Copy of `Southeast Regional Climate Center - Climate terms`

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Southeast Regional Climate Center - Climate terms Category: Meteorology and astronomy > Weather and Climate Date & country: 21/10/2013, USA Words: 165

longitude
the distance in degrees on the earth measured East and West from the Prime Meridian (in Greenwich England). Lines of a certain degree of longitude are called meridians, and because they run vertically over the earth, they are not parallel. Meridians converge at the North and South Poles.

low clouds
clouds found between the earth's surface and 2 kilometers (0-6500 feet) in all geographic regions. Contains stratocumulus and stratus clouds, and sometimes nimbostratus, cirrus and cumulonimbus clouds.

low pressure system
area of minimum air pressure, and cyclonic air movement.

lunar eclipse
when the earth is in a direct line between the sun and the moon. Because the moon reflects the sun's light and it cannot do this when the earth is in the way, it may appear dim or even orange in color.

meridian
If a circle is drawn vertically around Earth at its largest point and ran through both poles, one half of that circle running from the North pole to the South pole would be a meridian. Describes a line of longitude.

mesosphere
part of the atmosphere that has an altitude of between about 50 kilometers and about 70-80 kilometers.

meteorology
study of the phenomena of the atmosphere. Includes physics, chemistry and dynamics of the atmosphere as well as the direct effects upon the earth's surface, oceans and life in general. Oriented towards developing a complete understanding, accurate prediction, and artificial control of atmospheric occurrences.

middle clouds
clouds found between 2-4 kilometers (6500-13000 feet) in polar regions and 2-8 kilometers (6500-25000 feet) in tropical regions. Contains altocumulus and altostratus clouds, and sometimes nimbostratus.

moist adiabatic lapse rate
the decrease in temperature as a saturated parcel of air moves up through the atmosphere. This rate is 0.55

monsoon
when the principal wind direction changes noticeably with the season. The main cause is the heating and cooling of a nearby ocean depending on summer and winter, such as the Indian Ocean and the India monsoon for example.

nimbostratus
usually considered a middle cloud, is gray and often dark. The edges are not easy to see because of continuously falling rain, snow, or sleet. This cloud does not have lightning, thunder or hail.

nimbus
a rain cloud.

Northern Hemisphere
the half of the earth located above the equator, from 0

occluded front
when a cold front overtakes a warm front, and three air masses with different temperatures conflict. The resulting frontal boundary type will depend on how they meet.

orographic
weather phenomena caused by mountains.

orographic cloud
a cloud whose form is changed as high terrain, like a mountain, changes the airflow over the area. These clouds are often irregularly shaped, like a lens or a banner.

ozone layer
a place in the stratosphere (about 10-50 kilometers up) where the high ozone (O3 molecules) concentration shields the Earth from harmful ultraviolet radiation.

Pascal
The SI (Standard International)unit of pressure equal to the pressure resulting from a force of one Newton acting over an area of one square meter.

perihelion
opposite of aphelion. The point where the earth is nearest to the sun (147 million kilometers) while in its orbit. Currently, this occurs on January 3, but varies when there is a leap year.

permafrost
layer of soil or bedrock beneath earth's surface that is permanently frozen and has been for thousands of years.

pH scale
a measure of the range of acidity and alkalinity of a substance, on a scale from 0-14, with acids being on the lower end and bases on the higher end. A value of 7 is neutral.

precipitation
any form of water particles that fall from the clouds and reach the ground. Examples are rain, snow, sleet, and hail. Fog, dew, frost, and clouds are not forms of precipitation.

psychrometer
instrument used to measure the water vapor content of the air.

radar
an electronic instrument that broadcasts and receives microwave signals back from precipitation areas, and determines their location, height, movement, and intensity.

rainbow
an arc displaying all colors in the visible light spectrum. Formed when light from the sun is reflected and refracted through water droplets. Always appears on the side of the sky opposite of the sun.

reflectivity
a measure of how well a surface turns the part of the radiation it receives back in the direction from which the radiation came.

refraction
bending of light as it passes through something with different properties, such as a light beam bending as it travels through glass.

relative humidity
ratio of the actual vapor pressure of the air to the saturation vapor pressure for the surrounding air temperature. In other words, how much water the air is holding divided by how much water the air is capable of holding.

Saffir-Simpson Scale
a hurricane intensity scale created to quantify the amount of damage they will cause upon landfall. The scale is derived using wind speeds and the central atmospheric pressure of the storm, from 1 (minimal damage) to 5 (intense).

saturation
when the air is holding the maximum amount of water that it can hold. If any more water is added to the air, the water will condense and leave the air in the form of liquid.

season
a way of dividing up the calendar year according to regular occurrences such as the equinoxes and solstices. For example, in the Northern Hemisphere, from the vernal equinox to the summer solstice is Spring (March 21 to June21). From that solstice to the autumnal equinox is Summer (June21-September 22). From that equinox to the winter solstice is Autumn (September 22-December 22). From that solstice to the vernal equinox is Winter (December 22-March 21).

