Pcific Decadal Oscillation

Pcific Decadal Oscillation

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 term 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.

Pcific Decadal Oscillation(PDO):

• PDO is a long lived El Nino 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.
• Shift in 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 ElNino/La Nina impacts may be magnified.
• This in turn affects the northeast indian summer monsson 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 occuring.