Coriolis Force and Atmospheric Circulation

Coriolis Force and Its Implications

  • Observations of the Coriolis effect and its dependence on latitude:

    • Diameter of the Earth is similar at 5 degrees north and equator.

    • Apparent Coriolis force is small at 5 degrees north due to similar Earth diameter.

    • At 60 degrees north, distance traveled is less than at the equator, leading to lower eastward velocity.

    • An air parcel traveling in a straight line is affected by Earth's rotation underneath it.

    • According to Newton's first law, eastward velocity remains constant unless acted upon by a force.

Perspective Experiments

  • Northern Hemisphere Perspective:

    • Viewing the Earth with North Pole upwards and South Pole downwards.

    • An air parcel lifted from the equator travels at 1000 miles per hour eastward.

    • As it moves north, it appears to deflect to the right due to Earth's rotation beneath it.

    • Diagram shows a dark solid line curve representing perceived motion of the air parcel.

  • Southern Hemisphere Perspective:

    • Air parcel at the equator moves southward under pressure gradient forces.

    • The surface velocity of Earth is less at lower latitudes compared to the equator.

    • This results in air being perceived to turn to the left in the Southern Hemisphere due to the Coriolis force.

Coriolis Force and Air Movement

  • The deflection of air parcels in relation to pressure gradients:

    • Air moving from high to low pressure appears deflected to the right in the Northern Hemisphere and left in the Southern Hemisphere.

    • Both air and water experience this apparent force due to the Coriolis effect, leading to observed turbulence.

Surface and Air Resistance Explained

  • Visualizing friction and its effects on air movement:

    • A high-rise building at the equator rotates with the Earth without any change in vertical orientation (no spin).

    • A building at the pole appears to spin with Earth's rotation.

    • Spin varies with latitude: none at the equator, increasing to maximum at the poles.

  • Friction's role in atmospheric movements:

    • Friction acts opposite to movement.

    • Observations in rivers show how the edges cause slower movement and eddies to form.

    • Eddies can occur in water, air, etc., caused by differences in resistance.

    • In the atmosphere, friction affects air flows, particularly in the lower troposphere.

Understanding Atmospheric Circulation

  • Differentiation between high and low pressure systems:

    • Region of high pressure at the Earth's surface causes clear conditions.

    • In contrast, low pressure regions lead to cloudiness and precipitation.

  • Wind patterns around high and low pressure systems in the Northern Hemisphere:

    • Wind circulates counterclockwise around low pressure and clockwise around high pressure.

    • Combination of pressure gradient force, Coriolis, and friction explains observed wind directions.

Forces Acting on the Atmosphere

  • Four primary forces determining atmospheric behavior:

    • Pressure gradient force acts from high to low pressure.

    • Coriolis force affects motion across the rotating Earth.

    • Friction opposes the direction of flow.

    • Gravity pulls objects toward Earth's surface and intensifies in denser air regions.

    • Gravity has an acceleration of 9.8 \text{ m/s}^2.

Large Scale Atmospheric Circulation

  • Description of large-scale atmospheric circulation systems:

    • Air near the equator rises due to heating from solar radiation, causing convection.

    • This air diverges in the upper troposphere towards the poles.

    • The return flow occurs under the influence of the Coriolis effect, resulting in easterly winds near the equator and westerly winds at the mid-latitudes.

Circulation Cells and Atmospheric Dynamics

  • Three distinct circulation cells:

    • Hadley Cell: Air rises at the equator, moves north, and sinks at about 30 degrees north (subtropical latitudes).

    • Ferrel Cell: Acts as a transition between Hadley and Polar cells; characterized by westerly winds in mid-latitudes.

    • Polar Cell: Cold, dense air sinks at the poles, moving towards the equator at the surface.

Conclusion and Implications

  • Importance of understanding atmospheric circulation:

    • Changes in pressure systems influence local weather patterns and phenomena such as droughts in specific regions.

    • Exploration of future discussions on how these regions of pressure change with seasonal and global warming shifts.