Initialized decadal climate predictions focusing on the Pacific Gerald Meehl

Transcription

1 Initialized decadal climate predictions focusing on the Pacific Gerald Meehl National Center for Atmospheric Research Boulder Colorado

2 Following Zhang, Wallace and Battisti (1997) the Interdecadal Pacific Oscillation (IPO, Power et al., Folland et al. 1999) defined for entire Pacific; the Pacific Decadal Oscillation (PDO, Mantua et al. 1997, BAMS) defined for the North Pacific but patterns are comparable (Han et al 2014) Climate model simulations indicate IPO is internally generated Observations 13 year low pass IPO phase: Positive Unforced model control run (CCSM4) 13 year low pass Negative Positive Negative Big hiatus (Han et al., Cli.Dyn., 2014) Early 2000s slowdown Mid 70s Shift The observed IPO pattern resembles internally generated decadal pattern from an unforced model control run (pattern correlation= +0.63) (Meehl et al., 2009, J. Climate; Meehl and Arblaster, 2011, J. Climate; Henley et al., Env. Res. Lett., 2017)

3 There is skill in predicting Pacific SSTs associated with the IPO in initialized hindcasts in CCSM4 To guard against false alarms in future predictions: look at hindcasts of the IPO pattern of SSTs in the tropical Pacific (year 3 7 average predictions, each initial year from 1960, 10 ensemble members for each initial year prediction) The model shows significant skill except for the early 1970s and early 1990s when the post eruption sequence of Pacific SSTs after Fuego and Pinatubo did not match the ensemble average model response to the forcing (Agung and El Chichon better matched the model hindcasts) (Meehl et al., 2015, GRL) (Meehl, Hu, Teng, 2016, Nature Communications)

4 Could ENSO events on the interannual timescale trigger decadal shifts of the IPO?

5 Off equatorial ocean heat content in the tropical western Pacific can provide the conditions for ENSO events to trigger an IPO transition (Meehl, Hu, Teng, 2016, Nature Communications)

6 Nino3.4 SSTs, initialized January 1976 (black: observed; red: model initialized in Jan 1976) Initialized prediction of mid 1970s shift of IPO to positive associated with prediction of El Niño 3 7 year prediction for (initialized in Jan 1976) Pattern correlation = +0.81

7 Nino3.4 SSTs, initialized January 1996 (black: observed; red: model initialized in Jan 1996) Initialized prediction of lat 1990s of IPO to negative associated with prediction of La Niña 3 7 year prediction for (initialized in Jan 1996) Pattern correlation = +0.59

8 Model initialized in 2013 predicts small warming in 2014 followed by larger El Niño in Prediction (initialized in 2013) for years 3 7 ( ) shows transition to positive phase of the IPO (top) that is quite different from persistence (middle) or uninitialized (bottom) Initialized hindcasts show model qualitatively captures ENSO evolution in eastern equatorial Pacific and IPO transitions associated with offequatorial western Pacific ocean heat content anomalies (Meehl, G.A., A. Hu, and H. Teng, 2016, Nature Comms.)

9 Prediction initialized in 2013 (for the period ) produces larger rates of global warming associated with positive IPO compared to previous negative phase of IPO Predicted rate of global warming from 2013 initial year greater than during early 2000s slowdown and greater than uninitialized: Decadal GMST trend increases for predicted positive IPO phase in Observed: : +0.08±0.05 C/decade Predicted: : +0.22±0.13 C/decade Uninitialized : +0.14±0.12 C/decade Initialized prediction a factor of 3 larger than observed trend over observed early 2000s slowdown, and about 60% bigger than uninitialized (Meehl, G.A., A. Hu, and H. Teng, 2016, Nature Comms.)

10 Conclusions: There is evidence from initialized hindcasts that the IPO phase in the Pacific can be predicted (volcanoes complicate hindcast verification) Physical basis for prediction skill: Initialized hindcasts show model qualitatively captures eastern equatorial Pacific ENSO evolution that could trigger decadal timescale IPO transitions associated with off equatorial western Pacific ocean heat content anomalies The year 3 7 average prediction ( ) from the 2013 initial state shows a small El Niño in 2014, and a larger El Niño in , a transition to the positive phase of the IPO from the previous negative phase, and a resumption of larger rates of global warming consistent with a positive IPO phase