Appendix II — GLOSSARY 



SUBLIMATION. The transition of a substance 

 from the solid state directly to the vapor state, 

 or vice versa, without passing through an inter- 

 mediate liquid state. 



SUBSIDENCE. A descending motion of air 

 in the atmosphere, usually with the implication 

 that the condition extends over a rather broad 

 area. 



SUBSIDENCE INVERSION. A temperature in- 

 version produced by the adiabatic warming of 

 a layer of subsiding air. 



THERMAL HIGH. A high resulting from the 

 cooling of air by a cold underlying surface, and 

 remaining nearly stationary over the cold sur- 

 face. 



THERMAL LOW. An area of low pressure 

 due to high temperatures caused by intensive 

 heating at the earth's surface. They are non- 

 frontal, their circulation generally weak and 

 diffuse, and they remain stationary over the 

 area that produced them . 



TRADE WINDS. The wind system, occupying 

 most of the tropics, which blows from the sub- 

 tropical highs toward the equatorial trough; a 

 major component of the general circulation of 

 the atmosphere. The winds are northeasterly 

 in the Northern Hemisphere and southeasterly 

 in the Southern Hemisphere. 



TROUGH. An elongated area of relatively 

 low pressure. 



UPSLOPE FOG. A type of fog formed when 

 air flows upward over rising terrain and adia- 

 batically cooled to or below its dewpoint. 



UPSTREAM. In the direction from which 

 the wind or system is flowing. 



UPWELLING. The rising of water toward the 

 surface from subsurface layers of a body of 

 water. 



VALLEY WIND. A wind which ascends 

 a mountain valley during the day. 



VEERING. A change in wind direction in a 

 clockwise manner. 



ZONAL WIND. The wind, or wind component, 

 along the local parallel of latitude. The latitudinal 

 (east or west) component of existing flow. 



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