . corredorcentral 1 . 2 . 3 . 4 . 5 . . cordones 1 . 2 . 3 . 4 . 5 . . epiola 1 . 2 . 3 . 4 . 5 . 6 . . deriva 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . 10 . 11 . 12 . 13 . 14 . . archivo 1 . 2 . 3 . 4 . . Halcrow 1 . 2 . 3 . 4 . 5 . 6 . . frentehalino 1 . 2 . 3 . 4 . 5 . 6 . 7 . . emicampanaoculto 1 . 2 . 3 . 4 . 5 . 6 . 7 . . Costa del Plata 0 . 1 . 2 . 3 . 4 . 5 . 6 . . Costa del oro 1 . 2 . . IRSA 1 . 2 . 3 . 4 . . flujos . . segmentos . . pendientes 1 . 2 . 3 . 4 . 5 . 6 . . delta 1 . 2 . 3 . 4 . 5 . . propuesta . 1 . 2 . . correconvectivo 1 . 2 . 3 . 4 . 5 . 6 . . plataforma 1 . 2 . . termodinamica 1 . 2 . 3 . . ABL 1 . 2 . . congreso . . girh . . Acumar 1 . 2 . 3 . 4 . . evaluacion 1 . 2 . . BocaRiachuelo 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . 10 . 11 . 12 . 13 . 14 . 15 . 16 . 17 . 18 . 19 . 20 . . StoDomingo . . urgenciasatadas 1 . 2 . . inundabaires 1 . 2 . 3 . 4 . . sinsustento 1 . 2 . . emisarios 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . 10 . . UAG 1 . 2 . 3 . . áreas nuevas 1 . 2 . 3 . . acreencias 1 . 2 . 3 . 4 . 5 . . audiencia 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . . Valls 1 . 2 . . contrastes 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . 10 . . convexterna . . playas 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . . Plan Maestro 1 . 2 . 3 . . Parque Norte . 1 . 2 . . ribera . 1 . 2 . 3 . 4 . 5 . . jurisdiccion 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . 10 . 11 . 12 . . CSJNpisamr 1 . 2 . 3 . 4 . . zonas muertas . . Bermejo 1 . 2 . . Pilcomayo . . Samborombon . . Salado . . Uruguay 1 . 2 . . Parana . . Mar del Plata 1 . 2 . 3 . 4 . 5 . . PuntaRasa 1 . 2 . . PuntaMedanos . . Mar Chiquita . . Necochea . . Areco 1 . 2 . . Colonia . . MartinGarcia 1 . 2 . 3 . . Puertos 1 . 2 . . formula1 . . disocio . . senderos . . bajante . . . . oceano 1 . 2 . . hidrolinea 1 . 2 . 3 . . sustentable. 1 . 2 . . agua 1 . 2 . 3 . . antarticflows . . derrame . . luna 1 . 2 . 3 . 4 . 5 . 6 . . index .


La pregunta formulada a través del Scholar.google.com.ar sobre

Thermal boundary layer on sea borders

me regaló acceso al hermoso Glosario de la American Metheorological Society del cual reproduzco definiciones de algunos pocos términos

Glosario de la American Metheorological Society


boundary layer separation—A condition that occurs at sufficiently high Reynolds numbers in which the surface streamlines break away from the surface.
Separation is due to the presence of a solid boundary, at which the no-slip condition—that is, the velocity of the fluid particles in contact with the surface is the velocity of that surface—is satisfied and vorticity is generated. Separation of a steady boundary layer at a plane or rounded rigid wall occurs whenever the velocity of the fluid just outside of the boundary layer decreases in the mean flow direction sufficiently rapidly and by a sufficient amount. This can be accomplished by the imposition of an opposing pressure gradient in the direction of flow.
Batchelor, G. K., 1967: Fluid Dynamics, Cambridge University Press, p. 325.

boundary layer—1. The layer of fluid near a boundary that is affected by friction against that boundary surface, and possibly by transport of heat and other variables across that surface.
In meteorology, this is the atmospheric boundary layer. 2. In a physical or mathematical system, a region over which some property or term in the equations varies rapidly, that is, over its full range; conversely, a region outside of which certain terms may be neglected.

boundary mixing—Mixing occurring on sloping topography on the ocean margins or on seamounts primarily as the result of breaking internal waves.
Boundary mixing is thought to play a major role in the vertical transport of heat.

boundary of saturation—The surface between the saturated and unsaturated zones in a soil.
The boundary of saturation is the top of the capillary fringe.

boundary-value problem—A physical problem completely specified by a differential equation in an unknown, valid in certain information (boundary conditions) about the unknown given on the boundaries of that region.
The information required to determine the solution depends completely and uniquely on the particular problem. A great variety of meteorological problems are formulated as boundary-value problems. See also initial-value problem.

bottom water—1. The water mass at the deepest part of the water column.
It is the densest water that is permitted to occupy that position by the regional topography. In the case of a basin, bottom water may be formed locally, or it may represent the densest water that has existed at sill depth in the recent past. 2. Water masses found at the bottom of ocean basins.
The most important bottom waters of the World Ocean are Antarctic Bottom Water and Arctic Bottom Water. Baffin Bay Bottom Water has a salinity of 34.49 and a temperature of −0.4°C and is found in Baffin Bay below a depth of 1800 m; its low oxygen content of 3.6 ml l−1 indicates slow water renewal. Japan Sea Bottom Water has a salinity of 34.1 and a temperature of 0.04°C; it is formed by winter convection in the northern Japan Sea and occupies the Japan Sea basins at depths below 2000 m.

