{"id":3274,"date":"2025-07-15T18:44:59","date_gmt":"2025-07-15T16:44:59","guid":{"rendered":"https:\/\/www.astro-novinky.eu\/?p=3274"},"modified":"2025-07-15T18:45:47","modified_gmt":"2025-07-15T16:45:47","slug":"video-pozoruhodne-blesky","status":"publish","type":"post","link":"https:\/\/www.astro-novinky.eu\/index.php\/2025\/07\/15\/video-pozoruhodne-blesky\/","title":{"rendered":"Video: Pozoruhodn\u00e9 blesky"},"content":{"rendered":"<figure id=\"attachment_3275\" aria-describedby=\"caption-attachment-3275\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/www.astro-novinky.eu\/wp-content\/uploads\/2025\/07\/2012_07_03_Boure_Ondrejov_Hv_1_s2_startrails_cut-kopie.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3275 size-medium\" src=\"https:\/\/www.astro-novinky.eu\/wp-content\/uploads\/2025\/07\/2012_07_03_Boure_Ondrejov_Hv_1_s2_startrails_cut-kopie-300x189.jpg\" alt=\"Bou\u0159kov\u00e9 v\u00fdboje nad Prahou. Foto: Petr Hor\u00e1lek\" width=\"300\" height=\"189\" srcset=\"https:\/\/www.astro-novinky.eu\/wp-content\/uploads\/2025\/07\/2012_07_03_Boure_Ondrejov_Hv_1_s2_startrails_cut-kopie-300x189.jpg 300w, https:\/\/www.astro-novinky.eu\/wp-content\/uploads\/2025\/07\/2012_07_03_Boure_Ondrejov_Hv_1_s2_startrails_cut-kopie-1024x646.jpg 1024w, https:\/\/www.astro-novinky.eu\/wp-content\/uploads\/2025\/07\/2012_07_03_Boure_Ondrejov_Hv_1_s2_startrails_cut-kopie-768x484.jpg 768w, https:\/\/www.astro-novinky.eu\/wp-content\/uploads\/2025\/07\/2012_07_03_Boure_Ondrejov_Hv_1_s2_startrails_cut-kopie-1320x832.jpg 1320w, https:\/\/www.astro-novinky.eu\/wp-content\/uploads\/2025\/07\/2012_07_03_Boure_Ondrejov_Hv_1_s2_startrails_cut-kopie.jpg 1500w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3275\" class=\"wp-caption-text\">Bou\u0159kov\u00e9 v\u00fdboje nad Prahou. Foto: Petr Hor\u00e1lek<\/figcaption><\/figure>\n<p style=\"font-weight: 400;\">Bou\u0159ka je impozantn\u00ed p\u0159\u00edrodn\u00ed \u00fakaz. Vznik\u00e1 a rozv\u00edj\u00ed se ve spojitosti se specifick\u00fdm druhem oblaku, cumulonimbem. V\u00a0jin\u00fdch oblac\u00edch nevznik\u00e1. Cumulonimbus je oblak kumuliformn\u00edho typu s\u00a0velk\u00fdm vertik\u00e1ln\u00edm rozsahem. V\u00a0na\u0161ich zem\u011bpisn\u00fdch \u0161\u00ed\u0159k\u00e1ch m\u00edv\u00e1 z\u00e1kladnu kolem 1 a\u017e 2 kilometr\u016f nad zem\u00ed, vrcholy v\u00a0letn\u00edm obdob\u00ed kolem 12 a\u017e 15 kilometr\u016f, co\u017e je d\u00e1no v\u00fd\u0161kou tropopauzy a mo\u017enost\u00ed pr\u016fniku konvektivn\u00edho proudu do spodn\u00ed stratosf\u00e9ry. V\u00a0rovn\u00edkov\u00fdch oblastech sahaj\u00ed bou\u0159kov\u00e9 oblaky do je\u0161t\u011b v\u011bt\u0161\u00edch v\u00fd\u0161ek. A pr\u00e1v\u011b vertik\u00e1ln\u00ed rozsah oblaku je pro n\u00e1sledn\u00fd vznik blesk\u016f d\u016fle\u017eit\u00fd. Jsou v\u0161ak i jin\u00e9 druhy oblak\u016f, kter\u00e9 maj\u00ed velk\u00fd vertik\u00e1ln\u00ed rozsah, jako je nap\u0159\u00edklad nimbostratus, a p\u0159esto v\u00a0nich k\u00a0elektrick\u00fdm v\u00fdboj\u016fm nedoch\u00e1z\u00ed. Bou\u0159kov\u00fd cumulonimbus je oproti jin\u00fdm oblak\u016fm typick\u00fd zna\u010dn\u00fdmi vertik\u00e1ln\u00edm rychlostmi proud\u011bn\u00ed, kter\u00e9 p\u0159en\u00e1\u0161ej\u00ed hmotu vody, p\u0159\u00edpadn\u011b ledu, rychle nahoru a dol\u016f, a spolu s\u00a0vodn\u00edmi nebo ledov\u00fdmi \u010d\u00e1sticemi se p\u0159en\u00e1\u0161\u00ed tak\u00e9 elektrick\u00fd n\u00e1boj, kter\u00fd je pokr\u00fdv\u00e1. Vznik\u00e1 tak polarizovan\u00e9 elektrick\u00e9 pole, kter\u00e9 p\u0159i dostate\u010dn\u00e9 intenzit\u011b vede k\u00a0v\u00fdboji.<\/p>\n<p><iframe loading=\"lazy\" title=\"Pozoruhodn\u00e9 blesky\" width=\"800\" height=\"450\" src=\"https:\/\/www.youtube.com\/embed\/6NN84b_Wyt8?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe><\/p>\n<p style=\"font-weight: 400;\">V\u00fdboj v\u00a0plynu je docela samostatn\u00e1 kapitola, kter\u00e9 bychom mohli v\u011bnovat cel\u00e9 videopo\u0159ady. Obecn\u011b m\u016f\u017eeme rozli\u0161it v\u00fdboj, kter\u00fd prob\u011bhne za atmosf\u00e9rick\u00e9ho tlaku, nebo v\u00fdboj ve z\u0159ed\u011bn\u00e9m plynu za n\u00edzk\u00e9ho tlaku, nap\u0159\u00edklad v\u00a0katodov\u00e9 trubici. N\u00e1s bude zaj\u00edmat d\u011bn\u00ed p\u0159i blesku, kdy se ur\u010dit\u00fd prostor ve vzduchu rozsv\u00edt\u00ed. Sv\u00edt\u00edc\u00ed plyn zn\u00e1me z\u00a0p\u0159\u00edrody i z\u00a0um\u011ble navozen\u00e9 situace. P\u0159\u00edrodn\u00ed z\u00e1\u0159en\u00ed plynu je nap\u0159\u00edklad pol\u00e1rn\u00ed z\u00e1\u0159e, airglow nebo pr\u00e1v\u011b pr\u016fvodn\u00ed jev elektrick\u00fdch v\u00fdboj\u016f. Um\u011bl\u00e9 z\u00e1\u0159en\u00ed vyd\u00e1vaj\u00ed nap\u0159\u00edklad neonov\u00e9 trubice nebo doutnavky. P\u0159ipome\u0148me si, \u017ee sv\u011btlo vznik\u00e1 p\u0159i deexcitaci nebo rekombinaci excitovan\u00fdch nebo ionizovan\u00fdch atom\u016f. Sch\u00e9maticky \u0159e\u010deno, je to proces, kdy se do atomu dod\u00e1 zven\u010d\u00ed ur\u010dit\u00e1 energie, kter\u00e1 p\u0159esune elektron do vy\u0161\u0161\u00ed energetick\u00e9 hladiny, odkud se pak vrac\u00ed zp\u00e1tky do hladiny p\u016fvodn\u00ed a stejnou energii zase vyz\u00e1\u0159\u00ed, \u010dasto ve viditeln\u00e9m oboru spektra. P\u0159i ionizaci je elektron od atomu odd\u011blen \u00fapln\u011b a atom je pak p\u0159ipraven zachytit jin\u00fd elektron, op\u011bt p\u0159i vyz\u00e1\u0159en\u00ed ur\u010dit\u00e9 energie. Takov\u00e9 v\u011bci kolem n\u00e1s prob\u00edhaj\u00ed po\u0159\u00e1d. T\u0159eba takov\u00e9 sv\u011btlu\u0161ky nebo luminiskuj\u00edc\u00ed houby. V\u00a0jejich hmot\u011b prob\u00edh\u00e1 \u00fa\u010dinn\u00e1 chemick\u00e1 reakce, p\u0159i kter\u00e9 se excituj\u00ed atomy a p\u0159i n\u00e1sledn\u00e9 deexcitaci nast\u00e1v\u00e1 z\u00e1\u0159iv\u00fd nebo nez\u00e1\u0159iv\u00fd p\u0159echod do p\u016fvodn\u00edho stavu, \u0159\u00edk\u00e1 se tomu bioluminiscence nebo chemiluminiscence. S\u00a0trochou nads\u00e1zky bychom to nazvali skota\u010d\u00edc\u00ed elektrony a v\u00fdsledky jejich hem\u017een\u00ed vid\u00edme nep\u0159etr\u017eit\u011b kolem sebe. Sta\u010d\u00ed \u0161krtnout sirkou, jej\u00ed plam\u00ednek dod\u00e1v\u00e1 do okoln\u00edho plynu kolem dost tepeln\u00e9 energie, aby ho excitovala nebo ionizovala, a n\u00e1sledn\u011b p\u0159i deexcitac\u00edch a rekombinac\u00edch vznikalo sv\u011btlo. Pokud se m\u00e1 vytvo\u0159it atmosf\u00e9rick\u00fd blesk, je nutn\u00e9 nejprve navodit ionizovan\u00fd stav vzduchu.