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Tutorial I: Origin of Wind-Driven Ocean Circulation

Cédric Van Meerbeeck, Lic, MSc, PhD

Overview

  • Exploration of wind-driven ocean circulation, focusing on factors such as solar radiation, atmospheric circulation, and the Coriolis effect.

Surface Air Circulation

  • Mean Surface Wind (May NCEP/NCAR Reanalysis, 1979-1995)

    • Data representation showcasing global wind patterns over specified years.

    • Source: NOAA/NCEP/NCAR/The COMET Program.

Surface Ocean Circulation

  • Global Ocean Currents

    • Description of the significant ocean current systems that circulate water across the Earth's oceans.

    • Source: NGA/The COMET Program.

Similarity of Patterns

  • Mean Surface Wind and Global Ocean Currents

    • Observations of similarities between surface winds and ocean currents.

    • Source: NOAA/NCEP/NCAR/The COMET Program.

Key ConceptsOutline

  1. Solar radiation, global heat balance, and atmospheric circulation in a non-rotating Earth.

  2. Coriolis effect.

  3. Wind stress and ocean currents.

Solar Radiation and Earth's Heat Balance

  • Energy Density: Expressed in Watts/m².

    • Mean Annual Global Insolation: Visual representation showing solar radiation values.

    • Maximum energy values near the Equator and minimum values at the poles.

  • Annual Radiation Balance:

    • Annual outgoing radiation vs annual incoming radiation across different latitudes.

    • Indicate areas of net gain and net loss at various latitudes, e.g., Equator showing net gain, while poles show net loss.

Non-Rotating Earth - Global Air Circulation

  • Circulation Patterns:

    • Theoretical models of air movement influenced by solar radiation and Earth's heat imbalance.

  • Hadley Circulation:

    • Warm air rises around the Equator and cools, returning as surface winds, creating the Hadley cell structure.

Rotating Earth - Coriolis Effect

  • Coriolis Force:

    • Details how rotation of the Earth affects moving air and water, resulting in deflection patterns.

  • Wind Patterns:

    • Trade winds in tropics, Westerlies in mid-latitudes leading towards the poles; Doldrums at the equator indicating low wind.

Global Air Circulation Components

  • Hadley Cell:

    • Detailed description of wind flows:

    • Trade winds (NE and SE) converge at the equator.

    • Westerlies occur at mid-latitudes.

    • Polar easterlies influence polar regions.

Wind-Driven Currents

  • Wind Stress:

    • Process explained: Wind friction with ocean initiates movement, resulting in a surface current.

    • Current direction deviates from wind direction by 20° to 60°.

    • Example: Surface current direction is at a 45° angle to wind direction under ideal conditions.

The Ekman Spiral

  • Friction and Motion:

    • Surface water moves at a 45° angle; deeper water moves at a greater angle due to friction, leading to a net motion 90° from the wind direction as depth increases.

    • Illustrated through underwater flow dynamics across depths, showing how currents deviate further from wind as they descend.

Gyres and Surface Ocean Circulation

  • Gyres:

    • Explanation of major gyres in the ocean: North Atlantic, North Pacific, South Atlantic, South Pacific, and Indian Ocean currents, among others.

    • The role of gyres in global climate and ecosystem support.

Visual Representations

  • Various diagrams illustrate circulation models, current paths, and seasonal changes in air currents and pressures in the Earth's atmosphere.

Practical Applications

  • Exercises:

    • Sketching diagrams illustrating the Coriolis effect in the Southern Hemisphere.

    • Noting Ekman transport and upwelling/downwelling in relation to ocean currents, showcasing practical exercises for comprehension.

Additional Resources

  • Links for further exploration:

    • COMET Program links to ocean currents education.

Questions and Engagement

  • Open floor for questions, emphasizing the exploration of complex ocean-driven circulation mechanisms and their implications on climate and environment.