application of a subgrid orography scheme to cam and clm
DESCRIPTION
Application of a Subgrid Orography Scheme to CAM and CLM. Steven Ghan and Tim Shippert Pacific Northwest National Lab. Ghan, S. J., X. Bian, A. G. Hunt, and A. Coleman, 2002: The thermodynamic influence of subgrid orography in a global climate model, Climate Dynamics , 20 , 31-44. - PowerPoint PPT PresentationTRANSCRIPT
Application of a Subgrid Orography Scheme to CAM and CLM
Steven Ghan and Tim ShippertPacific Northwest National Lab
Ghan, S. J., X. Bian, A. G. Hunt, and A. Coleman, 2002: The thermodynamic influence of subgrid orography in a global climate model, Climate Dynamics, 20, 31-44.
Subgrid scheme
Implementation
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• Applies to all column physics– clouds– radiative transfer– vertical mixing– surface physics
Elevation ClassificationElevation Classifi cation
-10000
100020003000400050006000700080009000
Su
rfac
e E
leva
tio
n (
m)
Progress
• Scheme applied to CAM and CLM – Euler dycore– Finite-volume dycore (1-D and 2-D domain decomposition)
• Developmental branch updated to cam2_0_2_dev55 (IPCC physics)
• Bit-for-bit agreement between SP, SMP, SPMD• Restarts bit-for-bit agreement• Bit-for-bit agreement with dev trunk if subgrid scheme turned
off• Energy conservation demonstrated*• Load balancing within nodes for both dycores• Load balancing between nodes for both dycores (FV 1-D only)• Runoff distributed according to elevation of river transport
model surface elevation
Experiments
• AMIP SST • Initialize September 1977• T42
– TOPOG run through 1983– No TOPOG data taken from cam2_0_2_dev61_climo
• 2x2.5– TOPOG run through 1989– No TOPOG run through 1989
Evaluation
temperature
March snow
Does the Scheme Impact the Grid Cell Mean Climate?
The subgrid scheme changes the large-scale climate significantly for the FV dycore, but not the
EUL dycore.
Planetary Energy Balance
Global Annual Mean
T42TOPOG
T42 NOTOP
T42 2X2.5 TOPOG
2X2.5 NOTOP
2X2.5
FSNT 235.2 234.0 1.2 234.5 232.2 2.3
FSNS 160.6 159.2 1.5 161.5 157.3 4.2
FLNT 233.6 233.5 0.1 228.9 233.2 -4.4
FLNS 57.5 56.5 1.1 63.9 57.9 6.0
RAD -101.5 -102.1 0.6 -91.9 -100.4 8.5
SHFLX 20.2 19.6 0.6 24.0 17.8 6.2
LHFLX 80.7 82.0 -1.3 93.8 81.9 11.9
TFLX 100.9 101.5 -0.6 117.7 99.8 17.9
RAD+TFLX
-0.6 -0.6 0.0 25.8 -0.6 26.4
PREC 2.786 2.831 -0.046 3.237 2.829 0.408
QFLX 2.785 2.831 -0.046 3.239 2.829 0.410
What is Causing the FV Problem?
Divergence of T and ST
Computational Burden
Zonal Mean Burden
Global Burden
Spectral Resolution
T42 T85 T170
Average classes per cell 2.28 1.85 1.58
Maximum classes in a cell 11 11 10
Maximum zonal mean classes per cell
3.8 3.2 2.7
Balancing the Load•Distribute elevation classes across physics chunks
–Rank grid cells according to number of classes–Starting with cells with most classes, assign all classes in cell to the chunk with the least number of columns–Continue distribution until classes for all cells have been assigned to chunks–Save cell index and area corresponding to each chunk column
•Distribute chunks across nodes
-Minimize dynamic-physics transpose cost by assigning chunks to node with most dynamics grid cells from chunk
-fraction of columns assigned to same node as dynamics: 40% for T42 11 classes on 8 nodes
Distribution of Physics Load in Chunks
1 2 3 4 5 6 7 8 9 10 12 13 14 15 16
Columns In Chunk
Num
ber o
f Chu
nks
Distribution of Chunks Across Nodes
0
1
2
3
4
5
6
7
8
1 150Chunks on Node
Nu
mb
er o
f No
des
Load Balancing Performance
10
100
1000
1 10 100
MPI Processes
T4
2 W
allc
loc
k R
un
Tim
e
(se
co
nd
s/d
ay
)
NCLASS=1
NCLASS=11 No load balance
NCLASS=11 Load balance
Code Changes
• Unlike any other parameterization– All column physics applied to each elevation class
• Mostly manifest at higher levels– phys_grid
phys_grid_initcreate_chunksscatter_field_to_chunkgather_chunk_to_field
– phys_types– dp_coupling– history
Future Work
• Extend the T42 subgrid run and run control for comparison.• Correct the FV energy imbalance and rerun FV 2x2.5.• Apply load balancing to the finite-volume implementation of
the scheme, for 2D domain decomposition.• Present to CCSM LMWG for approval.• Submit proposal to CAM code review board.• Check in as permanent CAM and CLM option.• Perform simulations at higher resolution with subgrid
scheme.• Perform IPCC simulations with CAM using the subgrid
scheme and ocean surface conditions from CCSM simulations without the subgrid scheme.
• Adapt the scheme to CCSM.• Continue to update as CCSM changes.