4.6 El Niño and La Niña

El Niño and La Niña Overview

  • El Niño and La Niña are significant climatic phenomena affecting global weather patterns.

Key Features of El Niño and La Niña

El Niño

  • Characterized by a high-pressure system.

  • Alters the polar jet stream, resulting in unusual weather conditions.

  • Associated with increased wet conditions in some areas.

La Niña

  • Produces low-pressure systems which can lead to dry conditions.

  • Also affects the polar jet stream and the Pacific jet stream, leading to a varied storm track.

The Influence of Ocean Currents on Global Climate

  • Ocean currents significantly impact global climates through:

    • Heat emission into the atmosphere.

    • Affecting primary productivity in marine environments.

Drivers of Ocean Currents

Factors Influencing Ocean Currents

  • Ocean currents are influenced by several factors:

    • Temperature

    • Gravity

    • Prevailing winds

    • The Coriolis effect

    • Salinity

    • Locations of continents

  • Tropical surface waters warm, causing them to expand and rise (approximately 8 cm or 3 inches). This expansion leads to water moving away from the equator.

Role of Prevailing Winds

  • The movement of ocean surface waters is guided by prevailing winds:

    • In the Northern Hemisphere, winds push water from the north-east to the southwest.

Gyres and Water Circulation

  • Gyres are large-scale patterns of water circulation:

    • Clockwise in the Northern Hemisphere.

    • Counterclockwise in the Southern Hemisphere.

    • These gyres help redistribute heat throughout the atmosphere.

Upwelling Processes

  • Divergence of surface currents along continents (e.g., west coasts) leads to upwelling:

    • Deeper waters rise to replace displaced surface water.

    • Upwelled waters bring nutrients from the ocean bottom, supporting a rich ecosystem.

Thermohaline Circulation

  • Thermohaline circulation refers to a major oceanic current system:

    • Driven by differences in density based on temperature and salinity variations.

El Niño-Southern Oscillation (ENSO)

  • An event occurs every 3 to 7 years starting around December 25th.

Responding to Exam Questions

  1. Describe how gyres are formed:

    • Formed by the combination of wind patterns and the earth's rotation (Coriolis effect).

  2. Potential impact of climate change on thermohaline circulation:

    • Alterations in temperature and salinity patterns may disrupt current systems, affecting global climates.

  3. Role of salinity in driving deep ocean currents:

    • Changes in salinity levels affect water density, influencing the flow of deep ocean currents.

  4. Difference between El Niño and La Niña:

    • El Niño typically brings warmer ocean temperatures leading to wetter conditions, while La Niña results in cooler ocean temperatures and often drier conditions.