Clouds 101: Pyrocumulus/ Pyrocumulonimbus Clouds

Weather can be sneaky many times. It can play around with certain elements and conditions to create disasters and at the same time it can be kind enough to pour down exactly what makes a heaven-sent delight. Today I'm referring to a potent and magnificent mixture of forest-fires, droughts, cumulus clouds, strong winds, humidity, volcanoes, eruptions, columns of fiery rage and ease that extinguishes all flames. Let's start with forest-fires which as we know can be a natural ocurrence or man-made. Sometimes those same fires can actually create their own weather. Envision a ghastly, mad and angry fiery monster that feeds on and spits out flames, thunder and lightning. Forest fires can sometimes become unmanageable and inpredictible and strong enough to create their own weather systems of thunderstorms and rain. Forest fires are a powerful heat source on the ground and the rising hot air from the fire can create a local kind of cumulus cloud called a Pyrocumulus cloud. The prefix “pyro” comes from the Greek word for fire obviously indicating that pyrocumulus clouds are most likely to be found above a large fire. The heat source may be natural such as a volcanic eruption or forest fire or man-made.

Vrijeme
ponekada umije da bude bas podlo i da se poigra sa odredjenim elementima i
uvjetima kako bi kreiralo katastrofe. Istovremeno moze i da bude blago i
milosrdno da izlije dugo ocekivano olaksanje. Danas govorim o mocnoj
mjesavini sumskih pozara, susa, kumulusnih oblaka, jakih vjetrova,
vlaznosti, vulkanima, erupcijama, stubovima vatrene stihije te olaksanja
koje gasi sve plamene jezike. Pocnimo od sumskih pozara za koje svi
znamo da mogu biti prirodna pojava ili da ih prouzrokuje covjek.
Ponekada ti isti pozari mogu i sami kreirati vlastite vremenske uslove.
Zamislite grozomorno, bijesno i pomahnitalo cudoviste koje guta i bljuje
vatru, munje i grmljavinu. Sumski pozari se nekada mogu oteti kontroli i
biti potpuno nepredvidivi te dovoljno snazni da stvore vlastite
vremenske sisteme oluja i kise. Sumski pozari su mocan izvor topline na
povrsini tla i taj vruci zrak koji se iz pozara izdize moze proizvesti
vrstu kumulusnog oblaka pod nazivom Pirokumulus (pyrocumulus). Prefiks
“pyro” potice od grcke rijeci za vatru sto direktno upuje na cinjenicu
da se ovi oblaci najcesce formiraju iznad velike vatre. Izvor topline
moze biti prirodan u vidu vulkanske erupcije ili spomenutog sumskog
pozara i da ga je covjek izazvao.

Image Source

The mechanism behind the creation of this amazing and fierce cloud is relatively simple and is pretty much identical with the formation of a regular cumulus cloud, just a tad hotter. Warm air from the fire is lighter than cool air and it rises up into the atmosphere but when it rises up to certain levels in the atmosphere, it inevitably gets in contact with colder air which cools it down. When this air cools, the moisture it carries condenses into water droplets, much the same way that water droplets condense on the outside of a glass of ice water. Where does the moisture come from? The hot air that is created from all the trees and plants burning also contains the moisture that was in plants burned by the fire, plus water from streams and ponds. That moisture along with ash and debris is pulled upward by moving air currents and that's the reason why pyrocumulus clouds are likely to be brownish or grayish unlike the pretty, crisp white regular cumulus clouds. You know, the ones kids usually draw and remind me of popcorn and cotton candy. The cute ones. Pyrocumulus clouds can be considered to be their nasty counterparts. So the fires create smoke columns which can get very large, the top of the column can be 20, 30 even 50,000 feet. It is difficult to locate the bottom of a pyrocumulus cloud as it is often obscure by the ash generated by the fire or the volcanic eruption. Pyrocumulus clouds are basically a cumulous cloud that is fed by the fire. If lots of water vapor is available, the pyrocumulus can develop into a cumulonimbus which is called a Pyrocumulonimbus (PyroCb) or evolve into the thunderstorm phase. When it does reach that phase it gets affected by high winds exactly like regular thunderstorms and that's how you get lightning and rain. Lightning from pyrocumulus clouds can actually start other fires. At the same time, rain from pyrocumulus clouds can sometimes put fires out. The biggest concern for firefighters when these conditions develop is the wind. Downdrafts created by the thunderstorm conditions can cause fires to suddenly switch directions, and can even causes powerful tornados of fire. A similar cloud can form above an erupting volcano because lava which is brought to the surface from deep underground contains moisture, which is added to any moisture from plants consumed by lava flows. Pyrocumulus clouds have also been seen above the biggest fires in cities or at large industrial sites like refineries.

