( ( The waves ) ( ( have ( frequencies ( below ( ( ( the ( proton ( cyclotron frequency ) ) ) , ) ( which ( is ( ( ( ( about 0.001 ) Hz ) ( during ( the periods ) ) ) ( waves ( are observed ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NNS waves)) (VP (VBP have) (NP (NP (NNS frequencies)) (PP (IN below) (NP (NP (DT the) (JJ proton) (NN cyclotron) (NN frequency)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ is) (NP (NP (QP (RB about) (CD 0.001)) (NNS Hz)) (PP (IN during) (NP (DT the) (NNS periods))) (SBAR (S (NP (NNS waves)) (VP (VBP are) (ADJP (JJ observed))))))))))))) (. .)))
The waves have frequencies below the proton cyclotron frequency, which is about 0.001 Hz during the periods waves are observed.
(ROOT (S (NP (NP (DT The) (NN frequency)) (PP (IN of) (NP (DT a) (NN wave)))) (VP (VBZ is) (NP (NP (DT the) (NN reciprocal)) (PP (IN of) (NP (NP (DT the) (NN period)) (PP (IN of) (NP (DT the) (NN wave))))))) (. .)))