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Perpendicular

Denoting the latest stage of English Gothic church architecture, prevalent from the late 14th to mid 16th centuries and characterized by broad arches, elaborate fan vaulting, and large ...

frost creep

frost creep   Quick reference

A Dictionary of Geography (5 ed.)

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Subject Reference
Current Version:
2015

...creep The net downslope displacement that occurs when a soil, during a freeze–thaw cycle, expands perpendicular to the ground surface and settles in a nearly vertical direction. http://www.uspermafrost.org/glossary.php The US Permafrost Association...

irradiance

irradiance   Quick reference

A Dictionary of Geography (5 ed.)

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Subject Reference
Current Version:
2015

...The rate of flow of radiant energy through unit area perpendicular to a solar beam. Total solar irradiance is the dominant driver of global climate ( Mendoza (2005) Advances Space Res. 35, 5 ). See also Mishchenko et al. (2007) Bull. Am. Met. Soc. 88, 5...

friction coefficient

friction coefficient   Quick reference

A Dictionary of Geography (5 ed.)

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Subject Reference
Current Version:
2015

...coefficient The ratio of the force that maintains contact between an object and a surface and the frictional force that resists the motion of the object; the ratio of two forces acting, respectively, perpendicular and parallel to an interface, between two bodies under relative motion ( Blau (2001) Tribology Int. 34, 9 ). Under the same friction coefficient different normal stresses cause different friction levels ( Kame and Yamashita (2003) Geophys. J. Int. 155, 3 ). In a rockfall, the friction coefficient is the strongest factor in determining...

longshore drift

longshore drift   Quick reference

A Dictionary of Geography (5 ed.)

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Subject Reference
Current Version:
2015

...drift The movement of sand and shingle along the coast. Waves usually surge onto a beach at an oblique angle and their swash takes sediment up and along the beach. The backwash usually drains back down the beach at an angle more nearly perpendicular to the coast, taking sediment with it. Thus there is a zigzag movement of sediment along the coast. Longshore currents , initiated by waves, also move beach material along the coast. The term littoral drift is...

Coriolis force

Coriolis force   Quick reference

A Dictionary of Geography (5 ed.)

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Current Version:
2015

...It shows up, for example, in the movement of an air stream, relative to the rotating Earth beneath it. The Coriolis force is proportional to the wind speed U ( z ), and the Coriolis parameter , —where Φ ‎ is the latitude and Ω ‎ is the Earth’s rate of rotation—acts perpendicular to the wind direction ( Orr et al. (2005) Weather 60, 10...

Thiessen polygon

Thiessen polygon   Quick reference

A Dictionary of Geography (5 ed.)

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2015

...polygon A subdivision of a drainage basin, containing a rain gauge. Polygons are constructed by first siting the rain gauges, plotting them on a base map, and connecting the sites by straight lines. The lines are bisected with perpendiculars, which meet to form the polygons. The areas of the polygons are calculated and expressed as fractions of the total area. Each fraction is multiplied by the precipitation recorded by its rain gauge. The sum of these calculations represents total precipitation over the catchment area. For an account, see Yoo et al....

tropics

tropics   Quick reference

A Dictionary of Geography (5 ed.)

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Subject Reference
Current Version:
2015

...The Tropic of Cancer lies approximately along latitude 23° 30′ N. Around 21–2 June, the sun’s rays are perpendicular to the ground along this line and the sun exerts its maximum strength in the Northern Hemisphere. Conversely, the sun is overhead at the approximate latitude of 23° 30′ S, the Tropic of Capricorn , on 22–3 December when the sun’s heat is at its maximum in the Southern Hemisphere. Between these two lines of latitude lie the tropics. In America this zone is known as the neotropics and in Africa and South-East Asia as the palaeotropics...

Seasons

Seasons   Reference library

Encyclopedia of Climate and Weather (2 ed.)

Reference type:
Subject Reference
Current Version:
2011
Subject:
Science and technology, Earth Sciences and Geography, Social sciences, Environment
Length:
2,449 words
Illustration(s):
3

...24 hours of daylight, and the Arctic region is in total darkness. The solstice actually occurs when the perpendicular rays of the Sun strike the tropic of Cancer or tropic of Capricorn, respectively. Throughout the rest of the year, the perpendicular rays of the Sun fall at different points between these latitudes. The “figure 8” found on many globes, called an analemma ( Figure 3 ), shows the latitudes of declination where these perpendicular rays strike on each day of the year. On two of these days, the equinoxes , the noonday Sun is directly...

shear

shear   Quick reference

A Dictionary of Geography (5 ed.)

