Air mass

In meteorology, an air mass is a volume of air, covering many hundreds or thousands of square miles, defined by its temperature and humidity. Air masses are classified according to latitude and their continental or maritime source regions: colder air masses are termed polar or arctic, warmer ones tropical, continental and superior air masses are dry, and maritime and monsoon air masses are moist. Weather fronts separate air masses of different density, and once an air mass moves away from its source region the underlying land or water can quickly modify its character.