Detailed Notes on Air Masses and Weather Patterns

Air Masses

• Definition: Large bodies of air with uniform temperature and moisture characteristics.
• Size: Can extend thousands of square kilometers; ranges from hundreds to a thousand kilometers in diameter.
• Development Conditions: Best developed over source regions with uniform characteristics, such as purely land or water bodies (e.g., Tasman Sea, frozen water bodies).

Types of Air Masses

• Continental Arctic:

• Characteristics: Very cold and dry air, stable conditions.

• Formation: Develops over the Arctic Ocean during winter.

• Continental Polar:

• Characteristics: Cold, dry air; stable in winter, slightly unstable in summer.

• Formation: Develops over high latitude continental land masses (e.g., Northern Canada).

• Maritime Polar:

• Characteristics: Cool and moist air; can be unstable.

• Formation: Originates over high latitude oceans (e.g., North Atlantic, North Pacific).

• Maritime Tropical:

• Characteristics: Warm, moist, unstable air on the west side of oceans; stable on the east side.

• Formation: Influenced by subtropical high-pressure areas.

• Continental Tropical:

• Characteristics: Hot, dry, very unstable air.

• Formation: Develops in summer over regions like Arizona, New Mexico, and Northern Mexico.

• Precipitation: Limited, mainly convective thunderstorms.

Fronts

• Definition: Boundaries between different air masses, often resulting in weather phenomena; not finite boundaries.

• Cold Fronts:

• Characteristics: Steep boundaries; cold dense air displaces warm air.

• Weather: Typically accompanied by strong thunderstorms and rapid temperature drop.

• Warm Fronts:

• Characteristics: Gentle slopes; warm air rides over cold air.

• Weather: Results in extended rainfall over large areas, stratus-type clouds.

Weather Patterns Associated with Air Masses

• Air masses retain properties of their source regions but can modify over time due to interaction with other air masses.
• Examples of weather phenomena influenced by these air masses:
• Lake Effect Snow: Cold, dry air over warmer lake water leads to significant snowfall in areas downwind of lakes (e.g., Great Lakes).

Frontal Boundaries

• Defined by temperature, pressure, and wind direction differences on either side of the front.

• Cold front passage is indicated by drop in pressure, temperature decrease, change in wind direction, and often severe weather (e.g., thunderstorms).

• Warm front passage results in rising pressure, increased temperature and humidity, and prolonged, moderate rain events.

Cyclogenesis (Development of Mid-Latitude Cyclones)

• Initiated by strong divergence aloft leading to low-pressure areas at the surface.
• Stages of development:
• Incipient Stage: Initial development with no movement of air masses.
• Open Wave Stage: Warm front and cold front moving in opposite directions.
• Mature Cycle: Fully developed with potential for thunderstorms along cold fronts.
• Occluded Stage: Cold front catches up to warm front, cutting off warm air.

Observational Aspects

• Weather forecasting involves observing temperature, pressure, and wind shifts to identify front positions.
• Technological advancements allow for analysis at different atmospheric levels, improving forecast accuracy.

Graphical Representations

• Symbols used in weather maps to denote cold fronts (triangles) and warm fronts (semicircles).
• Cross-sectional profiles illustrate how air mass interactions lead to various weather outcomes.
• The landscape of the ground impacts how these fronts interact, influencing precipitation patterns and severity.