The circle of friends is flooded with messages! A "flying saucer cloud" appeared over Beijing! It indicates...

Talking about Cloud

Everyone is familiar with

Often seen in the sky

The shape of clouds

Various

Just a shot

It’s a gorgeous piece of film.”

Image source: Tuchong Creative

Image source: Tuchong Creative

I have seen all kinds of clouds.

But have you ever seen clouds like this?

Image source: Beijing Meteorological Bureau

Early morning of November 12

A pink "flying saucer cloud" appeared over Beijing

Many netizens took photos

Sweep the Moments

Image source: Little Travel Diary

Image source: Beijing Meteorological Bureau

Image source: Beijing Meteorological Bureau

So

Why do clouds have so many different shapes?

The colors are different too?

How is this "flying saucer cloud" formed?

Today, let me share some scientific knowledge with you

Why do clouds have such varying shapes?

Clouds are aggregates of countless small water droplets or ice crystals that are formed when water vapor in the atmosphere cools. They float in the air and form something visible to our naked eyes.

The shapes of clouds are ever-changing because the water droplets and ice crystals that make up the clouds move with the flow of the atmosphere in the clouds. The flow of the atmosphere is changing all the time, which also causes the shapes of clouds to be different.

In addition to their various shapes, clouds also come in a variety of colors. Why is that? Let’s take a look…

Why are clouds different colors?

In fact, this is related to the scattering of sunlight.

When the diameter of cloud droplet particles in the cloud is larger than the wavelength of sunlight, Mie scattering will occur. The various colors in the sunlight will be scattered evenly and eventually overlap to white, and what we see are white clouds.

But on cloudy days, the upper clouds block the sun, the sunlight reaching the lower clouds is weaker, and the Mie scattering will also be weaker, so the clouds we see will become darker.

When sunlight passes through the atmosphere, the shorter wavelength blue light will undergo Rayleigh scattering when it encounters suspended particles and be scattered into the air. In the morning and evening, because the sunlight is oblique and the propagation path in the atmosphere is longer, more blue light will be scattered.

When sunlight reaches the clouds, only the red light with a longer wavelength is left and is scattered in the clouds, so the morning and evening glow we see at sunrise and sunset are often red.

How are “flying saucer clouds” formed?

The "flying saucer clouds" we usually talk about are also called lenticular clouds. Depending on the altitude at which they appear, they may be lenticular altocumulus clouds or lenticular stratocumulus clouds. Their shape is a bit like a convex lens or an almond, and they got their name because they resemble the appearance of alien flying saucers in science fiction works.

Image source: Tuchong Creative

Most UFO clouds are related to the surrounding terrain. Generally, the leeward waves of the mountains are formed when the air flows over the mountains. The leeward waves spread downstream, and the rising and sinking air currents formed work together to form UFO clouds. Some UFO clouds are also caused by the fluctuations before the front arrives.

Most UFO clouds indicate stable atmospheric conditions, which bodes well for the future, but if they are brought by a cold front, such as the lenticular clouds seen near Mount Fuji in Japan, they often herald stormy weather.

Expert of this article: Zhang Feng, Deputy Chief Forecaster of the National Meteorological Center