GCMRCM coupling: Downscaling with the Rossby Centre Regional Atmosphere Model via the PRISM system

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GCM-RCM coupling Downscaling with the Rossby
Centre Regional Atmosphere Model via the PRISM
system

• typical applications of RCA
• dynamical downscaling of control and experiments
  climate scenarios
• Numerical weather prediction
• Process studies in high resolution
• (two-way-nesting)

• RCA Rossby Centre Atmosphere Model (SMHI)
• HIRHAM (DMI)

RCM
GCM

• Deliverables in WP5
• Completion of demonstration run and analysis of
  results

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Physical interface
Fields to pass during runtime
Initialization GCM to RCM
Fields read in during runtime for time-dependent
forcing of the RCM, time interpolation between
coupling timesteps, RCM lags one coupling
timestep
Fields used for initialization of the regional
model
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Coupling and Interpolation
ARCDI To support source and target coupling
domains that totally or partially overlap (e.g.
global atmosphere with a regional ocean, regional
model nested into global model, etc.).
GCM hybrid coordinates
RCM hybrid coordinates
RCM weigthed combination of regional solution
and interpolated GCM fields

• - multiple 2D interpolation from the GCM grid to
  the RCM grid (OASIS 4)
• simple vertical interpolation (OASIS 4)
• no flux conservation currently, only state
  fields are passed

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Prototype setup
Control (namcouple)
OASIS
Reader of global data OR GCM
RCM
ECHAM5 global data
PSMILe
PSMILe
3D interp.
Two way is an option
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Demonstration runs with GCM-RCM coupling

• Regionalizations of the global ECHAM model for
  Northern Europe.
• To demonstrate the feasibility of the PRISM
  system for GCM-RCM coupling,
• physical interface for GCM-RCM coupling
• Technical setup
• The coupling will be off-line and one way global
  to regional.
• RCM RCA (SMHI)
• GCM ECHAM5, DMI/MPI provided the global data to
  force the regional models.
• Simulation time 1 year control run
• These runs will be evaluated with respect to the
  technical feasibility and correctness of the
  approach.
• Runs carried out at the Swedish National
  Supercomputercenter (NSC), SGI Origin

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Downscaling 2-m temperature
RCA RCM
ECHAM5 GCM
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2-m temperature
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Summary and Conclusions

• GCM-RCM coupling with the PRISM system is
  demonstrated
• Deliverable is fulfilled
• Two-way-GCM-RCM coupling is possible (not to be
  demonstrated within PRISM)
• Frequent future application would need
• more outsourcing into the coupler (e.g. multiple
  2D coupling)
• adaptation of the interface by GCMs (for two-way
  coupling)