Ocean Currents and Geostrophic Flow

Overview of Ocean Currents

• Ocean water is constantly moving.
• Major surface currents are driven by wind energy transferred through friction.
• The direction of water movement is influenced by:
  • Coriolis deflection
  • Other currents
  • Geological features such as continents and island arcs.

Central Ocean Gyres

• Each large ocean basin features a central gyre.
• Gyres circulate water in large, roughly circular patterns.
• Despite appearance, winds do not directly create these currents.
• Earth's rotation complicates the gyre formation process.

Geostrophic Flow

• This is a type of movement influenced by Earth's rotation.
• Forces are weak relative to Earth's rotation, making Coriolis deflection a key factor.
• Example given:
  • A ball on an inclined plane influenced more by gravity.
  • When slope and ball size decrease, Coriolis deflection dominates.
  • The ball moves across or around the plane instead of down.

Hills of Water and Geostrophic Flow

• Ocean surface has water hills, particularly at mid-latitudes.
• These form due to the change from easterly trade winds to westerlies.
• Surface currents are deflected 90 degrees by Coriolis effect, leading to Ekman transport.
• Water piles up creating small hills, about a meter high.
• Pressure gradient forms due to elevation differences.
• Weak pressure gradient due to extended area allows for geostrophic flow.
  • Water flows along lines of equal pressure, not down the hill.

Formation of Ocean Gyres

• Starts with trade wind-driven Ekman transport piling water in basin centers.
• This creates a pressure gradient that pushes water away.
• Small pressure gradient spread over a large area results in geostrophic flow.
• Water circulates around the pile in a stable manner.

Conclusion

• Stable circulation of water around the gyre is maintained by a balance of Ekman transport energy and pressure gradient force.

Additional Information

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• Further learning resources are suggested for Ekman transport and the Coriolis effect.