Comparison of eastern tropical Pacific simulations by IPCC AR4 coupled models

1
Comparison of eastern tropical Pacific
simulations by IPCC AR4 coupled models

• Simon de Szoeke
• NOAA/ESRL/PSD3, Boulder, Colorado
• Shang-Ping Xie
• International Paci?c Research Center
• Honolulu, Hawaii

2
Tropical eastern Paci?c coupled processes

• equatorial coastal upwelling fronts and eddies
• stratus trade-wind cumulus clouds
• intertropical convergence zones (ITCZ)
• variability El Niño, TIWs, tropical depressions
• observations satellite TAO buoy monitoring
  EPIC (2001) VOCALS ?eld projects

EQ
EQ
SST ( C)
Robert Wood
3
Tropical eastern Paci?c
Ocean-atmosphere variability ENSO Pacific
North American (PNA) teleconnection

• End of the line for the Paci?c equatorial
  waveguide and embarkation point for the PNA
  atmospheric wave train
• The PNA connects ENSO to North American weather
  in winter.
• Seasonal cycle is important.
• Models fail to predict the season of ENSO
  variability (Saji et al., 2006).

convection
PNA winter pressure pattern (Horel and Wallace,
1981)
4
seasonal cycle of interannual SST variability
Saji, et al. (2006)
observed
5
Outline

• Assess current state-of-the-art coupled models
  IPCC AR4 20th century simulations.
• Signi?cant variety and biases exist among models!
• Introduce metrics.
• Beyond biasesinfer physical relationships from
  the ensemble of CGCMs.
• Regional coupled modeling.

6
Why the eastern Paci?c warm poolis in the north
Upwelling along a tilted coast (Philander
1996) Wind-evaporation-SST feedback (Xie and
Philander, 1994)
7
Southerly wind propagates asymmetry westward and
cools equator
cold
Wind-evaporation-SST feedback (Xie and Philander,
1994)
8
Precipitation (mm day-1)
9
Intergovernmental Panel on Climate Change 4th
Assessment Report (IPCC AR4) models

• Canadian Centre for Climate Modelling and
  Analysis CGCM3.1
• Centre National de Recherches Météorologiques
  (France) CNRM CM3
• CSIRO Atmospheric Research (Australia) CSIRO
  Mk3.0
• Geophysical Fluid Dynamics Laboratory
  (USA) GFDL CM2.0
• Geophysical Fluid Dynamics Laboratory GFDL
  CM2.1
• Hadley Centre for Climate Prediction and Research
  (UK) UKMO HadCM3
• Institute of Atmospheric Physics (China) FGOALS
  1.0g
• Institute of Numerical Mathematic (Russia) INM
  CM3.0
• Institut Pierre Simon Laplace (France) IPSL CM4
• Center for Climate System Research
  (Japan) MIROC3.2 medres
• Center for Climate System Research MIROC3.2
  hires
• Meteorological Research Institute (Japan) MRI
  CGCM2.3.2
• National Center for Atmospheric Research
  (USA) NCAR CCSM3.0
• National Center for Atmospheric Research NCAR
  PCM 1
• International Pacific Research Center
  (USA/Japan) IROAM
• 15 models from 8 nations

10
Eastern Paci?c average SST (Reynolds)and rain
(TRMM)
mm day
degrees longitude
C
degrees west
11
Eastern Pacific average SST (Reynolds)and rain
(TRMM)
mm day
degrees longitude
C
degrees west
12
Reynolds
TRMM
13
model a
meridional seasonal cycle of SST and rain 140-90
W
latitude
model b
14
latitude
seasonal SST and rain
15
Eastern tropical Pacific 140-90 W,10 N SST,
25 N precipitation
RMSE
Taylor (2001) diagram

0.2
2
0.4
0.6
correlation
0.7
1.5
d
0.8
d
7
1
5
f
0.9
c
2
7
9
4
8
3
c
2
0.95
3
a
5
6
e
6
0.5
e
8
b
1
4
9
a
1
f
0.99
b
0
0
1
2
normalized standard deviation s/sobs
16
latitude
seasonal SST, rain, and QuikSCAT wind
17
Semiannual equatorial SST bias
observed
latitude
Boreal spring cold bias correlated to northerly
wind at r-0.6.
18
March equatorial cold biasfrom northerly wind
no correlation in August
28
r0.61
9
0
8
f
e
26
b
1
6
a
4
March equatorial SST ( C)
5
c
24
3
2
7
d
22
0
2
4
March v (m s-1)
19
Meridional asymmetry NorthSouth SST
rain Seasonal cycle AugustMarch asymmetry
latitude
20
Annual cycle of equatorial SST governed by
meridional wind speed
AugMar equatorial SST ( C)
21
Westward and disconnected equatorial cold tongue
bias
SST ( C)
latitude
west longitude
warm
cold
Zonal wind small east of 90 W.
22
meridional winds role inequatorial upwelling
v
18 C
2 N
2 S
EQ

• Meridional wind drives a meridional cell in the
  equatorial ocean with upwelling on the windward
  side of the equator.
• ? cools equator

23
Niño 12 meridional wind cools SST
Nino 12 80-90 W 0-10S
24
meridional winds role in equatorial upwelling
near the coast

• Models with stronger southerly wind maintain
  cooler SST 80-90 W (r-0.6).
• Bjerknes (1969) feedback ampli?es and propagates
  cooling westward (Xie, 1998).

