( ( Warm air ) ( ( ( ( ( rises ( ( ( ( at ( the equator ) ) and ) then ) flows ) ) ( ( north and ) south ) ) , ) ( while ( ( ( corresponding flows ) ( of ( low ( altitude ( cold air ) ) ) ) ) ( move ( from ( ( the poles ) ( toward ( the equator ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Warm) (NN air)) (VP (VBZ rises) (NP (UCP (PP (IN at) (NP (DT the) (NN equator))) (CC and) (ADVP (RB then))) (NNS flows)) (ADVP (RB north) (CC and) (RB south)) (, ,) (SBAR (IN while) (S (NP (NP (JJ corresponding) (NNS flows)) (PP (IN of) (NP (JJ low) (NN altitude) (JJ cold) (NN air)))) (VP (VBP move) (PP (IN from) (NP (NP (DT the) (NNS poles)) (PP (IN toward) (NP (DT the) (NN equator))))))))) (. .)))
Warm air rises at the equator and then flows north and south, while corresponding flows of low altitude cold air move from the poles toward the equator.
(ROOT (S (NP (NP (DT The) (JJR lower) (NN density)) (PP (IN of) (NP (JJ warm) (NN air)))) (VP (VBZ causes) (S (NP (PRP it)) (VP (TO to) (VP (VB rise) (PP (IN above) (NP (JJ cold) (NN air))))))) (. .)))