Meteorology ch 11

Airmass

An airmass is defined as a large body of air that exhibits relatively uniform temperature and humidity characteristics in any horizontal direction at a given altitude. Understanding airmasses is crucial for meteorological studies as they influence weather patterns significantly.

Types of Airmasses

Arctic Region
- Continental Arctic: Extremely cold, dry, and stable air that originates over ice and snow-covered land surfaces. It is characterized by low moisture content and high stability.
- Polar: Cold, dry, and stable, this airmass forms over land and can contribute to colder weather when it moves southward.
Tropical Region
- Tropical Continental: Hot and dry air, typically stable in the upper levels but can lead to unstable surface air conditions, especially during summer months.
- Tropical Maritime: Warm, moist, and usually unstable air that develops over oceans, promoting cloud formation and precipitation.
Maritime
- Polar Maritime: This airmass brings cool, moist, and unstable conditions, usually associated with precipitation from frontal systems.
- Tropical Maritime: Warm and moist, often leading to instability and thunderstorms when it meets colder air.

Source Regions

The landscapes of source regions play a critical role in determining the characteristics of airmasses. Ideal source regions for airmasses are flat and uniform, enabling the airmasses to acquire specific temperature and moisture properties. The length of time an airmass spends in a source region directly influences the strength of its properties; longer durations enhance uniformity.

Fronts

A front is defined as the boundary where two different airmasses meet. Fronts and their dynamics are critical in weather prediction and include:

Frontogenesis: The process of the formation of a front due to initial movements of an airmass.
Frontolysis: The dying or weakening of a front, often leading to modifications in the properties of the airmass.
FROPA (Frontal Passage): Refers to the time when an airmass has fully passed through a location, altering local weather conditions.

Analyzing Fronts

A frontal analysis reveals important information about weather conditions, including:

Sharp temperature and moisture gradients,
Wind direction shifts,
Pressure patterns and changes,
Cloud formations and corresponding precipitation patterns.

Types of Fronts

Cold Front
- A cold front marks the boundary of an advancing cold air mass, which displaces warmer air. The leading edge is steep, resulting in strong upward motion and convection, which often leads to short but intense precipitation events, typically characterized by thunderstorms.
Warm Front
- This front signifies the boundary of an advancing warm air mass that gradually replaces cold air. These fronts have gentle slopes and are associated with less intense, more widespread stratiform precipitation, often producing layered clouds such as stratus and nimbostratus.
Stationary Front
- In stationary fronts, two airmasses converge but neither advances. The winds are usually light and parallel to the front, resulting in prolonged periods of precipitation, which can lead to flooding in some areas.
Occluded Front
- This occurs when a cold front catches up to and overtakes a warm front, typically resulting in complex weather patterns with multiple airmasses (cold, cool, warm) involved. Cold occluded fronts tend to bring more severe weather than warm occlusions, which are less common.
Dryline/Dewpoint Front
- A dryline is a boundary that separates hot, dry air from warm, moist air, often in the southern plains. It is notable for creating severe weather conditions, including tornados, and can lead to significant temperature changes as much as 10 degrees Celsius per kilometer of ascent.