<\/p>\n<p style=\"font-weight: 400;\">Vzduch je za b\u011b\u017en\u00fdch okolnost\u00ed elektricky t\u00e9m\u011b\u0159 nevodiv\u00fd, jeho vodivost je velice n\u00edzk\u00e1. Aby mohl vzduchem proch\u00e1zet elektrick\u00fd n\u00e1boj a vytvo\u0159it tak elektrick\u00fd proud, mus\u00ed se vzduch, jak jsme si \u0159ekli, nejprve ionizovat, to znamen\u00e1 odd\u011blit jeden nebo v\u00edce elektron\u016f z\u00a0atom\u016f a molekul dus\u00edku nebo kysl\u00edku, kter\u00e9 tvo\u0159\u00ed hlavn\u00ed obsah zemsk\u00e9 atmosf\u00e9ry. Bl\u00edzko u zemsk\u00e9ho povrchu zp\u016fsobuje ionizaci radioaktivn\u00ed z\u00e1\u0159en\u00ed, to v\u0161ak zasahuje jen do v\u00fd\u0161ek n\u011bkolika stovek metr\u016f, nanejv\u00fd\u0161 kilometr\u016f. Nad oce\u00e1ny je troposf\u00e9rick\u00e1 ionizace v\u00a0je\u0161t\u011b ni\u017e\u0161\u00ed vrstv\u011b. S\u00a0rostouc\u00ed v\u00fd\u0161kou se st\u00e1le v\u00edce uplat\u0148uje ionizace kosmick\u00fdm z\u00e1\u0159en\u00edm, tak\u017ee vodivost vzduchu s\u00a0rostouc\u00ed v\u00fd\u0161kou exponenci\u00e1ln\u011b nar\u016fst\u00e1. Ve v\u00fd\u0161ce 18 kilometr\u016f je vodivost vzduchu asi stokr\u00e1t vy\u0161\u0161\u00ed, ne\u017e u povrchu. Ve v\u00fd\u0161ce 50 a\u017e 60 kilometr\u016f se u\u017e vzduch d\u00e1 pova\u017eovat za docela dobr\u00fd vodi\u010d, tak\u017ee se tady elektrick\u00fd n\u00e1boj dob\u0159e rozprost\u0159e kolem cel\u00e9 zem\u011bkoule do vrstvy. Tento n\u00e1boj je kladn\u00fd, proto\u017ee ionizuj\u00edc\u00ed z\u00e1\u0159en\u00ed, p\u0159ich\u00e1zej\u00edc\u00ed z\u00a0vesm\u00edru, svoj\u00ed energi\u00ed odd\u011bl\u00ed elektron od atom\u016f atmosf\u00e9rick\u00fdch plyn\u016f, tak\u017ee tyto atomy pak vystupuj\u00ed jako kladn\u00e9 ionty. Tuto vrstvu ozna\u010dujeme jako elektrosf\u00e9ru a m\u016f\u017eeme ji pova\u017eovat za kulovou desku kondenz\u00e1toru. Druhou desku pak tvo\u0159\u00ed z\u00e1porn\u011b nabit\u00fd zemsk\u00fd povrch. Cel\u00fd tento ob\u0159\u00ed kondenz\u00e1tor tedy tvo\u0159\u00ed z\u00e1porn\u011b nabit\u00fd zemsk\u00fd povrch s\u00a0celkov\u00fdm n\u00e1bojem asi p\u016fl milionu Coulomb\u016f, a kladn\u011b nabit\u00e1 elektrosf\u00e9ra. Mezi t\u011bmito deskami je elektrick\u00e9 pole, jeho\u017e intenzita sm\u011b\u0159uje k\u00a0zemsk\u00e9mu povrchu. V\u00a0atmosf\u00e9rick\u00fdch v\u011bd\u00e1ch se ov\u0161em zav\u00e1d\u00ed intenzita elektrick\u00e9ho pole v\u00a0obr\u00e1cen\u00e9m sm\u011bru, budeme ji tedy uva\u017eovat, \u017ee m\u00ed\u0159\u00ed od povrchu vzh\u016fru. Povrch budeme pova\u017eovat za nulovou hladinu elektrick\u00e9ho potenci\u00e1lu. V\u00a0n\u00edzk\u00fdch vrstv\u00e1ch atmosf\u00e9ry za klidn\u00e9ho po\u010das\u00ed je tento potenci\u00e1l asi 130 Volt\u016f na metr, s\u00a0rostouc\u00ed v\u00fd\u0161kou roste i tento potenci\u00e1l.<\/p>\n<p style=\"font-weight: 400;\">Jak jsme \u0159ekli, atmosf\u00e9ra je u zemsk\u00e9ho povrchu t\u00e9m\u011b\u0159 nevodiv\u00e1 a vodivost roste s\u00a0v\u00fd\u0161kou. Ale i ta mal\u00e1 vodivost u zem\u011b sta\u010d\u00ed na to, aby tady proch\u00e1zel slab\u00fd elektrick\u00fd proud, jeho\u017e hustota v\u00a0cel\u00e9m rozsahu od zem\u011b do horn\u00edch vrstev atmosf\u00e9ry je asi 3kr\u00e1t 10 na m\u00ednus 12. Voltu na metr \u010dtvere\u010dn\u00ed. Co\u017e znamen\u00e1, \u017ee z\u00a0horn\u00ed desky pomysln\u00e9ho kondenz\u00e1toru proud\u00ed kladn\u011b nabit\u00e9 \u010d\u00e1stice sm\u011brem k\u00a0zemsk\u00e9mu povrchu a cel\u00fd kondenz\u00e1tor by se tak b\u011bhem n\u011bkolika minut vybil, nebo chcete-li, zneutralizoval, a cel\u00e9 zm\u00edn\u011bn\u00e9 elektrick\u00e9 pole by zaniklo. Jen\u017ee to nenast\u00e1v\u00e1, elektrick\u00e9 pole je dlouhodob\u011b st\u00e1l\u00e9. Jak je tohle mo\u017en\u00e9? Mus\u00ed existovat n\u011bjak\u00fd mechanismus, kter\u00fd n\u00e1\u0161 kondenz\u00e1tor zase nab\u00edj\u00ed, a za t\u00edm stoj\u00ed obla\u010dn\u00e1 elekt\u0159ina, zejm\u00e9na ta bou\u0159kov\u00e1. \u0158ekli jsme, \u017ee s\u00a0rostouc\u00ed v\u00fd\u0161kou roste tak\u00e9 elektrick\u00fd potenci\u00e1l, ale tento r\u016fst je nejvy\u0161\u0161\u00ed v\u00a0mal\u00fdch v\u00fd\u0161k\u00e1ch a \u010d\u00edm jsme v\u00fd\u0161, t\u00edm se tento n\u00e1r\u016fst zpomaluje, a\u017e se ve v\u00fd\u0161k\u00e1ch elektrosf\u00e9ry, tedy 50 a\u017e 60 kilometr\u016f, zastavuje. Mezi zemsk\u00fdm povrchem a elektrosf\u00e9rou je celkov\u00fd elektrick\u00fd potenci\u00e1l asi 10 na 5. Voltu.<\/p>\n<p style=\"font-weight: 400;\">Vra\u0165me se trochu do minulosti, kdy koncem 18. stolet\u00ed d\u011blal Coulomb prvn\u00ed m\u011b\u0159en\u00ed elektrick\u00e9 vodivosti atmosf\u00e9ry. Tehdy si myslel, \u017ee vzduchov\u00e9 \u010d\u00e1stice z\u00edsk\u00e1vaj\u00ed elektrick\u00fd n\u00e1boj d\u00edky n\u00e1raz\u016fm na zelektrovan\u00e1 t\u011blesa a n\u00e1sledn\u011b jsou od nich elektrick\u00fdmi silami odpuzeny. O sto let pozd\u011bji dal\u0161\u00ed badatel\u00e9 zjistili, \u017ee v\u00a0atmosf\u00e9\u0159e se vyskytuj\u00ed kladn\u011b i z\u00e1porn\u011b nabit\u00e9 \u010d\u00e1stice molekul\u00e1rn\u00edch rozm\u011br\u016f s\u00a0n\u00e1bojem velikosti elektronu. Je\u0161t\u011b o n\u011bco pozd\u011bji, v\u00a0roce 1905, byly zji\u0161t\u011bny i v\u011bt\u0161\u00ed elektricky nabit\u00e9 \u010d\u00e1stice, tvo\u0159en\u00e9 aerosoly, na kter\u00fdch se zachytily ionizovan\u00e9 molekuly. Dnes je dokonce zn\u00e1mo, \u017ee atmosf\u00e9rick\u00e9 ionty maj\u00ed \u0161irok\u00e9 spektrum velikost\u00ed, v\u00a0\u0159\u00e1du 10 na m\u00ednus 10. a\u017e 10 na m\u00ednus 7. metru. Nositeli elektrick\u00e9ho proudu v\u00a0atmosf\u00e9\u0159e jsou hlavn\u011b ty nejmen\u0161\u00ed \u010d\u00e1stice, kter\u00e9 maj\u00ed velkou pohyblivost. Naopak velk\u00e9 \u010d\u00e1stice jsou dost t\u011b\u017ek\u00e9 a kv\u016fli tomu jen m\u00e1lo pohybliv\u00e9. Mal\u00e9 \u010d\u00e1stice se d\u00edky pohyblivosti dob\u0159e zachycuj\u00ed na aerosolech a vytvo\u0159\u00ed tak \u010d\u00e1stice t\u011b\u017ek\u00e9. Aerosol\u016f je nejv\u00edc v\u00a0bl\u00edzkosti zemsk\u00e9ho povrchu, kde je tak\u00e9 obvykle nejvy\u0161\u0161\u00ed koncentrace t\u011b\u017ek\u00fdch iont\u016f a tud\u00ed\u017e nejslab\u0161\u00ed elektrick\u00e1 vodivost. Zne\u010di\u0161t\u011bn\u00ed atmosf\u00e9ry vede ke vzniku t\u011b\u017ek\u00fdch iont\u016f a zeslaben\u00e9 elektrick\u00e9 vodivosti. To se pozoruje i v\u00a0obla\u010dnosti nebo v\u00a0mlze, v\u0161ude se tu lehk\u00e9 ionty slu\u010duj\u00ed s\u00a0aerosolov\u00fdmi \u010d\u00e1sticemi a jako samostatn\u00fdch \u010d\u00e1stic t\u011bchto lehk\u00fdch iont\u016f proto ub\u00fdv\u00e1.