Here are the main air masses found in Western Europe that shape the weather we have.
Definition of a stable and unstable air mass #
In the atmosphere, air that rises or sinks because it is forced to do so is said to be unstable. If it does not move vertically, or only slightly, it is said to be stable. Thus, if we heat air, its tendency will be to rise, it becomes unstable. It remains unstable as long as its temperature is higher than that of its environment. As soon as its temperature reaches that of its environment, it stops rising.
Air masses in the Northern Hemisphere #
Air masses
Humidity: Low
Temperature: Very Low
Humidity: Very Low
Temperature: Variable
Humidity: High
Temperature: Very High
Humidity: Very High
Temperature: High
Humidity: Variable
Temperature: Very Low
Humidity: High
Temperature: High
From your deductions, describe a stable and unstable air mass
Answer
When the ground is heated by the Sun, the layers closest to the ground are warmed and since the warm air is less dense, the warmed air will tend to rise. If the pocket of warm air cools less quickly than the surrounding air, this parcel of air will accelerate upwards. We are then in the presence of an unstable air mass.
In the opposite case, the rising air becomes colder than the surrounding air, the upward movement will stop and the atmosphere is then stable.