( ( When ( ( such ( an ( air mass ) ) ) ( is detected ) ) ) ( , ( ( ( its impact ) ( on people ) ) ( ( is ( determined ( based ( upon ( ( a formula ) ( that ( includes ( ( the variables ) ( of ( ( temperature , ) ( ( time ( of ( ( year and ) length ) ) ) ( of ( a ( given ( hot spell ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (PDT such) (DT an) (NN air) (NN mass)) (VP (VBZ is) (VP (VBN detected))))) (, ,) (NP (NP (PRP$ its) (NN impact)) (PP (IN on) (NP (NNS people)))) (VP (VBZ is) (VP (VBN determined) (PP (VBN based) (PP (IN upon) (NP (NP (DT a) (NN formula)) (SBAR (WHNP (WDT that)) (S (VP (VBZ includes) (NP (NP (DT the) (NNS variables)) (PP (IN of) (NP (NP (NN temperature)) (, ,) (NP (NP (NN time)) (PP (IN of) (NP (NN year) (CC and) (NN length))) (PP (IN of) (NP (DT a) (VBN given) (JJ hot) (NN spell))))))))))))))) (. .)))
When such an air mass is detected, its impact on people is determined based upon a formula that includes the variables of temperature, time of year and length of a given hot spell.
(ROOT (S (NP (NP (NNP Time)) (, ,) (NP (NN mass)) (, ,) (NP (NN length)) (, ,) (CC and) (NP (NN temperature))) (VP (VBP are) (VP (VBN considered) (S (VP (TO to) (VP (VB be) (NP (NN base) (NNS units))))))) (. .)))