<\/p>\n<p style=\"font-weight: 400;\">Hlavn\u00edm v\u00fdrobcem iont\u016f ve vzduchu je kosmick\u00e9 z\u00e1\u0159en\u00ed. Ionizace nast\u00e1v\u00e1 nejv\u011bt\u0161\u00ed m\u011brou v\u00a0horn\u00ed atmosf\u00e9\u0159e a sm\u011brem dol\u016f k\u00a0povrchu jej\u00ed vliv kles\u00e1. Stejn\u011b tak vliv kosmick\u00e9ho ionizuj\u00edc\u00edho z\u00e1\u0159en\u00ed nar\u016fst\u00e1 sm\u011brem od rovn\u00edku k\u00a0p\u00f3l\u016fm. V\u00a0atmosf\u00e9\u0159e neust\u00e1le proud\u00ed z\u00e1porn\u011b nabit\u00e9 ionty od povrchu vzh\u016fru a kladn\u011b nabit\u00e9 ionty shora k\u00a0povrchu. Vodivost z\u00e1vis\u00ed na obsahu zne\u010di\u0161\u0165uj\u00edc\u00edch p\u0159\u00edm\u011bs\u00ed v\u00a0atmosf\u00e9\u0159e, kontaminace je vy\u0161\u0161\u00ed nad pevninou, zat\u00edmco nad oce\u00e1ny je n\u00edzk\u00e1. Nad pevninou je tak\u00e9 v\u00fdrazn\u011bj\u0161\u00ed denn\u00ed chod teploty a turbulentn\u00edho prom\u00edch\u00e1v\u00e1n\u00ed atmosf\u00e9ry v\u00a0n\u00edzk\u00fdch hladin\u00e1ch, a tak i elektrick\u00e1 vodivost m\u00e1 v\u00a0t\u011bchto vrstv\u00e1ch v\u00fdrazn\u00fd denn\u00ed chod. Nejvy\u0161\u0161\u00ed vodivost m\u00e1 vzduch u zemsk\u00e9ho povrchu r\u00e1no, proto\u017ee no\u010dn\u00ed klidn\u011bj\u0161\u00ed vzduch nen\u00ed tolik zne\u010di\u0161t\u011bn ve v\u011bt\u0161\u00edm vertik\u00e1ln\u00edm rozsahu. Dopoledne nar\u016fst\u00e1 turbulentn\u00ed prom\u00edch\u00e1v\u00e1n\u00ed vzduchu a aerosoly se tak dost\u00e1vaj\u00ed m\u00edrn\u011b v\u00fd\u0161e nad povrch, proto vodivost kles\u00e1. D\u00e1le b\u011bhem dne se aerosoly vlivem turbulence rozpt\u00fdl\u00ed do v\u011bt\u0161\u00edho rozsahu mezn\u00ed vrstvy a u povrchu pak vodivost zase m\u00edrn\u011b roste. K\u00a0ve\u010deru turbulentn\u00ed prom\u00edch\u00e1v\u00e1n\u00ed sl\u00e1bne a ust\u00e1v\u00e1, aerosoly klesaj\u00ed k\u00a0zemi a u povrchu je proto zase zhor\u0161en\u00e1 vodivost, kter\u00e1 se pak zlep\u0161\u00ed a\u017e v\u00a0noci. Maxim\u00e1ln\u00ed elektrickou vodivost maj\u00ed n\u00edzk\u00e9 vrstvy atmosf\u00e9ry ke konci noci.<\/p>\n<p style=\"font-weight: 400;\">Tohle v\u0161echno, co jsme si popsali, se diametr\u00e1ln\u011b zm\u011bn\u00ed v\u00a0p\u0159\u00edpad\u011b bou\u0159ek. Bou\u0159kov\u00e9 oblaky obsahuj\u00ed zna\u010dn\u011b velk\u00e9 elektrick\u00e9 n\u00e1boje a jsou zdrojem nab\u00edjen\u00ed toho ob\u0159\u00edho elektrick\u00e9ho kondenz\u00e1toru, o kter\u00e9m jsme mluvili prve. V\u00fdskyt bou\u0159kov\u00e9ho cumulonimbu v\u00a0ur\u010dit\u00e9m m\u00edst\u011b zcela zm\u011bn\u00ed strukturu elektrick\u00e9ho pole v\u00a0atmosf\u00e9\u0159e. Elektrick\u00e9 pom\u011bry v\u00a0atmosf\u00e9\u0159e m\u011bn\u00ed i jin\u00e9 druhy oblak\u016f, nicm\u00e9n\u011b ne tolik, jako cumulonimbus. Nejmen\u0161\u00ed vliv maj\u00ed oblaky, ze kter\u00fdch nevypad\u00e1vaj\u00ed sr\u00e1\u017eky. Ale t\u0159eba takov\u00fd sr\u00e1\u017ekov\u00fd nimbostratus u\u017e vykazuje polaritu rozlo\u017een\u00ed sv\u00fdch n\u00e1boj\u016f a intenzita elektrick\u00e9ho pole je v\u00a0tomto oblaku 10kr\u00e1t siln\u011bj\u0161\u00ed, ne\u017e p\u0159i bezobla\u010dn\u00e9 obloze. Ale ani to nesta\u010d\u00ed na vytvo\u0159en\u00ed bleskov\u00e9ho v\u00fdboje. Bou\u0159kov\u00fd cumulonimbus m\u00e1 rovn\u011b\u017e polarizovan\u00e9 rozlo\u017een\u00ed n\u00e1boje, av\u0161ak intenzita elektrick\u00e9ho pole je zde 100kr\u00e1t v\u011bt\u0161\u00ed, ne\u017e p\u0159i jasn\u00e9 obloze. V\u00a0horn\u00ed \u010d\u00e1sti oblaku se nahromad\u00ed zna\u010dn\u00fd kladn\u00fd n\u00e1boj, ve spodn\u00ed pak zna\u010dn\u00fd z\u00e1porn\u00fd. Kdy\u017e pak za\u010dnou z\u00a0oblaku vypad\u00e1vat sr\u00e1\u017eky, vytvo\u0159\u00ed se u z\u00e1kladny oblaku je\u0161t\u011b mal\u00e9 centrum kladn\u00fdch n\u00e1boj\u016f, pravd\u011bpodobn\u011b ale jen kdy\u017e v\u00a0t\u00e9to \u010d\u00e1sti oblaku jsou nadnulov\u00e9 teploty. Siln\u00fd z\u00e1porn\u00fd n\u00e1boj ve spodn\u00ed \u010d\u00e1sti oblaku pak indukuje na zemsk\u00e9m povrchu pod oblakem oblast kladn\u00e9ho n\u00e1boje, tedy opa\u010dn\u00e9ho, ne\u017e jak\u00fd tam je p\u0159i klidn\u00e9m ovzdu\u0161\u00ed. Elektrick\u00e9 pole v\u00a0cumulonimbu a jeho bl\u00edzk\u00e9m okol\u00ed tak nab\u00fdv\u00e1 slo\u017eit\u011bj\u0161\u00ed struktury. Pro\u010d je v\u00a0bou\u0159kov\u00e9m oblaku zrovna takov\u00e9to rozlo\u017een\u00ed a kvantita n\u00e1boje, to byla dlouho nezn\u00e1m\u00e1 odpov\u011b\u010f, a ani dnes nen\u00ed \u00fapln\u011b v\u0161echno dostate\u010dn\u011b zn\u00e1mo.<\/p>\n<p style=\"font-weight: 400;\">Dnes se v\u00ed, \u017ee podstatnou roli hraj\u00ed ledov\u00e9 \u010d\u00e1stice, kter\u00e9 se v\u00a0bou\u0159kov\u00e9m oblaku zcela b\u011b\u017en\u011b vyskytuj\u00ed. Vedle nich jsou tam tak\u00e9 kapky p\u0159echlazen\u00e9 vody, co\u017e jsou kapi\u010dky s\u00a0podnulovou teplotou a\u017e do m\u00ednus 40 \u00b0C, ale z\u016fst\u00e1vaj\u00ed v\u00a0kapaln\u00e9m stavu. Ledov\u00e9 \u010d\u00e1stice jsou n\u011bco jako termistor \u2014 k\u00a0chladn\u011bj\u0161\u00ed \u010d\u00e1sti se p\u0159esunou kladn\u00e9 n\u00e1boje, k\u00a0teplej\u0161\u00ed pak z\u00e1porn\u00e9. Kdy\u017e kapi\u010dka p\u0159echlazen\u00e9 vody v\u00a0oblaku naraz\u00ed na ledovou \u010d\u00e1stici, okam\u017eit\u011b p\u0159imrz\u00e1, ale p\u0159itom se uvoln\u00ed skupensk\u00e9 teplo mrznut\u00ed, tak\u017ee povrch ledov\u00e9ho krystalku se stane o n\u011bco teplej\u0161\u00ed, ne\u017e vnit\u0159ek. M\u016f\u017eeme tak \u0159\u00edci, \u017ee ledov\u00fd krystalek je obalen\u00fd z\u00e1porn\u00fdm n\u00e1bojem. No a v\u011bt\u0161\u00ed ledov\u00e9 \u010d\u00e1stice jsou t\u011b\u017e\u0161\u00ed a klesaj\u00ed ke spodn\u00ed \u010d\u00e1sti oblaku, zat\u00edmco men\u0161\u00ed krystalky jsou vyn\u00e1\u0161eny stoupav\u00fdmi proudy k\u00a0horn\u00ed partii oblaku, doch\u00e1z\u00ed k\u00a0separaci nabit\u00fdch \u010d\u00e1stic vlivem gravitace, turbulence a vertik\u00e1ln\u00edho proud\u011bn\u00ed v oblaku. Existuje je\u0161t\u011b druh\u00e1, slo\u017eit\u011bj\u0161\u00ed teorie, popisuj\u00edc\u00ed chemicko-fyzik\u00e1ln\u00ed procesy p\u0159eskupov\u00e1n\u00ed elektrick\u00e9ho n\u00e1boje s\u00a0podobn\u00fdm v\u00fdsledkem, tedy \u017ee v\u011bt\u0161\u00ed a nar\u016fstaj\u00edc\u00ed \u010d\u00e1stice ledu se nab\u00edj\u00ed z\u00e1porn\u011b a men\u0161\u00ed \u010d\u00e1stice kladn\u011b. Mezi cumulonimbem a zem\u00ed se vytvo\u0159\u00ed elektrick\u00e9 pole s\u00a0intenzitou 10 a\u017e 20 kilovolt na metr, tedy 100 a\u017e 200kr\u00e1t siln\u011bj\u0161\u00ed, ne\u017e p\u0159i klidn\u00e9m po\u010das\u00ed. Orientace vektoru intenzity je opa\u010dn\u00e1, shora dol\u016f, m\u00edn\u011bno zp\u016fsobem, jak\u00fdm se popisuje tato intenzita ve fyzice atmosf\u00e9ry. Um\u00edst\u011bn\u00ed center elektrick\u00e9ho n\u00e1boje v\u00a0bou\u0159kov\u00fdch oblac\u00edch se b\u011bhem v\u00fdvoje bou\u0159ky m\u011bn\u00ed, mechanismus toho v\u0161ak nen\u00ed zat\u00edm uspokojiv\u011b vysv\u011btlen\u00fd. Nicm\u00e9n\u011b, m\u00e1me u\u017e p\u0159edstavu rozvinut\u00e9ho siln\u00e9ho elektrick\u00e9ho pole, kter\u00e9 vytvo\u0159ily procesy v\u00a0bou\u0159kov\u00e9m oblaku.