boundary conditions—A set of mathematical conditions to be satisfied, in the solution of a differential equation, at the edges or physical boundaries (including fluid boundaries) of the region in which the solution is sought.
The nature of these conditions is usually determined by the physical nature of the problem, and is a necessary part of the problem's complete formulation. Common boundary conditions for the atmosphere are that the velocity component normal to the earth's surface vanish, and that the individual derivative of pressure vanish at the upper surface. The term is also used in the context of the time evolution of an “open” dynamical system that interacts with other “external” systems. The state of the external systems must be specified as a boundary condition to infer the evolution of the dynamical system under consideration. For example, the evolution of the earth's atmospheric state requires the specification of sea surface temperature as a boundary condition. See kinematic boundary condition, dynamic boundary condition, boundary-value problem, initial condition.

boundary currents—Ocean currents with dynamics determined by the presence of a coastline.
They fall into two categories: 1) western boundary currents, which are narrow, deep-reaching, and fast-flowing currents, not unlike jet streams, associated with current instability and eddy shedding; and 2) eastern boundary currents, which are shallow, cover a wider region, are of moderate strength, and are often associated with coastal upwelling and a subsurface countercurrent along the continental slope. Both are integral parts of the circulation in oceanic gyres. The rotation of the earth causes an accumulation of energy on the western side, which has to be dissipated in boundary currents; this gives the western boundary currents typical widths of 100 km and typical speeds of 2 m s−1 and causes them to shed eddies frequently to increase the dissipation of energy. No similar requirement of energy dissipation exists on the eastern side, so eastern boundary currents can be broad and slow. Their special character as a boundary current results from coastal upwelling, which brings the thermocline to the surface and as a result produces a temperature front and an associated geostrophic maximum in the current speed, known as the coastal jet. Because of the upwelling, eastern boundary currents are atmospheric heat sinks. Western boundary currents are atmospheric heat sinks if they move cold water toward the equator, which occurs in the subpolar gyres, and atmospheric heat sources where they move tropical water into temperate regions, as in the subtropical gyres.

capillarity—The action by which the surface of a liquid in contact with a solid (as in a capillary tube) is elevated or depressed depending on the relative attraction of the molecules of the liquid for each other and for those of the solid (e.g., the meniscus of a liquid column). See capillary action, capillary depression.

capillary action—The depression or elevation of the meniscus of a liquid contained in a tube of small diameter due to the combined effects of gravity, surface tension, and the forces of cohesion and adhesion.

When the liquid wets the walls of a container, the meniscus is shaped convex downward; if the liquid does not wet the walls of the container, the meniscus is shaped convex upward.

capillary collector—An instrument for collecting liquid water from the atmosphere.

The collecting head is fabricated of a porous material having a pore size of the order of 30 μm. The pressure difference across the water–air interface prevents air from entering the capillary system while allowing free flow of water.

capillary conductivity—Same as unsaturated hydraulic conductivity; not commonly used.

capillary depression—The depression of the meniscus of a liquid contained in a tube where the liquid does not wet the walls of the container (as in a mercury barometer). The meniscus is shaped convex upward, and this results in a depression of the meniscus

capillary diffusion—(Also called capillary movement.) The movement of fluids in unsaturated porous media due to surface tension and adhesive driving forces (capillarity).

capillary forces—The mechanical forces exerted on soil water resulting from the curved interface between the air and water caused by the combined effect of surface tension and effective contact angle.

capillary hysteresis—The phenomenon that the equilibrium positions of the air–water interfaces in a system of pores are dependent on whether the system is increasing or decreasing in water content (i.e., the wetting history).

capillary interstice—A pore space in sediment (interstitial pore space) small enough for the occurrence of appreciable capillary rise.

capillary pressure—The difference in pressure across the interface between two immiscible fluids. The pressure difference is proportional to the surface tension and inversely proportional to the effective radius of the interface.

capillary rise—(Also called height of capillary rise.) The height above a free surface to which a liquid will rise by capillary action.

capillary suction—Phenomenon resulting from capillary forces that induce a liquid to enter a porous medium.

coalescence efficiency—The fraction of all collisions between water drops of a specified size that results in actual merging of the two drops into a single larger drop.
In discussing the details of the growth of raindrops by collision and coalescence, it is important to distinguish clearly the terms coalescence efficiency, collision efficiency, and collection efficiency, the last being equal to the product of the first two.

coalescence—In cloud physics, the merging of two water drops into a single larger drop after collision.
Coalescence between colliding drops is affected by the impact energy, which tends to increase with the higher fall velocities of larger drops. Colliding drops having negligible impact energy compared to their surface energy behave as water spheres that collide with a collision efficiency (the fraction of small drops that collide with a large drop within the geometric collision cross section) predicted by the theory for falling spheres. The result of increasing impact energy is to flatten the colliding drops at the point of impact, impeding the drainage of the air and delaying contact between them. As the distortion relaxes, the drops rebound, reducing the coalescence efficiency for cloud drops and drizzle drops colliding with smaller drops. At larger impact energy, separation will occur if the rotational energy (fixed by conservation of angular momentum) is higher than the surface energy of the coalescing drops. This phenomenon, termed temporary coalescence, can result in satellite droplets considerably smaller than either of the parent drops. This phenomenon is also called partial coalescence because the large drop may gain mass as a result of the higher internal pressure in the small drop. At still larger impact energy, drop breakup occurs for the smaller drop. About 20% of the high-energy collisions between large raindrops (d > 3 mm) and drizzle drops (d > 0.2 mm) result in the disintegration of both drops. Other factors that affect coalescence are electric charge and electric field, both of which promote coalescence, leading to earlier onset of coalescence during an interaction so that coalescence efficiencies are increased by suppression of rebound and temporary coalescence. All of these processes are important in formation of precipitation in all liquid clouds both above and below 0°C. See collision– coalescence process.

