{"id":126,"date":"2004-12-24T16:17:47","date_gmt":"2004-12-24T16:17:47","guid":{"rendered":"http:\/\/informacyde.com\/blog\/?p=126"},"modified":"2008-08-08T16:34:30","modified_gmt":"2008-08-08T14:34:30","slug":"orages","status":"publish","type":"post","link":"https:\/\/informacyde.com\/blog\/divers\/orages\/","title":{"rendered":"Orages…"},"content":{"rendered":"

Qu’est-ce qu’un nuage d’orage ?<\/strong>
\nC’est un nuage dont le sommet a la forme d’une enclume et dont la base est plate. Celle-ci peut \u00eatre situ\u00e9e entre 500 et 2000 m; le sommet du nuage peut atteindre une altitude de 15000 m en moins d’une demi-heure. Il est bourgeonnant dans le ciel. \u00c0 l’int\u00e9rieur de ce nuage, de forts courants d’air chaud montent et d’air froid descendent. Tout d’un coup, un vent violent nous avertit qu’un orage est sur le point d’\u00e9clater.<\/p>\n

Formation d’un orage<\/strong>
\nLorsque de l’air anormalement froid recouvre de l’air anormalement chaud, les conditions sont favorables au d\u00e9clenchement des orages. De violents courants d’air verticaux entra\u00eenent l’humidit\u00e9, les fragments de glace, les gr\u00ealons et les gouttelettes d’eau \u00e0 l’int\u00e9rieur du nuage. Ces frottements cr\u00e9ent une s\u00e9paration des charges \u00e9lectriques. Les particules les plus fines, charg\u00e9es d’\u00e9lectricit\u00e9 positive, se dirigent vers le sommet. Les plus lourdes charg\u00e9es d’\u00e9lectricit\u00e9 n\u00e9gative vont vers la base. \u00c0 cause des mouvements verticaux tr\u00e8s violents et puissants, il y a d\u00e9s\u00e9quilibre entre les charges \u00e9lectriques \u00e0 l’int\u00e9rieur du nuage ainsi qu’\u00e0 l’ext\u00e9rieur, entre la base n\u00e9gative du nuage et le sol positif. Quand les charges accumul\u00e9es deviennent trop importantes, et surtout lorsqu’il y a opposition directe entre ces charges, il y a d\u00e9charge \u00e9lectrique (\u00e9clair) et un orage \u00e9clate.<\/p>\n

Temp\u00e9rature de l’air autour de l’\u00e9clair<\/strong>
\nLa temp\u00e9rature de l’air est tr\u00e8s \u00e9lev\u00e9e, environ 30000 degr\u00e9s (5 fois la temp\u00e9rature du soleil!) le long du trajet de l’\u00e9clair. (N’oubliez pas que l’air travers\u00e9 par l’\u00e9clair est \u00ab\u00a0grill\u00e9\u00a0\u00bb!).<\/p>\n

Quelle est l’\u00e9nergie d\u00e9gag\u00e9e par l’\u00e9clair ?<\/strong>
\nUn \u00e9clair consomme au maximum l’\u00e9quivalent en \u00e9nergie d’une machine de 2800 KW\/h. Les 44000 \u00e9clairs qui se produisent par jour dans le monde fourniraient l’\u00e9quivalent de 100 \u00e9clairs\/s. Ceci correspond \u00e0 un d\u00e9versement d’\u00e9nergie de 4 milliards de KWatts. M\u00eame \u00e0 1 cent le KW\/h, cette \u00e9nergie vaudrait 200 000 000$\/jour. L’intensit\u00e9 \u00e9quivaudrait \u00e0 10000 amp\u00e8res. Mais capter cette \u00e9nergie est aussi difficile que de construire un pont de la terre \u00e0 la lune !<\/p>\n

Comment se prot\u00e9ger de l’orage :<\/strong><\/p>\n

\n

– Dans une maison \u00e0 charpente m\u00e9tallique (car le courant suit le m\u00e9tal)
\n– Sous un toit m\u00e9tallique dont tous les coins sont reli\u00e9s \u00e0 la terre
\n– Dans un \u00e9difice \u00e9quip\u00e9 d’un paratonnerre.<\/p>\n<\/blockquote>\n

