Examining Fresh Water Flux over Global Oceans in the NCEP GDAS, CDAS, CDAS2, GFS, and CFS P. Xie1), M. Chen1), J.E. Janowiak1), W. Wang1), C. Huang1), C.-L. Shie2), and L. Chiu3) 1) NOAA Climate Prediction Center 2) UMBC / NASA Goddard Space Flight

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Examining Fresh Water Flux over Global Oceansin
the NCEP GDAS, CDAS, CDAS2, GFS, and CFSP.
Xie1), M. Chen1), J.E. Janowiak1), W. Wang1), C.
Huang1), C.-L. Shie2), and L. Chiu3)1) NOAA
Climate Prediction Center2) UMBC / NASA Goddard
Space Flight Center3) GMU / NASA Goddard Space
Flight Center
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Objective

• To examine the oceanic precipitation and
  evaporation fields generated by NCEP reanalyses
  and climate model simulations through comparison
  with corresponding observations
• Uncertainties in oceanic observations considered
  by using multiple data sources and taking into
  account the standard deviation among the
  different observations

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Precipitation Observation Data

• Three sets of observation data sets used
• CMAP / GPCP / TRMM
• Annual climatology (mm/day) for 1988 2000
• Largest uncertainties (standard deviation among
  observations) over ITCZ and high latitudes
• Standard Deviation about 10 of the mean values

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Evaporation Observation Data

• Four products
• GSSTF2 / HOAPS3
• J-OFURO-2 / SOC1.1a
• Annual climatology (mm/day) for 1988 2000
• Large uncertainties over tropical oceans,
  especially over E. Pacific and over oceans around
  the Maritime Continent
• Standard Deviation about 10 of the mean values

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E-P Annual Climatology

• Based on 12 sets of E/P combinations
• Standard Deviation about 10 - 20 of the mean
  values
• Less uncertainties in zonal mean

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DJF Precipitation Climatology

• Spatial patterns
• reproduced well by
• all products
• Pattern in GDAS in
• close agreement with
• observations
• Orientation of SPCZ
• in CDAS1 too flat
• Precipitation too heavy in GDAS, CDAS2, GFS
  and CFS
• Atlantic ITCZ shirted southward and double
  ITCZ over E. Pacific in CFS

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Precipitation Annual Cycle over Atlantic

• 30oW-20oW
• Excessive preci-
• pitation in GDAS,
• CDAS2, GFS and CFS
• Migration of ITCZ
• extremely well
• simulated in GDAS
• ITCZ location shifted
• in CDAS2, GFS, and CFS
• Southward shift of ITCZ reaches 10o during
  Spring in CFS

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DJF Evaporation Climatology

• Large-scale pattern
• reproduced reasonably
• well in all products
• Over S.H., magnitude
• in all products close
• to that in the
• observations
• Over N.H., excessive amount of evaporation
  compared to the observations

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DJF E-P Climatology

• Large-scale pattern
• reproduced reasonably
• well in all products
• Larger magnitude
• in GDAS and CDAS2
• over tropics
• Excessive incoming E-P flux along Pacific
  ITCZ in GFS and CFS

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Latitudinal Profile of Annual Mean

• Location of maxima and minima well caught
• CDAS1 reproduced the magnitude of E and P very
  well
• All other products generated excessive amount of
  E / P over most latitudes

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Anomaly Correlation for Precip.

• Correlation very high (gt0.8) between the two
  observations from 50oS-50oN
• Monthly anomaly reproduced very well by GDAS over
  most oceanic regions
• Reasonable agreements for CDAS1 and CDAS2,
  especially over Pacific and North Atlantic

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Standard Deviation of Precipitation Anomaly

• Insufficient / excessive magnitude of
  inter-annual variations in precipitation
  simulated in CDAS1 / CDAS2
• Results for GDAS not included due to short data
  record without major ENSO events

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Anomaly Correlation for Evap.

• Correlation very high (gt0.8) between the two
  observations over extra-tropics and reasonably
  high (gt0.6) over tropics
• Evaporation anomaly reproduced well over
  extra-tropics but less desirable over tropics
  (rlt0.5)
• GDAS presents better agreements with the
  observations

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Standard Deviation of Evaporation Anomaly

• Distribution of anomaly standard deviation for
  CDAS1 compares well with the observations in both
  pattern and magnitude
• Patterns generated by CDAS2 is similar to but
  magnitude is much larger than those in the
  observations

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GDAS Performance

• Time series of pattern correlation between GDAS
  simulation and observations (CMAP/HOAPS3)
• Slight improvements in precipitation simulation
  from mid of 2003
• Steady improvements in evaporation, especially
  over tropics

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Summary

• Seasonal variations and interannual
  variability of oceanic precipitation and
  evaporation in GDAS, CDAS1, CDAS2, GFS and CFS
  are broadly consistent with observations
• GDAS presents the best performance among the
  five products examined
• However, certain consistent errors are seen
• The ITCZ is too weak in CDAS1 and too strong in
  the GDAS and GFS
• Shift in ITCZ / SPCZ positions, especially over
  Atlantic
• Systematic differences between GFS and CFS
• Excessive evaporation in GDAS, CDAS2, GFS and CFS

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MAM Precipitation Climatology

• Double ITCZ over
• E. Pacific reproduced
• well in GDAS, CDAS1,
• CDAS2 and GFS
• ITCZ over E. Pacific
• (northern branch)
• weak and ITCZ over
• Atlantic shifted
• southward
• ITCZ too strong over Pacific and Atlantic
  in GDAS, CDAS2, GFS, and CFS

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JJA Precipitation Climatology

• Spatial patterns
• reproduced well by
• all products
• Pattern in GDAS in
• close agreement with
• observations
• Precipitation too heavy
• in GDAS, CDAS2,
• GFS and CFS

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JJA Evaporation Climatology

• Large-scale pattern
• reproduced reasonably
• well in all products
• Larger amount of
• evaporation in all
• products over Indian
• Ocean
• Reasonable magnitude of evaporation
  elsewhere

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JJA E-P Climatology

• Large-scale pattern
• reproduced reasonably
• well in all products
• Larger magnitude
• in GDAS and CDAS2
• over tropics
• Excessive/deficit incoming E-P flux over
  East / West Pacific ITCZ in GFS and CFS

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DJF Evap. Anomaly Pattern ENSO

• Regressional coeffi-
• cients of evaporation
• against NINO3.4
• Magnitude of evapo-
• ration anomaly is much
• smaller (1/5) than that
• of precipitation
• Anomaly pattern well
• simulated by CDAS1, CDAS2 and GFS,
  especially over Atlantic
• Anomaly pattern poorly simulated by CFS
  over Pacific