RB

Wind and Atmospheric Circulation Study Guide

Atmospheric Pressure

  • Definition: The force exerted by the weight of air.

  • At Sea Level:

    • 14.7 psi or 1 kg/cm²

    • Standard sea-level pressure = 1013.2 mb (millibars)

  • Effect of Pressure:

    • Decreases with altitude.

    • Dropping pressure = "bad" weather.

    • Rising pressure = "fair" weather.

Wind (Horizontal Movement of Air)

  1. Pressure Gradient Force:

    • Causes air to move from high-pressure areas to low-pressure areas.

    • Mapped by isobars (lines of equal pressure).

  2. Coriolis Effect:

    • Apparent deflection of wind due to Earth's rotation.

    • In Northern Hemisphere: Wind deflects right.

    • In Southern Hemisphere: Wind deflects left.

  3. Friction:

    • Affects wind mainly near the surface, slowing air movement.

  4. Geostrophic Winds:

    • Winds that move parallel to isobars (at upper altitudes, independent of friction).

  5. Jet Stream:

    • A fast-flowing river of air at high altitudes (120–240 km/h).

Cyclones and Anticyclones

  1. Cyclones (Low-Pressure Centers):

    • Rising air; pressure decreases toward the center.

    • In Northern Hemisphere: Winds move inward (convergence) and counterclockwise.

    • In Southern Hemisphere: Winds move inward (convergence) and clockwise.

    • Usually bring clouds and precipitation.

  2. Anticyclones (High-Pressure Centers):

    • Sinking air; pressure increases toward the center.

    • In Northern Hemisphere: Winds move outward (divergence) and clockwise.

    • In Southern Hemisphere: Winds move outward (divergence) and counterclockwise.

    • Usually bring fair weather.

Local Winds (Small-Scale)

  • Land and Sea Breezes: Local winds caused by the temperature difference between land and sea.

  • Mountain and Valley Breezes: Caused by air moving up or down mountains.

  • Chinook and Santa Ana Winds: Warm, dry winds influenced by local geography.

General Atmospheric Circulation

  1. Cause: Unequal surface heating on Earth.

  2. Atmospheric Cells: 3 pairs that redistribute heat (Hadley cells).

  3. Global Circulation:

    • Equatorial Low: Rising air and abundant precipitation (ITCZ).

    • Subtropical High: Stable, dry air near 30° latitude (location of deserts).

      • Winds from here: Trade Winds (equatorward) and Westerly Winds (poleward).

Subpolar and Polar Zones

  1. Subpolar Low: Warm and cool winds meet, creating the polar front and stormy weather.

  2. Polar High: Cold, sinking air, creating polar easterlies that move equatorward.

Influence of Continents (Monsoons)

  • Monsoon: Seasonal wind pattern.

    • Summer: Warm, moist air flows onto land.

    • Winter: Dry, continental air flows off land.

Circulation in the Mid-Latitudes

  • Westerlies (30°–60°): Air moves west to east in the Northern Hemisphere.

    • Rossby Waves: Airflow interrupted by cyclones and anticyclones.

    • Jet Streams: Guide cyclones and anticyclones.

Air Masses

  • Large bodies of air with consistent temperature and humidity.

  • 4 Types:

    1. Continental Polar (CP): Cold and dry.

    2. Continental Tropical (CT): Hot and dry.

    3. Maritime Polar (MP): Cool and moist.

    4. Maritime Tropical (MT): Warm and moist.

Types of Fronts

  • Warm Front: Warm air slides over cold air.

  • Cold Front: Cold air pushes under warm air.

  • Occluded Front: A warm front is overtaken by a cold front.

El Niño and La Niña

  1. El Niño:

    • A countercurrent flows southward along the coasts of Ecuador and Peru.

    • Causes warmer ocean waters and disrupts marine ecosystems.

    • Southern Oscillation (ENSO): Change in pressure between eastern and western Pacific.

    • Results in warm water flowing eastward.

  2. La Niña:

    • Opposite of El Niño.

    • Caused by colder than average temperatures in the eastern Pacific.