Si vous \u00eates surpris \u00e0 l’ext\u00e9rieur par l’orage :<\/em><\/strong><\/p>\n

\n

– Trouvez un abri \u00e0 l’int\u00e9rieur sinon r\u00e9fugiez-vous dans une crevasse, sous une falaise ou dans une grotte
\n– Eloignez-vous des arbres isol\u00e9s
\n– Evitez les zones sur\u00e9lev\u00e9es et la lisi\u00e8re d’un bois
\n– Lorsque l’orage est tr\u00e8s violent, n’h\u00e9sitez pas \u00e0 vous asseoir ou \u00e0 vous coucher dans un foss\u00e9
\n– Ne vous approchez pas \u00e0 plus de 30 m d’une cl\u00f4ture en fil de fer \u00e0 cause du risque \u00e9lev\u00e9 d’\u00e9lectrocution m\u00eame si la foudre a frapp\u00e9 la cl\u00f4ture \u00e0 1 km de l\u00e0
\n– Il n’est pas n\u00e9cessaire de fermer portes et fen\u00eatres, sinon pour emp\u00eacher la pluie d’entrer (la foudre traverse la brique!)
\n– Il n’y a aucun rapport entre les courants d’air et la trajectoire de la foudre
\n– Les golfeurs devraient \u00e9viter de lever leur b\u00e2ton au-dessus de leur t\u00eate
\n– Les nageurs devraient sortir de l’eau
\n– En auto, ne pas se garer pr\u00e8s d’un grand arbre ou d’une cl\u00f4ture grillag\u00e9e.<\/p>\n<\/blockquote>\n

Quelques statistiques<\/strong><\/p>\n

\n

– Il y a environ 20 millions d’orages par an. (50000 par jour).
\n– Ils sont moins fr\u00e9quents aux latitudes septentrionales.
\n– En moyenne, il y a 20 jours par an d’orages dans la partie sud de la vall\u00e9e du St-Laurent (dans le Golfe, il y en a 10 jours par an).
\n– Diam\u00e8tre d’un orage: 15 \u00e0 25 km.
\n– Extension verticale 10, 12 ou 15 km.
\n– Dur\u00e9e 1 ou 2 heures (ou plus si bien violent).
\n– \u00c0 tout moment, 100 \u00e9clairs frappent la surface terrestre: total annuel mondial: 32,000,000 \u00e9clairs; total annuel canadien: 100,000 \u00e9clairs.<\/p>\n<\/blockquote>\n

\u00c0 retenir :<\/strong><\/p>\n

\n

– Les animaux n’attirent pas la foudre.
\n– Laisser les fen\u00eatres ou les portes ouvertes n’invite pas la foudre \u00e0 entrer.
\n– La foudre peut s’abattre plus d’une fois au m\u00eame endroit; il n’est donc pas s\u00e9curitaire de se placer \u00e0 un endroit o\u00f9 elle a d\u00e9j\u00e0 frapp\u00e9 (l’Empire State Building \u00e0 New York, a \u00e9t\u00e9 frapp\u00e9 15 fois en 15 minutes!).<\/p>\n<\/blockquote>\n

\n\"orage\"
\"orage\"
\"orage\"
\n\"orage\"
\"orage\"<\/p>\n

(source : Meteo.org<\/a>)<\/p>\n","protected":false},"excerpt":{"rendered":"

Qu’est-ce qu’un nuage d’orage ? C’est un nuage dont le sommet a la forme d’une enclume et dont la base est plate. Celle-ci peut \u00eatre situ\u00e9e entre 500 et 2000…<\/p>\n","protected":false},"author":10,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[8],"tags":[],"class_list":["post-126","post","type-post","status-publish","format-standard","hentry","category-divers"],"yoast_head":"\nOrages... - Informacyde<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/informacyde.com\/blog\/divers\/orages\/\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Orages... - Informacyde\" \/>\n<meta property=\"og:description\" content=\"Qu’est-ce qu’un nuage d’orage ? 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