Impact of initial conditions and atmospheric model resolution in predicting

“Climate Hiatuses”

Susanna Corti ISAC - CNR

Thanks to:

Magdalena Balmaseda, Sarah Keeley, Kristian Mogesen, Tim Stockdale, Antje Weisheimer at ECMWF

Jost von Hardenberg and Paolo Davini at ISAC-CNR

Initialized and uninitialized predictions

Cartoon from Corti et al. 2015 – Journal of Climate

Experiments

SWAP experiments Hindcasts where the initial conditions and the forcing are swapped. Three sets:

1988-1994 [I. C. from Nov1988 and F from 1994 and I.C. from Nov1994 and F from 1988]

1988-2002 [I. C. from Nov1988 and F from 2002 and I.C. from Nov2002 and F from 1988]

1994-2002 [I. C. from Nov1994 and F from 2002 and I.C. from Nov2002 and F from 1994]

ECMWF Special Project “Sensitivity of multi-annual forecasts to model resolution”

Control: IFS Cycle 40R1 at T255 with 91 levels in vertical (this is the current resolution of the ECMWF System4 coupled model for seasonal predictions). NEMO-ORCA1 (~1˚). LIM2 – CMIP5 forcing (but no volcanoes) Full Initialisation – ECMWF ORAS4 Reanalysis – ERA-Interim A-HiRes: IFS Cycle 40R1 at T511 with 91 levels vertical. 3-year long hindcasts 22 starting dates (Nov 1988 - Nov 2009) with 5 ensemble members.

Year 1

Control ACC TAS HiRes

Years 2-3

TAS – Global – First year - CTL

TAS – Global – First year - HiRes

TAS – Global – years 1-3 - CTL

TAS – Global – years 1-3 - HiRes

TAS – Global – years 2-3 - CTL

TAS – Global – years 2-3 - HiRes

TAS – Global – year 1 – HiRes Swapping forcing between 1988 and 2002

TAS – Global – year 1 – HiRes Swapping forcing between 1994 and 2002

TAS – Global – year 1 – HiRes Swapping forcing between 1988 and 1994

TAS – Global – years 2-3 – HiRes Swapping forcing between 1988 and 2002

TAS – Global – years 2-3 – HiRes Swapping forcing between 1994 and 2002

TAS – Global – years 2-3 – HiRes Swapping forcing between 1988 and 1994

North Atlantic

Year 1

Years 2-3

Years 1-3

North Atlantic

Year 1

Years 2-3

Years 1-3

North Atlantic

Year 1

Years 2-3

Years 1-3

North Atlantic

Year 1

Years 2-3

Years 1-3

North Atlantic

Year 1

Years 2-3

Years 1-3

Year 1

Years 2-3

Years 1-3

North West Pacific

Year 1

Years 2-3

Years 1-3

North West Pacific

North West Pacific Year 1

Years 2-3

Years 1-3

North West Pacific Year 1

Years 2-3

Years 1-3

North West Pacific Year 1

Years 2-3

Years 1-3

Summary Positive impact of increased atmospheric model horizontal resolution on: Multi-year predictions (yr 2-3 average) over North-Atlantic SPG, Southern Europe, North Africa and North Pacific for Near surface air Temperature and Mean sea level pressure Over time scales longer than about 1 yr, the predictability of surface air temperatures on a global scale arises mainly from the external forcing. However, the correct initialization has a longer impact on surface air temperature predictability over specific regions such as the North Atlantic and the northwestern Pacific. When forcing and initial conditions are swapped between Nov2002 and Nov1988 (or Nov1994) the forcing start to affect the predictions on a global domain since the first year. Over the North Atlantic region it was found a high sensitivity to changes in the forcing for the forecasts initiated in Nov1994 (when the forcing is swapped with Nov1988). Over the northwestern Pacific the forecast was more sensitive to swapping 1988 and 1994 with 2002