Air mass
Appearance
![](http://upload.wikimedia.org/wikipedia/commons/thumb/2/2f/Air_masses.svg/220px-Air_masses.svg.png)
An air mass is a volume of air defined by its temperature and water vapor content. Air masses cover many hundreds or thousands of square miles. Colder air masses are called polar or arctic, while warmer air masses are called tropical.