17 January 2018

How would the 21st-Century Warming Influence Pacific Decadal Variability and its Connection to North American Rainfall: Assessment Based on a Revised Procedure for IPO/PDO

Science

In this paper, we revisited the procedures currently used to derive the modes of the Interdecadal Pacific Oscillation (IPO) or the decadal Pacific Oscillation (PDO) in order to remove the non-linear effect the background warming on these two internal climate modes. We found the removal of the local ensemble mean time series is the most effective way to separate the internal variability and the forced response from the model data. After this revisit, we found that the revised IPO/PDO index is purely indicative of internal decadal variability. In the 21st century warmer climate, IPO/PDO has a weaker amplitude in space, a higher frequency in time, and a muted impact on global and North American temperature and rainfall

Impact

In reality and model simulations, the effects of the external forcings and the internal variability on the regional and global climate are entangled. How to effectively separate these effects is a significant challenge for us. Here we tried to find a better and unified way to derive the Interdecadal Pacific Oscillation (IPO) or Decadal Pacific Oscillation (PDO) for both 20th and 21st century climate. Our new methodology can be more effectively removing the forced responses in the climate system and enable us better understand the influence of the internal variability on the regional and global climate under a changing background climate.

Summary

The new methodology derived from this research provides a much better way to separate the influences of the external forcings and internal variability on the regional and global climate. Results show that in the future warmer climate, IPO/PDO has a weaker amplitude in space, a higher frequency in time, and a muted impact on global and North American temperature and rainfall.      

Contact
Aixue Hu
National Center for Atmospheric Research (NCAR)