( ( To ( ( find out ) ( how ( ( these ( southward winds ) ) ( are ( sustained ( throughout ( the summer ) ) ) ) ) ) ) ) ( we ( ( need ( to ( ( know more ) ( about ( mesosphere-mesopause ( wind speeds ) ) ) ) ) ) . ) ) )
(ROOT (S (S (VP (TO To) (VP (VB find) (PRT (RP out)) (SBAR (WHADVP (WRB how)) (S (NP (DT these) (JJ southward) (NNS winds)) (VP (VBP are) (VP (VBN sustained) (PP (IN throughout) (NP (DT the) (NN summer)))))))))) (NP (PRP we)) (VP (VBP need) (S (VP (TO to) (VP (VB know) (NP (JJR more)) (PP (IN about) (NP (JJ mesosphere-mesopause) (NN wind) (NNS speeds))))))) (. .)))
To find out how these southward winds are sustained throughout the summer we need to know more about mesosphere-mesopause wind speeds.
(ROOT (S (NP (DT The) (NN mesopause)) (VP (VBZ is) (PP (IN at) (NP (NP (DT the) (NN top)) (PP (IN of) (NP (DT the) (NN mesosphere)))))) (. .)))