EQ
25
Central American December-February gap winds and
SST
Gap winds prematurely end northern warm pool and
ITCZ.
26
Gap winds cool northern SSTand lead equatorial
northerlies
(2N)
(5-20N, 80-110W)
27
Southern stratocumulus deck influence on
asymmetry through insolation
degrees longitude
C
degrees west
28
Insolation drives SST but is not significantly
correlated to meridional wind
29
Eastern Pacific IPCC AR4 20th centurymodel
roundup

• Seasonal cycle of meridional asymmetry exhibits a
  wide range of behavior.
• Models form an ensemble with signi?cant
  inter-model correlations between
• SST and rain meridional asymmetry (r0.8)
• meridional asymmetry and equatorial v (r0.6)
• equatorial v speed and cold tongue SST. (r0.6)
• Double ITCZ bias is now mostly an alternating
  ITCZ bias.
• semiannual cycle of wind and equatorial SST
  affects interannual variability

30
Eastern Pacific IPCC AR4 20th centurymodel
variations

• The seasonal cycle of meridional asymmetry
  governs equatorial wind and SST.
• Meridional wind is important for equatorial
  upwelling 0-10 offshore.
• Central American gap northeasterlies in boreal
  winter cool the eastern Pacific warm pool, which
  sends the ITCZ south.
• End of part 1

31
International Pacific Research Center
(IPRC)Regional Ocean Atmosphere Model (IROAM)

• Realistic boundary conditions constrain the model
  isolate local coupled feedbacks.
• Better resolution of orographic and mesoscale
  circulations
• Verify with point observations.
• Sensitivity experiments
• Assess parameterizations
• Propose strategies to diminish GCM biases.
• Regional effects of scenarios e.g. last glacial
  maximum (cool North Atlantic 2C at 21,000 ybp)

32
IPRC Regional Ocean-Atmosphere Model (IROAM)
Atmosphere forcedby observed SST
Land surface model
Ocean forced by NCEP reanalysis
Interactive
Atmosphere IRAM, Y. Wang (2003, 2004) Ocean
MOM2, Pacanowski Griffies (1999)
Ocean spin-up
Coupled
19901995
19962003
IROAM is run on Earth Simulator in Yokohama,
Japan.
33
IROAM and COADS seasonal cycle of SST
30 C
30 N
20 C
EQ
30 S
80 W
140 W
110 W
34
Stratus and stratocumulus clouds

• Low cloud affects how much sunlight reaches the
  surface.
• SST affects low cloud
• Cool SST strengthens the capping inversion,
  enhancing clouds (Klein Hartmann 1993)
• Stratiform clouds have been identi?ed as an
  important contributor to coupled climate.
• Model cloud representation varies widely.
• Uncertainty in cloud parameterizations
  entrainment, convection, drizzle, and aerosol
  feedbacks.

35
Surface solar cloud radiative forcing (SSCRF)
ISCCP satellite retrieval
IROAM
W m-2
36
Stratiform clouds reinforce meridional asymmetry
Sc cool
37

• Shallow cumulus convection scheme
• Tiedtke (1989) mass flux scheme for deep,
  shallow, and midlevel convection
• Shallow convection is activated when
• surface evaporation gt 90 of the boundary layer
  (PBL) moisture source
• or
• cloud layer is less than 200 hPa deep.
• no shallow convection (noSC) experiment
• All convection is prohibited when either shallow
  convection condition is met.
• Conditional instability in the lower troposphere
  must be relieved by turbulence or deep convection.

38
Shallow cumulus convection affects stratiform
clouds

• Shallow convection vents moisture from the
  boundary layer and entrains dry air in.

700 hPa
39
Shallow cumulus convection affects stratiform
clouds

• Shallow convection vents moisture from the
  boundary layer and entrains dry air in.
• Reduced venting increases stratiform clouds,
• which block sunlight from reaching the surface.

noSC
40
Vertical structurestratus clouds at 15 S,
September
noSC
IROAM control
pressure (hPa)
cloud water, 10-4 kg kg-1
41
surface solar cloud radiative forcing(W m-2)
IROAM control
noSC
Stratiform clouds dim sunlight by 50-100 W m-2.
42
Seasonal cycle (80-140 W)
latitude
mm day-1
C
43
Regional Ocean-Atmosphere Modeling

• simulates realistic eastern Pacific climate.
• is useful for testing ideas
• Without SC, stratus cloud is 0.1-0.6 greater and
  SST 1-4 C cooler.
• Thermodynamically coupled SST is essential to
  many sensitivity experiments.
• IROAM will be validated against EPIC and VOCALS
  observations.

44
Eastern Paci?c coupled GCM biases

• are largely due to incorrect seasonal cycle and
  meridional temperature asymmetry.
• affect wind on the equator and cold tongue SST.
• The mean state and seasonal cycle affect
  interannual variability.