<\/p>\n<p style=\"font-weight: 400;\">Ud\u011blejme zase kr\u00e1tk\u00fd exkurz do minulosti, do doby, kdy se za\u010d\u00ednaly zkoumat blesky, o kter\u00fdch se v\u016fbec netu\u0161ilo, co to vlastn\u011b je. Star\u00fd dobr\u00fd Aristoteles se domn\u00edval, \u017ee blesk jsou vzn\u00edcen\u00e9 v\u00fdpary, stoupaj\u00edc\u00ed ze zem\u011b a kondenzuj\u00edc\u00ed v\u00a0obla\u010dnosti. Uplynulo 2 tis\u00edce let, kdy\u017e p\u0159i\u0161el Benjamin Franklin, v\u00fdznamn\u00fd americk\u00fd politik a podnikatel, kter\u00e9ho zaj\u00edmaly tak\u00e9 poznatky soudob\u00e9 p\u0159\u00edrodn\u00ed v\u011bdy, a p\u0159esto\u017ee byl jen vyu\u010den\u00fd knihtiska\u0159 a v\u00a0oboru p\u0159\u00edrodn\u00edch v\u011bd samouk, dos\u00e1hl pozoruhodn\u00fdch poznatk\u016f, kter\u00e9 posunuly v\u011bdu dop\u0159edu. Mimo jin\u00e9 dal do souvislosti blesk a atmosf\u00e9rickou elekt\u0159inu. Zkoumal to v\u00a0roce 1752 se sv\u00fdm synem pomoc\u00ed draka, vypou\u0161t\u011bn\u00e9ho do v\u00fd\u0161ky pod bou\u0159kov\u00fdm oblakem. Dnes v\u00edme, \u017ee to nen\u00ed zrovna nejlep\u0161\u00ed n\u00e1pad, proto\u017ee bleskov\u00fd v\u00fdboj vyvol\u00e1 v\u00a0lanku draka siln\u00fd elektrick\u00fd proud, kter\u00fd m\u016f\u017ee p\u0159\u00edtomn\u00e9ho batatele snadno zab\u00edt, a to se i skute\u010dn\u011b stalo jin\u00fdm experiment\u00e1tor\u016fm. Franklin na\u0161t\u011bst\u00ed za\u017eil jen jisk\u0159en\u00ed na sv\u00e9 ruce a pokus p\u0159e\u017eil a ani mu to nevzalo chu\u0165 k\u00a0dal\u0161\u00edmu b\u00e1d\u00e1n\u00ed. Dosp\u011bl pak ke konstrukci bleskosvodu a i kdy\u017e toto za\u0159\u00edzen\u00ed vymysleli i jin\u00ed, tak Franklin je pova\u017eov\u00e1n za jeho vyn\u00e1lezce. V\u00a0\u010desk\u00fdch zem\u00edch je zn\u00e1m\u00fd Prokop Divi\u0161, kter\u00fd postavil p\u0159\u00edstroj na ods\u00e1v\u00e1n\u00ed atmosf\u00e9rick\u00e9 elekt\u0159iny p\u0159ibli\u017en\u011b ve stejn\u00e9 dob\u011b, jako Franklin. V\u00a0pr\u016fb\u011bhu dal\u0161\u00edch stalet\u00ed se dosp\u011blo k\u00a0takov\u00fdm vychyt\u00e1vk\u00e1m, jako jsou aktivn\u00ed bleskosvody, kter\u00e9 jsou vybaveny tak, aby jejich hrotov\u00fd vrchol ionizoval vzduch kolem a vytvo\u0159ily se podm\u00ednky pro v\u00fdboj mezi oblakem a pr\u00e1v\u011b \u0161pi\u010dkou bleskosvodu. D\u011blalo se to nap\u0159\u00edklad pomoc\u00ed radioaktivn\u00edho materi\u00e1lu na \u0161pici bleskosvodu, kdy radioaktivita zp\u016fsobovala tu ionizaci. Dnes se m\u00edsto radionuklid\u016f pou\u017e\u00edv\u00e1 kondenz\u00e1tor, kter\u00fd se p\u0159i bou\u0159ce s\u00e1m nabije a pomoc\u00ed n\u00e1sobi\u010de nap\u011bt\u00ed vytvo\u0159\u00ed siln\u011bj\u0161\u00ed elektrick\u00e9 pole, ne\u017e jak\u00fdm disponuj\u00ed okoln\u00ed povrchy. S\u00e1m tak nab\u00edz\u00ed bleskov\u00e9mu v\u00fdboji optim\u00e1ln\u00ed c\u00edl k\u00a0vybit\u00ed. Tato technologie ov\u0161em nen\u00ed v\u0161emocn\u00e1 ani stoprocentn\u011b \u00fa\u010dinn\u00e1.<\/p>\n<p style=\"font-weight: 400;\">P\u0159esu\u0148me pozornost k\u00a0samotn\u00e9mu blesku. Uk\u00e1zali jsme si, \u017ee v\u00a0bou\u0159kov\u00e9m oblaku se v\u00a0jeho spodn\u00ed \u010d\u00e1sti udr\u017euje zna\u010dn\u00fd z\u00e1porn\u00fd n\u00e1boj, proti kter\u00e9mu le\u017e\u00ed pod oblakem na zemsk\u00e9m povrchu n\u00e1boj kladn\u00fd. Mezi ob\u011bma oblastmi je siln\u00e9 elektrick\u00e9 pole, ve kter\u00e9m doch\u00e1z\u00ed k\u00a0ionizaci vzduchu. Mimochodem, v\u0161imli jste si n\u011bkdy, \u017ee t\u011bsn\u011b p\u0159ed bou\u0159kou m\u00e1te pozoruhodn\u011b dobrou n\u00e1ladu? S\u00e1m to m\u00e1m tak, \u017ee kdy\u017e jsem nap\u0159\u00edklad zabr\u00e1n do pr\u00e1ce a nem\u00e1m p\u0159ehled o po\u010das\u00ed venku, v\u0161imnu si n\u00e1hl\u00e9ho zlep\u0161en\u00ed celkov\u00e9 n\u00e1lady, a\u017e m\u011b napadne, jestli se nebl\u00ed\u017e\u00ed bou\u0159ka \u2014 a v\u017edycky se tref\u00edm. Vzduch, kter\u00fd obsahuje zv\u00fd\u0161enou koncentraci z\u00e1porn\u011b nabit\u00fdch aniont\u016f, m\u00e1 prok\u00e1zan\u00fd p\u0159\u00edzniv\u00fd vliv na na\u0161i psychiku. Do t\u011bla se anionty dost\u00e1vaj\u00ed p\u0159edev\u0161\u00edm d\u00fdch\u00e1n\u00edm. P\u0159i bou\u0159ce v\u00a0jej\u00edm siln\u00e9m elektrick\u00e9m poli doch\u00e1z\u00ed k\u00a0ionizaci. Elektrony, odd\u011blen\u00e9 od atom\u016f, se d\u00edky vysok\u00e9 intenzit\u011b elektrick\u00e9ho pole pohybuj\u00ed velkou rychlost\u00ed sm\u011brem ke kladn\u011b nabit\u00e9mu zemsk\u00e9mu povrchu a b\u011bhem tohoto pohybu nar\u00e1\u017eej\u00ed na dal\u0161\u00ed atomy, respektive molekuly, kter\u00e9 t\u011bmito n\u00e1razy rovn\u011b\u017e ionizuj\u00ed. Po\u010det ionizovan\u00fdch molekul p\u0159itom lavinovit\u011b roste. Kdy\u017e se v\u00a0takov\u00e9mto siln\u00e9m elektrick\u00e9m poli um\u00edst\u00ed vodiv\u00fd p\u0159edm\u011bt opat\u0159en\u00fd hrotem, vodiv\u011b spojen\u00fd se zem\u00ed, m\u00e1 tento hrot stejn\u00fd elektrick\u00fd potenci\u00e1l jako zemsk\u00fd povrch. Hrot je v\u0161ak um\u00edst\u011bn v\u00a0ur\u010dit\u00e9 v\u00fd\u0161ce nad zem\u00ed a tak kolem n\u011bj dojde k\u00a0zak\u0159iven\u00ed a zhu\u0161t\u011bn\u00ed elektrick\u00fdch silo\u010dar, v\u00a0d\u016fsledku toho nastane zes\u00edlen\u00ed intenzity elektrick\u00e9ho pole. V\u00a0okol\u00ed hrotu se tak vytvo\u0159\u00ed podm\u00ednky pro ionizaci n\u00e1razem, tak\u017ee tu vznikne oblak z\u00e1porn\u00fdch iont\u016f, kter\u00e9 jsou pak vodiv\u00fdm p\u0159edm\u011btem p\u0159en\u00e1\u0161eny do zemsk\u00e9ho povrchu, na kter\u00e9m se rozprost\u0159ou. Takto vznikaj\u00ed hrotov\u00e9 v\u00fdboje na \u0161pi\u010dk\u00e1ch strom\u016f, na bleskosvodech, sto\u017e\u00e1rech a jin\u00fdch p\u0159edm\u011btech, kter\u00e9 maj\u00ed hroty. Tyto \u00fakazy zn\u00e1me jako sr\u0161en\u00ed, naz\u00fdvan\u00e9 tak\u00e9 jako Eli\u00e1\u0161\u016fv ohe\u0148, jak ho pojmenovali n\u00e1mo\u0159n\u00edci na plachetnic\u00edch, kdy\u017e pozorovali modrav\u00e9 elektrick\u00e9 sr\u0161en\u00ed na sto\u017e\u00e1rech sv\u00fdch lod\u00ed v\u00a0dob\u011b bou\u0159ky.