Pacific Decadal Oscillation (PDO)
The Pacific decadal oscillation (PDO) is a robust, recurring pattern of ocean-atmosphere climate variability centered over the mid-latitude Pacific basin.
The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20°N.
PDO is a long-term ocean fluctuation of the Pacific Ocean, which waxes and wanes approximately every 20 to 30 years.
Just like El Nino/La Nina in the tropical Pacific, PDO has a signature for a longer time (on the decadal scale) in the sea surface temperatures and its interaction with the atmosphere.
The PDO consists of a warm and cool phase which alters upper-level atmospheric winds.
The PDO can remain in the same phase for 20 to 30 years.
PDO phase can have significant implications for the global climate, affecting Pacific and Atlantic hurricane activity, droughts and flooding around the Pacific basin, the productivity of marine ecosystems, and global land temperature patterns.
Pacific Decadal Oscillation (PDO) and the frequency of equatorial-origin cyclones
The PDO has different phases—positive and negative.
A study (published in the journal Nature Communications) found that when the PDO is in a positive or ‘warmer’ phase, there are fewer tropical cyclones originating near the Equator.
Conversely, when the PDO enters a cooler, negative phase, as it has since 2019, it may lead to an increase in such cyclones.
How does global warming interact with PDO in influencing cyclone frequency?
The study suggest that the combination of global warming and the cyclical nature of PDO could make tropical cyclones originating near the Equator more frequent in the coming years.
Global warming may increase sea surface temperatures, which, coupled with a negative phase of PDO, could create conditions more conducive to cyclone formation and intensification.
However, unlike an ENSO, 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.
According to the study, ENSO with a positive PDO generally leads to less rain in India, but when linked with a negative PDO, it brings more rain to the country.
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