Glossary of Physical Geography Unit 1

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The solid, inorganic portion of the Earth. Also, tectonic plates consisting of the crust and upper rigid mantle. Sometimes used as a general term for the entire solid Earth.
The gaseous envelope of air that surrounds the Earth.
Total water realm of Earth, including the oceans, surface waters of the lands, groundwater, and water held in the atmosphere.
The living organisms of Earth.
The parallel of 0 latitude.
Great circle
Circle on a globe formed by the intersection of Earth's surface with any plane that passes through Earth's center.
Small circle
Circle on a globe formed by the intersection of Earth's surface with any plane that does not pass through Earth's center.
Circle of illumination
The edge of the sunlit hemisphere that is a great circle seperating the Earth into a light half and and a dark half.
Location described as an angle measured north and south of the equator.
A circle resulting from an isoline connecting all points of equal latitude.
The network of parallels and meridians on a map.
Location described as an angle measured east and west from the prime meridian on Earth's surface.
An imaginary line of longitude extending from pole to pole, crossing all parallels at right angles, and being aligned in true north-south directions.
Prime Meridian
The meridian passing through the Royal Observations at Greenwich, just east of London, and from which longitude is measured.
The point in its orbit at which a planet is nearest the Sun.
The point in Earth's elliptical orbit at which the Earth is farthest from the Sun.
Plane of the Ecliptic
The imaginary plane that passes through the Sun and through Earth at every position in its orbit around the Sun; the orbital plane of the Earth.
The tilt of Earth's rotational axis relative to its orbital plane.
A characteristic of Earth's axis wherein it always points toward Polaris at every position in Earth's orbit around the Sun. Also called parallelism.
Incoming solar radiation.
Tropic of Cancer
The parallel of 23.5 degrees north latitude, which marks the northernmost location reached by the vertical rays of the Sun in the annual cycle of Earth's revolution.
Arctic Circle
The parallel of 66.5 degrees north latitude.
Antartic Circle
The parallel of 66.5 degrees south latitude.
Tropic of Capricorn
The parallel of 23.5 degrees south latitude, which marks the southernmost location reached by the vertical rays of the Sun in the annual cycle of Earth's revolution.
One of those two times of the year in which the Sun's perpendicular rays hit the northernmost or southernmost latitudes reached during the Earth's cycle of revolution.
The time of the year when the perpendicular rays of the Sun strike the equator, the circle of illumination just touches both poles, and the periods of daylight and darkness are each 12 hours long all over the Earth,
The colloquial term for mixture of gases and impurities that make up the atmosphere.
Composed of distinct particles or small pieces.
A gas composed of molecules consisting of three atoms of oxygen, O3.
Ozone Layer
A layer of ozone between 16 and 40 kilometers (10-25 miles) high, which absorbs ultraviolet solar radiation.
Thermal Layers
Layers of the atmosphere largely defined by differences in thermal characteristics.
The lowest thermal layer of the atmosphere, in which temperature decreases with height.
Atmospheric layer directly above the troposhere.
Atmospheric layer above the stratopause, where temperature decreases with height; also refers to the rigid part of the deep mantle, below the asthenosphere.
The highest recognized thermal layer in the atmosphere, above the mesopause, where temperature remains relatively uniform for several kilometers and then increases continually with height.
The highest zone of Earth's atmosphere.
A transition zone at the top of the troposphere, where temperature ceases to decrease with height.
The top of the stratosphere elevation, about 48 kilometers (30 miles), where maximum temperature is reached.
Transition zone at top of the mesosphere.
A zone of homogenous composition comprising the lowest 80 kilometers of the atmosphere, where the principal gases have a uniform pattern of vertical distribution.
That portion of the atmosphere above the homosphere where there is an irregular layering of gases in accordance with their molecular weights.
Zone of relatively rich concentration of ozone in the atmosphere.
A deep atmospheric layer containing electrically charged molecules and atoms in the upper mesosphere and lower thermosphere.
The short-term atmospheric conditions for a given time and a specific area.
An aggregate of day-to-day weather conditions
Elements of weather and climate
The basic ingredients of weather and climate - temperature, pressure, wind, and moisture.
Controls of weather and climate
The most important influences acting upon the elements of weather and climate.
The capacity to do work.
A form of energy associated with the random motion of molecules. Things are made hotter by the collision of the moving molecules.
