Climate Dynamics: El Niño, Weather Risks, and Global Circulation

El Niño and La Niña Phenomena

Causes of El Niño

• Global warming, which reduces the thermal contrast between the two shores of the Pacific. This decreases the intensity of trade winds and ocean currents.
• Increased volcanic activity of oceanic ridges, which raises the temperature of the ocean.

When the trade wind subsides and does not blow westward, upwelling ceases. This leads to storms in the arid zones of Peru and Chile. The El Niño effect implies that fisheries production declines, and the global ocean temperature rises. Storms and rainfall increase in Peru, California, and East Africa, while droughts occur in Brazil and the Philippines.

La Niña

La Niña is characterized by an exaggeration of normal conditions. The trade winds blow harder, coastal waters are colder than normal, and there is increased rainfall in the Eastern Pacific and droughts in South America.

Understanding Climate and Weather

Climate Definition

Climate is a set of weather phenomena that characterizes the atmospheric situation and weather in a particular place on Earth. It is studied over periods of 30 years.

Climatic Elements and Factors

• Latitude
• Continentality
• Elevation
• Orientation with respect to winds

The Foehn Effect

When a moist air mass hits the windward slope of a mountain, it rises, and condensation occurs, leading to precipitation. This is known as orographic precipitation. Downwind, the air is already dry, creating what is visually known as a rain shadow.

Weather Risks

• Risk Due to Rain

  • Polar fronts
  • Snowstorms
  • Cold Drop (Gota Fría): In late summer and early autumn, cold air descends from high altitudes, spiraling due to warm surface air, causing intense storms.

• Risk Due to Floods

• Risk Due to Winds

Global Atmospheric Circulation

In equatorial areas, intense solar radiation causes strong vertical convection, leading to the formation of equatorial storms. In polar regions, intense cold creates polar anticyclones.

Theoretically, a surface wind would flow directly from polar anticyclones to equatorial storms, and similarly at higher altitudes. However, the Coriolis effect causes this transport to occur through three main cell types:

Atmospheric Circulation Cells

• Convective Cells

  These are closed systems of moving air, involving vertical and horizontal winds.

• Hadley Cell

  This is the most energetic cell, driven by the vertical incidence of solar radiation. Hot air rises from equatorial storms to the tropopause and then moves horizontally towards the poles. Due to the Coriolis effect, winds are deflected, and air descends as part of the subtropical anticyclones in desert areas. The Azores anticyclone and the continental Sahara anticyclone influence the climate of the Canary Islands.

• Polar Cell

  Surface winds originating from the polar anticyclones flow towards 60 degrees latitude, where they rise to form subpolar storms. These storms can extend to 40-30° north-south in winter.

• Ferrel Cell

  This cell is located between the Hadley and Polar cells, receiving surface winds from the west, blowing from subtropical high-pressure zones (deserts) towards polar regions.