<\/p>\n<p style=\"font-weight: 400;\">Blesk, jak ho zn\u00e1me z\u00a0bou\u0159ky, je v\u0161ak trochu jin\u00fd, ne\u017e hrotov\u00fd v\u00fdboj. Zat\u00edmco hrotov\u00e9 v\u00fdboje se odehr\u00e1vaj\u00ed v\u00a0mal\u00e9m prostoru kolem popsan\u00fdch p\u0159edm\u011bt\u016f, blesk prob\u00edh\u00e1 na podstatn\u011b v\u011bt\u0161\u00edch rozm\u011brech, a to bu\u010f uvnit\u0159 oblaku mezi horn\u00edm centrem kladn\u00e9ho a spodn\u00edm centrem z\u00e1porn\u00e9ho n\u00e1boje, mezi dv\u011bma ne moc vzd\u00e1len\u00fdmi r\u016fzn\u00fdmi bou\u0159kov\u00fdmi oblaky, nebo mezi centrem z\u00e1porn\u00e9ho n\u00e1boje ve spodn\u00ed \u010d\u00e1sti oblaku a zem\u00ed pod oblakem. Dal\u0161\u00edm speci\u00e1ln\u00edm p\u0159\u00edpadem jsou bleskov\u00e9 v\u00fdboje sm\u011b\u0159uj\u00edc\u00ed nahoru nad oblak. Dodnes se v\u0161ak st\u00e1le p\u0159esn\u011b nev\u00ed, jak funguje spou\u0161t\u011bc\u00ed mechanismus samotn\u00e9ho blesku. Nap\u011bt\u00ed mezi oblakem a zem\u00ed je vysok\u00e9, av\u0161ak ke spu\u0161t\u011bn\u00ed v\u00fdboje nesta\u010d\u00ed, k\u00a0tomu je pot\u0159eba potenci\u00e1l asi 10kr\u00e1t vy\u0161\u0161\u00ed. Zd\u00e1 se pravd\u011bpodobn\u00e9, \u017ee k\u00a0vyvol\u00e1n\u00ed elektrick\u00e9ho pr\u016frazu p\u0159isp\u00edvaj\u00ed rychl\u00e9 elektrony, kter\u00e9 vznikaj\u00ed p\u0159i interakci vysoce energetick\u00e9ho kosmick\u00e9ho z\u00e1\u0159en\u00ed s\u00a0atmosf\u00e9rou jako produkt ionizace, no a v\u00a0takto ionizovan\u00e9m vzduchu lze doc\u00edlit pr\u016frazu i za st\u00e1vaj\u00edc\u00edho elektrick\u00e9ho potenci\u00e1lu. Je tak\u00e9 dost mo\u017en\u00e9, \u017ee dal\u0161\u00edm p\u0159isp\u011bvatelem jsou ledov\u00e9 krystalky v\u00a0oblaku, kolem jejich\u017e \u0161pi\u010dat\u00e9ho tvaru se vytvo\u0159\u00ed hrotov\u00e9 v\u00fdboje.<\/p>\n<p style=\"font-weight: 400;\">P\u0159ed z\u00e1bleskem se pod z\u00e1kladnou cumulonimbu vyskytuje oblast siln\u00e9ho z\u00e1porn\u00e9ho n\u00e1boje. P\u0159i z\u00e1blesku se u z\u00e1kladny oblaku na milisekundu zm\u011bn\u00ed n\u00e1boj na neutr\u00e1ln\u00ed nebo dokonce m\u00edrn\u011b kladn\u00fd, aby se potom za kr\u00e1tkou dobu vr\u00e1til zp\u011bt k\u00a0z\u00e1porn\u00fdm hodnot\u00e1m. B\u011bhem elektrick\u00e9ho pr\u016frazu tak na krati\u010dk\u00fd \u010das dojde k\u00a0oslaben\u00ed center n\u00e1boj\u016f v\u00a0oblaku. Samotn\u00fd pr\u016fb\u011bh blesku za\u010dne v\u016fd\u010d\u00edm v\u00fdbojem, kter\u00fd se naz\u00fdv\u00e1 leader, kter\u00fd p\u0159i sv\u00e9m \u0161\u00ed\u0159en\u00ed pod oblakem ionizuje dal\u0161\u00ed molekuly vzduchu a p\u0159ipravuje tak podm\u00ednky k\u00a0hlavn\u00edmu v\u00fdboji. V\u016fd\u010d\u00ed v\u00fdboj p\u0159edstavuje elektrick\u00fd proud, prov\u00e1zen\u00fd slab\u011b sv\u00edt\u00edc\u00edm viditeln\u00fdm z\u00e1\u0159en\u00edm. Vznikaj\u00edc\u00ed kan\u00e1l vede po ur\u010dit\u00fdch skoc\u00edch, proto\u017ee na jeho dr\u00e1ze doch\u00e1z\u00ed k\u00a0poklesu gradientu nap\u011bt\u00ed a\u017e pod ur\u010ditou kritickou hodnotu, p\u0159i kter\u00e9 se pohyb v\u00fdboje na des\u00edtky mikrosekund pozastav\u00ed, aby pak intenzita elektrick\u00e9ho pole zase vzrostla a v\u00fdboj pokra\u010doval v\u00a0dal\u0161\u00edm skokov\u00e9m \u00faseku, a\u017e dokud po asi 20 a\u017e 50 milisekund\u00e1ch nedoraz\u00ed bl\u00edzko nad zemsk\u00fd povrch. D\u00e9lka skok\u016f je v\u00a0pr\u016fm\u011bru asi 50 metr\u016f, nejv\u00fd\u0161e asi 200 metr\u016f. Pr\u016fm\u011br kan\u00e1lu v\u00fdboje b\u00fdv\u00e1 od n\u011bkolika milimetr\u016f do n\u011bkolika centimetr\u016f, n\u011bkdy i v\u00edce ne\u017e 10 centimetr\u016f. V\u016fd\u010d\u00ed v\u00fdboj se obvykle ve sm\u011bru \u0161\u00ed\u0159en\u00ed rozv\u011btvuje, i kdy\u017e ne v\u017edycky. Rychlost \u0161\u00ed\u0159en\u00ed v\u00fdboje je asi 100 a\u017e 300 kilometr\u016f za sekundu a elektrick\u00fd proud v\u00a0n\u011bm m\u00e1 hodnotu od stovek amp\u00e9r do 2000 amp\u00e9r. V\u016fd\u010d\u00ed v\u00fdboj indukuje na zemi dal\u0161\u00ed kladn\u00fd n\u00e1boj, proto\u017ee elektrony, p\u0159ibli\u017euj\u00edc\u00ed se v\u00a0podob\u011b v\u016fd\u010d\u00edho v\u00fdboje, p\u016fsob\u00ed na elektrony na zemsk\u00e9m povrchu coulombovskou silou a odpuzuj\u00ed je.<\/p>\n<p style=\"font-weight: 400;\">M\u016f\u017eeme \u0159\u00edci, \u017ee v\u016fd\u010d\u00ed v\u00fdboj, bl\u00ed\u017e\u00edc\u00ed se shora k\u00a0zemi, vlastn\u011b odh\u00e1n\u00ed elektrony od m\u00edsta, kde se v\u00fdboj dotkne zem\u011b. Elektrony na zemi nemaj\u00ed probl\u00e9m se z\u00a0toho m\u00edsta vzd\u00e1lit, proto\u017ee zemsk\u00fd povrch je velmi dobr\u00fd vodi\u010d. U\u017e jsme si prve \u0159ekli, \u017ee u\u017e d\u0159\u00edve se pod bou\u0159kou vytvo\u0159ila oblast siln\u00e9ho kladn\u00e9ho n\u00e1boje, kter\u00e1 se p\u0159esouv\u00e1 spolu s\u00a0oblakem, a kdy\u017e se k\u00a0zemi z\u00a0oblaku p\u0159ibl\u00ed\u017e\u00ed v\u016fd\u010d\u00ed v\u00fdboj, hodnota kladn\u00e9ho n\u00e1boje tady je\u0161t\u011b vzroste, tedy je\u0161t\u011b o n\u011bco zes\u00edl\u00ed intenzita elektrick\u00e9ho pole. Mezi polohou v\u016fd\u010d\u00edho v\u00fdboje a zem\u00ed vznikne nap\u011bt\u00ed asi 100 mili\u00f3n\u016f Volt\u016f. To p\u016fsob\u00ed doslova jako v\u00fdtah pro kladn\u00e9 n\u00e1boje ze zem\u011b a hlavn\u011b z\u00a0vyv\u00fd\u0161en\u00fdch objekt\u016f. Tyto n\u00e1boje stoupaj\u00ed do v\u00fd\u0161ky, p\u0159itahov\u00e1ny coulombovskou silou k\u00a0elektron\u016fm, kter\u00e9 se bl\u00ed\u017e\u00ed shora. Kladn\u00e9 n\u00e1boje proud\u00ed nahoru po budov\u00e1ch, stromech a v\u0161ech jin\u00fdch vodiv\u00fdch p\u0159edm\u011btech, nap\u0159\u00edklad i po lidech nebo zv\u00ed\u0159atech, a tento proud naz\u00fdv\u00e1me vst\u0159\u00edcn\u00fd v\u00fdboj. Ten pokra\u010duje ve sv\u00e9 cest\u011b nahoru, a\u017e se ve v\u00fd\u0161ce n\u011bkolika stovek metr\u016f potk\u00e1 s\u00a0protilet\u00edc\u00edmi elektrony. T\u00edm se uzav\u0159e elektrick\u00fd obvod a nastane hlavn\u00ed v\u00fdboj. Do zem\u011b b\u011bhem milisekundy p\u0159ejde 10 na 25. elektron\u016f a zapo\u010dne hlavn\u00ed v\u00fdboj, sm\u011b\u0159uj\u00edc\u00ed nahoru k\u00a0oblaku rychlost\u00ed asi 80 a\u017e 100 tis\u00edc kilometr\u016f za sekundu. Takov\u00e1 rychlost p\u0159edstavuje extr\u00e9mn\u011b siln\u00fd elektrick\u00fd proud o hodnot\u011b a\u017e stovek kiloamp\u00e9r. Tento proud vyvol\u00e1v\u00e1 mohutnou ionizaci vzduchu, p\u0159i kter\u00e9 se uvoln\u00ed mno\u017estv\u00ed dal\u0161\u00edch elektron\u016f a nastane oslniv\u00e1 z\u00e1\u0159e, kterou dob\u0159e zn\u00e1me. Pr\u016fchod takto extr\u00e9mn\u00edho elektrick\u00e9ho proudu zp\u016fsob\u00ed tak\u00e9 zah\u0159\u00e1t\u00ed vzduchov\u00e9ho kan\u00e1lu na 25 a\u017e 30 tis\u00edc Kelvin\u016f, co\u017e se zjistilo spektr\u00e1ln\u00edm rozborem z\u00e1\u0159en\u00ed blesk\u016f. Vzduch se zah\u0159\u00e1t\u00edm velkou rychlost\u00ed rozp\u00edn\u00e1 a tato expanze vytvo\u0159\u00ed r\u00e1zovou vlnu, ve kter\u00e9 je asi desetin\u00e1sobn\u00fd tlak oproti norm\u00e1ln\u00edm podm\u00ednk\u00e1m. R\u00e1zov\u00e1 vlna se pak od bleskov\u00e9ho kan\u00e1lu \u0161\u00ed\u0159\u00ed do v\u0161ech stran obvyklou rychlost\u00ed zvuku a my ji ozna\u010dujeme jako hrom. Expanze vzduchu vznik\u00e1 v\u00a0r\u016fzn\u00fdch v\u011btven\u00fdch \u010d\u00e1stech blesku v\u00a0r\u016fz\u00fdch vzd\u00e1lenostech od n\u00e1s, proto k\u00a0na\u0161emu sluchu doch\u00e1zej\u00ed r\u00e1zov\u00e9 vlny v\u00a0n\u011bkolika period\u00e1ch, sly\u0161\u00edme tak\u00e9 r\u016fzn\u00e9 ozv\u011bny a v\u0161echno dohromady d\u011bl\u00e1 zvukovou kulisu, trvaj\u00edc\u00ed i n\u011bkolik sekund.