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Le onde del mare e degli oceani
Skip to content Che si tratti di piccole increspature o di cavalloni tempestosi, il movimento delle onde da sempre evoca la potenza del mare . Le onde sono masse d’acqua messe in moto da forme di energia esterna , in particolare dall’energia cinetica del vento che soffia sulla superficie del mare. A livello della cresta dell’onda la gravità spinge l’acqua verso il basso e le imprime un moto circolatorio.
Di solito le onde generate dal vento viaggiano sulla superficie marina e alla fine, quando raggiungono la costa, rilasciano l’energia accumulata . Le onde piu’ grandi si registrano in regioni dell’oceano molto ventose come l’Atlantico: lungo le coste meridionali dell’Australia sono frequenti onde alte sino a 3 metri. I venti impetuosi provocano spesso onde che possono raggiungere i 6 metri du altezza ed in zone come l’Atlantico settentrionale si possono formare onde alte sino a 33 metri.
Come si formano le onde Il vento che si muove sugli oceani genera un corrispondente movimento della superficie dell’acqua. Un vento costante che agisce a grandi distanze tende a generare increspature lunghe ed uniformi. Invece nella zona della risacca, vicino alla costa, le particelle di acqua si muovono in cerchi che diventano piu’ grandi avvicinandosi alla superficie. Quando arrivano in acque basse, si frangono sul fondo e si appiattiscono. A causa della spinta in avanti, vicino alla riva si formano creste e cavalloni.
Le onde interne Le onde possono formarsi al di sotto della superficie del mare, spesso alla base di un termoclino dove uno strato di acqua calda confina con uno strato di acqua fredda e densa. Le onde interne generate da correnti , maree o venti possono raggiungere i 30m di altezza.
L’energia delle onde Molti paesi con notevole estensione costiera stanno valutando la possibilità di sfruttare le onde dell’oceano ed il vento per produrre energia rinnovabile. Le tecnologie già sperimentate comprendono generatori azionati dal moto ondoso, turbine subacquee e centrali eoliche costiere che sfruttano la costante brezza del mare. Anche il moto incessante delle maree può essere convertito in energia.
Il dizionario delle onde La lunghezza dell’onda è la distanza tra due creste consecutive, mentre l’altezza è la distanza verticale tra il cavo d’onda e la cresta. La rapidità dell’onda è l’angolo disegnato tra il piano orizzontale ed il vertice della cresta che segue.
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