Air mass

Airmassesorigin

Air masses

Cold front (left) above Zdiměřice in Czechia, 2017

Snow Clouds in Korea

Air mass is a term used in meteorology to describe a large body of air that is approximately homogeneous in its horizontal properties, especially temperature and humidity. The concept of an air mass is fundamental to understanding weather patterns and climate variations, as the movement and interaction of different air masses can influence weather conditions over large areas.

Characteristics

An air mass is characterized by its temperature, humidity, and stability, which are determined by the region over which it forms, known as its source region. Source regions are typically vast, flat, and uniform areas where the air can acquire the properties of the underlying surface over a period of days or weeks. These regions can be classified into several types, including maritime (over oceans) and continental (over land), and polar (cold) or tropical (warm), leading to the basic air mass types: maritime polar (mP), maritime tropical (mT), continental polar (cP), and continental tropical (cT).

Formation and Modification

Air masses form when the atmosphere remains over a homogeneous area with a consistent pattern of temperature and humidity. This process allows the air to 'take on' the characteristics of the surface below. Once formed, air masses can travel away from their source regions, moving over other regions and potentially modifying their characteristics through processes such as heating, cooling, or mixing with other air masses.

Impact on Weather

The interaction between different air masses can lead to the formation of weather fronts, which are boundaries that separate air masses of different densities (usually due to differences in temperature and humidity). Fronts are associated with most of the significant weather events, including rain, snow, storms, and changes in temperature. For example, the collision between a warm, moist maritime tropical air mass and a cold, dry continental polar air mass can lead to the development of a cyclone.

Classification

Air masses are classified based on their source region and nature. The main categories are:

• Maritime Polar (mP): Cold and moist air masses formed over the cold waters of the polar regions.
• Maritime Tropical (mT): Warm and moist air masses that form over the warm waters of the tropics.
• Continental Polar (cP): Cold and dry air masses that form over the large land masses in the polar regions.
• Continental Tropical (cT): Hot and dry air masses that form over desert regions in the tropics.

Examples

One well-known air mass that affects the weather in North America is the maritime polar air mass that originates over the North Pacific Ocean. It brings cool, moist weather to the western coast of North America. Another example is the continental tropical air mass that forms over the deserts of Mexico, bringing hot, dry weather to the southwestern United States.

Conclusion

Understanding air masses and their characteristics is crucial for predicting weather patterns and climate variations. The study of air masses and their interactions is a fundamental aspect of meteorology and helps in the preparation for and mitigation of weather-related disasters.