coastal front—A shallow (typically < 1 km deep) mesoscale frontal zone marked by a distinct cyclonic windshift in a region of enhanced thermal contrast (≈ 5°–10°C/10 km).
These fronts typically develop in coastal waters or within 100–200 km of the coast during the cooler half of the year when the land is cold relative to the ocean. In the United States coastal fronts are most frequent in New England, the Middle Atlantic states, the Carolinas, and Texas. The typical coastal front is oriented quasi-parallel to the coast and may extend for several hundred kilometers. During the winter, the coastal front may mark the boundary between frozen and nonfrozen precipitation. Given that coastal front development usually precedes synoptic-scale cyclogenesis and marks an axis of enhanced thermal contrast and a maximum in cyclonic vorticity and convergence, the coastal front often serves as a boundary along which intensifying synoptic- scale cyclones move poleward. Surface coastal front development typically occurs beneath the forward side of advancing troughs following the passage of the ridge axis aloft. Coastal fronts most frequently form equatorward of cold anticyclones where a warmer onshore flow encounters a colder continental air stream. Damming of cold air on coastal orographic barriers such as the Appalachians often appears to play an important role in coastal front development. Coastal thermal contrasts are augmented by differential diabatic heating where the onshore flow has passed over oceanic thermal boundaries such as the Gulf Stream and the adjacent continental airstream has passed over snow-covered land. Coastal fronts may form independently of cold anticyclones and associated cold air damming. In situ coastal front developments can occur near mountain barriers where upslope flow results in differential airmass cooling and stabilization and where offshore troughs form due to differential heating across oceanic thermal boundaries. Coastal front dissipation typically occurs with the cessation of onshore flow following cyclone passage.
coastal upwelling—The rising of water from between 200 and 400 m to the surface along coastlines where an alongshore blowing wind has the coast on its left in the Northern Hemisphere or on its right in the Southern Hemisphere.
Because the surface currents of the Ekman spiral are deflected offshore in these situations, the surface water is drawn away from the coast, causing the colder water from deeper layers to upwell. The associated lowering of the sea surface temperature results in atmospheric heat loss and modifies the local climate. The upwelled water is also rich in nutrients, and coastal upwelling regions are among the most important fishing regions of the World Ocean. The most important coastal upwelling regions are found in the eastern boundary currents of the subtropical gyres, that is, in the Peru/Chile, California, Benguela, and Canary Currents. The Somali, East Arabian, and South Java Currents develop upwelling on a seasonal basis.

Coastal Zone Color Scanner—(Abbreviated CZCS.) A scanning radiometer with six channels flown on Nimbus 7 (launched October 1978) designed to monitor ocean color and phytoplankton production in coastal areas.
Four channels are in the visible part of the spectrum, one in the near-infrared, and one in the thermal infrared.

coastal zone—A region a few kilometers wide on either side of the shoreline where local thermal circulations such as the sea breeze and land breeze occur.

coefficient of thermal expansion—The relative increase of the volume of a system (or substance) with increasing temperature in an isobaric process.
In symbols this coefficient is

where V is the volume, T the temperature, and p the pressure. See Charles–Gay–Lussac law; compare coefficient of compressibility, coefficient of tension

colloidal system—(Also called colloidal dispersion, colloidal suspension.) An intimate mixture of two substances, one of which, called the dispersed phase (or colloid), is uniformly distributed in a finely divided state through the second substance, called the dispersion medium (or dispersing medium).
The dispersion medium may be a gas, a liquid, or a solid and the dispersed phase may also be any of these, with the exception of one gas in another. A system of liquid or solid particles colloidally dispersed in a gas is called an aerosol. A system of solid substance or water-insoluble liquid colloidally dispersed in liquid water is called a hydrosol. There is no sharp line of demarcation between true solutions and colloidal systems or between mere suspensions and colloidal systems. When the particles of the dispersed phase are smaller than about 10−3 μm in diameter, the system begins to assume the properties of a true solution; when the particles dispersed are much greater than 1 μm, separation of the dispersed phase from the dispersing medium becomes so rapid that the system is best regarded as a suspension. According to the latter criterion, natural clouds in the atmosphere should not be termed aerosols; however, since many cloud forms apparently exhibit characteristics of true colloidal suspensions, this strict physico-chemical definition is often disregarded for purposes of convenient and helpful analogy. Condensation nuclei and many artificial smokes may be regarded as aerosols.

colloidal instability—A property attributed to clouds (regarded in analogy to colloidal systems or aerosols) by virtue of which the particles of the cloud tend to aggregate (through Brownian motion) into masses large enough to precipitate.
The viewpoint that regards an atmospheric cloud as an aerosol somewhat strains the physical chemist's definition thereof, for cloud particles are much larger than the particles typically treated as colloidally dispersed materials either in a gas or in a liquid.
convection—1. In general, mass motions within a fluid resulting in transport and mixing of the properties of that fluid.
Convection, along with conduction and radiation, is a principal means of energy transfer. Distinction is made between free convection (gravitational or buoyant convection), motion caused only by density differences within the fluid; and forced convection, motion induced by mechanical forces such as deflection by a large-scale surface irregularity, turbulent flow caused by friction at the boundary of a fluid, or motion caused by any applied pressure gradient. Free and forced convection are not necessarily exclusive processes. On a windy day with overcast sky, the heat exchange between ground and air is an example of forced convection. On a sunny day with a little wind where the ground temperature rises, both kinds of convection take place. 2. (Or gravitational or buoyant convection.) Motions that are predominantly vertical and driven by buoyancy forces arising from static instability, with locally significant deviations from hydrostatic equilibrium.
Atmospheric convection is nearly always turbulent. Convection may be dry, that is, with relative humidities less than 100%, especially in the boundary layer, but is commonly moist, with visible cumuliform clouds. Most convective clouds are driven by positive buoyancy, with virtual temperature greater than the environment, but clouds with precipitation, evaporation, and/or melting can produce negatively buoyant convection. See slantwise convection. 3. As specialized in atmospheric and ocean science, a class of relatively small-scale, thermally (can be driven by salt concentration in the ocean) direct circulations that result from the action of gravity upon an unstable vertical distribution of mass. (In the case of slantwise convection, though, the motions are larger scale, and are driven by a combination of gravitational and centrifugal forces acting at an angle to the vertical.)
Almost all atmospheric and oceanic convection is fully turbulent and is generally composed of a collection of convection cells, usually having widths comparable to the depth of the convecting layer. In the atmosphere, convection is the dominant vertical transport process in convective boundary layers, which are common over tropical oceans and, during sunny days, over continents. In the ocean, convection is prominent in regions of high heat loss to the atmosphere and is the main mechanism of deep water formation. Moist convection in the atmosphere is characterized by deep, saturated updrafts and downdrafts, and unsaturated downdrafts driven largely by the evaporation and melting of precipitation. This form of convection is made visible by cumulus clouds and, in the case of precipitating convection, by cumulonimbus clouds. Moist convection and radiation are the dominant modes of vertical heat transport in the Tropics. 4. In atmospheric electricity, a process of vertical charge transfer by transport of air containing a net space charge, or by motion of other media (e.g., rain) carrying net charge.

