SEASONAL and LONG TERM Atmospheric Response to Reemerging North Pacific Ocean Temperature Variability

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SEASONAL and LONG TERM Atmospheric Response to
Reemerging North Pacific Ocean Temperature
Variability

• Zhengyu Liu
• Center for Climatic Research
• University of Wisconsin-Madison
• Collaborators
• Yun Liu, Yafang Zhong, UW-Madison
• Lixin Wu, The Ocean Univ. of China
• R. Jacob, Argonne National Lab./DOE

Liu et al., 2007 J. Climate
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Atmospheric Response to mid-latitude SST ?

• Problems
• In the observation
• What?
• What is the response (if any) ?
• 2. Why?
• What is the mechanism?

!
3. Relative to the tropical SST forcing!
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Atmospheric Response to mid-latitude SST ?
Seasonal Evolution ?

• Model evidence Peng et al. (1995),

• Questions
• Model Consistence?
• Response in the observation?

A Combined Statistical and Dynamical Approach
a) StatDyn application to a coupled model ?
verification of methodology b) Statistical
application to observation ? response in the
observation
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Statistical Assessment EFA (Equilibrium
Feedback Assessment) Frankignoul et al.,
1998, JPO

• H(t) ? T(t) N(t)
• H heat flux (atmos), T SST, N atmos noise
• Because ltT(t-?), N(t)gt 0
• lt T(t-?), H(t)gt ? lt T(t-?), T(t)gt lt T(t-?),
  N(t)gt
• ? lt H(t), T(t-?)gt/ltT(t),T(t-?)gt

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Statistical Evidence CorltZ, SSTgt
Model (FOAM) (400-yr)
NCEP (40-yr)
Z250
Z850
SST lead
SST lead
Z850 lead
Z850 lead
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Statistical Assessment (Early Winter)
Obs. (NCEP)
Surface wind
850 hPa ?
250 hPa ?
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Initial value in coupled model
Dynamical Assessment
Coupled Ensemble Experiment in FOAM
Ensemble simulations (4 years)
Initial KOE Tgt0 (Sept.1st)
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Seasonal Response and the Role of Ocean Memory
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Ensemble mean response
Early winter (NDJ-Yr1)
SST
Q
Z250
Z850
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Seasonal Evolution
SST EOF1 (66)
Heat Flux EOF1 (56)
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Dynamic assessment vs. Statistic assessment
Model
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Scatter Diagram of Ensemble Members Monthly
Noise and Signal
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What about long term response?
Monthly response weak and subtle
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Long term (4-year) mean response
SST
Q
Z850
Z250
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Scatter Diagram of Ensemble Members Monthly
Noise and Signal
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Signal vs NoiseZ250 (30-60N)
En Std(Z250)
En Mean(Z250)
Std(Z250)/Mean(Z250)
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Summary and Implication

• Atmospheric response to mid-latitude SST likely
  has a strong seasonal cycle in the observation,
  with dominant warm-ridge response early winter
  but weaker and different responses later the rest
  of year

• Atmospheric response to mid-latitude oceanic
  variability, and the associated feedback, is
  important at long (interannual to decadal) time
  scales

In contrast to atmospheric response to tropical
SST, which is important at shorter (monthly to
seasonal) time scales as well

• Importance of statistical assessment of general
  atmospheric response (non-local), to provide a
  target for AMIP experiments (Liu et al.,
  submitted)

• Confirmed in CCSM3

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CCSM3 (T31) Response (ND)
Statistic
Dynamic
Z250
Z850
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CCSM3 Vertical GPH response
--- statistical, --- dynamical
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CCSM3 Long term response signal
Signal/Noise
Signal
Noise
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CCSM3 Results

• Confirm FOAM results on
• consistent statistical-dynamic assessment
• seasonal cycle of response
• enhanced signal/noise ration for long term
  response
• However
• the early winter response is dominated by
  warm-low, and later winter by warm--high

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SST EOF1 (66)
Heat Flux EOF1 (56)
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Similar to Fig.14 of Liu et al. (2007). (upper)
GHT250 (lower) GHT850 averaged in 30N-50N for
1mon, 3mon, 6mon, 1yr and 2yr binning.
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CCSM3 (T31) Response