Atmosphere - Part of the energy received from the Sun is captured by the atmosphere. The other part is absorbed by the Earth or reflected in the form of heat. Greenhouse gases heat up the atmosphere by slowing the release of heat to space.

Barometer - An Instrument that measures air pressure.

Beaufort wind scale - A scale that uses observations of the effects of wind to estimate its speed.

Biosphere - Living beings (such as plants) influence weather and climate. They form the foundations of ecosystems, which use minerals, water, and other chemical compounds. They contribute materials to other subsystems.

Cirrus Cloud - High cloud, delicate, hair like and feathery looking.

Cyclone Atmospheric circulations that rotate clockwise in the southern hemisphere, (anti-clockwise in the northern hemisphere). Cyclones are areas of lower pressure and generally associated with stronger winds, unsettled conditions, cloudiness and rainfall.

Dew Point - (or Dew-point Temperature) - A measure of atmospheric moisture. It is the temperature to which air must be cooled in order to reach saturation (assuming air pressure and moisture content are constant).

Doppler Radar - Radar that can measure radial velocity, the instantaneous component of motion parallel to the radar beam (i.e., toward or away from the radar antenna).

Evaporation - The surfaces of water bodies maintain the quantity of water vapor in the atmosphere within normal limits.

Humidity - Generally, a measure of the water vapor content of the air. Popularly, it is used synonymously with relative humidity.

Hydrosphere - The hydrosphere is the name for all water in liquid form that is part of the climatic system. Most of the lithosphere is covered by liquid water, and some of the water even circulates through it.

Precipitation - Water condensing in the atmosphere forms droplets, and gravitational action causes them to fall on different parts of the Earth's surface.

Relative Humidity - A dimensionless ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Since the latter amount is dependent on temperature, relative humidity is a function of both moisture content and temperature. As such, relative humidity by itself does not directly indicate the actual amount of atmospheric moisture present.

Winds - The atmosphere is always in motion. Heat displaces masses of air, and this leads to the general circulation of the atmosphere.