convective boundary layer—(Abbreviated CBL.) Same as mixed layer.
See also atmospheric boundary layer.

current—1. Any movement of material in space. See air current, ocean current. 2. Any movement of electric charge in space, by virtue of which a net transport of charge occurs as, for example (in atmospheric electricity), in a conduction current, convection current, or precipitation current.

dynamic viscosity—(Also called coefficient of molecular viscosity, coefficient of viscosity.) A fluid property defined as the ratio of the shearing stress to the shear of the motion.
It is independent of the velocity distribution, the dimensions of the system, etc., and for a gas it is independent of pressure except at very low pressures. For the dynamic viscosity μ of a perfect gas, the kinetic theory of gases gives

where is the gas density, c is the average speed of the random heat motion of the gas molecules and is proportional to the square root of the temperature, and L is the mean free path. For dry air at 0°C, the dynamic viscosity is about 1.7 × 10−4 g cm−1s−1. While the dynamic viscosity of most gases increases with increasing temperature, that of most liquids, including water, decreases rapidly with increasing temperature. See kinematic viscosity, eddy viscosity, Newtonian friction law.

eddy—1. By analogy with a molecule, a “glob” of fluid within the fluid mass that has a certain structure and life history of its own, the activities of the bulk fluid being the net result of the motion of the eddies.
The concept is applied with varying results to phenomena ranging from the momentary spasms of the wind to storms and anticyclones. 2. Any circulation drawing its energy from a flow of much larger scale, and brought about by pressure irregularities, as in the lee of a solid obstacle. 3. In studies of the general circulation, departures of a field (e.g., temperature or relative vorticity) from the zonal mean of that field. 4. A closed circulation system produced as an offshoot from an ocean current.
Eddies are the result of the turbulence of the oceanic circulation and are common throughout the World Ocean. The corresponding features in the atmosphere are the wind currents around high and low pressure disturbances. Oceanic cyclonic eddies have a shallow thermocline at the center and are therefore also known as cold-core eddies; anticyclonic eddies are associated with a depressed thermocline in the center and are also known as warm-core eddies. The most prominent eddies are those shed by western boundary currents, also known as rings; they are about 200 km in diameter and reach beyond a depth of 1500 m. Another class of eddies is produced by shear between currents flowing in opposing directions. These eddies tend to be smaller (10–50 km in diameter) and shallower.

Eddy diffusion of air containing a net charge gradient may also yield a convection current.

eddy viscosity—The turbulent transfer of momentum by eddies giving rise to an internal fluid friction, in a manner analogous to the action of molecular viscosity in laminar flow, but taking place on a much larger scale.
The value of the coefficient of eddy viscosity (an exchange coefficient) is of the order of 1 m2 s−1, or one hundred thousand times the molecular kinematic viscosity. Eddy viscosity is often represented by the symbol K, and the turbulence parameterization that uses eddy viscosity is called K-theory. In this theory, the eddy flux in kinematic units is related to the mean vertical gradient, such as in this example for vertical flux of horizontal momentum:

where w is vertical velocity, U is horizontal wind in the x direction, the overbar represents an average, and the prime denotes the deviation or perturbation from an average. Eddy viscosity is a function of the flow, not of the fluid. It is greater for flows with more turbulence. The eddy viscosity or K-theory approach is a parameterization for the eddy momentum flux (Reynolds stress) that works reasonably well when only small eddies are present in the flow, but that behaves poorly when large-eddy coherent structures, such as thermals in the convective mixed layer, are present. See Reynolds stresses, eddy correlation; compare transilient turbulence theory.

energy—A measurable physical quantity, with dimensions mass times velocity squared, that is conserved for an isolated system.
Energy of motion is kinetic energy; energy of position is potential energy. See energy conversion, internal energy, enthalpy.
Feynman, R. P., R. B. Leighton, and M. Sands, 1963: The Feynman Lectures in Physics, Vol. I, p. 4-2.

energy transfer—Any process in which a system interacts with its surroundings in such a way that the energy of the system increases (or decreases) while that of the surroundings decreases (or increases) by the same amount.
See also energy conversion.

energy conversion—(Also energy transformation, energy transfer.) A process in which energy changes from one form to another.
Energy is conserved for a system that does not interact with its surroundings, and the total energy of such a system may often be expressed as the sum of energies of different kinds:

Thus if E1 decreases in any process, E2, etc., must increase correspondingly for E to remain constant, and we may say that energy of type 1 has been converted into energies of type 2, 3, etc.