<\/p>\n<p style=\"font-weight: 400;\">Zp\u011btn\u00fd v\u00fdboj je\u0161t\u011b neznamen\u00e1 ukon\u010den\u00ed blesku, v\u011bt\u0161inou ve zlomku sekundy nast\u00e1vaj\u00ed dal\u0161\u00ed procesy nebo n\u011bkolikan\u00e1sobn\u00e9 opakov\u00e1n\u00ed toho, co jsme si popsali. Elektrony, kter\u00e9 se odd\u011bluj\u00ed od molekul vzduchu p\u0159i masivn\u00ed ionizaci zp\u011btn\u00e9ho v\u00fdboje, se dr\u017e\u00ed v\u00a0kan\u00e1lu blesku a pokud je jich dostatek, vyvolaj\u00ed je\u0161t\u011b dal\u0161\u00ed v\u00fdboj, kter\u00fd se pohybuje k\u00a0zemi rychlost\u00ed asi 10 tis\u00edc kilometr\u016f za sekundu. Tento v\u00fdboj m\u00e1 u\u017e ni\u017e\u0161\u00ed hodnotu elektrick\u00e9ho proudu, asi 1000 amp\u00e9r. Kdy\u017e se tento v\u00fdboj spoj\u00ed se zem\u00ed, dojde ke krati\u010dk\u00e9mu zp\u011btn\u00e9mu v\u00fdboji s\u00a0proudem 10 a\u017e 15 kiloamp\u00e9r. Od po\u010d\u00e1te\u010dn\u00ed iniciace blesku do t\u00e9to chv\u00edle uplynula zhruba necel\u00e1 desetina sekundy. Po posledn\u00edm zm\u00edn\u011bn\u00e9m zp\u011btn\u00e9m v\u00fdboji trv\u00e1 asi v\u00a0polovin\u011b p\u0159\u00edpad\u016f je\u0161t\u011b n\u011bkolik desetin sekundy takzvan\u00fd pr\u016fb\u011b\u017en\u00fd proud o hodnot\u011b do 100 amp\u00e9r. To sta\u010d\u00ed na to, aby se zasa\u017een\u00e9 m\u00edsto v\u00fdznamn\u011b zah\u0159\u00e1lo a p\u0159\u00edpadn\u011b se zap\u00e1lilo. Je to jedna z\u00a0p\u0159\u00ed\u010din nap\u0159\u00edklad lesn\u00edch po\u017e\u00e1r\u016f nebo po\u017e\u00e1r\u016f jin\u00fdch objekt\u016f.<\/p>\n<p style=\"font-weight: 400;\">D\u00e9lka bleskov\u00e9ho v\u00fdboje je r\u016fzn\u00e1. Ve st\u0159edn\u00ed Evrop\u011b byl zm\u011b\u0159en\u00fd blesk o d\u00e9lce asi 70 a\u017e 80 kilometr\u016f. Ve Spojen\u00fdch st\u00e1tech americk\u00fdch zm\u011b\u0159ili v\u00a0roce 2020 d\u00e9lku blesku 768 kilometr\u016f, co\u017e je doposud nejv\u011bt\u0161\u00ed zji\u0161t\u011bn\u00e1 d\u00e9lka v\u00fdboje.<\/p>\n<p style=\"font-weight: 400;\">Asi 90 a\u017e 95 procent blesk\u016f sm\u011b\u0159uje od oblaku k\u00a0zemi. Zb\u00fdvaj\u00edc\u00ed \u010d\u00e1st jsou blesky opa\u010dn\u011b polarizovan\u00e9. Jejich v\u016fd\u010d\u00ed v\u00fdboj se \u0161\u00ed\u0159\u00ed od zemsk\u00e9ho povrchu do oblaku, kter\u00fdm prostupuje a\u017e do vrcholov\u00fdch parti\u00ed, kde \u010dasto zm\u011bn\u00ed sm\u011br na p\u0159ibli\u017en\u011b vodorovn\u00fd skrze \u010d\u00e1st oblaku zvanou incus. Proto\u017ee tento obla\u010dn\u00fd chochol zauj\u00edm\u00e1 prostor daleko okolo vlastn\u00edho cumulonimbu, m\u016f\u017ee tak vzniknout dojem, \u017ee viditeln\u00fd blesk nastal ve velk\u00e9 vzd\u00e1lenosti od bou\u0159ky, doslova z\u00a0\u010dist\u00e9ho nebe.<\/p>\n<p style=\"font-weight: 400;\">Speci\u00e1ln\u00edm p\u0159\u00edpadem, doposud ne zcela vysv\u011btlen\u00fdm, je kulov\u00fd blesk. Vzhledem k\u00a0tomu, \u017ee tento jev se vyskytuje velmi sporadicky, jsou k\u00a0dispozici jen sv\u011bdectv\u00ed laick\u00fdch pozorovatel\u016f, nav\u00ed emotivn\u011b zat\u00ed\u017een\u00e1. Doposud m\u00e1me jen jedin\u00e9 skute\u010dn\u011b v\u011bdeck\u00e9 pozorov\u00e1n\u00ed kulov\u00e9ho blesku, k\u00a0n\u011bmu\u017e do\u0161lo n\u00e1hodou p\u0159i monitoringu spekter b\u011b\u017en\u00fdch blesk\u016f a do z\u00e1znamu se dostal jeden blesk kulov\u00fd. Tak\u017ee zn\u00e1me jeho spektrum. Ob\u011b spektra jsou odli\u0161n\u00e1. B\u011b\u017en\u00fd blesk vykazuje ve spektru s\u00e9rii emisn\u00edch spektr\u00e1ln\u00edch \u010dar jedenkr\u00e1t ionizovan\u00e9ho dus\u00edku, co\u017e je vzhledem ke slo\u017een\u00ed atmosf\u00e9ry o\u010dek\u00e1vateln\u00e9. Ve spektru kulov\u00e9ho blesku v\u0161ak z\u00e1\u0159\u00ed emisn\u00ed \u010d\u00e1ry k\u0159em\u00edku, v\u00e1pn\u00edku a \u017eeleza, a v\u00a0daleko slab\u0161\u00ed intenzit\u011b tak\u00e9 dus\u00edku. Jedno z mo\u017en\u00fdch vysv\u011btlen\u00ed je, \u017ee b\u011b\u017en\u00fd blesk ude\u0159il do zem\u011b, kde se vyskytuj\u00ed zm\u00edn\u011bn\u00e9 prvky, dojde k\u00a0prudk\u00e9mu zah\u0159\u00e1t\u00ed p\u016fdy a n\u00e1sledn\u011b se do vzduchu dostanou oxiduj\u00edc\u00ed k\u0159emi\u010dit\u00e9 \u010d\u00e1stice ve tvaru mal\u00e9ho oblaku. Toto vysv\u011btlen\u00ed ale nepokr\u00fdv\u00e1 v\u0161echny jevy, spojen\u00e9 s\u00a0kulov\u00fdm bleskem.<\/p>\n<p style=\"font-weight: 400;\">Blesk m\u00e1 sf\u00e9rick\u00fd tvar o rozm\u011brech jednotek a\u017e des\u00edtek centimetr\u016f, b\u00edl\u00e9, \u017elut\u00e9 nebo namodral\u00e9 barvy. Pohybuj\u00ed se vzduchem rychlost\u00ed decimetr\u016f a\u017e metr\u016f za sekundu, \u010dasto pod\u00e9l vodiv\u00fdch p\u0159edm\u011bt\u016f. Trv\u00e1n\u00ed je 10 a\u017e 20 sekund, pak dojde k\u00a0rozpadu, n\u011bkdy prov\u00e1zen\u00e9mu hlukem. Asi polovina p\u0159\u00edpad\u016f kon\u010d\u00ed v\u00fdbuchem, 40 procent rozpad\u016f je pomal\u00fdch a prov\u00e1zen\u00fdch sy\u010den\u00edm, zb\u00fdvaj\u00edc\u00edch 10 procent se rozpad\u00e1 na men\u0161\u00ed \u010d\u00e1sti. Kulov\u00fd blesk je schopen prop\u00e1lit okno nebo prorazit ze\u010f, dokonce byla zaznamen\u00e1na i destrukce domu nebo zbo\u0159en\u00ed kom\u00ednu. Nen\u00ed v\u016fbec zn\u00e1mo, kde kulov\u00fd blesk z\u00edskal takovou energii, aby mohl tyto procesy vykonat. Kulov\u00fd blesk se zat\u00edm jen \u010d\u00e1ste\u010dn\u011b poda\u0159ilo vyvolat i laboratorn\u011b. Brazil\u0161t\u00ed v\u011bdci vytvo\u0159ili k\u0159em\u00edkov\u00fd obloukov\u00fd v\u00fdboj, ze kter\u00e9ho vze\u0161ly z\u00e1\u0159\u00edc\u00ed plazmov\u00e9 kuli\u010dky o pr\u016fm\u011bru 1 a\u017e 4 centimetry s\u00a0\u017eivotnost\u00ed do 5 sekund.