Assessing CFS Model Bias Associated with the Marine Stratus over Southeastern Pacific P. Xie1), W. Wang1), W. Higgins1), M. Cronin2), P.A. Arkin3), and R. Weller4) 1) NOAA Climate Prediction Center 2) NOAA Pacific Marine Environmental Laboratory 3)

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Assessing CFS Model Bias Associated with the
Marine Stratus over Southeastern PacificP.
Xie1), W. Wang1), W. Higgins1), M. Cronin2),
P.A. Arkin3), and R. Weller4)1) NOAA Climate
Prediction Center2) NOAA Pacific Marine
Environmental Laboratory3) ESSIC, Univ. of
Maryland4) Woods Hole Oceanographic
InstitutionAcknowledgementsMingyue Chen, Ake
Johansson, and Suranjana Saha
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Warm SST Bias over SE Pacificin CFS CMIP
Simulations
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Questions for This Year

• How long does it take for the warm bias to
  develop in the CFS forecasts from its initial
  condition to what is observed in CFS/CMIP?
• examining CFS hindcasts
• To what extent the warm bias is caused by the
  insufficiently simulated stratus clouds over SE
  Pacific?
• performing CMIP simulations with radiation
  over SE Pacific corrected

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Examining the Evolution of Warm SST Bias

• Looking at CFS hindcasts with different forecast
  leading times and comparing them the with initial
  (GODAS/R2) and balanced conditions (CMIP)
• Daily and monthly climatology of CFS hindcasts
  for a 23-year period from 1981 to 2003
• Initiating date / month
• Leading time from 1-45 days and 0 8 months for
  the daily and monthly hindcast climatologies,
  respectively

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Evolution of the Warm SST BiasMonthly
Climatology of CFS Hindcasts

• Averaged with respect to different leading months
  using hindcasts with all different initiating
  months
• Warm bias starts from coastal areas and spreads
  steadily toward NW
• After 8 months, warm bias reaches very close to
  its balanced condition (CMIP)

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Evolution of the Warm SST BiasDaily
Climatologyof CFS Hindcasts

• Warm bias grows quite fast along the coast during
  the first month

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Mean SST Bias over SE Pacific

• Evolution of mean warm SST bias over the SE
  Pacific as seen from the daily (top) and monthly
  (bottom) CFS hindcasts
• Warm SST bias reaches 80 of that in the CFS/CMIP
  after 8 months

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Bias Evolution in the Hindcasts with Different
Initial Months

• Warm SST bias starts at different coastal regions
  and evolves through different processes

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SEP Mean Bias Evolution for Hindcasts with
Different Initiating Times

• Warm bias develops relatively quickly in the
  first month
• Warm bias grows very fast during boreal spring
• Warm bias reaches close to the balanced condition
  from the spring of the second year
• Bias evolution seasonally dependent

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Bias Evolution Near the Coast 76oW13oS

• Warm bias reaches close to its balanced condition
  in the first month
• Warm bias may grow at a rate of more than
  0.1oK/day during the first 30 days of hindcasts
  (e.g. in September)

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Bias Evolution Over Open Ocean 85oW20oS

• Warm bias develops relatively fast in the first
  30 days (but not as much as that over the coastal
  region)
• Bias evolution regionally dependent

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Evolution of Cloudiness in the CFS Models

• Averaged with respect to different leading times
  using hindcasts with all different initiating
  months
• Cloudiness reached very close to its balanced
  condition in the first month

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Evolution of Net Radiation in the CFS Model

• Net downward radiation biased in the initial
  condition
• Adjusted to its balanced condition in a month
• Positive radiation bias over a narrow band along
  the coast

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Radiation and SST Biases for Different Months

• Monthly hindcasts climatology for the first
  targeting month
• Seasonal variations in location and distribution
  for both the SST and the radiation biases during
  early months of forecasts
• The SST and the radiation biases are co-located
  through the seasonal cycle
• Excessive incoming radiation caused by
  insufficiently simulated stratus clouds is a
  major contributor to the warm SST bias

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Radiation and SST Biases in the Hindcasts of
Diff. Leading Months

• Positive radiation bias confined within coastal
  areas throughout the forecast periods
• Warm SST bias spreads out from the coastal region
  toward NW during the forecast period
• Other mechanisms responsible for the spreading
  the warm bias

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Examining the Impacts of the Insufficiently
Simulated Stratus Clouds over SE Pacific

• Quantifying the stratus clouds contributions to
  the warm SST bias under balanced condition (CMIP)
• Performing CFS CMIP simulations with radiation
  budget over SE Pacific corrected with daily
  climatology of observed radiation (SRB)
• Comparing radiation-corrected CMIP simulations
  with the standard CMIP runs

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Annual Mean Bias

• The warm SST bias over the SEP is reduced by
  about half

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Interannual Variability

• Interannual standard deviation of monthly SST
• Tropical interannual variability is weakened with
  the reduction of the warm SST bias over SE Pacific

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ENSO

• NINO3.4 index
• Intensity of ENSO reduced compared to the
  standard CFS CMIP simulations and observations

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Answers (?)

• How Long Does it take to develop the warm bias?
• Seasonal and regionally dependent
• Faster during spring and reaches close to balance
  spring of the 2nd year
• More rapidly over coastal region than over open
  ocean
• On average, the warm bias reaches 80 of its
  balanced condition after 8 months
• To what extent the insufficiently simulated
  stratus clouds play in forming and maintaining
  the warm bias
• Triggering the warm bias over the narrow band
  along the coast
• Providing excessive energy to the model ocean
  over the coastal region
• Other mechanisms (oceanic and ar-sea
  interactions) responsible for re-distributing the
  energy and spreading the warm SST bias
• Warm bias reduced by half if the excessive
  incoming radiation is corrected
• Insufficiently simulated stratus clouds not the
  only factor contributing to the warm SST bias