enthalpy—A thermodynamic state function H defined as

where U is the internal energy, p is pressure, and V is volume.
Specific enthalpy of a homogeneous system, h, is its enthalpy divided by its mass, m, defined by

where u is specific internal energy and v is specific volume. With aid of the gas laws, the specific enthalpy of an ideal gas may also be written as

where T is temperature and cp is the specific heat at constant pressure. The specific enthalpy of a liquid, hl;t7, is

where cl is the liquid's specific heat, which is nearly independent of pressure and specific volume. For a system consisting of a mixture of components, the total enthalpy is the mass-weighted sum of the enthalpies of each component. Thus, the total enthalpy of a system consisting of a mixture of dry air, water vapor, and liquid water is

where md, mv, and mw are the masses of dry air, water vapor, and liquid water, respectively; cpd and cpv the specific heats of dry air and water vapor; and cw is the specific heat of liquid water. This quantity is commonly called moist enthalpy, with specific moist enthalpy given by h = H/(md + mv + mw). With the aid of the definition of the latent heat of vaporization (see latent heat), moist enthalpy may also be written as

where mt is the mass of vapor plus liquid and Lv is the latent heat of vaporization. Similar relations can be written to include the effects of ice. In an adiabatic, reversible process, enthalpy and specific enthalpy are conserved, although the component specific enthalpies may not be, due to the exchange of enthalpy between components in phase changes.

equation of piezotropy—(Also called physical equation.) An equation relating the thermodynamic variables in processes of a piezotropic fluid.
In its general form it expresses the density as a function of the pressure p:

The derivative d/dp is called the coefficient of piezotropy. The most familiar such equation is that for polytropic changes of state in an ideal gas:

where λ is the modulus of the polytropic process. Prior to the discovery of the first law of thermodynamics in the midnineteenth century, the equation of piezotropy was used to complete the hydrodynamic equation set consisting of the equations of motion and the conservation of mass.

estuary—1. The portion of a river that is affected by tides. 2. A semi-enclosed body of water where the salinity of ocean water is measurably reduced by freshwater input.
Estuaries are very important nursery regions for many coastal ocean species of fish and invertebrates.

exchange coefficients— [Also called turbulent transfer coefficient, eddy diffusivity, austausch coefficients (obsolete).] The ratio of the turbulent flux of a conservative property through a surface to the gradient of the mean of the property normal to the surface.
See diffusion, eddy flux, turbulence.

flood current—The movement of a tidal current toward the shore or up a tidal river or estuary. See flood tide.

geostrophic—Referring to the balance, in the atmosphere, between the horizontal Coriolis forces and the horizontal pressure forces.
See geostrophic wind, geostrophic equilibrium, geostrophic balance.

gradient—1. The space rate of decrease of a function.
The gradient of a function in three space dimensions is the vector normal to surfaces of constant value of the function and directed toward decreasing values, with magnitude equal to the rate of decrease of the function in this direction. The gradient of a function f is denoted by −f (without the minus sign in the older literature) and is itself a function of both space and time. The ascendent is the negative of the gradient. In Cartesian coordinates, the expression for the gradient is

For expressions in other coordinate systems, see Berry et al. (1945). 2. Often loosely used to denote the magnitude of the gradient or ascendent (i.e., without regard to sign) of a horizontal pressure field.
Berry, F. A., E. Bollay, and N. Beers, 1945: Handbook of Meteorology, 224–225

gradient current—In oceanography, a current determined by the condition that the horizontal pressure gradient due to the (hydrostatic) distribution of mass balances the Coriolis force due to the earth's rotation.
The gradient current corresponds to the geostrophic wind in meteorology. In practice, the distribution of density is determined by measurements of salinity and temperature at a series of depths in a number of positions. From this the geopotential topography of any isobaric surface relative to any other isobaric surface may be computed and the horizontal pressure gradient may be expressed by the geopotential slope of the isobaric surface. In this way relative isobaric surface currents are obtained, corresponding to thermal wind in meteorology. If one isobaric surface is known to be level, the absolute geopotential topography of any other surface may be computed by reference to this, and hence absolute gradient currents are obtained. Where no isobaric surface is known to be level, the total gradient current will consist of the relative gradient current, due to the distribution of density, and the slope current, due to that portion of the inclination of the isobaric surfaces that is not the result of the distribution of density. See also geostrophic current.

heat—1. (Or heat content.) A form of energy transferred between systems, existing only in the process of transfer. 2. Same as enthalpy.
Heat, used as a noun, is confusing and controversial in its scientific meaning. The differential of heat is considered imperfect in that its value depends on the process applied. In the thermodynamic definitions in this glossary, heat is avoided as a noun or adjective except where required by established use. The process of heating is, however, defined as the net absorption of internal energy by a system.

internal energy—The energy of a system exclusive of its kinetic energy of mass motion and its potential energy arising from external forces.
The internal energy of a system of molecules is the sum of their translational kinetic energies, their vibrational (kinetic and potential) and rotational (kinetic) energies, and the total potential energy arising from forces between molecules. An ideal gas is defined as one for which the intermolecular potential energy is zero. The internal energy of such a gas depends only on its temperature

kinematic viscosity—A coefficient defined as the ratio of the dynamic viscosity of a fluid to its density.
The kinematic viscosity of most gases increases with increasing temperature and decreasing pressure. For dry air at 0°C, the kinematic viscosity is about 1.46×10−5 m2 s−1. Common symbols for these variables are μ for dynamic viscosity and ν for kinematic viscosity.
          List, R. J., 1951: Smithsonian Meteorological Tables, 6th rev. ed., 394–395.

kurtosis—(Symbol β2 or α4.) A descriptive measure of a random variable in terms of the flatness of its probability distribution.
It is defined as follows:

where μ4 is the fourth (statistical) moment about the mean and σ2 the variance. For the normal distribution, β2 = 3; and it is commonly (though not invariably) found that curves for which β2 > 3 are more sharply peaked than the normal, while those for which β2 < 3 are flatter than the normal. In particular, the rectangular distribution f(x) = 1 (0 < x < 1) has β2 = 1.8. The terms leptokurtic, mesokurtic, and platykurtic refer to curves for which the values of β2 are, respectively, greater than 3, equal to 3, and less than 3. Excess is a relative expression for kurtosis, and the coefficient of excess γ2 is defined as β2 − 3.

last glacial—The most recent time (15 000 to 80 000 years ago) during which continental glaciers covered subpolar regions and existed at elevations as much as 1000 m lower than today; corresponding to periods in which oxygen isotopes from marine sediment cores indicate that global sea level was 50–150 m lower and global temperature 5°–10°C lower than today.

last interglacial—The most recent time (115 000 to 125 000 years ago) during which global temperatures were as high as or higher than in the postglacial, when continental glaciers were limited to the Arctic and Antarctic, and sea levels were near current positions.