<\/p>\n<p style=\"font-weight: 400;\">Dal\u0161\u00ed zna\u010dn\u011b neprozkoumanou aktivitou jsou pozemsk\u00e9 gama z\u00e1blesky, sm\u011b\u0159uj\u00edc\u00ed z\u00a0bou\u0159kov\u00fdch oblast\u00ed sm\u011brem z\u00a0atmosf\u00e9ry nahoru. Zji\u0161t\u011bny byly neo\u010dek\u00e1van\u011b rentgenov\u00fdm detektorem na dru\u017eici COMPTON. Trv\u00e1n\u00ed z\u00e1blesk\u016f bylo v\u00a0\u0159\u00e1du stovek mikrosekund a\u017e n\u011bkolik milisekund. V\u00fdzkum t\u011bchto z\u00e1blesk\u016f pokra\u010doval pomoc\u00ed dru\u017eice RHESSI, jej\u00edm\u017e hlavn\u00edm \u00fakolem bylo m\u011b\u0159en\u00ed gama a rentgenov\u00e9ho z\u00e1\u0159en\u00ed p\u0159i slune\u010dn\u00edch erupc\u00edch. Pozd\u011bji se p\u0159idalo m\u011b\u0159en\u00ed i z\u00a0pozemsk\u00fdch stanic. Uk\u00e1zalo se, \u017ee fotony z\u00a0pozemsk\u00fdch gama z\u00e1blesk\u016f maj\u00ed v\u011bt\u0161\u00ed energii, ne\u017e gama z\u00e1\u0159en\u00ed ze Slunce. Pozemsk\u00e9 gama z\u00e1\u0159en\u00ed vych\u00e1z\u00ed z\u00a0obla\u010dnosti se silnou bou\u0159kovou aktivitou t\u011bsn\u011b p\u0159ed \u00faderem b\u011b\u017en\u00e9ho blesku a posledn\u00ed v\u00fdzkumy nazna\u010duj\u00ed, \u017ee gama z\u00e1blesky jsou pr\u016fvodn\u00edm jevem p\u0159i skoc\u00edch v\u016fd\u010d\u00edho v\u00fdboje uvnit\u0159 oblaku v\u00a0po\u010d\u00e1te\u010dn\u00edch f\u00e1z\u00edch p\u0159i jeho pohybu zdola, od centra z\u00e1porn\u00e9ho n\u00e1boje, nahoru k\u00a0centru kladn\u00e9ho n\u00e1boje. O t\u011bchto gama z\u00e1blesc\u00edch se dlouho nev\u011bd\u011blo, na cel\u00e9 planet\u011b se jich denn\u011b odehraje asi 50.<\/p>\n<p style=\"font-weight: 400;\">Atraktivn\u00edm t\u00e9matem jsou nadobla\u010dn\u00e9 blesky, ozna\u010dovan\u00e9 jako Transient Luminous Event. Tyto optick\u00e9 jevy se pozoruj\u00ed nad siln\u00fdmi supercel\u00e1rn\u00edmi bou\u0159kami, zasahuj\u00ed od vrchol\u016f bou\u0159kov\u00fdch oblak\u016f do v\u00fd\u0161ek 60 a\u017e 90 kilometr\u016f v\u00a0z\u00e1vislosti na denn\u00ed nebo no\u010dn\u00ed dob\u011b. V\u00fdjime\u010dn\u011b se daj\u00ed zaznamenat i prost\u00fdm zrakem, b\u011b\u017en\u011b si jich ale nepov\u0161imneme. Mo\u017en\u00e1 proto dlouho unikaly na\u0161\u00ed pozornosti a jejich podrobn\u011bj\u0161\u00ed v\u00fdzkum za\u010dal a\u017e po\u00a0roce 1990. Podle fotografick\u00fdch z\u00e1znam\u016f dnes zn\u00e1me hlavn\u00ed tvary t\u011bchto z\u00e1blesk\u016f, pojmenovan\u00e9 red sprite, halo, blue starter, blue jet, gigantic jet nebo elf. Nej\u010dast\u011bji se pozoruje red sprite, rud\u00fd sk\u0159\u00edtek. Podobn\u011b jako spektrum kulov\u00e9ho blesku, i red sprite byl zaznamen\u00e1n n\u00e1hodou, kdy\u017e v\u00a0roce 1990 zkou\u0161el americk\u00fd v\u011bdec Franz kameru na z\u00e1znam pol\u00e1rn\u00edch z\u00e1\u0159\u00ed a nam\u00ed\u0159il ji ke vzd\u00e1len\u00fdm bou\u0159k\u00e1m, seskupen\u00fdm do tzv. mezom\u011b\u0159\u00edtkov\u00e9ho konvektivn\u00edho syst\u00e9mu. Red sprite vyst\u0159eluje do v\u00fd\u0161ek 60 a\u017e 90 kilometr\u016f nad zemsk\u00fd povrch, jejich \u0161\u00ed\u0159ka m\u016f\u017ee dos\u00e1hnout a\u017e 40 kilometr\u016f. P\u0159edch\u00e1z\u00ed mu siln\u00fd blesk z\u00a0oblaku do zem\u011b. Zat\u00edmco kan\u00e1l b\u011b\u017en\u00e9ho blesku m\u00e1 silnou ionizaci vzduchu, tak oblast v\u00fdskytu red spritu je ionizovan\u00e1 jen slab\u011b. \u00datvar halo m\u00e1 tvar disku. Blue jet je dost vz\u00e1cn\u00fd, zasahuje do v\u00fd\u0161ky asi 40 kilometr\u016f rychlost\u00ed 100 kilometr\u016f za sekundu. Gigantic jet je ve spodn\u00ed \u010d\u00e1sti modr\u00fd, ve v\u011bt\u0161\u00ed v\u00fd\u0161ce p\u0159ech\u00e1z\u00ed do \u010derven\u00e9 barvy. To je zp\u016fsobeno typem atom\u016f a molekul, kter\u00e9 jsou v\u00fdbojem excitov\u00e1ny. Zasahuje do v\u00fd\u0161ek 90 kilometr\u016f a p\u0159i jeho spu\u0161t\u011bn\u00ed se tak\u00e9 rozz\u00e1\u0159\u00ed vrcholov\u00e1 \u010d\u00e1st bou\u0159kov\u00e9ho oblaku. Elf je nejrychlej\u0161\u00ed a nejv\u011bt\u0161\u00ed typ t\u011bchto v\u00fdboj\u016f. Vyskytuje se ve v\u00fd\u0161k\u00e1ch 100 kilometr\u016f jako kruhov\u00fd disk, kter\u00fd se rozr\u016fst\u00e1 do pr\u016fm\u011bru i stovek kilometr\u016f. Vznik\u00e1 tak, \u017ee elektromagnetick\u00e9 vlny, doprov\u00e1zej\u00edc\u00ed siln\u00e9 blesky, dodaj\u00ed energii elektron\u016fm ve spodn\u00ed ionosf\u00e9\u0159e, a tyto elektrony potom nar\u00e1\u017eej\u00ed na molekuly dus\u00edku, ionizuj\u00ed je a n\u00e1sledn\u011b doch\u00e1z\u00ed rekombinac\u00ed k\u00a0z\u00e1\u0159en\u00ed ve tvaru zm\u00edn\u011bn\u00e9ho rozs\u00e1hl\u00e9ho kruhu.<\/p>\n<p style=\"font-weight: 400;\">O blesc\u00edch a bou\u0159k\u00e1ch bychom si mohli vypr\u00e1v\u011bt je\u0161t\u011b dlouho. Ionizace p\u0159i bleskov\u00fdch aktivit\u00e1ch hraje nap\u0159\u00edklad roli p\u0159i formov\u00e1n\u00ed n\u011bkter\u00fdch organick\u00fdch molekul a tak se ned\u00e1 vylou\u010dit, \u017ee se bou\u0159ky mohly pod\u00edlet na vzniku \u017eivota na Zemi. Pozd\u011bji, kdy\u017e u\u017e \u017eivot na na\u0161\u00ed planet\u011b existoval, zp\u016fsobovaly bou\u0159ky lesn\u00ed po\u017e\u00e1ry, a to je ud\u00e1lost, kter\u00e1 dost zasahuje do rozvoje biosf\u00e9ry a \u017eivotn\u00edho cyklu lesa. V\u00a0sou\u010dasn\u00e9 dob\u011b snad nepot\u0159ebujeme, aby se bou\u0159ky pod\u00edlely na vzniku dal\u0161\u00edch forem \u017eivota, ale mus\u00edme p\u0159ed nimi chr\u00e1nit formy st\u00e1vaj\u00edc\u00ed, v\u010detn\u011b sebe. Jak se tedy uchr\u00e1nit p\u0159ed z\u00e1sahem blesku? To je ot\u00e1zka, kterou jako meteorolog ob\u010das dost\u00e1v\u00e1m. Podle m\u00e9ho n\u00e1zoru je nejlep\u0161\u00ed ochranou z\u016fstat v\u00a0budov\u011b a nevych\u00e1zet ven, kdy\u017e je bou\u0159ka. Tak\u017ee je d\u016fle\u017eit\u00e9 bedliv\u011b sledovat p\u0159edpov\u011b\u010f po\u010das\u00ed i jeho aktu\u00e1ln\u00ed stav, a podle toho se pokud mo\u017eno za\u0159\u00eddit.<\/p>\n<p style=\"font-weight: 400;\">Chr\u00e1n\u011bni jsme tak\u00e9 uvnit\u0159 kovov\u00e9 schr\u00e1nky, nap\u0159\u00edklad v\u00a0aut\u011b se zav\u0159en\u00fdmi okny. Pokud p\u0159ece jenom jsme v\u00a0otev\u0159en\u00e9m prostoru bez mo\u017enosti ochrany, sedn\u011bme si na bobek s\u00a0chodidly u sebe, abychom sn\u00ed\u017eili pravd\u011bpodobnost \u00faderu blesku do n\u00e1s a tak\u00e9 abychom vylou\u010dili krokov\u00e9 nap\u011bt\u00ed, kdyby blesk uhodil do na\u0161\u00ed bl\u00edzkosti. Vhodn\u00e9 je takto se um\u00edstit do n\u011bjak\u00e9 prohlubn\u011b. Rozhodn\u011b se neukr\u00fdvejme v\u00a0jeskyn\u00edch, proto\u017ee tu je vysok\u00e1 vlhkost, zv\u00fd\u0161en\u00e1 radioaktivita a t\u00edm ionizace vzduchu, p\u0159\u00edpadn\u011b tu m\u016f\u017ee b\u00fdt z\u00e1bradl\u00ed jako\u017eto vodi\u010d elektrick\u00e9ho proudu. Pr\u00e1v\u011b v\u00a0jeskyn\u00edch doch\u00e1z\u00ed k\u00a0hromadn\u00fdm \u00faraz\u016fm p\u0159i z\u00e1sahu bleskem. Vhodn\u00fd je pobyt pobl\u00ed\u017e bleskosvodu, zdroje uv\u00e1d\u011bj\u00ed relativn\u011b bezpe\u010dnou z\u00f3nu v\u00a0okruhu 500 metr\u016f kolem n\u011bj. Nedot\u00fdkejme se vodiv\u00fdch p\u0159edm\u011bt\u016f. Nezdr\u017eujme se na vyv\u00fd\u0161en\u00fdch m\u00edstech. Rozhodn\u011b se neschov\u00e1vejme pod stromem, riziko z\u00e1sahu bleskem je tu vysok\u00e9, strom obsahuje vodu, kter\u00e1 se p\u0159i \u00faderu blesku prudce oh\u0159eje a zv\u011bt\u0161en\u00ed jej\u00edho objemu vede ke zlomen\u00ed stromu, kter\u00fd na n\u00e1s spadne. Pokud jsme v\u00a0lese, zdr\u017eujme se sp\u00ed\u0161e v\u00a0centru lesa ne\u017e p\u0159i jeho okraji, kde blesky prob\u00edhaj\u00ed \u010dast\u011bji. I tak ale mus\u00edme b\u00fdt co nejd\u00e1l od kmene a st\u00e1t s\u00a0nohama u sebe. Sundejme ze sebe v\u0161echny kovov\u00e9 v\u011bci a dejme co nejd\u00e1l od sebe. Nebezpe\u010dn\u00fd je \u00fakryt ve stanu nebo pod skaln\u00edm p\u0159evisem, v\u00a0bl\u00edzkosti potok\u016f nebo jin\u00fdch vodn\u00edch ploch, pod kovov\u00fdm mostem. I kdy\u017e jsme doma, nedot\u00fdkejme se vodovodn\u00edho potrub\u00ed nebo radi\u00e1toru.