Air masses are large bodies of air that create distinctive weather conditions across the globe.
An air mass is defined as a body or 'mass' of air with uniform weather conditions, such as similar cloud types, temperature and humidity. Air masses may cover several million square kilometres and extend high up into the atmosphere.
They are primarily defined by the area in which they originate, this is called the 'source region'. The characteristics of an air mass can then be modified as they travel across the globe. Where two air masses of different temperatures meet, a boundary forms which is termed a 'front'.
In the following video and the other pages in this section, the formation and behaviour of air masses will be looked at more detail.
Last updated: 30 September 2013
Air mass source regions
The source region of an air mass defines its main characteristics.
Air mass modification
Air masses can become modified as they move away from their source region.
Air mass types
Air masses are classified into groups depending on their basic temperature and humidity characteristics.