Little Ice Age—A period between approximately A.D. 1550 (or perhaps as early as 1300) and 1850 in which mountain glaciers advanced in many parts of the world.
The precise timing of the advances and retreats varied from region to region. Temperatures were not uniformly colder throughout this period, but rather showed marked variations on decadal timescales.

mass-transfer method—Method for estimating the actual evaporation from a body of water, assuming it is proportional to the product of wind velocity (perhaps raised to a power less than one), the difference between the saturation vapor pressure at water surface temperature and the vapor pressure of the ambient air, and an empirical mass-transfer coefficient.

mass transport—The momentum, u, where is the fluid density and u the velocity vector, considered as the transport of fluid mass from one region of space to another

mixed layer—1. (Abbreviated ML; sometimes called convective mixed layer, convective boundary layer, or mixing layer in air-pollution meteorology.) A type of atmospheric boundary layer characterized by vigorous turbulence tending to stir and uniformly mix, primarily in the vertical, quantities such as conservative tracer concentrations, potential temperature, and momentum or wind speed.
Moisture is often not so well mixed, showing a slight decrease with height. The vigorous turbulence can be caused by either strong winds or wind shears that generate mechanical turbulence (called forced convection), or by buoyant turbulence (called free convection) associated with large thermals. The buoyantly generated mixed layers are usually statically unstable, caused by heating at the bottom boundary such as the earth's surface or radiative cooling at the tops of cloud or fog layers within the mixed layer. The terms mixed layer, convective mixed layer, and convective boundary layer commonly imply only the buoyantly stirred layer. During fair weather over land, mixed layers are usually daytime phenomena generated buoyantly, with growth caused by entrainment of free-atmosphere air into the mixed-layer top. See mixed-layer depth, entrainment zone, radix layer, uniform layer. 2. In oceanography, a fully turbulent region of quasi-isopycnal water (i.e., virtually uniform potential density) that, in the case of the surface mixed layer, is bounded above by the air-sea interface and below by the transition layer.
Mixed layer depth is often defined as the depth at which potential density differs from that of the surface by 0.01 kg m−1.

multiple correlation—The correlation between a random variable and its regression function.
If Y denotes the regression function of a random variable (variate) y with respect to certain other variates x1, x2 . . ., xn then the coefficient of multiple correlation between y and the x's is defined as the coefficient of simple, linear correlation between y and Y. However, the constants of the regression function automatically adjust for algebraic sign, with the result that the coefficient of correlation between y and Y cannot be negative; in fact, its value is precisely equal to the ratio of their two standard deviations, that is, σ(Y)/σ(y). Therefore, the coefficient of multiple correlation ranges from 0 to 1, and the square of the coefficient of multiple correlation is equal to the relative reduction (or percent reduction), that is, the ratio of explained variance to total variance. Since, in practice, the true regression function Y is seldom known, it is ordinarily necessary to hypothesize its mathematical form and determine the constants by least squares, thus obtaining the approximation Y′. In that case, the conventional estimate of the multiple correlation is the sample value of the simple linear correlation (symbol R) between y and Y′, although a better estimate is obtained by incorporating a correction for degrees of freedom. Such a corrected value R′ is given as follows:

where N denotes the sample size and n + 1 equals the total number of constants (including the absolute term) determined from the data. In case (N − 1) R2 < n, the value of R′ is taken as zero. See regression.

polytropic process—A thermodynamic process in which changes of pressure p and density are related according to the formula

where λ is a constant and subscript zeros denote initial values of the variables.
Therefore pressure and temperature are similarly related:

where k is the coefficient of polytropy. For isobaric processes, k = 0; for isosteric processes, k = 1; for adiabatic processes k = cp/R, where cp is the specific heat at constant pressure and R is the gas constant; sometimes applied to circumstances when adiabatic heating or cooling combine with slow ascent or descent to produce a particular lapse rate. In meteorology this formula is applied to individual air parcels and should be distinguished from that for a polytropic atmosphere, which describes a distribution of pressure and temperature in space. See also equation of piezotropy.

rip current—A narrow current in the surf zone flowing seaward from the shore.
It usually appears as a visible band of agitated water and is the return movement of water piled up on the shore by incoming waves and winds.

skewness—Departure from symmetry.
In statistics, the coefficient of skewness γ1 of a random variable or of a probability distribution is defined as γ1 = μ3/σ3, where μ3 is the third moment about the mean and σ is the standard deviation. Where γ1 > 0 the typical curve trails off toward the right and hence is said to be skewed to the right; when γ1 < 0 the longer tail is on the left, and the curve is said to be skewed to the left.

thermal conductivity—The proportionality factor between energy flux and temperature gradient (see conduction).
Thermal conductivity is to an extent an intrinsic property of a medium but may depend on temperature. The thermal conductivity of air is about 50% greater than that of water vapor and that of both increases (approximately) as the square root of absolute temperature. The thermal conductivity of liquid water is about 25 times that of air. Thermal conductivities of solids, especially metals, are thousands of times greater than that of air.

thermocline—A vertical temperature gradient, in some layer of a body of water, that is appreciably greater than the gradients above and below it; also a layer in which such a gradient occurs.
The permanent thermocline refers to the thermocline not affected by the seasonal and diurnal changes in the surface forcing; it is therefore located below the yearly maximum depth of the mixed layer and the influence of the atmosphere. The seasonal thermocline refers to the thermocline not affected by the diurnal changes in the surface forcing. In general, it is established each year by heating of the surface water in the summer, and is destroyed the following winter by cooling at the surface and wind-driven mixing. The diurnal thermocline refers to the thermocline that, in general, is established each day by heating of the surface water and is destroyed the following night by cooling and/or mixing. See also transition layer.