<\/p>\n<p style=\"font-weight: 400;\">V\u011b\u0159\u00edm, \u017ee se n\u00e1m v\u0161em poda\u0159\u00ed uchr\u00e1nit p\u0159ed riziky bou\u0159ky a budeme si je v\u017edy prohl\u00ed\u017eet jako kr\u00e1sn\u00fd fyzik\u00e1ln\u00ed \u00fakaz, kter\u00fd doposud ukr\u00fdv\u00e1 je\u0161t\u011b mnoho v\u011bdeck\u00fdch tajemstv\u00ed.<\/p>\n<h4>O autorovi<\/h4>\n<figure id=\"attachment_3170\" class=\"wp-caption alignright fbx-instance\" aria-describedby=\"caption-attachment-3170\"><a class=\"fbx-link\" href=\"https:\/\/www.astro-novinky.eu\/wp-content\/uploads\/2025\/01\/376269909_10232584020169449_1108385783673315256_n.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-3170\" src=\"https:\/\/www.astro-novinky.eu\/wp-content\/uploads\/2025\/01\/376269909_10232584020169449_1108385783673315256_n-300x300.jpg\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" srcset=\"https:\/\/www.astro-novinky.eu\/wp-content\/uploads\/2025\/01\/376269909_10232584020169449_1108385783673315256_n-300x300.jpg 300w, https:\/\/www.astro-novinky.eu\/wp-content\/uploads\/2025\/01\/376269909_10232584020169449_1108385783673315256_n-150x150.jpg 150w, https:\/\/www.astro-novinky.eu\/wp-content\/uploads\/2025\/01\/376269909_10232584020169449_1108385783673315256_n-768x768.jpg 768w, https:\/\/www.astro-novinky.eu\/wp-content\/uploads\/2025\/01\/376269909_10232584020169449_1108385783673315256_n.jpg 960w\" alt=\"RNDr. Petr Dvo\u0159\u00e1k\" width=\"300\" height=\"300\" \/><\/a><figcaption id=\"caption-attachment-3170\" class=\"wp-caption-text\">RNDr. Petr Dvo\u0159\u00e1k<\/figcaption><\/figure>\n<p><strong>Petr Dvo\u0159\u00e1k<\/strong>\u00a0(*1966) \u2014 absolvent Matematicko-fyzik\u00e1ln\u00ed fakulty Univerzity Karlovy v Praze, katedry fyziky atmosf\u00e9ry. Meteorolog, pilot mal\u00fdch letadel, lektor a u\u010ditel. Autor mnoha populariza\u010dn\u00edch knih o po\u010das\u00ed, v letech 2010 a\u017e 2018 tak\u00e9 tiskov\u00fd mluv\u010d\u00ed \u010cesk\u00e9ho hydrometeorologick\u00e9ho \u00fastavu. Kon\u00ed\u010dkem jsou p\u0159\u00edrodn\u00ed v\u011bdy, zejm\u00e9na astronomie a astrofyzika, letectv\u00ed, cyklistika, turistika, m\u00e9dia, fotografov\u00e1n\u00ed a produkce videoblog\u016f pro pobaven\u00ed p\u0159\u00e1tel nebo pro popularizaci meteorologie a jin\u00fdch atmosf\u00e9rick\u00fdch v\u011bd.<\/p>\n<h4>Kontakty a dal\u0161\u00ed informace:<\/h4>\n<p><strong>RNDr. Petr Dvo\u0159\u00e1k<br \/>\n<\/strong><em>Fyzik, meteorolog<br \/>\n<\/em>Telefon: +420 770 690 333<br \/>\nEmail: <a href=\"mailto:petr.dvorak@jasno.cz\" target=\"_blank\" rel=\"noopener\">petr.dvorak@jasno.cz<\/a>,\u00a0<a href=\"http:\/\/fotton330@gmail.com\/\" target=\"_blank\" rel=\"noopener\" data-saferedirecturl=\"https:\/\/www.google.com\/url?q=http:\/\/fotton330@gmail.com&amp;source=gmail&amp;ust=1752682212295000&amp;usg=AOvVaw0GiAHt41XWiHqa-hZ_xqoO\">fotton330@gmail.com<\/a><br \/>\nFacebook:\u00a0<a href=\"https:\/\/www.facebook.com\/petr330\">www.facebook.com\/petr330<\/a><br \/>\nYoutube kan\u00e1l:\u00a0<a href=\"https:\/\/www.youtube.com\/@Fotton330channel\">www.youtube.com\/@Fotton330channel<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Bou\u0159ka je impozantn\u00ed p\u0159\u00edrodn\u00ed \u00fakaz. Vznik\u00e1 a rozv\u00edj\u00ed se ve spojitosti se specifick\u00fdm druhem oblaku, cumulonimbem. V\u00a0jin\u00fdch oblac\u00edch nevznik\u00e1. Cumulonimbus je oblak kumuliformn\u00edho typu s\u00a0velk\u00fdm vertik\u00e1ln\u00edm rozsahem. V\u00a0na\u0161ich zem\u011bpisn\u00fdch \u0161\u00ed\u0159k\u00e1ch m\u00edv\u00e1 z\u00e1kladnu kolem 1 a\u017e 2 kilometr\u016f nad zem\u00ed, vrcholy v\u00a0letn\u00edm obdob\u00ed kolem 12 a\u017e 15 kilometr\u016f, co\u017e je d\u00e1no v\u00fd\u0161kou tropopauzy a mo\u017enost\u00ed pr\u016fniku konvektivn\u00edho proudu do spodn\u00ed stratosf\u00e9ry. V\u00a0rovn\u00edkov\u00fdch oblastech sahaj\u00ed bou\u0159kov\u00e9 oblaky do je\u0161t\u011b v\u011bt\u0161\u00edch v\u00fd\u0161ek. A pr\u00e1v\u011b vertik\u00e1ln\u00ed rozsah oblaku je pro n\u00e1sledn\u00fd vznik blesk\u016f d\u016fle\u017eit\u00fd. Jsou v\u0161ak i jin\u00e9 druhy oblak\u016f, kter\u00e9 maj\u00ed velk\u00fd vertik\u00e1ln\u00ed rozsah, jako je nap\u0159\u00edklad nimbostratus, a p\u0159esto v\u00a0nich k\u00a0elektrick\u00fdm v\u00fdboj\u016fm nedoch\u00e1z\u00ed. Bou\u0159kov\u00fd cumulonimbus je oproti jin\u00fdm oblak\u016fm typick\u00fd zna\u010dn\u00fdmi vertik\u00e1ln\u00edm rychlostmi proud\u011bn\u00ed, kter\u00e9 p\u0159en\u00e1\u0161ej\u00ed hmotu vody, p\u0159\u00edpadn\u011b ledu, rychle nahoru a dol\u016f, a spolu s\u00a0vodn\u00edmi nebo ledov\u00fdmi \u010d\u00e1sticemi se p\u0159en\u00e1\u0161\u00ed tak\u00e9 elektrick\u00fd n\u00e1boj, kter\u00fd je pokr\u00fdv\u00e1. Vznik\u00e1 tak polarizovan\u00e9 elektrick\u00e9 pole, kter\u00e9 p\u0159i dostate\u010dn\u00e9 intenzit\u011b vede k\u00a0v\u00fdboji.<\/p>\n","protected":false},"author":7,"featured_media":3275,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"colormag_page_container_layout":"default_layout","colormag_page_sidebar_layout":"default_layout","footnotes":""},"categories":[26,27,30],"tags":[],"class_list":["post-3274","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-aktuality","category-clanky","category-ukazy"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Video: Pozoruhodn\u00e9 blesky - Astro-novinky.eu<\/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:\/\/www.astro-novinky.eu\/index.php\/2025\/07\/15\/video-pozoruhodne-blesky\/\" \/>\n<meta property=\"og:locale\" content=\"sk_SK\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Video: Pozoruhodn\u00e9 blesky - Astro-novinky.eu\" \/>\n<meta property=\"og:description\" content=\"Bou\u0159ka je impozantn\u00ed p\u0159\u00edrodn\u00ed \u00fakaz. 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