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A branch of meteorology that examines the effects and impacts of weather and climate on crops, rangeland, livestock, and various agricultural operations. Agricultural meteorology, or agrometeorology, addresses topics that often require an…

Natural and artificial substances in the atmosphere that affect human health or well-being, or the well-being of any other organisms in the environment. Air pollution also applies to situations in which contaminants affect structures and artifacts…

The branch of mathematics dealing with the solution of equations. These equations involve unknowns, or variables, along with fixed numbers from a specified system (Fig. 1). The origins of algebra were based on the need to develop equations that…

The study of the cycling of chemicals between organisms and the surface environment of the Earth. The chemicals either can be taken up by organisms and used for growth and synthesis of living matter or can be processed to obtain energy. The chemical…

A heart-shaped curve generated by a point of a circle that rolls (without slipping) on a fixed circle of the same diameter. In point-wise construction of the curve, let O be a fixed point of a circle C of diameter a, and Q a variable point of C. Lay…

The long-term records of precipitation, temperature, wind, and all other aspects of the Earth's climate. Climate, like the Earth itself, has a history extending over several billion years. Climatic changes have occurred at time scales ranging from…

Construction of a mathematical model of the climate system of the Earth capable of simulating its behavior under present and altered conditions. The Earth's climate is continually changing over time scales ranging from hundreds of years to a few…

The scientific study of climate. Climate is the expected mean and variability of the weather conditions for a particular location, season, and time of day. The climate is often described in terms of the mean values of meteorological variables such…

A calcarenite or clastic limestone whose detrital particles are chiefly fossils, whole or fragmented. The term coquina is most frequently used for an aggregate of large shells more or less cemented by calcite (see illustration). If the rock consists…

The response of corals to environmental stress in which they eject the single-cell algae that live within the transparent coral tissue, making the white coral skeleton visible. Corals (Fig. 1) are animals that live in a partnership (symbiosis) with…

Pathological conditions affecting the health of coral and causing its physiological dysfunction. Broadly defined, coral disease (Fig. 1) is any impairment to coral health resulting in physiological disturbance and breakdown. It usually involves…

A measure of the three-dimensional structure of live coral communities on reefs. Coral reef structural complexity is an intrinsic element of coral reef ecosystems and quantitates the surface area of coral in relation to its linear area. The…

A vortex in which the sense of rotation of the wind about the local vertical is the same as that of the Earth's rotation. Thus, a cyclone rotates clockwise in the Southern Hemisphere and counterclockwise in the Northern Hemisphere. In meteorology…

A vertical sequence of several different kinds of distinctive sedimentary rock units that is repeated upward through the stratigraphic succession. Originally defined in the rock succession of Pennsylvanian age in the Illinois Basin in the 1930s, the…

A mathematical operation performed on a function to determine the effect of a change in the value of the independent variable. Functions of one variable are considered in this article. For differentiation of functions of several variablesPartial…

The monoclinic pyroxene mineral which in pure form has the formula CaMgSi2O6. Its space group is C2/c. Pure diopside melts congruently at 1391°C (2536°F) at atmospheric pressure; the effect of pressure up to 50 kilobars (5 gigapascals) on its…

For a polynomial f(x) = an xn + an−1 xn−1 + + a1 x + a0, the discriminant is given by the expression where x1, x2, …, xn are the roots of the equation f(x) = 0. There are n(n − 1)/2 terms (xi − xj)2 in the product corresponding to all possible…

Skin diving, or diving without the aid of special equipment, is a technique to investigate underwater environments and to gather shellfish or other items of commercial importance. In breath-hold diving, fins and faceplate are usually employed to…

The carbonate mineral CaMg(CO3)2. Dolomite is a very common mineral, occurring in a variety of geologic settings. It is often found in ultrabasic igneous rocks, notably in carbonatites and serpentinites, in metamorphosed carbonate sediments, where…

A nesosilicate mineral with composition Al7(BO)3(SiO4)3O3. Dumortierite crystallizes in the orthorhombic system but well-formed crystals are rare; the mineral usually occurs in parallel or radiating fibrous aggregates. There is one direction of poor…

A mathematical abstraction corresponding to an expression of the type βγ + δ∊ + · · · , in which the elements (dyad symbols) consist of two vector symbols in juxtaposition without the intervention of either the dot (·) or cross (×). Essentially a…

A state of fluid flow in which the distribution of mass and momentum is unstable. Fluid flows are subject to a variety of instabilities which generally cause the flow to become more complex and which often lead to turbulent, chaotic flow.…

The low-density outermost layer of the Earth above the Mohorovičić discontinuity (the Moho), a global boundary that is defined as the depth in the Earth where the compressional-wave seismic velocity increases rapidly or discontinuously to a value in…

A disruption of the usual tropical Pacific Ocean and atmospheric circulation patterns that includes a few seasons of warmer-than-normal sea-surface temperatures in the central and eastern equatorial Pacific Ocean, weaker mid-Pacific trade winds, and…

