OM

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.