1. A tasty new flavour of the GENIE earth-system model, applied to paleoclimates
D. Lunt (1), A. Yool (2), R.Marsh(2), P.Valdes(1) , and the GENIE team
Bristol Research Initiative for the Dynamic Global Environment (BRIDGE), Bristol University, UK
Southampton Oceanographic Centre, UK
Introduction and Motivation
The GENIE modelling framework
Results
Tuning the IGCM atmosphere
Ensemble of Last Glacial Maximum simulations
Moisture flux experiments with Goldstein
4) Conclusions and future work

2. INTRODUCTION AND MOTIVATION

3. THE GENIE MODEL IGCM EMBM Goldstein Slab Atmosphere Fixed Land surface
MOSES/
TRIFFID
Simple
Seaice
Goldstein
Slab
Ocean
Ice-sheet
GLIMMER
Energy-balance
Biogeochemistry
BIO-GEM

4. RESULTS(1) – Tuning the IGCM atmosphere
Methodology:
(1) Identify tuneable parameters (29) .
(2) Carry out an initial control simulation.
(3) For each of the 29 tuneable parameters, carry out 4 simulations, 2+ve pertubations, 2-ve pertubations.
(4) Calculate a skill score for every simulation (based on mean error cf NCEP temp. and precip., DJF and JJA).
(5) Create a new control simulation by applying the best 5 pertubations to the previous control.
(6) Repeat from (2)

5. RESULTS(1) – Tuning the IGCM atmosphere
Most improving parameters:
1st iteration: humidity at which large scale-clouds form.
2nd iteration: bulk aerodynamic coefficient for L,H
Other improving parameters:
e.g. roughness length of ocean, typical timescale for convection.
Also, turning off the convection scheme improves precip!

6. RESULTS(1) – Tuning the IGCM atmosphere
IGCM untuned
IGCM tuned
DJF surface temperature - NCEP
11% DJF
17% JJA
HadAM3

7. RESULTS(1) – Tuning the IGCM atmosphere
IGCM untuned
IGCM tuned
JJA precip - NCEP
0.1% DJF
10% JJA
HadAM3

8. RESULTS(2) – Ensemble of Last Glacial Maximum simulations
Is the LGM or the modern climate more sensitive to uncertainties in internal model parameters?
59-member ensemble of LGM and modern simulation pairs.
Each of 58 pairs represent a +ve or –ve anomaly of one of 29 parameters. Plus control pair.
PMIP boundary conditions except ICE5G ice-sheets for LGM.
‘Relative sensitivity’, RS, parameters calculated for each pair
RS=log( abs( (LGM-LGMcont)/(PD-PDcont) ) )
RS +ve means LGM more sensitive than modern
RS –ve means modern more sensitive than LGM
RS calculated for 28 parameters, NH/SH DJF/JJA temp/precip +ve/-ve
= 448 values.

9. RESULTS(2) – Ensemble of Last Glacial Maximum simulations
212 modern vs. 162 LGM. In particular, SH winter temperatures.

10. RESULTS(3) – Moisture flux experiments with Goldstein
Decreasing flux, Inreasing flux
Lohman (LGM)
Oort (modern)
IGCM (LGM)
Miller+Rusell (LGM)

11. FUTURE WORK
To complete the coupling of the IGCM atmosphere to Goldstein ocean to MOSES/TRIFFID land surface to GLIMMER ice-sheet.
Integrate Tiedtke convection scheme into IGCM.
Tune the modern model components with EnKF scheme.
Long-term transient simulations (glacial/interglacial cycle)
Short-timescale experiments, e.g. 8.2 kyrBP holocene cooling event.

12. CONCLUSIONS
IGCM has been tuned with sledgehammer approach. Temperature responds well, precip not much improved – need to replace with new scheme.
Modern atmosphere is more sensitive to internal model parameters than the LGM.
Goldstein ocean sensitive to LGM Atlantic-Pacific freshwater flux. Coupling to IGCM will allow an investigation of the ocean’s response to interannual, decadal, and centennial variations in this flux.
Many experiments/investigations to be carried out soon!