According to a research paper, a combination of global warming and a cyclical event called the Pacific Decadal Oscillation (PDO) that repeats every 20-30 years, could make equatorial-origin tropical cyclones or more frequent in the coming years.
Key points
- The research study was published in the journal Nature Communications titled “Pacific Decadal Oscillation Causes Fewer Near-Equatorial Cyclones in the North Indian Ocean”.
- The low-latitude cyclones or Tropical cyclones that originate near the Equator (originating between 5°N and 11°N) have been unusually subdued in recent decades. The last major cyclone of this kind in the Indian neighbourhood was the 2017 Cyclone Okchi which devastated Kerala, Tamil Nadu and Sri Lanka.
- PDO is a long-term ocean fluctuation of the Pacific Ocean. The PDO waxes and wanes approximately every 20 to 30 years. It has a ‘cool’ and ‘warm’ phase.
- The last PDO phase shift was in 2014, when it turned strongly positive (warm). In the ‘warm’ or ‘positive’ phase, the west Pacific Ocean becomes cool and the wedge in the east warms.
- The number of such equatorial-origin cyclones was 43% fewer in 1981-2010 compared with 1951-1980, and this was because the PDO was in a ‘warmer’ or positive phase.
- A warming of the Central Equatorial Pacific, called an El Nino, frequently corresponds to reduced rainfall over India whereas cooler-than-normal temperatures, or a La Nina, is linked to excessive rainfall.
- This pattern collectively called the El Nino Southern Oscillation (ENSO) phenomenon, repeats in the Pacific over two-seven years.
- However, the PDO isn’t an annual occurrence and, on average, corresponds to a warmer than average Western Pacific Ocean and relatively cooler Eastern Pacific.
- Unlike an ENSO, whose stage can be determined any year, a ‘positive’ or ‘warmer phase’ of a PDO can be known only after several years of measuring ocean temperatures and their interaction with the atmosphere.
- In 2019, the PDO entered a cooler, negative phase and if it remains so, could mean more tropical cyclones in the post-monsoon months that originate near the equator. It’s usually rare for cyclones to form near the Equator but when the waters are warm, they can gain more moisture and rise in intensity.
- ENSO with a positive PDO is generally not good, but when linked with a negative PDO, brings more rain to India.
