Unit 8

Troposphere- layer of the atmosphere closest to Earth’s surface, where most of the mass of atmosphere is found and in which most weather takes place and air pollution collects.

Stratosphere- layer of Earth’s atmosphere that is located above the tropopause and is made up primarily of concentrated ozone.

Mesosphere- layer of Earth’s atmosphere above the stratopause.

Thermosphere- layer of Earth’s surface that is located above the mesopause; oxygen atoms absorb solar radiation causing the temperature to increase in this layer.

Exosphere- outermost layer of Earth’s atmosphere that is located above the thermosphere with no clear boundary at the top, transitional region between Earth’s atmosphere and outer space.

Radiation- the transfer of thermal energy by electromagnetic waves; the transfer of thermal energy from the Sun to the Earth by radiation.

Conduction- the transfer of thermal energy between objects in contact by the collisions between the particles in the objects.

Convection- the transfer of thermal energy by the movement of heated material from one place to another.

Greenhouse effect- natural process where certain atmospheric gases absorb heat radiating off the planet’s surface and prevents this heat from being lost to space, which helps keep Earth warm enough to sustain life.

Temperature inversion- increase in temperature with height an atmospheric layer, which inverts the temperature-altitude relationship and can worsen air-pollution problems.

Humidity- amount of water vapor in the atmosphere at a given location on Earth’s surface.

Saturation- the point at which water molecules leaving the water’s surface equals the rate of water molecules returning to the surface.

Relative humidity- ratio of water vapor contained in a specific volume of air compared with how much water vapor that amount of actually can hold; expressed as a percentage.

Dew point- temperature to which air is cooled at a constant pressure to reach saturation, at which point condensation can occur.

Latent heat- stored energy in water vapor that is not released to warm the atmosphere until condensation takes place.

Condensation nucleus- small particle in the atmosphere around which cloud droplets can form.

Orographic lifting- cloud formation that occurs when warm, moist air is forced to rise up the side of a mountain.

Cumulus- puffy, lumpy-looking clouds that usually occur below 2000 m.

Stratus- a layered sheetlike cloud that covers much or all of the sky in a given area.

Cirrus- high clouds made up of ice crystals that form at heights of 6000 m.

Precipitation- all solid and liquid forms of water- snow, sleet, hail- that fall from clouds.

Coalescence- process that occurs when cloud droplets collide and form larger droplets, which eventually become too heavy to remain aloft and can fall to Earth as precipitation.