The Indian Ocean Dipole (IOD) refers to the oscillation of sea-surface temperatures between warm and cool phases in the Indian Ocean basin, particularly to the south of Sri Lanka. This climatic phenomenon plays a crucial role in influencing weather patterns across the region.
A positive IOD event is characterized by warmer sea-surface temperatures on the western side of the Indian Ocean basin. This condition significantly affects weather patterns and is often associated with the enhancement of India's South-West monsoon, leading to increased rainfall in certain areas.
The IOD index is a quantitative measure of the deviation of sea-surface temperatures from the established norm. It is expressed in degrees Celsius (°C) and is essential for determining the intensity of the IOD event.
The positive IOD threshold is typically around +0.4°C, which represents the minimum deviation from the norm required for an IOD event to be classified as positive. Crossing this threshold indicates potential climatic changes that can affect various regions.
During positive IOD events, there is often an enhancement of the South-West monsoon in India, which can lead to increased rainfall in specific regions, significantly impacting agriculture and water resources.
The Australian Bureau of Meteorology has forecasted a potential IOD event for 2023, suggesting it might be shorter in duration compared to the strong event recorded in 2019. However, some climate models indicate the possibility of a relatively strong event occurring.
The 2019 IOD event was one of the most potent on record, with peak index values nearing +2.0°C. In contrast, predictions for the 2023 event suggest a peak value around 1.5°C, indicating a less intense event.
The IOD influences rainfall patterns across various regions, including Sri Lanka, parts of Kerala and Tamil Nadu, Nepal, Bhutan, East Asia, and Central and West Africa. During a positive IOD event, some areas may experience wetter-than-normal conditions.
In Australia, a positive IOD event can lead to lower rainfall, a delayed onset of the monsoon, and reduced tropical cyclone activity from October to December. When combined with El Nino, the impacts may become more severe, extending further into the wet season.
Positive IOD events can have diverse implications for various regions, affecting monsoon patterns, rainfall distribution, and even cyclone activity. The specific outcomes depend on the interaction with other climate factors and the unique geographic characteristics of each region.
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