View:

Overview

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 ...

ground cover

ground cover   Quick reference

A Dictionary of Ecology (5 ed.)

Reference type:
Subject Reference
Current Version:
2015

...cover The area of ground that is covered by a plant when its canopy edge is projected downwards perpendicularly...

sea-floor spreading

sea-floor spreading   Quick reference

A Dictionary of Ecology (5 ed.)

Reference type:
Subject Reference
Current Version:
2015

...that the ocean floor is created at the spreading (accretionary) plate margins within the ocean basins. Igneous rocks rise along conduits from the mantle , giving rise to volcanic activity in a narrow band along the mid-ocean ridges. The newly formed oceanic crust spreads perpendicularly away from the...

cover

cover   Quick reference

A Dictionary of Ecology (5 ed.)

Reference type:
Subject Reference
Current Version:
2015

...In descriptions of plant communities, the proportion of ground, usually expressed as a percentage, that is occupied by the perpendicular projection down on to it of the aerial parts of individuals of the species under consideration. The most widely used visual scales are the Domin scale and the Braun-Blanquet five-point scale. A more objective estimate may be obtained using a pin-frame or point-quadrat...

Cartesian projection

Cartesian projection   Quick reference

A Dictionary of Ecology (5 ed.)

Reference type:
Subject Reference
Current Version:
2015

...projection A mapping technique in which every plane in the area being mapped is projected on to a plane in the map and every line on to a line. Each point in the area under study is identified by three values, representing its location in relation to three mutually perpendicular axes (the Cartesian coordinates of the point). These coordinates are transformed mathematically into a homogeneous set of four coordinates which can then be plotted to produce a graphic representation (a map). The word ‘Cartesian’ is derived from the name of the French...

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...

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...

Geopotential

Geopotential   Reference library

Encyclopedia of Climate and Weather (2 ed.)

Reference type:
Subject Reference
Current Version:
2011

...By contrast, a parcel constrained to remain on a surface on which Φ is constant will have the same potential energy at every location, and therefore it will have no tendency to change its motion in response to the force of gravity. In other words, the force of gravity is perpendicular to such a constant-Φ surface; there is no component of the force of gravity along the surface. This allows meteorologists and oceanographers to consider pressure gradient forces acting in the horizontal plane (along the geopotential surface) independently of any gravitational...

Occluded Fronts

Occluded 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:
1,909 words
Illustration(s):
1

...cyclones over the oceans, which often undergo a different frontal evolution from the polar front model (the Shapiro–Keyser cyclone model). [ See Cyclones, subentry on Midlatitude Cyclones .] In these oceanic cyclones, the cold front separates from and then moves perpendicularly to the warm front, and hence never catches up. The strong winds ahead of the warm front carry the warm front around the low center, forming a so-called back-bent front. [ See Cyclones, subentry on Explosive Cyclones .] By generalizing the occlusion process to one in which...

Coriolis Force

Coriolis Force   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:
1,640 words
Illustration(s):
2

...that bears his name in a scientific paper in 1835 . The total Coriolis force ( CF ) is mathematically expressed as the vector cross product of the motion vector V and the vector of Earth's rotation (Ω), specifically: CF   = − 2 Ω   ×   V , (1) so that CF is mutually perpendicular to the Earth's axis and the direction of the motion, toward CORIOLIS FORCE. Figure 1. Comparison of the same trajectory as viewed from inertial and noninertial frames of reference. The path of the moving object, although straight relative to the inertial frame of...

Vorticity

Vorticity   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:
1,882 words
Illustration(s):
1

...parcels. For example, if ω a · ∇ u has only a z -component, namely ζ a (∂ w /∂ z ), where ζ a is the z -component of ω a , w the z -component of u , and if ∂ w /∂ z is positive, the fluid parcel must be elongating in the direction of ω a and contracting in the perpendicular direction (from Equation 2 ). The resulting increase in ω a is said to be caused by vortex stretching. The term ω a · ∇ u in Equation 3a is obviously zero in the case of two-dimensional flow, and if, further, ν is negligible, then ω a would be constant following...

View: