( ( ( Air ( Masses ( and ( Weather ( Fronts Air ) ) ) ) ) ( that ( has ( acquired ( a ( ( fairly uniform ) ( ( temperature and ) humidity ) ) ) ) ) ) ) ( ( ( over ( ( a ( large area ) ) ( of ( ( the ( Earth 's ) ) surface ) ) ) ) ( ( ( is called ) ( an ( air mass ) ) ) . ) ) ( ( Air masses ) ( ( are ( of ( ( ( ( four ( main ( types arctic ) ) ) ( -LRB- ( A -RRB- ) ) ) or ) ( ( ( ( ( ( ( ( antarctic ( -LRB- ( AA -RRB- ) ) ) , ) ( polar ( -LRB- ( P -RRB- ) ) ) ) , ) ( tropical ( -LRB- ( T -RRB- ) ) ) ) , ) and ) ( equatorial ( -LRB- ( E -RRB- ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (NP (NP (NNP Air) (NNPS Masses) (CC and) (NNP Weather) (NNP Fronts) (NNP Air)) (SBAR (WHNP (WDT that)) (S (VP (VBZ has) (VP (VBN acquired) (NP (DT a) (ADJP (RB fairly) (JJ uniform)) (NN temperature) (CC and) (NN humidity))))))) (PRN (SINV (PP (IN over) (NP (NP (DT a) (JJ large) (NN area)) (PP (IN of) (NP (NP (DT the) (NN Earth) (POS 's)) (NN surface))))) (VP (VBZ is) (VP (VBN called))) (NP (DT an) (NN air) (NN mass)) (. .))) (NP (NNP Air) (NNS masses)) (VP (VBP are) (PP (IN of) (NP (NP (NP (CD four) (JJ main) (NNS types) (JJ arctic)) (PRN (-LRB- -LRB-) (NP (NNP A)) (-RRB- -RRB-))) (CC or) (NP (NP (NP (NN antarctic)) (PRN (-LRB- -LRB-) (NP (NNP AA)) (-RRB- -RRB-))) (, ,) (NP (NP (JJ polar)) (PRN (-LRB- -LRB-) (NP (NNP P)) (-RRB- -RRB-))) (, ,) (NP (NP (JJ tropical)) (PRN (-LRB- -LRB-) (NP (NNP T)) (-RRB- -RRB-))) (, ,) (CC and) (NP (NP (NN equatorial)) (PRN (-LRB- -LRB-) (NP (NNP E)) (-RRB- -RRB-))))))) (. .)))
Air Masses and Weather Fronts Air that has acquired a fairly uniform temperature and humidity over a large area of the Earth's surface is called an air mass. Air masses are of four main types arctic (A) or antarctic (AA), polar (P), tropical (T), and equatorial (E).
(ROOT (S (NP (NP (DT The) (NN movement)) (PP (IN of) (NP (NP (DT an) (NN air) (NN mass)) (PP (IN over) (NP (NP (NN earth) (POS 's)) (NN surface)))))) (VP (VBZ causes) (NP (JJ local) (NN weather) (NNS changes))) (. .)))