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Subject Reference
Current Version:
2015

...exceed soil shear strength ( Simoni et al. (2008) Hydrol. Procs 22, 4 ). Shear stress happens when the applied force acts tangentially to the surface of the body (the down-slope component). It is opposed to a normal stress (the slope-normal component) which is applied perpendicularly. See Namikas (2000) J. Sed. Res. 72, 2 on measuring bed shear stress during aeolian saltation; Sime et al. (2007) Water Resources Res. 43 , W03418 on estimating river bed shear. Within a glacier, the level of shear stress ( τ ‎) experienced at any point is dependent...

Squall Lines

Squall Lines   Reference library

Encyclopedia of Climate and Weather (2 ed.)

Reference type:
Subject Reference
Current Version:
2011
Subject:
Science and technology, Earth Sciences and Geography, Social sciences, Environment
Length:
1,254 words
Illustration(s):
2

...rain forms to the rear. The strongest rain and most active convection is usually on the line's most easterly side. Sometimes the line is made up of distinct individual cells; at other times, the pattern is nearly uniform along the line. The flow features that are perpendicular to the leading edge of a squall line are shown in Figure 2 . From the leading edge through the stratiform region (one of light uniform rain), front-to-back flow dominates in the lowest 6 kilometers. The convective region has forward flow above 6 kilometers. A region of weak...

Shear Instability

Shear Instability   Reference library

Encyclopedia of Climate and Weather (2 ed.)

Reference type:
Subject Reference
Current Version:
2011
Subject:
Science and technology, Earth Sciences and Geography, Social sciences, Environment
Length:
1,166 words
Illustration(s):
2

...streamlines, resembling a long row of cats' eyes, which is depicted. Thus there are parallel rolls perpendicular to the plane of Figure 1 ; of course, in practice they may be observed from a different direction. The wavelength—the distance between adjacent “eyes”— varies considerably from instance to instance of shear instability in the atmosphere, but is typically in the range of 40 to 100 meters. The rolls usually stretch several wavelengths perpendicular to the plane of flow shown. The whole pattern is carried along by the wind. It grows and may soon...

Orbital Parameters and Equations

Orbital Parameters and Equations   Reference library

Encyclopedia of Climate and Weather (2 ed.)

Reference type:
Subject Reference
Current Version:
2011
Subject:
Science and technology, Earth Sciences and Geography, Social sciences, Environment
Length:
3,181 words
Illustration(s):
4

...within the orbit at that time. In the case of a planet moving in an elliptic orbit about the Sun, it is convenient to take a set of rectangular axes in and perpendicular to the plane of reference, with the origin at the center of the Sun. The x -axis may be taken toward the ascending node N , the y -axis being in the plane of reference and 90° from x , while the z -axis is taken to be perpendicular to this reference plane, so that the three axes form a right-handed coordinate system. The reference point from which the angles are measured is γ 0 . As the...

Cumulonimbus Clouds

Cumulonimbus Clouds   Reference library

Encyclopedia of Climate and Weather (2 ed.)

Reference type:
Subject Reference
Current Version:
2011

...also produces subsiding air currents called downdrafts, which achieve downward velocities typically less than 5 meters per second. When the downdraft penetrates to the surface and spreads laterally, severe wind gusts and wind shear (change of wind speed and direction perpendicular to the wind direction) called downbursts can result. Downdrafts also can form on the underside of the anvil, producing downward penetrating plumes of cloudy air called mammatus clouds. These ominous-looking clouds are sometimes mistaken for funnel clouds. The cumulonimbus...

Fronts

Fronts   Reference library

Encyclopedia of Climate and Weather (2 ed.)

