Pacific Decadal Oscillation (PDO)

Mains Paper 1 : Geographical Features & Their Location |

Note4Students

From UPSC perspective, the following things are important :

Prelims level : PDO

Mains level : Factors affecting Monsoon


News

Low monsoon rainfall in NE

  • Northeast India, one of the wettest places on the Earth has been experiencing rapid drying, especially in the last 30 years.
  • Some places which used to get as high as 3,000 mm of rain during the monsoon season have seen a drop of about 25-30%.
  • This decreasing monsoon rainfall is associated with natural changes in the subtropical Pacific Ocean.
  • The team used observed rainfall and sea surface temperature data for the period 1901-2014 for the study.
  • The results show out that the reduction in rainfall during a major part of the last 114 years may be associated with global man-made factors, while the trend during the last 36 years is associated with natural phenomena.
  • Only about 7% of the rainfall in this region is associated with local moisture recycling, which means that anthropogenic activities can affect only this small percentage.
  • So the rapid drying is a part of inter-decadal variability of monsoonal rainfall which is strongly associated with the PDO.

Pacific decadal oscillation (PDO)

  • PDO is a long-lived El Niño-like pattern of Pacific climate variability.
  • Both PDO and ENSO have similar spatial climate fingerprints yet the major difference is that PDO persists for 20-30 years while the typical ENSO persists for 6 to 18 months.
  • The PDO, like ENSO, consists of a warm and cool phase which alters upper level atmospheric winds.
  • During a “warm”, or “positive”, phase, the west Pacific becomes cooler and part of the eastern ocean warms; during a “cool” or “negative” phase, the opposite pattern occurs.
  • Shifts in the PDO phase can intensify or diminish the impacts of ENSO according to its phase.
  • If both ENSO and the PDO are in the same phase, it is believed that El Niño/La Nina impacts may be magnified.
  • This in turn affects the northeast Indian summer monsoon during its negative phase.
  • Conversely, if ENSO and the PDO are out of phase, it has been proposed that they may offset one another, preventing “true” ENSO impacts from occurring.
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