Here's why:

* Circulation refers to the movement of fluids (including air) in a continuous loop. This can be on a small scale, like the air flow around a building, or on a large scale, like the global air circulation patterns.

* Large-scale air circulation patterns are often referred to by more specific names, like:

* Hadley Cells: Large circulation patterns that occur near the equator, driven by solar heating.

* Ferrel Cells: Mid-latitude circulation patterns located between the Hadley Cells and the Polar Cells.

* Polar Cells: High-latitude circulation patterns that occur near the poles.

So, while "circulation" is the general term, specific names are used to describe different types of large-scale air movement.