Mehanizam koji stoji iza formiranja ovog nevjerovatnog i divljeg oblaka je relativno jednostavan te je skoro identican formaciji obicnih kumulusnih oblaka, samo sto je malcice topliji. Vruc zrak koji dopire od pozara je laksi od hladnog zraka i podize se u atmosferu ali kada dosegne odredjene nivoe atmosfere dolazi u kontakt sa hladnim zrakom koji ga ohladi. Kada se ohladi ovaj prethodno vruc zrak, sva vlaga koju je donio kondenzira se u kapljice vode na vrlo slican nacin na koji se vodene kapljice kondenziraju na vanjskoj strani case u kojoj se nalazi hladna voda. Odakle ta vlaga? Vruci zrak koji nastaje sagorijevanjem drveca i biljaka naravno da sadrzi i vlagu iz tih biljaka i drveca plus tu imamo i vodu iz okolnih potoka i jezera. Oslobodjena sagorijevanjem, zajedno sa pepelom i ostalim nusproduktima sagorijevanja, biva podignuta u visinu snaznim strujanjem vjetra i to je razlog zbog kojeg su pirokumulusi smedjkaste ili sivkaste boje za razliku od lijepih, cisto bijelih obicnih kumulusa. Znate na koje mislim oblacice? Njih djecica crtaju po svom djecijem nebu a mene podsjecaju na kokice i secernu vunu. To su najsladji pufnasti oblacici. Pirokumulusni oblaci bi mogli biti njihove zloceste polovine. I tako pozari stvaraju stubove dima koji mogu biti uistinu ogromni. Do te mjere da im vrh doseze 20, 30 pa nekada i 50,000 stopa. Tesko je odrediti bazu pirokumulusa zato sto je mutna i sakrivena pepelom pozara ili vulkanske erupcije. Pirokumulusi su u sustini kumulusi koji se hrane vatrom. Ako je u igri ogromna kolicina vodene pare ovi pirokumulusi se mogu razviti u kumulonimbus (olujni oblak) kioji se onda zove Pirokumulonimbus (Pyrocumulonimbus/PyroCb) koji ce da se razvije do faze potpuno formirane oluje. Kada dodje u tu kompletnu olujnu fazu podleci ce utjecajem visinskih vjetrova bas kao i obicni olujni oblaci i tako dobijemo grmljavinu, munje i kisu. Munje iz pirokumulusa mogu da izazovu nove pozare. U isto vrijeme, kisa koja pada iz pirokumulusa moze nekada i da ugasi pozar. Ono cega se vatrogasci najvise pribojavaju su uslovi koji se mogu razviti zbog vjetra. Struje vjetra koje pusu ka tlu iz pirokumulusa mogu promijeniti smjer pozara te nekada i prouzrokovati strasni tornado od vatre. Slican oblak se moze proizvesti iznad vulkana koji eruptira zbog lave koja putuje iz velikih dubina do povrsine i sa sobom nosi vlagu. Ta vlaga se onda pomijesa i sa kolicniom vlage iz biljaka koje je lava progutala. Pirokumulusni oblaci su vidjeni i iznad najvecih pozara u gradovima ili velikih industrijskih mjesta i rafinerija.

Image Source

 Image Source

 Image Source

 Image Source

 Image Source

 Image Source

 Image Source

Pyrocumulonimbus clouds caused by volcanic eruption

Pirokumulonimbusni oblaci izazvani vulkanskom erupcijom

 Image Source

 Image Source

Image Source

Man-made Pyrocumulus 

Pirokumulusi izazvani covjekovim djelovanjem

 Image Source

 Image Source

Image Source