​Air Masses and Their Source Regions

An air mass is a large body of air with relatively uniform temperature and humidity, formed over a particular source region such as oceans, deserts, or high‑latitude land. Air masses are commonly labeled by moisture (continental “c” for dry, maritime “m” for moist) and temperature (Tropical “T”, Polar “P”, Arctic “A”).
For example:
  • Continental polar (cP) air mass is cold and dry and often affects East Asia in winter, while
  • Maritime tropical (mT) air mass is warm and humid and can bring moist air from the oceans toward southern China and Hong Kong.