A measure of the degree of hotness or coldness of a substance.
Sensible Temperature
A concept of relative temperature that is sensed by a person's body.
Ultraviolet Waves
Waves in the electromagnetic spectrum between 0.1 and 0.4 micrometers in length.
Visible light
Waves in the electromagnetic spectrum in the narrow band between about 0.4 and 0.7 micrometers in length.
Infrared Radiation
Electromagnetic radiation in the wavelength range of about 0.7 to 1000 micrometers; wavelengths just longer than visible light.
Longwave Radiation
Wavelengths of thermal infrared radiation emitted by Earth and the atmosphere; also referred to as terrestrial radiation.
Shortwave Radiation
Wavelengths of radiation emitted by the Sun, especially ultraviolet, visible and short infrared radiation.
Solar Constant
The fairly constant amount of solar insolation received at the top of the atmosphere, slightly less than 2 calories per square centimeter per minute, or 2 langleys per minute.
Langley (ly)
The unit of measure of radiation intensity that is 1 calorie per square centimeter.
The process by which energy is emitted from a body, the flow of energy in the form of electromagnetic waves.
The ability of an object to assimilate energy from electromagnetic waves that strike it.
The ability of an object to repel waves without altering either the object or the waves.
A change in direction, but not in wavelength, of light waves.
The ability of a medium to allow electromagnetic rays to pass through it.
Greenhouse effect
The warming in the lower troposphere because of differential transmissivity for shortwave and longwave radiation; the atmosphere easily transmits shortwave radiation from the Sun but inhibits the transmission of longwave radiation from the surface. The most important greenhouse gases are water vapor and carbon dioxide.
The movement of energy from one molecule to another without changing the relative positions of the molecules. It enables the transfer of heat between different parts of a stationary body.
Vertical movements of parcels of air due to density differences.
Horizontal movement of air across the Earth's surface.
Adiabatic Cooling
Cooling by expansion in rising air.
Adiabatic Warming
Warming by contraction in descending air.
Process by which liquid water is converted to gaseous water vapor; a cooling process because latent heat is stored.
Process by which water vapor is coverted to liquid water; a warming process because latent heat is released.
Latent Heat
Energy stored or released when a substance changes state. For example, evaporation is a cooling process because latent heat is stored and condensation is a warming process because latent heat is released.
The reflectivity of a surface. The fraction of total solar radiation that is reflected back, unchanged, into space.
Angle of Incidence
The angle at which the Sun's rays strike Earth's surface.
Specific Heat
The amount of energy required to raise the temperature of 1 gram of a substance by 1 degree celsius.
Average Lapse Rate
The average rate of temperature decrease with height in the troposhere - about 6.5 degrees Celsius per kilometer (3.6 degrees F per 1000 feet).
Temperature Inversion
A situation in which temperature increases upward and the normal condition is inverted.
Radiation Inversion
Surface inversion that results from rapid radiational cooling of lower air, typically on cold winter nights.
Advectional Inversion
An inverted temperature gradient caused by a horizontal inflow of colder air into an area; usually colder air "draining" downslope into a valley or by cool maritime air blowing into a coastal locale. Advectional inversions are usually short-lived and shallow and are more common in winter than in summer.
Cold-air-drainage inversion
Temperature inversion developing when cooling air slides down a slope into valley displacing slightly warmer air.
Large-scale downward movement of air.
A line joining points of equal atmospheric temperature.
Mass of a substance per unit volume.
Instrument used to measure atmospheric pressure.
An "absolute" measure of pressure, consisting of one-thousandth part of a bar, or 1000 dynes per square centimeter.
A line joining points of equal atmospheric pressure.
Pressure Gradient
Change in atmospheric pressure over some horizontal distance.
Small-scale upward movement of air.
Small-scale downward movement of air.
Large-scale upward movement of air.
Coriolis effect
The apparent deflection of free-moving objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, in response to the rotation of Earth.
Geostrophic Wind
A wind that moves parallel to the isobars as a result of the balance between the pressure gradient force and the Coriolis effect.
A high-pressure center.
Low-pressure center.
Hadley cells
Two complete vertical convective circulation cells between the equator, where warm air rises in the ITCZ and 25 degrees to 30 degrees of latitude, where
Sub-tropical high (STH)
Large semipermanent high-pressure cells centered at around 30 degrees latitude over the oceans, which have average diameters of 3200 kilometers (2000 miles) and are usually elongated east-west.
