Ubac-
The shady (usually poleward, or north in the Northern Hemisphere) side of a mountain.
Unltraviolet radiation-
Electromagnetic radiation of shorter wavelength than visible radiation but longer than x rays.
Unstable air-
Air in which static instability prevails.
Updraft curtains-
Long narrow sheets of warm air rising from a heated surface.
Upslope fog-
A type of fog formed when air flows upward over rising terrain and is, consequently, adiabatically cooled to or below its dewpoint.
Upslope wind-
A wind directed up a slope, often used to describe winds produced by processes larger in scale than the slope.
Upwelling-
An ascending motion of subsurface water by which water from deeper layers is brought into the surface layer and is removed from the area of upwelling by divergent horizontal flow.
