What is a cloud?

Earth science


It is already March, the beginning of spring.
When I went out for a midday walk, the air was fresh and clean, and the warm sunshine and cool breeze were pleasant.

It was sunny today, but I spotted a few oddly shaped clouds floating in the sky here and there and suddenly wondered, “What are clouds?” So I looked it up and put it all together.

Conclusion, “What is a cloud?”

Clouds are small water/ice particles called “cloud droplet” floating in the atmosphere.

What are “cloud droplet” are the source of clouds?

Cloud droplet are tiny water droplets or ice crystals with a diameter of about 0.01 mm, and there are several hundred cloud particles in 1㎤ of cloud.
The white appearance of these water droplets and ice crystals due to diffuse reflection of light is the true nature of “clouds”.

・”cloud droplet” are small water droplets or ice crystals about 0.01 mm in diameter.
・There are about several hundred cloud droplet in 1㎤ of clouds.

This site by the Weather Lab compares it to the thickness of a mechanical pencil lead. It is intuitively easy to understand because it is represented in a diagram.

↓This is a TIPS that there are two ways to read “cloud droplet” in Japanese. I call it “kumotsubu” because of its cute pronunciation.



How cloud droplet are formed


In order for cloud droplet to form, we first need cloud condensation nuclei and ice nuclei.

Cloud condensation nucleus means “a center for squeezing and hardening”.

An ice nuclei is an ice version of that nucleus, but because it is nucleated at a cooler altitude, it is composed of lighter material than the condensation nucleus that would reach the upper atmosphere.

It is the fine particles (aerosols) floating in the atmosphere that become cloud condensation and ice nuclei, for example,

・Dust, dirt
・Smoke, soil particles
・splash of seawater

Cloud droplet may not include ice crystals.


How it’s made

Cloud droplet are formed when water vapor in the air collects around a material nucleus such as a condensation nucleus.

What I found interesting is that “without a nucleus, clouds cannot form”.
Without a nucleus, water vapor continues to exist as water vapor. This state is called supersaturation.

In other words, If we could bring cloud condensation nuclei into a supersaturated state, you can create clouds.

Airplane clouds are clouds formed when the material released by the flight of an airplane becomes a cloud condensation nucleus. I see.


The flow of clouds forming

Prerequisite Knowledge:
・Air becomes lighter as its temperature rises.
・The higher the altitude, the lower the temperature.
 (100m higher altitude results in a decrease of about 0.6°C)

・When it is cold, the amount of water vapor that can be contained in the air is reduced.

Clouds can be created primarily through the following process.

  1. Air containing water vapor cools
  2. Saturates (excess water is released)
  3. Excess water and other substances gather around the nucleus and form cloud particles, which become clouds.


1.Air containing water vapor rises into the sky and cools

First, since air becomes lighter as its temperature rises, air heated near the earth’s surface becomes lighter and rises into the sky.

2.Saturates (excess water is released)3.Excess water and other substances gather around the nucleus and form cloud particles, which become clouds.

Next, the higher the altitude, the lower the temperature, which cools the air and reduces the amount of water vapor that can be contained in the air (saturated water vapor content).

This causes excess water to stick to the nucleus and form “cloud particles” that become the “clouds” we see.

What clouds did you see today?

After doing some research, I wondered if there are different types of nuclei, or if I could create my own clouds.

I am also interested in the types of clouds such as “iridocumulus” and “sardine clouds,” so I will look them up one by one on the day I see such clouds. I am looking forward to seeing the sky again tomorrow.

See you again!