Decadal predictions using the higher resolution HiGEM climate model Len Shaffrey, National Centre for Atmospheric Science, University of Reading

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1 Decadal predictions using the higher resolution HiGEM climate model Len Shaffrey, National Centre for Atmospheric Science, University of Reading Dave Stevens, Ian Stevens, Dan Hodson, Jon Robson, Ed Hawkins, Ag Stephens, Doug Smith, Irene Polo, Rowan Sutton, Alan Iwi, Grenville Lister

2 Decadal Prediction Days Months Years Decades Centuries? Weather Forecasting Seasonal Forecasting Climate Model Projections Initial Value Predictability Boundary Value Predictability

3 Decadal Prediction Days Months Years Decades Centuries Decadal Prediction Weather Forecasting Seasonal Forecasting Climate Model Projections Initial Value Predictability Boundary Value Predictability

4 The higher resolution HiGEM climate model HiGEM based on the Met Office Hadley Centre coupled ocean-atmosphere climate model, HadGEM1 The atmosphere has a resolution of 1.25 o x0.83 o and 38 levels in the vertical The ocean resolution is 1/3 o x1/3 o (an eddy-permitting resolution) and 40 levels in the vertical, Shaffrey et al. (2009) Increasing resolution leads to many improvements including: Reduced SST biases (Roberts et al. 2009); ENSO, NH planetary waves (Shaffrey et al. 2009); representation of stratocumulus decks (Toniazzo et al. 2010); and extratropical storms (Catto et al. 2010, 2011).

5 HiGEM SST biases HadGEM1.2 HiGEM year annual mean HadGEM1.2 and HiGEM1.2 SST errors relative to Reynolds SSTs. Units K Shaffrey et al. 2009, J. Climate.

6 Science Questions How skilful are decadal predictions with HiGEM? Does having an improved representation of climate lead to improved forecast skill?

7 Decadal Predictions using HiGEM CMIP5 10 year hindcasts (start dates: 1960, 1965, , 2005) with 4 members with Historical RCP forcing until 2005 and RCP4.5 after 2005 Initialisation based on the Met Office DePreSys anomaly assimilation. This initialises observed anomalies of ocean Temperature and Salinity dt / dt assim = - T mod T obs / τ where T mod and T obs are model and observed temperature anomalies, and τ is a relaxation timescale. τ is 15 days. Right: Near-global SST from HadISST, EN3 and the HiGEM ASSIM experiment (Shaffrey et al. 2016, Climate Dynamics)

8 Surface Air Temperature Forecasts HiGEM DF SAT ACC skill HiGEM DF - NOASSIM SAT ACC skill Upper: SAT ACC correlation skill for the HiGEM decadal forecasts for lead times of 1, 2-3, 4-6 and 7-10 years. Lower: Significant differences in correlation skill for the HiGEM decadal forecasts minus the HiGEM NOASSIM transient runs Shaffrey et al. 2016, Climate Dynamics

9 Surface Air Temperature Forecasts HiGEM DF SAT ACC skill HiGEM DF - NOASSIM SAT ACC skill Upper: SAT ACC correlation skill for the HiGEM decadal forecasts for lead times of 1, 2-3, 4-6 and 7-10 years. Lower: Significant differences in correlation skill for the HiGEM decadal forecasts minus the HiGEM NOASSIM transient runs Shaffrey et al. 2016, Climate Dynamics

10 Decadal Predictions using HiGEM Anomaly correlation for the Subpolar Gyre (Atlantic SSTs: 50N to 65N) for the HiGEM DF (red), the HiGEM transient experiments sampled for the same periods as the decadal forecasts (green) and HiGEM NOASSIM transient experiments sampled every year (green dashed). Red circles indicate 90% significance. Shaffrey et al. 2016, Climate Dynamics

11 Subpolar Gyre Predictions using HiGEM Time-series of North Atlantic subpolar gyre 500m ocean heat content anomalies from observations (black), individual HiGEM decadal forecasts (blue) and ensemble mean forecast (cyan). Robson et al. 2016, in preparation.

12 10 22 J Temperature K Decadal Predictions using HiGEM Upper: Time-series of SPG 500m temperatures for observations (black), transient experiments (blue) and 1995 HiGEM decadal predictions. Year Robson et al. 2016, in preparation. Time-series of integrated temperatures fluxes in the SPG for the 1995 HiGEM decadal predictions. Total tendency (black), advective fluxes (blue), surface flux (purple), convective flux (ref) and oceanice fluxes (yellow).

13 Decadal Predictions using HiGEM SAT anomalies from the HiGEM decadal predictions (left); HiGEM transient experiments (middle) and observations (right). Additional HiGEM forecasts every years from from and using lead times from years 1 to 5.

14 Decadal Predictions using HiGEM Mean Sea Level Pressure (lower) and SAT (upper) anomalies from the HiGEM decadal predictions (left); HiGEM transient experiments (middle) and observations (right).

15 Improvements in forecast skill? HiGEM DF SAT ACC skill HiGEM DF - HadCM3 SAT ACC skill Upper: SAT correlation skill for the HiGEM decadal forecasts for lead times of 1, 2-3, 4-6 and 7-10 years. Lower: Significant differences in correlation skill from for the HiGEM decadal forecasts minus the CMIP5 DEPRESYS HadCM3 forecasts Shaffrey et al. 2016, Climate Dynamics

16 Decadal Predictions using HiGEM How skilful are decadal predictions with HiGEM? - Years 1-3: Skill in Atlantic, W. Pac and W. Europe SAT - Years 4-10: Skill in Atlantic, W. Pac and NH land SAT - Increases in skill due to initialisation, especially in the N. Atlantic Subpolar Gyre for years Changes in the SPG driven by ocean advection. Does having an improved representation of climate lead to improved forecast skill? - Incremental increase in skill compared to CMIP5 HadCM3 Depresys but, HiGEM is a lot more computationally expensive

17 ENSO in HiGEM DJF El Nino SST Composites Observations HiGEM1.2 HadGEM1.2 Shaffrey et al. 2009, J. Climate

18 A test: The 97/98 El Nino A test of the HiGEM-DP system, forecasting the 1997/1998 ENSO from Dec 1996 Nino3.4 SST anomalies from observations (colour) and five HiGEM Dec 1996 hindcasts (thin black) and ensemble mean (thick black)