Why in news?  According to study, Cyclone frequency may rise over Indian coast from the warming of Pacific ocean

Highlights:

• Tropical cyclones that originate near the Equator have been unusually decreased in recent decades.
• The study was inspired from cyclone Ockhi (2017) which devastated Kerala and formed near the equator that is very rare tropical cyclones (TCs) form near the equator

What are the major findings of the report?

• The number of equatorial-origin cyclones was 43% less in the period from 1981 to 2010 compared with 1951 to 1980, and this was because the PDO was in a ‘warmer’ or positive phase.
• A combination of global warming and Pacific Decadal Oscillation can lead to more cyclones
• Low-latitude cyclones, those forming in the near-equatorial region, will increase in frequency and intensity in the coming years during a favourable phase of a Pacific climate phenomenon called the Pacific Decadal Oscillation
• Pacific Decadal oscillation results in more cyclones that will be forming closer to India’s Peninsular coast for the North Indian Ocean region because as it entered negative phase that favour low latitude cyclones.

What is Pacific Decadal oscillation ?

• It is a robust, recurring pattern of ocean-atmosphere climate variability centered over the mid-latitude Pacific basin. It waxes and wanes approximately every 20 to 30 years
• The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20°N
• 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.
• A positive, or warm phase PDO, produces climate and circulation patterns that are very similar to El Niño. Likewise, a negative, or cool phase PDO, produces climate and circulation patterns similar to La Niña
• The change in location of the cold and warm water masses alters the path of the jet stream.

How PDO is different from El Nino-Southern Oscillation (ENSO)?

• The difference between the PDO and ENSO is the time scale.
• ENSO events tend to persist on the order of one year, the PDO signature can last up to 30 years
• PDO primarily affects the North Pacific region, its effects can be felt near the equator. Conversely, ENSO primarily affects the climate of lower latitudes, but its secondary effects are felt in the North Pacific

Why Cyclones rarely form near the equator?

• Tropical cyclones are difficult to form over a region within 5 degrees of latitude from the Equator because the Coriolis force there is too small to generate a vortex.