Update%20on%20surface%20atmospheric%20pressure%20errors

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• Update on surface atmospheric pressure errors
• (comparing pressure fields from ECMWF and NCEP
  operational analyses and available data over the
  oceans)
• Rui M. Ponte
• (work with David Salstein and Karen Cady-Pereira)
• Atmospheric and Environmental Research, Inc.
• Tides/HF Aliases Splinter
• Ocean Surface Topography Science Team Meeting
• Hobart, Australia, March 2007

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ECMWF and NCEP differences
RMS (ECMWF-NCEP)
1993-95
Ponte Dorandeu (2003, J. Atmos. Oce.
Tech.) ECMWF and NCEP analyses
substantially closer together in more recent
years
2002-03
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ECMWF/NCEP/data (st. deviation)
Standard deviation (range 0-5 hPa) OBS - NCEP
Automated Data Processing/Global Surface
Observations
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ECMWF/NCEP/data biases
Bias (range 2.5 hPa)
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Recommendations

• Error statistics can and do seem to vary with
  time (provide two different estimates of
  uncertainty for earlier and later part of the
  altimeter record)
• Analyses differences lt(E-N)2gt(ltE2gtltN2gt-2ltENgt
  ) provide a lower bound due to possible
  correlated errors and Ponte Dorandeu (2003)
  suggest using twice lt(E-N)2gt for an upper bound
• For earlier period, use values from Ponte
  Dorandeu
• For later period, use current estimates with
  equipartition of errors between ECMWF and NCEP
  (indicated by comparisons to data)
• Estimates can be used to derive errors in dry
  tropospheric and inverted barometer corrections,
  which are simply proportional to surface pressure
• Estimates can be used as one input in deriving HF
  correction errors, although other model errors
  can probably dominate the budget