Ilmamassan

Ilmamassan, often referred to as an air mass, is a large body of air that extends horizontally over thousands of square kilometers and vertically through much of the troposphere, possessing relatively uniform temperature and humidity characteristic of its source region. Air masses form when the lower atmosphere remains over a region long enough for its properties to become aligned with the surface beneath, and they can persist for days to weeks, moving with prevailing winds.

Classification combines temperature and moisture. Temperature-based names include tropical, polar, and arctic. Moisture-based names include maritime and continental, yielding common air masses such as maritime tropical (mT), maritime polar (mP), continental tropical (cT), and continental polar (cP). Additional variants exist, such as maritime arctic (mA) and continental arctic (cA), though their formation and persistence are regionally variable.

Fronts form where contrasting air masses meet, leading to weather changes such as precipitation, cloud formation, and temperature shifts. As air masses move, they are modified by the surfaces they traverse or by interactions with other air masses, becoming warmer, cooler, moister, or drier. Topography and surface characteristics, including mountains, oceans, and land cover, further influence their structure, stability, and the development of weather systems.

Understanding ilmamassan is central to weather forecasting and climate studies, as large-scale air masses govern seasonal patterns and short-term weather. Modern forecasting employs satellite data, radiosondes, and numerical models to track air-mass boundaries and predict their impact on temperature, humidity, and precipitation.