01
· Cloud types
· 20 · VII · 26
· 5 min
Cloud classification
I have chosen to focus this very first article on the basics: how are clouds classified?
We often hear about cumulus or cumulonimbus clouds, but what do these terms actually mean? How do we distinguish one type of cloud from another?
For a long time, this question remained unanswered, even though humans have recognized since ancient times that changes in cloud cover often herald changes in the weather. The earliest evidence of systematic observations linking the appearance of clouds to weather evolution dates back to the third millennium BCE in Mesopotamia. Such observations were an essential tool for ensuring successful harvests.
However, it was not until the beginning of the 19th century that two men proposed a complete cloud classification system: the French naturalist Jean-Baptiste Lamarck and the British amateur meteorologist Luke Howard. In a future article, I plan to tell the story of the struggle Howard faced in getting his classification adopted—and who ultimately won that battle.
This classification system, first published in 1803, has been revised several times over the years, but the foundations of Howard's work have remained largely unchanged for more than two centuries. It is based on Latin names (as we have already seen) and on the physical characteristics of clouds, such as their altitude, extent, and shape. Today, the classification of clouds is presented in the International Cloud Atlas, which is continuously updated by the World Meteorological Organization (WMO), a specialized agency of the United Nations. You can find the official website here: Home | International Cloud Atlas
Today, clouds are grouped into several families according to the altitude of their base and then classified into different genera according to their general appearance. For this first article, I have chosen to introduce only the cloud families (based on altitude) and their genera (based on overall shape). Beyond these, there are also species, varieties, and supplementary features, which will be the subject of future articles.
Approximate Altitudes and Cloud Genera by Level
High-Level Clouds
Genera: Cirrus, Cirrocumulus, Cirrostratus- Polar regions: 3 to 8 km
- Temperate regions: 5 to 13 km
- Tropical regions: 6 to 18 km
Mid-Level Clouds
Genera: Altocumulus, Altostratus, Nimbostratus*- Polar regions: 2 to 4 km
- Temperate regions: 2 to 7 km
- Tropical regions: 2 to 8 km
Low-Level Clouds
Genera: Stratus, Stratocumulus, Cumulus, Cumulonimbus*- From the Earth's surface to 2 km in all climatic regions
*The cloud genera containing the term “nimbus” (nimbostratus and cumulonimbus) are generally associated with precipitation and may extend through several atmospheric levels, sometimes reaching heights of up to 13 km. These are known as clouds with great vertical development.
The higher a cloud is in the atmosphere, the more likely it is to be composed primarily of ice crystals. In contrast, low-level clouds mainly consist of liquid water droplets.
The following illustration, provided by Météo-France, offers a clear visual representation of how clouds are distributed among the different atmospheric levels. 
In the upcoming articles, I will take a closer look at each of the ten cloud genera recognized by the World Meteorological Organization.
— Baptiste Lorient