Reference type:
Subject Reference
Current Version:
2011
Subject:
Science and technology, Earth Sciences and Geography, Social sciences, Environment
Length:
3,597 words
Illustration(s):
2

...the frontal surface provides a means of classifying fronts. Anafronts have ascending air over the frontal surface, as described above; katafronts have descending air over the frontal surface. The horizontal movement of a front is approximately equal to the speed of the wind perpendicular to the zone. This can vary greatly. A speed of 80 kilometers per hour (50 miles per hour) would be quite rapid but possible. The presence of mountains can greatly complicate the movement and structure of fronts. Fronts are found in mid or high latitudes, where large horizontal...

Gravity

Gravity   Reference library

Encyclopedia of Climate and Weather (2 ed.)

Reference type:
Subject Reference
Current Version:
2011
Subject:
Science and technology, Earth Sciences and Geography, Social sciences, Environment
Length:
3,063 words
Illustration(s):
4

...equivalent measurements at sea level, and the undulations of the geoid can be traced. The differences between the gravity of the geoid and that of the reference spheroid are called gravity anomalies. If vertical is defined as perpendicular to the spheroid, then the difference between the direction of a plumb line (which is perpendicular to the geoid) and the vertical is the deflection of vertical. The broad features of the Earth's gravitational field are best found by observing the orbits of artificial satellites. The field can be expressed in a mathematical...

Friction

Friction   Reference library

Encyclopedia of Climate and Weather (2 ed.)

Reference type:
Subject Reference
Current Version:
2011

...downdrafts that produce damaging winds at the Earth's surface. Stress. Up to this point we have considered the straightforward concept of wind resistance by obstacles. This “pushing” pressure force on a cube of air with imaginary sides acts on the faces of the cube that are perpendicular to the wind. To understand friction away from obstacles, we must consider the more subtle “pulling” forces associated with actions across the other faces of the cube. We will focus on the top and bottom faces to understand the complicated effects of friction at different...

Global Electric Circuit

Global Electric Circuit   Reference library

Encyclopedia of Climate and Weather (2 ed.)

Reference type:
Subject Reference
Current Version:
2011
Subject:
Science and technology, Earth Sciences and Geography, Social sciences, Environment
Length:
1,337 words
Illustration(s):
1

...100 kilometers, where it reaches values of about 10 −5 siemens per meter. Above that altitude the electrical conductivity is influenced by the direction of the Earth's magnetic field and attains different values depending on whether the direction of conduction is along or perpendicular to the magnetic field line. The electrical conductivity also exhibits a latitudinal variation owing to the shielding effect of the Earth's magnetic field. The magnetic field deflects incoming cosmic rays away from the equatorial region more effectively than from the polar...

Barometric Pressure

Barometric Pressure   Reference library

Encyclopedia of Climate and Weather (2 ed.)

Reference type:
Subject Reference
Current Version:
2011

...The precise manner in which air flows in response to pressure gradients is complicated by the fact that other forces also act on air, such as the Coriolis force. [ See General Circulation, subentry on An Overview .] Outside the tropical regions, the winds tend to blow perpendicularly to the direction of the horizontal pressure gradient force, which itself is oriented directly toward lower pressure. In the Northern Hemisphere, lower pressure will be to the left of the wind orientation, whereas in the Southern Hemisphere lower pressure is to the right....

Models and Modeling

Models and Modeling   Reference library

Encyclopedia of Climate and Weather (2 ed.)

Reference type:
Subject Reference
Current Version:
2011

...acting oppositely on each parcel separately. The faster air will tend to decelerate, while the slower neighboring air will tend to accelerate. The existence of a pressure gradient causes a net force on a parcel of air because the external air pressure (force = pressure × perpendicular area) forcing inward on one end of the parcel is different from the pressure forcing inward on the opposite end of the parcel, so that there is a net force on the mass enclosed by the volume. When all six sides of an imaginary cube surrounding the parcel are considered, the...

Orographic Effects

Orographic Effects   Reference library

Encyclopedia of Climate and Weather (2 ed.)

Reference type:
Subject Reference
Current Version:
2011

...mass is especially cold, then its descent will not warm it appreciably; a dry, cold wind resulting from such conditions is called a bora or mistral in Europe. Mountain waves. If the air is stable and flows at high speed over a mountain barrier, with a direction approximately perpendicular to the ridge line, waves often form in the airflow. The first wave is over the ridge line, and additional waves form downstream at regular intervals of about 10 kilometers. The waves are stationary, fixed in position with respect to the ground. The air rises into the upstream...

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