Influence of Subtropical Air-Sea Interaction on the Multidecadal AMOC Variability in the NCEP CFS...
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Transcript of Influence of Subtropical Air-Sea Interaction on the Multidecadal AMOC Variability in the NCEP CFS...
Influence of Subtropical Air-Sea Interaction on the Multidecadal
AMOC Variability in the NCEP CFS
Bohua Huang1, Zeng-Zhen Hu2, Edwin K. Schneider1 Zhaohua Wu3, Yan Xue2
1George Mason University and COLA2Climate Prediction Center, NCEP3Florida State University
Scientific Questions• What role does the ocean-
atmosphere interaction play in the multidecadal AMOC oscillation?
• Does the tropical-subtropical Atlantic Ocean also play a part in the multidecadal AMOC oscillation?
CFS Simulation• CFS-v1, operational system for seasonal to interannual prediction
at NCEP since August 2004• Atmospheric component: GFS (2003), T62 (~200 km), 64 sigma
levels (prescribed sea ice cover affects surface flux into the ocean)• Oceanic component: MOM3, 1ox1o (1/3o lat within 10oS-10oN),
40 levels, non-polar (70oS-65oN)no transport between Atlantic and Arctic Oceanno sea-ice formation mechanism
• Daily coupling over active ocean domain (without flux correction)• Initial condition: January 1, 1985, Atmosphere: NCEP Reanalysis
2; Ocean: GODAS• Integration is ongoing, 400-yrs done
AMOC Index
Year-to-Year
Interannual
Decadal
Multidecadal
Century
AMOC Index
Year-to-Year
Interannual
Decadal
Multidecadal
Multidecadal+
Century
Leading MSSA (EXEOF) Modes, 5-yr Running Mean 30-Year Lags
MSSA 1(22.3%)
-EEMD C
MSSA2-3 (7.6%+6.4%)
-EEMD M
-PC1
-PC1
Cen
tury
Mod
eM
ultid
ecad
al M
ode
MSSA1
MSSA2-3
Mul
ti-D
ecad
al M
ode
Mul
ti-D
ecad
al M
ode
Mul
ti-D
ecad
al M
ode
Mul
ti-D
ecad
al M
ode
Mul
ti-D
ecad
al M
ode
cm/s
AMOC Feedback Loops
StrongAMOC
Warm HC, SSTaround 30o-45oN
Wind curl (-)Downwelling
StrongAMOC
Weak Subtr. High
Weak N.E.Trade Wind
WarmSubtr. SST
Wind Curl (+)Subtr.Upwelling
Cold Subtr.HCWeak STC
Delayed AMOC
Weakening
AM
OC
lead
sA
MO
C la
gs
Summary• AMOC fluctuates on a wide range of time
scales in CFS.• An intermittent multidecadal (30-yr)
oscillation is generated by ocean-atmosphere feedback within the Atlantic sector.
• Delayed response of the northern subtropical cell is crucial for the oscillation.
Leading MSSA (EXEOF) Modes, Seasonal mean Lag 20 seasons (5-yrs)
PC2 COR 0.52 NINO3 leads 5 seasons—Normalized NINO3 index
PC1 COR 0.57 NINO3 lags 1 season
28.4%
ENSO Mode
68.2%
MSSA1-2 (3.7%+3.6%)
EOF1 EOF2
EN
SO M
ode
EN
SO M
ode