Air masses are large bodies of air that maintain relatively uniform temperature and humidity characteristics. They acquire their distinct properties from the surface over which they form. The interaction between the air and the underlying land or ocean allows the air mass to take on specific thermal and moisture qualities.
Understanding Continental Polar Air Masses
A continental polar (cP) air mass is characterized by its cold and dry nature. It forms over land (continental) in high-latitude (polar) regions. The “continental” aspect means it originates over land, resulting in low moisture content, while “polar” signifies its formation in cold, higher-latitude areas.
These air masses are very stable, meaning the air does not readily rise and mix, which often leads to clear skies. In contrast, maritime air masses, which form over oceans, tend to be moist, and tropical air masses, originating from lower latitudes, are warm.
Key Formation Zones
Continental polar air masses primarily form over large, high-latitude landmasses in the Northern Hemisphere. Northern Canada and Alaska are significant source regions for air masses affecting North America. Another prominent formation zone is Siberia in northern Asia.
These regions are conducive to the formation of continental polar air masses due to their vast, flat expanses. The extensive land allows for prolonged contact between the air and the cold surface, enabling the air to acquire uniform characteristics.
Atmospheric Conditions for Formation
The development of a continental polar air mass requires specific atmospheric conditions that promote extreme cooling and stability. Prolonged clear skies allow heat to escape directly from the ground into space through radiative cooling, efficiently cooling the surface and the air above it.
Light winds are another contributing factor, as they prevent the mixing of the cold surface air with warmer air from higher altitudes. This calm atmospheric state allows the cold air to settle and deepen over the source region. The resulting stable atmosphere, often associated with high-pressure systems, inhibits vertical air movement and cloud formation, reinforcing the cold, dry conditions.
The low sun angle in polar regions plays a role, especially during winter, by minimizing solar heating and allowing temperatures to drop considerably. This reduced solar radiation, combined with extensive snow and ice cover, reflects much of the incoming sunlight, further contributing to the extreme cold. As these conditions persist, the overlying air mass becomes increasingly cold and stable.