Clouds 101 Special: Kelvin-Helmholtz Clouds

This time I have a truly interesting cloud type on my repertoir. These wave clouds are certainly something we would imagine in a Sci-Fi scene, to be formations from another planet (indeed they can be seen on ther planets and I will show you that as well). These are the famous Kelvin-Helmholtz clouds and are named after Lord Kelvin and Hermann von Helmholtz


Ovaj put na svom repertoaru imam uistinu interesantnu vrstu oblaka. Ovi valoviti oblaci su nesto sto bi mogli zamisliti u filmovima naucne fantastike ili da su formacije sa drugih planeta (i zaista se mogu vidjeti i na drugim planetama sto cu vam kasnije pokazati). U pitanju su poznati Kelvin-Helmholtz oblaci koji su dobili ime po Lord Kelvinu i Hermannu von Helmholtzu

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These clouds are also known as billow clouds, shear-gravity clouds and KHI clouds and are produced in specific conditions. These clouds are formed between two layers of air, with different densities, traveling at different speeds. The upper layers of air are moving at higher speeds and will often scoop the top of the cloud layer into these wave-like rolling structures. 

Poznati su i kao oblaci-valovi, gravitacijsko-smicajni oblaci i KHI oblaci koji nastaju u specificnim uvjetima. Formiraju se izmedju dva zracna sloja razlicite gustine, koji se krecu po razlicitim brzinama. Gornji slojevi zraka se brze krecu i po vecim brzinama te ce cesto zagrabiti vrh oblacnog sloja te ga oblikovati u ove valovite formacije.


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The stable lower air being lifted, cooled, and condensed so that this process becomes visible, though this commonly happens many places without being visible. These clouds often form on windy days where there is a difference in densities of the air, such as in a temperature inversion. Therefore, if a warm, less dense layer exists over a layer of colder, denser air, and the wind shear across the two layers is strong enough, eddies will develop along the boundary. The rolling eddies seen at the top of the cloud layers are usually evenly spaced and easily identifiable. 

Stabilna zracna masa biva podignuta, ohladjena i kondenzirana tako da sav taj proces nama postane vidljiv iako se sve to uobicajeno desava na mnogim lokacijama, samo sto to mi ne vidimo. Ovi se oblaci cesto formiraju tokom vjetrovitih dana kada je prisutna razlika u gustinama zracnih masa, kao i kod temperaturne inverzije. To znaci da ako topao sloj manje gustine postoji iznad sloja hladnijeg, gusceg zraka te ako je smicanje vjetra izmedju njih dovoljno jako, mali kovitlaci ce se razviti na njihovoj granici. Valjuskasti vrtlozi koje vidjamo na vrhu oblacnog sloja su najcesce medjusobno na jednakim razmacima i lako ih je prepoznati. 

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These clouds are often good indicators of atmospheric instability and the presence of turbulence for aircraft. However, if the air layers are traveling at the same speed, such waves will not occur. And as I mentioned before, the same phenomenon occurs on other planets. Here is a picture of Kelvin-Helmholtz clouds on Saturn.


Ovi oblaci su inace izvrstan indikator nestabilnosti u atmosferi i ukazuju na prisustvo turbulencije sto je bitno za avione. Medjutim, ako se zracni slojevi krecu po istoj brzini, ovi valoviti oblaci se nece razviti. Kao i sto sam prethodno spomenula, isti fenomen se pojavljuje i na drugim planetama. Pogledajte sliku Kelvin-Helmholtzovih oblaka na Saturnu.

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2 Comments

    • Februar 9, 2013 / 6:45 pm

      Ima i nekih snimaka KH oblaka iznad npr. Birminghama na you Tube-u i tek tada se ustvari percipira njihova neuobicajenost. Hvala na posjeti 🙂

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