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4a_AtmosOceanicCirculation1_Slides

The Energy-Atmosphere System

Atmospheric and Oceanic Circulations

  • Understanding the interactions between the atmosphere and oceans is crucial for comprehending weather patterns and climate.

Air Pressure

  • Defined as the pressure exerted by the weight of air above a given point.

  • Measured in millibars (mb) or inches of mercury (in. Hg).

Air Pressure Measurement

  • Mercury Barometer:

    • A glass tube containing mercury under vacuum.

    • Air pressure pushes down on mercury in a dish, causing it to rise or fall.

  • Aneroid Barometer:

    • A small, sealed chamber partially emptied of air.

    • Connected to a mechanism sensitive to air pressure changes, which moves a needle on a dial to indicate pressure.

Air Pressure Readings

  • Refer to Figure 6.3 for visual representation.

Wind Description and Measurement

  • Wind: Horizontal motion of air across Earth’s surface.

  • Turbulence: Refers to wind updrafts and downdrafts.

Measuring Wind

  • Anemometer: Measures wind speed.

  • Wind Vane: Determines wind direction.

  • Doppler Radar: Uses backscatter from radar pulses to detect moisture direction, indicating wind speed and direction.

Winds Represented On Maps

  • Driving Forces within the Atmosphere:

    • Gravity

    • Pressure Gradient Force

    • Coriolis Force

    • Frictional Force

Pressure Gradient Force

  • Created by pressure differences between high and low-pressure areas.

  • Winds move from high to low pressure.

  • Isobars: Lines of equal pressure; closer lines indicate stronger winds.

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Coriolis Effect

  • Describes the apparent deflection of objects moving on a rotating platform.

Coriolis Force and Global Scale Winds

  • Air moving across Earth’s surface appears to curve due to the spherical shape and rotation of the planet.

  • In the northern hemisphere, air curves to the right; in the southern hemisphere, it curves to the left.

Geostrophic Winds

  • Characteristic of upper tropospheric circulation involving pressure gradient and Coriolis forces.

  • Refer to Figure 6.8 for visual representation.

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Wind Frictional Force

  • Effects of wind friction extend to about 500 m (1650 ft) above the surface.

Variables Affecting Friction

  • Surface texture

  • Wind speed

  • Time of day and year

  • Atmospheric conditions

Wind Dynamics

  • Friction near surface disrupts equilibrium between Pressure Gradient and Coriolis forces.

  • Causes surface winds to flow at angle to isobars, leading to:

    • Anticyclone: High pressure area with diverging surface winds.

    • Cyclone: Low pressure area with converging surface winds.

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Surface Winds Behavior

  • Surface winds diverge from high-pressure areas, rotating clockwise in the northern hemisphere.

  • Surface winds converge towards low-pressure areas, rotating counterclockwise in the northern hemisphere.

  • Geostrophic and Surface Winds:

    • Air converges and sinks in high-pressure areas and rises in low-pressure areas.

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High- and Low-Pressure Areas

  • Primary Pressure Areas:

    • Form uneven belts that stretch globally (e.g., equatorial low-pressure trough, subtropical high-pressure cells).

  • Secondary Pressure Areas:

    • Smaller and formed within primary areas, ranging from a few hundred to a few thousand kilometers in diameter.

Pressure Distribution

  • Troposphere characteristics:

    • Warm near the equator (orange) where air rises.

    • Cold near the poles (blue) where air is denser and compressed.

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Jet Streams

  • Occur at boundaries of contrasting air masses.

Intertropical Convergence Zone (ITCZ)

  • A low-pressure belt created by rising warm air in the equator.

  • Also known as the "Doldrums": limited winds, monotonous weather.

  • Climate effects: often wet, leading to rainforests.

Trade Winds

  • Northern hemisphere: Trade winds blow towards the southwest (N.E. Trade Winds), crucial for maritime travel, historical significance in navigation by Columbus.

  • Southern hemisphere: Trade winds blow towards the northwest (S.E. Trade Winds).

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Conclusion of Lecture 4a

  • Review of energy-atmosphere and circulatory systems essential for understanding global climates and weather patterns.