In it, I described how our senses of smell and sight, and at times taste, can distinguish the type, origin and travels of the air surrounding me at any given moment. Meteorologists, particularly those involved with weather forecasting, understand that differences in the properties of air masses reveal clues about the weather to come. Formal characterization of air masses emerged about a century ago from the famed Bergen School of Norwegian meteorologists, particularly Tor Bergeron. Until the 17th Century, early weather observers, like the wine taster, relied on their senses to distinguish differences between air masses. Once networks of simultaneous weather observations became established, air masses were revealed to be very large volumes of air with similar temperature and moisture characteristics.
Air masses are distinct in their temperature and moisture content due to their place of birth.
When polar continental areas are the birth place, air masses are cold and dry. Hot, dry air masses are born over continents at lower latitudes, particularly in desert or other arid regions. A number of such breeding grounds ring the globe, tucked away from strong global wind belts so that the nascent air mass can mature. Eventually, all air masses are pushed from their nest by global wind currents forcing them mingle with other traveling air masses. Cold air masses generally seek warmer latitudes while warm ones prefer northward journeys.