An Analysis of Subseasonal Variability

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An Analysis of Subseasonal Variability in the
NCEP CFS and NASA NSIPP Coupled GCMs Myong-In
Lee1,2, Siegfried Schubert2, Max Suarez2, Phil
Pegion2, Ben Kirtman3, Kathy Pegion3, Arun
Kumar4, Bhaskar Jha4, and Duane Waliser4 1
Goddard Earth Sciences and Technology Center/
UMBC 2 NASA/GSFC Global Modeling and Assimilation
Office 3 COLA/George Mason University 4 NCEP/
Climate Prediction Center 5 NASA/Jet Propulsion
Laboratory/CalTech
2
Questions ??

• How well do the current coupled models reproduce
  the leading patterns of extratropical subseasonal
  variability?
• CGCM intercomparisons ( CFS and NSIPP CGCM)
• Coupling versus prescribed (comparison with AMIP)
• How well do the current coupled models reproduce
  the changes in subseasonal variability associated
  with ENSO ?
• ENSO simulation in CGCMs
• Subseasonal variance changes

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Model Descriptions

• NCEP CFS T62L64
• NCEP Global Forecast System (GFS) for the
  atmospheric component
• GFDL Modular Ocean Model version 3 (MOM3) for the
  ocean component
• NASA NSIPP CGCM v.1
• NSIPP1 AGCM (1x1.25)
• Poseidon v4 (1/3x5/8xL27) OGCM

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Datasets

• 50 years of NCEP/NCAR Reanalysis-1
• 1951-2000
• Daily and monthly GPH200
• Monthly U200
• 50 years of monthly HadISST
• 50 years coupled runs
• NCEP CFS (T62L64)
• NSIPP CGCM (1x1.25)
• 50 years of AMIP (1951-2000) Runs
• NCEP GFS T62L64 (T62L64)
• 9-member NSIPP AGCM ensemble runs (2x2.5)

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• Principal patterns of monthly 200 mb height
  (Rotated EOFs)

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AO
ENSO
AAO
PNA
meters per STDV
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ENSO
AO
AAO
PNA
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NAO
9
Variance of Leading Patterns
(Unit meter2)
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ENSO
GFS AMIP
(var.340 m2)
NSIPP AMIP
(var.3649 m2)
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AO
12
AAO
13
PNA
14
NAO
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• Ensemble spreads in NSIPP AMIP runs
• (spaghetti diagram of EOFs)
• - contours from each ensemble members
• - compared with the reanalysis (shading)

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ENSO response from NSIPP 9 AMIPs
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AO from NSIPP 9 AMIPs
AAO from NSIPP 9 AMIPs
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PNA from NSIPP 9 AMIPs
NAO from NSIPP 9 AMIPs
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• ENSO simulations in the CGCMs

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Time-Longitude SSTA (5S-5N)
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Nino3 SSTA (5S-5N, 150-90W)
Warm SST Composite (gt 1s)
Cold SST Composite (lt -1s)
Reanalysis
CFS
NSIPP
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• Subseasonal Variance Analysis
• - GPH200 daily
• - remove seasonal cycle
• (0-3 harmonics of 50 year-averaged daily
  climatology)
• - 10-60 day band-pass filtered
• - variance in NH winter (DJF)

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Subseasonal Variance Changes (La Nina-El Nino)
contour 200mb u-wind difference
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• Rotated EOFs from daily band-pass (10-60d)
  filtered 200 mb height

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• Variance of PCs (daily 200 mb height)

CFS (coupled)
GFS AMIP
PNA
Reanalysis
AO
NAO
PNA
NAO
AO
AAO
AAO
PNA
NAO
AO
AAO
NSIPP AMIP
NSIPP (coupled)
AO
NH pattern
PNA
NAO
SH pattern
AO
NAO
PNA
Total variance(0.1)
AAO
AAO
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Pattern 4
Pattern 3
Pattern 2
Pattern 1
Reanalysis
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Pattern 8
Pattern 7
Pattern 6
Pattern 5
Reanalysis
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Pattern 12
Pattern 11
Pattern 10
Pattern 9
Reanalysis
7
10
8
14
GFS AMIP
r0.92
r0.87
r0.80
r0.96
8
10
13
9
NSIPP AMIP
r0.92
r0.96
r0.94
r0.95
4
13
6
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CFS (coupled)
r0.95
r0.94
r0.82
r0.89
14
11
6
7
NSIPP (coupled)
r0.84
r0.92
r0.96
r0.94
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• Variance difference (cold-warm) reconstructed
  from EOFs

(1000 m2)
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• Variance difference (cold-warm) - Reanalysis

NAO
PNA
p3
p4
p2
p1
AO
p7
p8
p6
p5
p11
p12
p10
p9
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• Variance difference (cold-warm) GFS AMIP

NAO
PNA
p3
p4
p2
p1
AO
p7
p8
p6
p5
p11
p12
p10
p9
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• Variance difference (cold-warm) NSIPP AMIP

NAO
PNA
p3
p4
p2
p1
AO
p7
p8
p6
p5
p11
p12
p10
p9
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• Variance difference (cold-warm) CFS coupled

NAO
PNA
p3
p4
p2
p1
AO
p7
p8
p6
p5
p11
p12
p10
p9
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• Variance difference (cold-warm) NSIPP coupled

NAO
PNA
p3
p4
p2
p1
AO
p7
p8
p6
p5
p11
p12
p10
p9
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Summary

• 1. Current models reproduce the leading
  wintertime extra-tropical patterns of monthly
  variability reasonably well
• REOFs identify the patterns of ENSO, AO, AAO, PNA
  and NAO
• an assessment of the spread of the NSIPP AMIP
  ensemble shows these patterns to be robust in
  samples of 50 years
• there are, however, large differences in the
  variance of individual patterns
• total monthly variance is in general weaker in
  the simulations

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Summary (continued)

• 2. An assessment of the full subseasonal (10-60
  day) variance shows the following
• the variance is weak in the coupled runs, whereas
  it is comparable to the reanalysis in the AMIP
  runs
• but, all models have a sign of variance increase
  over the northern reach of Pacific and Alaska
  region and decrease over the arctic and northern
  Atlantic region
• REOFs from daily band-pass 200 mb height show a
  much richer spectrum of patterns compared with
  the monthly results, apparently a variation of
  several leading principal patterns
• interannual changes in the subseasonal variance
  associated with ENSO have realistic patterns (but
  are weak, especially in the coupled runs)
• changes in the PNA and NAO are robust, though not
  so for other leading patterns
• 3. Future work will focus on furthering our
  understanding of the nature of the various
  subseasonal patterns and their underlying
  dynamics

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• Thank You !

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Reanalysis
nao
pna
ao
pna
nao
ao
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