Tiny particles of matter that have a special chemical affinity for water molecules, so that condensation may take place on these nuclei at relative humidities under 100 percent.

A shallow, upslope flow of air that develops during daylight hours within mountain valleys.

An instrument designed to monitor relative humidity by measuring the changes in the length of human hair that accompany humidity variations.

A thin envelope of gasses (also containing suspended solid and liquid particles and clouds) that encircles the globe.

The altitude at which air parcels rising with the updraft of a convection cell reaches saturation; coincides with the base of cumuliform clouds.

The atmosphere above 80 km (50 mi) where gases are stratified, with concentrations of the heavier gases decreasing more rapidly with altitude than concentrations of the lighter gases.

(ITCZ) Discontinuous belt of thunderstorms paralleling the equator and marking the convergence of the Northern and Southern Hemisphere surface trade winds.

Ozone (O3) within the stratosphere that filters out potentially lethal intensities of ultraviolet radiation (UV) from the sun.

Transition zone between cold polar easterlies and mild midlatitude westerlies.

A conventional representation on a weather map using standard symbols of weather conditions at some locality.