The effect of changes in pressure and temperature on electrical properties of rocks. There has been increasing interest in the electrical properties of rocks at depth within the Earth and the Moon. The reason for this interest has been consideration…

The application of geology and other Earth sciences to solve engineering problems. The branches of the Earth sciences most applicable are surficial geology, petrofabrics, rock and soil mechanics, geohydrology, and geophysics, particularly…

The study of the flows of air and water, of the chemical and biological species carried by them, and of their interactions with geological, biological, social, and engineering systems in the vicinity of a planet's surface. The environment on the…

Radioactivity that originates from natural and anthropogenic sources, including radioactive materials in food, housing, and air, radioactive materials used in medicine, nuclear weapon tests in the open atmosphere, and radioactive materials used in…

A semienclosed coastal body of water which has a free connection with the sea and within which the seawater is measurably diluted by freshwater derived from land drainage. In estuaries, the seawater diluted by freshwater is called brackish water,…

Variation with time of the chemical composition and total weight of the Earth's atmosphere. The atmosphere is a most tenuous envelope; its mass is less than one-millionth that of the solid Earth; its density even at sea level is less than…

A numerical analysis technique for obtaining approximate solutions to many types of engineering problems. The need for numerical methods arises from the fact that for most engineering problems analytical solutions do not exist. While the governing…

A method of dating geological and archeological specimens by counting the radiation-damage tracks produced by spontaneous fission of uranium impurities in minerals and glasses. During fission two fragments of the uranium nucleus fly apart with high…

An elongated, sloping zone in the troposphere, within which changes of temperature and wind velocity are large compared to changes outside the zone. Thus the passage of a front at a fixed location is marked by rather sudden changes in temperature…

The formation of ice on the ground, on plants, or on structures near the Earth's surface as a result of the drop in air temperature to lower than 32°F (0°C) and the presence of water vapor or liquid water in the air. The causes of the cooling, and…

Conditions in which two or more phases of fused-salt mixtures can coexist in thermodynamic equilibrium. Phase diagrams of these equilibrium conditions summarize basic knowledge about fused salts. Numerous advances in the technologies which are based…

The theory of games of strategy can briefly be characterized as the application of mathematical analysis to abstract models of conflict situations. The first such models analyzed by the theory were parlor games such as chess, poker, and bridge.…

The scientific study of the processes and impacts of ice sheets, valley glaciers, and other ice masses on the Earth's surface, both on land and in ocean basins. The processes include understanding how ice masses move, erode, transport, and deposit…

The history of glaciation on Earth, extending back in geological time to the Proterozoic and possibly the Archean. Global glaciations have occurred during every geological period except the Jurassic. This persistence of global glaciation, as well as…

The rise in the surface temperature of the Earth. Global warming is one of the names given to the systematic increase of globally averaged surface temperature that has been measured since the mid-nineteenth century. There is abundant evidence that…

Procedures and techniques for visually representing on paper or a screen information pertaining to data analysis and decision making or relationships between variables by means of diagrams or charts.Structural information is usually depicted by a…

The ability of a planetary atmosphere to inhibit heat loss from the planet's surface, thereby enhancing the surface warming that is produced by the absorption of solar radiation. The greenhouse effect acts like a thermal blanket, limiting heat loss…

The Gulf of Mexico is a subtropical semi-enclosed sea bordering the western North Atlantic Ocean. The Gulf of Mexico (Fig. 1) is the northern-most basin of the Intra-Americas Sea. The Gulf of Mexico connects to the Caribbean Sea on the south through…

Any nonplanar curve all of whose tangents make the same angle with a fixed line. Other characteristic properties are that all principal normals are parallel to a plane and that the ratio of torsion to curvature is constant. If a helix has constant…

A mineral belonging to the zeolite family of silicates and crystallizing in the monoclinic system. It usually occurs in crystals with prominent side pinacoid, often having a diamond shape. There is perfect side pinacoid cleavage on which the luster…

The study of the occurrence, movement, and changes in the state of water in the atmosphere. The term is also used in a more restricted sense, especially by hydrologists, to mean the study of the exchange of water between the atmosphere and…

A hot spring on the ocean floor, where heated fluids exit from cracks in the Earth's crust. Most hydrothermal vents occur along the central axes of mid-oceanic ridges, which are underwater mountain ranges that wind through all of the deep oceans.…

The application of meteorological information to industrial, business, or commercial problems. Generally, industrial meteorology is a branch of applied meteorology, which is the broad field where weather data, analyses, and forecasts are put to…

The application to biological systems of the theory of encoding effects on signal transmission and communications efficiency. In everyday language, information is associated with knowledge, meaning (semantics), and the influence of information on…

Low-frequency sound waves that cannot be sensed by the human ear. Infrasound was first detected on barometers around the world following the eruption of the volcano Krakatoa in 1883. We now know subaudible sounds are generated by a wide variety of…

Surfaces along which the entropy and potential temperature of air are constant. Potential temperature, in meteorological usage, is defined by the relationship given below,in which T is the air temperature, P is atmospheric pressure expressed in…