thermodynamics—A collection of ideas and axioms, leading to differential equations specifying rates of change, that describes our experience with processes that involve fluxes of heat and changes in energy content.
Thermodynamics introduces a new concept—temperature—absent from classical mechanics and other branches of physics. Classical thermodynamics deals with equilibrium states, concentrating on initial and final configurations, not on the processes involved in evolution.
Dutton, J. A., 1995: Dynamics of Atmospheric Motion, Dover Press, 35–36, 406–410.
Richards, P. I., 1959: Manual of Mathematical Physics, Pergamon Press, p. 30.
Sommerfeld, A., 1964: Thermodynamics and Statistical Mechanics, Academic Press, v, 1

thermohaline circulation—That part of the large-scale ocean circulation driven by the fluxes of heat and freshwater at the ocean surface.
The freshwater flux affects salinity, and both temperature and salinity changes cause density changes that drive the thermohaline circulation. The present-day forcing consists of cooling and net precipitation in high latitudes, warming and evaporation in subtropical latitudes; note the opposing effects on density. The present-day thermohaline circulation consists of 1) sinking of strongly cooled, moderately saline water in relatively small regions located in areas of relatively strong winter cooling; 2) deep flow throughout the global ocean basins; and 3) slow upwelling toward the surface. Its transport is small compared to wind-driven transport, but it is believed that the thermohaline circulation is responsible for much of the heat transported by the ocean. See gradient current.

tide—1. The periodic rising and falling of the earth's oceans and atmosphere.
It results from the tide-producing forces of the moon and sun acting upon the rotating earth. This disturbance actually propagates as a wave through the atmosphere and along the surface of the waters of the earth. Atmospheric tides are always so designated, whereas the term “tide“ alone commonly implies the oceanic variety. Sometimes, the consequent horizontal movement of water along the coastlines is also called “tide,” but it is preferable to designate the latter as tidal current, reserving the name tide for the vertical wavelike movement. See equatorial tide, neap tide, spring tide, tropic tide. 2. See rip current, red tide, storm tide.

transition layer—1. The thin layer that separates thicker layers of different characteristics. 2. The capping inversion or entrainment zone at the top of the convective mixed layer. 3. The statically stable layer near the base of convective clouds in the Tropics. 4. A stratified layer of a body of water between the mixed layer and the undisturbed fluid beneath it; it refers to the uppermost (closest to the surface) thermocline at any given time

viscosity—(Also called internal friction.) The transport of mass motion momentum solely by the random motions of individual molecules not moving together in coherent groups.
Viscosity is a consequence of gradients in velocity fields in fluids. Sometimes described as fluid friction because velocity gradients in fluids are damped as a consequence of viscosity. See viscous force, stress tensor, dynamic viscosity, kinematic viscosity, Newtonian friction law, Navier– Stokes equations, eddy viscosity.

viscosity coefficientSee dynamic viscosity, kinematic viscosity, eddy viscosity

viscous-convective subrange—The range of wavenumbers in large Prandtl number flows in which viscosity is important, resulting in temperature fluctuations being reduced by the strain-rate field, but where thermal diffusivity is not yet effective

viscous dissipationSee dissipation

viscous drag—(Or skin friction.) See drag

viscous fluid—A fluid for which the molecular viscous effects of diffusion and dissipation can have significant effects on the flow.
The importance of viscosity depends on the relevant velocity and length scales of the flow and the viscosity of the fluid. The nondimensional measure of the relative importance of viscosity is the reciprocal of the Reynolds number, Re. For typical atmospheric flows, Re > 107, implying that viscous effects may be neglected relative to the leading [O(1)] terms in the Navier–Stokes equations. However, in a turbulent flow, such as in the boundary layer, vortex stretching causes a continuous nonlinear cascade of turbulence kinetic energy, TKE, from large scales to smaller scales. The largest-scale eddies are responsible for the Reynolds stresses and conversion of mean flow energy into TKE. At some point in the cascade, the eddies will have length and velocity scales that are sufficiently reduced for the Reynolds number to be of order 1. At these scales the TKE of eddies can be converted into internal energy through viscous dissipation. These small eddies will have a much shorter timescale than the largest eddies in the flow and are thus statistically independent of the large-scale motion. For a developed turbulent flow, the rate at which the mean flow energy is converted into turbulence at the largest scales must be equal to the rate at which it is ultimately dissipated by viscosity by the small-scale eddies. These smallest eddies have scales that are very much larger than those of the molecular motions, and the continuum hypothesis is still valid for describing eddies of this size. Although dissipation occurs at the smallest possible eddies in the flow and the TKE is contained in the largest-scale eddies, the viscous dissipation is a leading term in the TKE budget and may not be ignored. See turbulence spectrum, turbulence length scales.
          Tennekes, H., and J. L. Lumley, 1972: A First Course in Turbulence, MIT Press, 256–262.

viscous force—The force per unit volume or per unit mass arising from the action of tangential stresses in a moving viscous fluid; this force may then be introduced as a term in the equations of motion.
By far the most satisfactory hypothesis to date is that of Navier and Stokes, a generalization of the Newtonian friction law, which evaluates the stress tensor as directly proportional to the rate of deformation, the constant of proportionality being the dynamic viscosity. In this case, the viscous force per unit mass becomes


where ν is the kinematic viscosity, V the velocity vector, and the del operator. The divergence term, ·V, vanishes for an incompressible fluid, and the Navier–Stokes assumption is seen as leading to a simple diffusion of momentum. “It may seem a little strange that viscosity, which is a diffusion of momentum, can also diffuse energy and even Reynolds stresses. . . . A viscous stress acts both to convert mechanical energy into heat and to accelerate neighboring fluid, and this acceleration is an energy transfer. . . .” (Townsend 1956). See Navier–Stokes equations.
          Townsend, A. A., 1956: The Structure of Turbulent Shear Flow, Cambridge University Press, p. 30.