Trade winds
The major easterly wind system of the tropics, issuing from the equatorward sides of the subtropical highs and diverging toward the west and toward the equator.
Intertropical Convergence Zone (ITCZ)
The region near or on the equator where the northeast trades and the southeast trades converge.
Horizontal air movement.
A zone of discontinuity between unlike air masses.
Lapse Rate
The rate of temperature decrease with height in the troposphere. The average lapse rate has been calculated to be about 6.5 degrees Celsius per kilometer (3.6 degrees F per 1000 feet)
Horse latitudes
Areas in the subtropical highs characterized by warm, tropical sunshine and an absence of wind.
Belt of calm air associated with the region between the trade winds of the Northern and Southern hemispheres, generally in the vicinity of the equator. The region of the intertropical convergence zone (ITCZ)
The great wind system of the midaltitudes that flows basically from West to East around the world in the latitudinal zone between 30 degrees and 60 degrees both North and South of the equator.
Polar front jet stream
Upper troposphere jet stream typically found at a latitude of about 55 degrees North and South at an elevation of 9 to 12 kilometers (30,000-40,000 feet)
Sub-tropical jet stream
Upper troposhere jet stream typically found at a latitude of about 30 degrees North and South at an elevation of 15 kilometers (50,000 feet).
Rossby Waves
A very large north-south undulation of the upper-air westerlies
Polar High
A high-pressure cell situated over either polar region.
Polar Easterlies
A global wind system that occupies most of the area between the Polar Highs and about 60 degrees of latitude. The winds move generally from east to west and are typically cold and dry.
Subpolar Low
A zone of low pressure that is situated at about 50 degrees to 60 degrees of latitude in both Northern and Southern hemispheres (also referred to as the polar front).
Polar front
The contact between unlike air masses in the subpolar low-pressure zone.
Antitrade winds
Tropical upper-air westerly winds that blow toward the northeast in the Northern Hemisphere and toward the southeast in the Southern Hemisphere.
A seasonal reversal of winds; a general onshore movement in summer and a general offshore flow in winter, with a very distinctive seasonal preciptation regime.
Onshore flow
Wind movement from water to land.
Offshore flow
Wind movement from land to water.
Water vapor
The gaseous state of moisture.
Hydrologic cycle
A series of storage areas interconnected by various transfer processes, in which there is a ceaseless interchange of moisture in terms of its geographical location and its physical state.
Vapor Pressure
The pressure exerted by water vapor in the atmosphere.
Saturation (with water vapor)
Circumstance in which the air contains the maximum amount of water vapor for a given temperature; condensation typically will begin when the air is saturated with water vapor.
The transfer of moisture to the atmosphere by transpiration from plants and evaporation from soil and plants.
Potential Evapotranspiration
The maximum amount of moisture that could be lost from soil and vegetation if the water were available.
Absolute Humidity
A direct measure of the water vapor content of air, expressed as the mass of water vapor in a given volume of air, usually as grams of water per cubic meter of air.
Water vapor in the air.
Specific Humidity
A direct measure of water-vapor content expressed as the mass of water vapor in a given mass of air (grams of vapor/kilograms of air)
Relative Humidity
An expression of the amount of water vapor in the air in comparison with the total amount that could be there if the air were saturated. This is a ratio that is expressed as a percentage.
Dew Point
The critical air temperature at which water vapor saturation is reached.
Hygroscopic Particles
Tiny particles suspended in the atmosphere that act as nuclei for water vapor condensation.
Dry Adiabatic Lapse Rate
The rate at which a particle of unsaturated air cools as it rises. 10 degrees celsius per kilometer.
Lifting Condensation Level
The altitude at which rising air cools sufficiently to reach 100 % relative humidity at the dew point temperature, and condensation begins.
Saturated Adiabatic Lapse Rate
The diminished rate of cooling, averaging about 6 degrees per kilometer of rising air above the lifting condensation level.
Cirriform clouds
A cloud that is thin and wispy, composed of ice crystals rather than water particles, and found at high elevations.
Stratiform cloud
A cloud form characterized by clouds that appear as grayish sheets or layers that cover most or all of the sky, rarely being broken into individual cloud units.
Cumuliform cloud
A cloud that is massive and rounded, usually with a flat base and limited horizontal extent, but often billowing upward to great heights.

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