SI Unit
short for International System of Units, and denotes the standard unit used internationally for different measures of variables.

solar eclipse
when the moon is in a direct line between the earth and the sun, and the sun appears obscured. The moon's shadow will be cast on the earth, making some parts of the earth dark for a short length of time.

solar radiation
electromagnetic waves that come from the sun. Examples are UV rays, visible light, and infrared radiation.

solstice
point in the earth's orbit of the sun where the sun's rays are shining directly as far north or as far south as they possibly can shine, due to the tilt of the earth on its axis. In the Northern Hemisphere, the summer solstice is June 21, and the winter solstice is December 22. The dates are reversed for the Southern Hemisphere.

Southern Hemisphere
the half of the earth located below the equator, extending from 0

stability
a state of the atmosphere when a parcel of air will return to its starting position when moved up or down. This is because the parcel of air is denser than its surrounding air. Stability is often associated with fair weather.

storm surge
a rise in sea level that comes with a hurricane or other intense storm.

stratosphere
the layer between the troposphere and the mesosphere in the earth's atmosphere. It is located at an altitude between 10 and 50 kilometers, and is the area where most beneficial ozone formation occurs.

stratus clouds
a low cloud type that forms a gray layer with a uniform base. Does not usually produce precipitation. Overcast skies.

temperature inversion
when a layer of air has a temperature increase instead of decrease with altitude.

thermal pollution
an increase in air or water temperature caused by heat from man-made sources.

thermocline
A temperature gradient within layer of a body of water that is notably greater than the temperature gradients above and below it.

thermometer
an instrument used for measuring temperature.

thermosphere
the atmospheric shell that goes from the top of the mesosphere to outer space. The temperature increases with altitude, and its height is about 80 kilometers.

tidal wave
1) the periodic variations of sea level caused by the moon's pull, and also caused by earthquakes 2) in everyday language, referring to any unusually high and destructive water level along a shore.

tornado
small mass of air that spins rapidly about an almost vertical axis and forms a funnel cloud that contacts the ground. Comes down from a cumulonimbus cloud and is considered probably the most destructive of all weather systems.

trade winds
wind system in the tropics that blows from the subtropical high pressure areas to the equatorial low pressure area. They are northeast winds in the Northern Hemisphere and southeast winds in the Southern Hemisphere.

transpiration
process where water in plants is transferred to water vapor in the atmosphere through the leaf pores.

Tropic of Cancer
furthest north parallel (latitude line) where the sun's rays will shine directly overhead during the summer solstice, located at 23

Tropic of Capricorn
furthest south parallel (latitude line) where the sun's rays will shine directly overhead during the summer solstice, located at 23

tropopause
boundary between the troposphere and the stratosphere where there is a change in the lapse rate of the atmospheric temperature.

troposphere
the layer of the atmosphere that goes from the earth's surface to the tropopause. The lowest 6-16 kilometers (4-10 miles), where all the earth's weather takes place.

typhoon
a severe tropical cyclone with sustained surface wind speeds greater than 74 mph in the western North Pacific. Same as a hurricane, but given a different name depending on the location of the storm.

ultraviolet radiation
electromagnetic radiation with wavelengths ranging from 1-300 nanometers. Can be divided into three types-UVA (responsible for tanning the skin and some types of skin cancers), UVB (responsible for sunburn and skin cancers), and UVC (potentially lethal radiation, but does not reach the earth's surface because of protection from the ozone layer).

unsaturated
is able to hold more water than it currently is holding.

visible radiation
part of the electromagnetic radiation spectrum with wavelengths between 0.39 and 0.76 micrometers (between ultraviolet and infrared). The normal human eye is sensitive to this radiation, it is the light that we see.

warm front
any front that moves so that warm air replaces colder air.

warning
for a tornado, thunderstorm, flood, or hurricane. Indicates that the event is definitely going to happen or is in the process of occurring. Issued by the U.S. National Weather Service.

watch
for a tornado, thunderstorm, flood, or hurricane. Indicates that the conditions are ideal for one of the aforementioned events to occur. Issued by the U.S. National Weather Service so that the public can take the necessary precautions or even leave the area before the event occurs.

westerlies
the dominant west-to-east motion of the atmosphere centered over the middle latitudes (35

wind chill equivalent temperature
air temperature index that attempts to quantify how cold the air feels when skin is exposed to low air temperature and wind. The faster the wind blows, the colder the air will feel.

wind shear
the rate of change of wind speed or wind direction over a short period of time and a short distance. Can occur vertically or horizontally.

wind vane
instrument used to measure wind direction.

zephyr
any soft, gentle breeze.