A tasty new flavour of the GENIE earth-system model,

applied to paleoclimates

1) Introduction and Motivation

2) The GENIE modelling framework

3) Results

Tuning the IGCM atmosphere

Ensemble of Last Glacial Maximum simulations

Moisture flux experiments with Goldstein

4) Conclusions and future work

D. Lunt (1), A. Yool (2), R.Marsh(2), P.Valdes(1) , and the GENIE team

(1) Bristol Research Initiative for the Dynamic Global Environment (BRIDGE), Bristol University, UK

(2) Southampton Oceanographic Centre, UK

d.j.lunt@bristol.ac.uk

www.genie.ac.uk

INTRODUCTION AND MOTIVATION

THE GENIE MODEL

Atmosphere IGCM EMBM Fixed

Land surface MOSES/

TRIFFID

Simple Fixed

Seaice Goldstein Slab Fixed

Ocean Goldstein Slab Fixed

Ice-sheet GLIMMER Energy-balance

Biogeochemistry BIO-GEM

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)

RESULTS(1) – Tuning the IGCM atmosphere

Results:

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!

RESULTS(1) – Tuning the IGCM atmosphere

IGCM untuned IGCM tuned

HadAM3

DJF surface temperature - NCEP

11% DJF17% JJA

RESULTS(1) – Tuning the IGCM atmosphere

IGCM untuned IGCM tuned

HadAM3

JJA precip - NCEP 0.1% DJF

10% JJA

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 modernRS –ve means modern more sensitive than LGM

RS calculated for 28 parameters, NH/SH DJF/JJA temp/precip +ve/-ve = 448 values.

RESULTS(2) – Ensemble of Last Glacial Maximum simulations

212 modern vs. 162 LGM. In particular, SH winter temperatures.

RESULTS(3) – Moisture flux experiments with Goldstein

Decreasing flux, Inreasing flux

Oort (modern)

Lohman (LGM)

IGCM (LGM)Miller+

Rusell (LGM)

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.

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!