viscous stresses—The components of the stress tensor remaining after the pressure, that is, the mean of the three normal stresses, has been subtracted out from each of the normal stresses.
See Reynolds stresses.

viscous subrange—The range of wavenumbers where the dissipation of turbulence kinetic energy occurs due to viscosity

water—1. A transparent, colorless, odorless, and tasteless liquid found near the surface of the earth.
In the lithosphere, hydrosphere, and atmosphere of the earth, water is found as a gas, liquid, and solid. Water falls from the clouds as rain, hail, sleet, graupel, snow, etc., and runs off and through soils to form creeks, streams, rivers, and lakes. In its solid form, it is referred to as ice or snow. Water as a liquid and as ice covers 70.8% of the surface of the earth and plays a fundamental part in the earth–atmosphere energy balance. Water (chemical formula H2O) corresponds to two parts hydrogen and one part oxygen on a molecular basis; by weight, water is 11.19% hydrogen and 88.81% oxygen. Water has a melting point of 0°C (32°F), a boiling point of 100°C (212°F), and a specific gravity of 1.000 at 4°C (39°F), by definition. 2. Can refer to a body of water, such as a lake or a stream, or even a larger body of water such as a sea or part of an ocean, for example, international waters. 3. Used to describe water in specific locales; for example, hydrologists refer to soil water, surface water, and groundwater. 4. As a verb, used to describe irrigation corresponding to the application of water to plants, the grounds surrounding a residence, or to a garden.

water circulation coefficient—The ratio of a region's total precipitation to the amount of “external” precipitation originating as evaporation from the oceans as opposed to evapotranspiration from the land.

water mass—A body of water with a common formation history, for example, convection caused by surface cooling, having its origin in a particular region of the ocean.
Water masses are identified by their temperature, salinity, and other properties such as nutrients or oxygen content. They have exclusive occupation of an oceanic region only in their formation region; elsewhere they share the ocean with other water masses with which they mix. Just as air masses in the atmosphere, water masses are physical entities with a measurable volume.

water molecule—A molecule, consisting of one central oxygen atom and two hydrogen atoms along an angle of 104°, forming an electrostatic dipole because of the asymmetric distribution of charge.
The dipole results in a high dielectric constant for water, whether in vapor, liquid, or solid form. Resonances in the intermolecular bonds result in absorption and emission of electromagnetic radiation at near- and thermal-infrared wavelengths, hence the importance of water vapor in the greenhouse effect in the atmosphere and water substance as precipitation in the scattering and absorption of radar waves.

water potential—The potential energy per unit mass of water with reference to pure water at zero potential.
The water potential τ is made up of several components,

where τg is the component due to gravity, τm is the matrix potential that arises from the attraction of the soil matrix for water and water molecules for each other, τp is the pressure potential that is the ratio of the hydrostatic or pneumatic pressure to the density of water, and τo is the osmotic potential that is a driving force for water movement when solute movement is restrained with a semipermeable membrane

water resources—Water in all states (solid, liquid, or vapor), in storage or in flux within the hydrologic cycle, that is necessary for a sustainable quality of life, as well as for sustaining the natural environment.

water structure—The arrangement of water molecules in the liquid state.
Unlike the case of ideal gas (random distribution) and ideal crystal (perfect order) models, there is no simple way to describe the ideal liquid water structure. It is known that the structure has short range order (similar to ice) but no long range order (similar to a gas), as shown by x- ray diffraction studies. Several competing models exist that attempt to explain the observed properties of water. Examples include the quasi-crystalline model, which assumes that water consists of broken-down pieces of ice; the clathrate model, which suggests that water resembles the clathrate structure of gas hydrates; and the bend-bond model, which suggests that the bonds are bent to various degrees. Other models also exist. Water has several properties of direct meteorological interest [e.g., maximum density at +4°C; maximum visible refractive index at +1°C; maximum thermal capacity at +35°C; large static dielectric constant (80) and its frequency variation] with which such models need to be consistent.

water-supply forecast—Statement of the expected volume of available water for a specified period and a specified area; may be associated with time distribution and probability

water-supply sensitivity—The sensitivity of water supply systems to climatic fluctuations.

water-table aquifer—See unconfined aquifer.

water vapor—(Also called aqueous vapor, moisture.) Water substance in vapor form; one of the most important of all constituents of the atmosphere.
Its amount varies widely in space and time due to the great variety of both “sources” of evaporation and “sinks” of condensation that provide active motivation to the hydrologic cycle. Approximately half of all of the atmospheric water vapor is found below 2-km altitude, and only a minute fraction of the total occurs above the tropopause. Water vapor is important not only as the raw material for cloud and rain and snow, but also as a vehicle for the transport of energy (latent heat) and as a regulator of planetary temperatures through absorption and emission of radiation, most significantly in the thermal infrared (the greenhouse effect). The amount of water vapor present in a given air sample may be measured in a number of different ways, involving such concepts as absolute humidity, mixing ratio, dewpoint, relative humidity, specific humidity, and vapor pressure.

water vapor feedback—The change in the radiative effect of water vapor in response to an external perturbation of the climate.
Water vapor, the most important greenhouse gas, absorbs only a small amount of sunlight but is a very efficient absorber of the earth's thermal infrared emission. Changes in either the amount or the vertical distribution of water vapor can therefore change the planet's ability to radiate heat to space. Climate models predict, without exception, that the water vapor feedback is positive. Changes in the distribution of water vapor in the middle and upper troposphere are inordinately important to this feedback process, because molecules that absorb upwelling infrared radiation at these altitudes emit it to space at a much colder temperature and therefore emit less than would be the case in their absence. The concentration of high-altitude water vapor is controlled by poorly understood dynamic and thermodynamic processes and is inadequately observed, thus contributing to uncertainty in the magnitude of the water vapor feedback.


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