The point in the 11-year solar cycle at which sunspot activity is highest.

The point in the 11-year solar cycle at which sunspot activity is lowest.

A compound composed of one sulfur and two oxygen molecules. Sulfur dioxide emitted into the atmosphere through natural and anthropogenic processes is changed in a complex series of chemical reactions [..]

The outermost shell of the atmosphere, between the mesosphere and outer space; where temperatures increase steadily with altitude.

A remote-sensing system that transmits its own radiation to detect an object or area for observation and receives the reflected or transmitted radiation. Radar is an example of an active system. Compa [..]

The air surrounding the Earth, described as a series of shells or layers of different characteristics. The atmosphere, composed mainly of nitrogen and oxygen with traces of carbon dioxide, water vapor [..]

The radiation emitted in the spectral wavelength greater than 4 micrometers corresponding to the radiation emitted from the Earth and atmosphere. It is sometimes referred to as 'terrestrial radia [..]

Climate as it existed in the distant past, particularly before historical records.

A system sensing only radiation emitted by the object being viewed or reflected by the object from a source other than the system. See active system.

Chart showing meteorological conditions over a region at a given time; weather map.