The Indian Institute of Sciences (IISc) in Bengaluru has recently published a study examining the impact of the Equatorial Indian Ocean Oscillation (EQUINOO) on the Indian Summer Monsoon. The research suggests that the positive phase of EQUINOO is beneficial for this pivotal weather period. In the summer of 2019, for instance, despite an initial delay, the monsoon gathered momentum due to increased cloud formation, a characteristic feature of a positive EQUINOO phase.
A Background on the Equatorial Indian Ocean Oscillation (EQUINOO)
EQUINOO is an oscillatory pattern involving the interaction of cloud formation and rainfall over the Western Equatorial Indian Ocean (WEIO) and the Eastern Equatorial Indian Ocean (EEIO), situated west of Sumatra. This fluctuation process is contingent on the respective sea surface temperatures and the subsequent clouding events in these regions.
Understanding the Positive Phase of EQUINOO
In the positive phase of EQUINOO, the surface sea temperature in the WEIO is above 27.5 degrees Celsius. This leads to enhanced cloud formation, resulting in suppression of clouding over the EEIO. This elevated clouding activity at higher temperatures contributes significantly to the intensification of the summer monsoon in India.
Effects of the Positive Phase on Rainfall Over India
During the positive phase of EQUINOO, there is increased cloud formation and subsequent rainfall in the western part of the equatorial ocean near the African coast, whereas clouding and rainfall are notably less near Sumatra. The imbalance caused by this distribution pattern tends to result in substantial rainfall over most regions of India.
| Equatorial Indian Ocean Oscillation Phase | Sea Surface Temperature (WEIO) | Cloud Formation (WEIO) | Cloud Formation (EEIO) |
|---|---|---|---|
| Positive | Above 27.5°C | Enhanced | Suppressed |
| Negative | Below 27.5°C | Suppressed | Enhanced |
Effect on the Indian Summer Monsoon
The study from the IISc, Bengaluru suggests that the positive phase of EQUINOO has a vital role in the intensification and success of the Indian Summer Monsoon. The increase in clouding and rainfall activity in the WEIO contributes to the triggering and amplification of the monsoon, notwithstanding initial delays. Thus, understanding the EQUINOO patterns can help predict monsoon dynamics, aiding better preparedness for this crucial climatic event.
