Do we observe sea level properly in order to understand interannual and longterm sea level variation

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Modified title Do we observe sea level properly
and are we doing the right analyses of the
observations in order to understand interannual
and long-term sea level variations, and if we
don't what can the ESEAS contribute?
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Questions

• Open Questions
• Observational infrastructure for observing local
  sea level
• Do we need more comparative studies of sea level
  sensors?
• Should the ESEAS recommend a 'standard tide gauge
  configuration' (including operational routines)?
• Should the ESEAS focus on/include sub-hourly
  phenomena?
• Should the ESEAS take a lead in providing a
  web-based, automated QC server?
• Can the ESEAS facilitate the timely delivery of
  monthly means to the PSMSL?

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Questions

• Open Questions
• Observations of vertical land motion
• Can the ESEAS organise operational QC for CGPS
  observations?
• How should the reference frame issues be resolved
  and what cooperation should the ESEAS seek with
  other programmes?
• What are the right products for vertical
  displacements in the ESEAS context - secular
  trends or time series of e.g. monthly means?

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Questions

• Open Questions
• Description of decadal sea level variations
• What is noise (we don't understand it), what
  signal (we do understand it)?
• What do we learn about sea level as a
  climate-related quatity from characterising the
  how and not the why?
• Does it make sense to reduce the records to
  trends?
• Can we understand sea level variations without
  looking at the forcing?
• How can the empirical model of decadal sea level
  variations be set up?

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Requirements

• Open Questions
• Understanding decadal sea level variations
• Should the ESEAS focus on extremes (i.e. their
  decadal variability), too?
• Should there be a focus on the 'why' (was not
  included in ESEAS-RI) and not so much on the
  'how'?
• Can hydrodynamical model output be a tool to
  understand sea level given the potential problems
  with the forcing?
• What spatial scales do we have to look at for
  decadal to longer time scales? Local, regional,
  global?

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GPS analysis strategy

• Observations
  Goal of monitoring vertical displacements
• Site documentation
  lt 1 mm/yr accuracy
• Elements of appropriate strategy
• Separation of global and local parameter
• orbits, clocks and EOPs based on a global,
  "stable", network
• coordinate time series of CGPS sites
  subsequently determined
• Each site at least three software/strategies,
  e.g.
• GIPSY/OASIS/ppp
• Bernese/DD
• GAMIT/DD
• Use of physical parameters and models
• All models should be conventional (IERS
  conventions)
• Open issues concerning what to include in GPS
  analysis/what leave to time series analysis?
• ESEAS should follow IERS development Loading in
  next ITRF and in Conventions
• Output

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Example 1
Some selected results

• regression coefficient for pgs sensitive to
  model parameters,
• regression depends on time window

• Greenland appears to have been melting, high
  rate
• Antarctica appears to have been melting in the
  1950-2000 window
• Steric signal smaller than predicted by models
  and observations
• Total rise over the last 50 years approximately
  2.5 mm/year

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Interpretation
Spatial Representation

• Time series at individual tide gauges requires
  time series of all forcing factors
• Trends at individual tide gauges requires
  interpolation of grids to tide gauge location
• Trends as grids requires interpolation of all
  parameters on a common grid