Clouds 101: Pileus

Pileus (Latin for felt cap) is a thin tropospheric sheet of cloud made of ice crystals on the top of or directly above another cloud (usually cumulus or cumulonimbus calvus). Pileus looks like a cap-like formation on top of its associated cloud. A senior meteorologist once referred to it not as a cloud – rather as a cloud haircut. When I noticed that someone on the net called it the same way, I bursted into tears from laughing. When you look at it (with a help of a little imagination), it kinda does look like a dashing Brigitte Bardot bouffant (Amy Winehouse? or Donald Trump's head piece?). Pileus clouds form when air in a cloud ascends quickly (approx 20-50 km/h) causing a moist airmass to be thrust upward and causing the water inside it condense into a pileus cloud as the airmass cools. A pileus will change shape quickly and usually fades away or joins its associated cloud after a short while. Eventually, the cumulus will grow into and penetrate the pileus cloud, after which the pileus may remain as a cloud skirt around the cumulus before the two completely merge. Some pileus clouds may not form above cumulus or cumulonimbus clouds, but rather above volcanic ash clouds or above mountainsides. This type of cloud is caused by strong, relatively fast upward motion. Situations where this occurs include quickly growing thunderheads, volcanic eruptions and even nuclear explosions. In each case, something pushes warm, moist air upward quickly. Pileus clouds look similar to the smooth caps sometimes seen on top of cumulus clouds, which are actually ice caps. If you have very strong convection, pushing quickly and very high, it forms more of an ice cloud because it is high enough for the crystals to freeze. It’s nothing more mysterious than things freezing and they also form above some mushroom clouds of high-yield nuclear detonations. Pileus or ‘cap’ clouds are thin, freshly formed and with uniform sized droplets. They are ideal to produce iridescent colours by diffraction. The bright, iridescent colors seen in pileus are diffracted sunlight. Iridescent colors are strongest when the diffracting droplets are small and similar in size. The newly formed pileus droplets all of similar provenance are ideal for iridescence. Enjoy.

Pileus (latinski za klobuk) je tanki, troposferni oblacni sloj koji je sacinjen od kristala i lociran direktno iznad, odnosno na vrhu drugog oblaka (obicno kumulusa ili kumulonimbusa kalvusa). Pileus je oblacna formacija koja slici kapi, naslonjenoj na ‘majcinski’ oblak. Jedan iskusni meteorolog je u razgovoru o pileus oblaku spomenuo kako on na njega ne gleda striktno kao na oblac vec – kao frizuru drugog oblaka. Tu istu referencu sam primjetila jos jednom na internetu i doslovno je oko zasuzilo od smijeha. I zaista, kada pogledate ovaj oblak (i upotrijebite malo maste), stvarno slici ‘kosnici’ kakvu je nosila Brigitte Bardot (ili Amy Winehouse? a sta mislite lici li na umetak kose Donalda Trumpa?). Pileus oblak se formira kada se zracna masa u oblaku brzo spusta (cca 20-50 km/h) cineci da se vlazna zracna masa naglo podize te uzrokuje kondenz vode koji se transformira u pileus oblak kako se zrak pocne hladiti. Pileus oblak ce brzo promijeniti oblik te obicno izblijedi ili se pridruzi ‘majcinskom’ oblaku. Eventualno taj ‘majcinski’ kumulusni oblak se moze razviti te doslovno probusiti pileus-a, nakon cega pileus ostaje u vidu oblacne ‘suknje’ koja pada lezerno preko kumulusa, prije nego se ova dva oblaka stope jedan u drugog. Neki pileus oblaci se nece formirati iznad kumulusa/kumulonimbusa vec iznad mjesta vulkanske aktivnosti ili cak nuklearnih eksplozija. U svakom slucaju, nesto ce posluziti da pogura topao, vlazan zrak naglo u visinu. Pileus oblak moze izgledati poput glatkih kapa koje ponekada bivaju vidjene iznad pojedinih kumulusa ali tada se vecinom radi o ledenim kapicama. Ukoliko imate snaznu konvekciju koja zracnu masu silovito gura u velike visine, formira se ledeni oblak posto je na dovoljno visokom nivou da se kristali slede. Nije u pitanju nista misterioznije od oblicnog sledjivanja a ovi ledeni oblacici se takodjer formiraju i iznad pojedinih ‘gljiva’ oblaka, nastalih uslijed zestokih nuklearnih detonacija. Pileus (ili kapica ili friz oblacic) je u biti tanak, svjeze formiran oblak koji se sastoji od kapljica uniformnih (ujednacenih) dimenzija. Te kapljice su idealne za kreiranje iridizacije tj. pojave boja duge putem prelamanja tj. defrakcije svjetlosti. Svijetle, impresivne boje duge koje se nekada mogu vidjeti razlivene na pileus oblaku nisu nista vec prelamanje sunceve svjetlosti. Te boje su najintenzivnije kada se svjetlost prelama o kapljice koje su sitnih i ujednacenih dimenzija. Novoformirani pileus oblak koji jeste sastavljen od upravo takvih kapljica je idealan za formiranje ove pojave. Uzivajte.


 Image Source

 Image Source

 Image Source

 Image Source

 Image Source

 Image Source

 Image Source

 Image Source

 Image Source

Komentariši

Vaša email adresa neće biti objavljivana. Neophodna polja su označena sa *