The El Nino-Southern Oscillation (ENSO) is a complex climate phenomenon that affects weather patterns and sea surface temperatures in the equatorial Pacific Ocean. UPSC Exam requires comprehensive understanding of ENSO, its different phases, and its impact on global weather systems. Here is a brief knowledge.
El Nino Phase
During El Nino, the trade winds weaken or reverse, allowing warm water to move eastward across the Pacific. This redistribution of warm water alters atmospheric circulation patterns and can have widespread effects on global weather. Key characteristics of the El Nino phase include:
- Abnormally warm sea surface temperatures in the eastern equatorial Pacific.
- Weakened trade winds and reduced upwelling of cold, nutrient-rich waters.
- Increased rainfall over the central and eastern Pacific, leading to droughts in some regions.
- Disrupted weather patterns worldwide, including increased storm activity in the Pacific and suppressed Atlantic hurricane activity.
La Nina Phase
La Nina is the opposite phase of El Nino, characterized by cooler-than-average sea surface temperatures in the eastern equatorial Pacific. It influences global weather patterns differently from El Nino. Key characteristics of the La Nina phase include:
- Cooler sea surface temperatures in the eastern equatorial Pacific.
- Strengthened trade winds and enhanced upwelling of cold, nutrient-rich waters.
- Increased rainfall over the western Pacific and Indonesia, potentially causing flooding.
- Altered weather patterns, including a higher likelihood of tropical cyclone formation in the Atlantic basin and decreased storm activity in the Pacific.
Southern Oscillation Index (SOI)
The Southern Oscillation Index (SOI) is a widely used measure of the atmospheric pressure difference between Tahiti and Darwin. It provides insight into the strength and phase of ENSO. Positive values indicate the presence of La Nina, while negative values suggest El Nino conditions. The SOI is an essential tool for monitoring and predicting ENSO events.
Walker Circulation and ENSO
The Walker Circulation is an east-west atmospheric circulation pattern in the tropical Pacific Ocean. During normal conditions, the trade winds blow from east to west, pushing warm surface waters toward the western Pacific. This process, known as upwelling, brings cold, nutrient-rich waters to the surface in the eastern Pacific. However, during El Nino, the Walker Circulation weakens, disrupting the normal east-west flow and leading to the accumulation of warm water in the central and eastern Pacific.
Teleconnections and ENSO
ENSO can exert influence on weather patterns in regions far from the tropical Pacific through teleconnections. These teleconnections are large-scale atmospheric linkages that connect ENSO to climate anomalies in different parts of the world. Examples of teleconnections include the Pacific Decadal Oscillation (PDO), which influences the North Pacific, and the Indian Ocean Dipole (IOD), which affects weather patterns in the Indian Ocean region.
Table: Key Data on El Nino-Southern Oscillation
| Term | Definition |
| El Nino | A phase of ENSO characterized by the abnormal warming of sea surface temperatures in the eastern equatorial Pacific Ocean. It can cause significant disruptions to global weather patterns. |
| La Nina | The opposite phase of El Nino, featuring cooler-than-average sea surface temperatures in the eastern equatorial Pacific Ocean. It also influences weather patterns but in a different manner. |
| Southern Oscillation Index (SOI) | An index that measures the atmospheric pressure difference between Tahiti and Darwin. It indicates the strength and phase of ENSO. Positive values represent La Nina, while negative values represent El Nino. |
| Walker Circulation | The east-west atmospheric circulation pattern in the tropical Pacific Ocean, driven by differences in air pressure. It plays a crucial role in the development and maintenance of ENSO. |
| Teleconnections | The influence of ENSO on weather patterns and climate anomalies in regions far from the tropical Pacific. Examples include the Pacific Decadal Oscillation (PDO) and the Indian Ocean Dipole (IOD). |
