We often think of raindrops as spherical or tear-shaped, but, in reality, a falling droplet’s shape can be much more complicated. Large drops are likely to break up into smaller droplets before reaching the ground. This process is shown in the collage above. The initially spherical drops on the left are exposed to a continuous horizontal jet of air, similar to the situation they would experience if falling at terminal velocity. The drops first flatten into a pancake, then billow into a shape called a bag. The bags consists of a thin liquid sheet with a thicker rim of fluid around the edge. Like a soap bubble, a bag’s surface sheet ruptures quickly, producing a spray of fine droplets as surface tension pulls the damaged sheet apart. The thicker rim survives slightly longer until the Plateau-Rayleigh instability breaks it into droplets as well. (Image credit: V. Kulkarni and P. Sojka)
middle-earth meme: [1/5 quotes]
By all that you hold dear on this good earth, I bid you stand, Men of the West!
In this time of term papers I wanted to draw my patron deity, Bullshitticus, god of students and general last minute fudgery, sitting upon his Golden Futon, attended by the muses Caffeina and Thesaurae, whose powers of artificial energy and pretentious vocabulary can be invoked in case of the all-nighter.
I like to think he’s Dionysus’s second cousin or something.
Hi, I was wondering how we are able to see clouds? If they're a gas, how can we see them? If they're a liquid, how do they not just fall out of the sky without forming clouds at all?
Clouds are actually made up of tiny water droplets or ice crystals suspended in the air. When they’re in cloud form, they aren’t heavy enough to fall, so they drift – the same effect you see with dust motes in a beam of sunlight.
But why can we see them? Well, even though they are too small to fall, the water droplets in a cloud are more than sufficient to scatter light. The average droplet is about ten micrometres in diameter. The wavelengths of visible light are somewhat smaller (less than one micrometre*), so light is easily interrupted and scattered by the droplets, meaning that the cloud stands out from the background sky and becomes visible. And, because all of the visible wavelengths of light scatter roughly evenly in all directions, our eyes pick up all of the colours at once, meaning that we see white.
Or rather, we see white most of the time. Rain clouds, on the other hand, usually look grey – but how?
The even distribution of light by a white cloud is a special type of scattering called Mie scattering, which applies to any situation where the particles doing the scattering aren’t too different in size from the wavelengths of light being scattered (for an example of what happens when the particles are much smaller, check out this earlier post on Rayleigh scattering).
Mie scattering means that the light is scattered in all directions. As rain clouds build up, though, they become taller and thicker, meaning that light has to pass through more and more layers of suspended droplets in order to reach the ground below. Because all of these layers will scatter some light off to the sides or back up toward the source, the thicker the cloud, the less light reaches the ground (and the observer’s eye). That’s what makes storm clouds look grey – and now you also know that the darker the cloud, the thicker it probably is and the more water is up there just waiting to fall!
* The visible light spectrum ranges from about 390-700 nanometres. The shortest wavelengths are violet and blue (and if you go even shorter, you end up with ultraviolet light), whereas the longest are orange and red (and if you go even longer, you end up with infrared light).
You made a really great comment about meteorology and I was sold then and there
At least I can always count on my science snark!
the shield's the mightiest
Come visit me at C12/13 at Anime Expo this thursday to sunday!!
So…is it serious, you two?