High resolution simulations of Last Glacial Maximum climate over Europe

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High resolution simulations of Last Glacial
Maximum climate over Europe a solution to
discrepancies with observations?
D. Lunt (1), A. Jost (2), P. Valdes (1), A.
Abe-Ouchi(3) , M. Kageyama(2) , G. Ramstein,(2)

1. Bristol Research Initiative for the Dynamic
   Global Environment (BRIDGE), Bristol University,
   UK
2. LSCE, Gif-sur Yvette, France
3. CCSR, Tokyo University, Japan

• Motivation
• Experiment aims and description of models
• Results
• LMDz, CCSR, HadRM compared to observations
• Discussion of results
• 4) Conclusions and future work

d.j.lunt_at_bristol.ac.uk
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MOTIVATION (previous work by Kageyama et
al) Intercomparison of PMIP model results. No
model simulated enough cooling over Europe at the
LGM, compared to pollen data. Perhaps due to
relatively low resolution (also, ice-sheet
reconstruction, dust, vegetation changes).
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EXPERIMENT AIMS MODELS USED

• Does increasing the horizontal resolution of
  climate models improve the agreement with
  observations of Last Glacial Maximum temperature
  and precipitation? Use PMIP boundary conditions
  (CLIMAP SSTs, Peltier ICE4G ice sheets)
• LMDz GCM
• Low res 3.75ox2.5o global
• High res 1.0ox0.5o (zoom centered on Paris (!) )
• CCSR GCM
• Low res 6.0ox5.0o global
• High res 1.0ox1.0o global
• HadAM/HadRM.
• Low res 3.75ox2.5o global.
• High res 0.45ox0.45o (regional model)

LMDz low res present
LMDz high res present
LMDz low res LGM
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RESULTS (1) - Tcold
LMDz low res, Tcold (LGM-present)
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RESULTS (2) - Tcold
CCSR, low res, Tcold, M9.0 M11.9
HadAM, low res, Tcold, M8.4 M10.6
LMDz, low res, Tcold, M6.5 M9.6
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RESULTS (3) - Tcold
HadRM high res, Tcold (LGM-present)
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RESULTS (4) - Tcold
CCSR, high res, Tcold, M12.4 (cf 11.9)
HadRM, high res, Tcold, M5.9 (cf 10.6)
LMDz, high res, Tcold, M9.8 (cf 9.6)
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• DISCUSSION - Tcold
• HadRM has the best simulation of Tcold. Why?
• Very cold sea-ice in North Atlantic.
• Regional model has good representation of
  structure and intensity of storms. More
  high-windspeed events larger surface fluxes
  greater cooling. Feedback due to increase in
  meridional temperature gradient with increasing
  sea-ice.

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CCSR low res
CCSR high res
RESULTS (1) - Pann
Mean absolute error
LOW HIGH
CCSR 270 230
LMDz 240 260
Had 240 400
LMDz low res
LMDz high res
HadAM low res
HadRM high res
Reason for wetter LGM in Hadley Centre
model Relatively high CLIMAP SSTs In
Mediterranean. Cold air above advected from
sea-ice
-900mm
900mm
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• CONCLUSIONS
• In the Hadley Centre model, agreement with Tcold
  LGM data is much improved in the regional high
  res. model compared to standard global model.
  This is due to very cold sea-ice in North
  Atlantic, linked to high surface heat fluxes,
  linked to intense storm activity. Feedback is
  via increased meridional temperature gradient.
• In the same model, precipitation worsens,
  possibly due to the CLIMAP Mediterranean SSTs,
  which may be too high.
• However, LMDz and CCSR do not show large
  differences between high and low resolutions.
  Maybe due to different approach, or critical
  resolution.

The Last Glacial Maximum climate over Europe
High resolution simulations, Jost,
Lunt,Kageyama, Abe-Ouchi, Peyron, Valdes, and
Ramstein, in prep.
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• FUTURE WORK
• Investigate sea-ice issues further inclusion of
  leads.
• Validation of sea-ice surface temperatures for
  the modern.
• New interpretation of data more modern
  analogues.
• Inclusion of a small Alpine ice-cap.
• Updated SST reconstructions.