Cumulus cloud: Definition and description

Cumulus cloud


Clouds are suspended water particles and ice particles in the air at a slight elevation above the earth’s surface formed by condensation. There are various types of clouds, cumulus clouds are one of them. Below is a discussion of what a cumulus cloud is and how it is formed.

The color of the cloud depends on the density of water particles. If the density of the cloud is high, it blocks most of the sunlight. So the lower part of the cloud looks a little black. The main conditions for cloud formation are atmospheric stability and rising air. 

Water vapors are generated from the water bodies due to solar heat and mix with the air. As the amount of water vapor in the air increases, the air becomes lighter and gradually rises. When this water vapor rises to a certain height, and when the temperature of the air reaches the dew point, the water droplets sometimes turn into snow or ice particles. 

But these water droplets cannot float in the atmosphere alone, they require very fine particles, called aerosols (fine dust particles, and salt particles). When the water particles are enclosed by this aerosol, dense black clouds are formed. 

The cloud is divided into four categories. These are high clouds, mid-altitude clouds, low clouds, and vertical clouds. One of the important vertical clouds is cumulus clouds (1) & (3).

What are cumulus clouds?


A low-level cloud is often described as a flat-based cloud as it is cotton-like. The term cumulus is derived from the Latin word cumulo which means heap or pile.

Cumulus cloud

A cumulus cloud is a low-level cloud formed due to condenses of water vapor associated with relative humidity reaching 100%. It is fluffy, cotton-like white-colored clouds. Cumulus clouds are formed due to atmospheric convection when the air warms to the surface and rises up to the atmosphere at an altitude of 2,000 m. 

It is formed through atmospheric convection when the air warms on the surface and rises up to the atmosphere, rise of air decreases its warming condition and drops the temperature causing a lapse rate. Temperature decreases subsequently humidity increases.

Water vapor condenses when relative humidity reaches 100% and releases latent heat and forms cumulus clouds (3).

Some interesting features of cumulus clouds

  • Cumulus cloud’s bases are relatively dark. 
  • A cumulus cloud is a thick cloud that extends vertically like a tower. 
  • It can be seen on land during the day.
  • Convection currents can be noticed in these clouds. 
  • Bright sunlight can be seen through these clouds.
  • The symbolic name of this cloud is Cu. 
  • When these clouds gather in the sky, there is clear weather.
  • These clouds look bright white at sunrise, but the lower part of the cloud is flat and black. 
  • Cumulus clouds gradually grow larger to form cumulonimbus clouds.
  • The upper part of these clouds is as wide as cauliflower (1).

How does the cumulus cloud form?

Cumulus clouds form because of atmospheric convection. Air is heated on the surface due to sunlight in the daytime. Then the warm air rises up into the atmosphere and mixes with cold air, thus forming cumulus clouds via condensation.

In the coastal areas, the cumulus clouds are formed over land during the daytime because sea breezes bring moist air which warms up quickly due to sunlight. And during the nighttime, this becomes reversed as the land is having lowers temperature than the sea thus, cumulus clouds formed over the sea (1).

Classification of cumulus clouds

There are four types of cumulus clouds found in the atmosphere. These are

1. Cumulus humilis 

It indicates fair weather conditions and is broader in structure. sometimes they present countless in the sky.

2. Cumulus mediocris

These clouds are robust in structure.

3. Cumulus congestus

They look like a long chimney and are an indication of the probability of rain and drizzle.

4. Cumulus fractus

Mostly fragmented and irregular in appearance. Responsible for wind movement and warm storms rather than precipitation and snowfall (1) & (2).

Importance of Cumulus clouds

Cumulus clouds are important due to various reasons like

1. Cumulus clouds indicate fair weather conditions.

2. It indicates bright sunny days or dry conditions. Because the condensation power of this cloud is less thus cannot bring much rainfall.

3. This type of cloud is responsible for drizzling or light rain.

4. Cumulus clouds can turn into strong cumulonimbus clouds, which can cause heavy rain (3).


1. How are cumulus clouds formed?

Cumulus clouds are formed by atmospheric convection as warm air from the surface begins to rise. As the air rises, the temperature decreases, resulting in an increase in relative humidity. At a certain level, the relative humidity reaches 100% and the weight-adiabatic phase begins. At this stage, water vapor condenses on the various nuclei present in the air, forming cumulus clouds (1).

2. Cumulus and stratus clouds belong to which group of clouds?

Cumulus Clouds are low-level clouds formed due to atmospheric convection. It is puffy and cotton-like.

Stratus clouds are low-level clouds. It is layered. They form horizontally by appearing in many layers like sheets (1).

3. What are Cumulus clouds made of?

Cumulus clouds are made of different components. The prime components that are responsible for forming cumulus clouds are water and air.

Water plays an important role to form cumulus clouds but has not any direct role. Its various forms like ice crystals, water droplets, supercooled droplets, water vapor, etc. are responsible for forming cumulus clouds.

4. What do Cumulus clouds look like?

Cumulus clouds look like fluffy cotton floating in the sky.

5. How do cumulus clouds form?

Cumulus clouds are formed due to the atmospheric convection currents. The warm air rises to the top. Then the temperature decreases. As a result relative humidity increases. When the convection reaches a certain level, the relative humidity reaches 100%.  Then the water vapor condenses, emits latent heat, warms the air, and encourages more convection. In this way water vapor condenses on the various nuclei present in the atmosphere, forming cumulus clouds. 


1. Savindra Singh. Climatology. Pravalika Publications, Allahabad. Chapter 2: Origin, composition, and structure of the atmosphere. Page No: 20.