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GLOSS - The Global Sea Level Observing System
Global Level of the Sea Surface 1. Monitoring
and Measuring Sea Level Why and How? 2. The
GLOSS Programme Network and Activities 3.
Sea Level Data
Thorkild Aarup, GLOSS Technical
Secretary t.aarup_at_unesco.org
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GLOSS - The Global Sea Level Observing System

• Establishment of high quality global and
  regional sea level networks
• for application to climate, oceanographic and
  coastal sea level
• research
• Sea level stations around the world for long
  term climate change
• and oceanographic sea level monitoring
• Coordinated by the Intergovernmental
  Oceanographic Commission
• (IOC)
• Major contributor to IOCs Global Ocean
  Observing System (GOOS)

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Why Measure the Sea Level?

• Scientific research e.g. to measure long term
  changes in
• global sea level and ocean circulation
• Practical applications e.g. to predict flood
  risks in coastal
• regions

How to Monitor the Sea Level?

• Satellite radar altimetry
• Tide gauges
• In the deep ocean bottom pressures obtained
  from sea bed
• devices

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Measuring Sea Level Changes
Altimeter System
Bottom Pressure Gauge
Tide Gauge (float)
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Why Tide Gauges in the Age of Altimetry?

• Principle of continuity, relative low cost of
• gauges
• Long records for secular trend/acceleration
• studies (e.g. for input to IPCC)
• Higher frequency sampling important in straits
• and other areas
• High latitude regions of ice coverage
• Altimeter calibrations (absolute and
  relative)
• Coastal applications (GOOS Coastal Module)

Acoustic Gauge in Australia
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Sea-Level Changes

• Different Time-Scales
• Momentary changes due to tsunamis
• Daily changes due to tides and surges
• Seasonal changes
• Interannual changes e.g. due to ENSO
• Long term changes due to climate change
• Causes of Sea Level Change
• Local processes in river/coastal regimes
• Ocean circulation changes
• Regional and global climate changes
• Geological processes

Maldives Int. Airport
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Long Term Changes in Sea Level

• Past 100 years
• Most records show evidence for
• rising sea levels during the past
• century
• IPCC concluded that there has
• been a global rise of
• approximately 10-20 cm
• during the past 100 years

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Long Term Changes in Sea Level

• Next 100 years
• a rise between 9 and 88 cm
• a central value of 48 cm
• a rate of approx. 2.2 - 4.4
• times that of the past
• 100 years

Projected sea level rise, IPCC 2001
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The GLOSS Programme/Networks

• GLOSS Core Network (GCN)
• Regional Densifications
• of the GCN
• Long Term Trends (LLT)
• Altimeter calibration
• (GLOSS-ALT set)
• Ocean Circulation
• (GLOSS-OC set)

GLOSS Core Network (GCN) with approx. 280 stations
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GLOSS Activities

• Regional Developments
• Regional networks of gauges with greater spatial
  density, to serve
• the particular oceanographic interests of
  those regions - examples
• IOCARIBE (Caribbean), MedGLOSS (Mediterranean
  Black Seas)
• National Activities
• Contribution to the activities of national
  agencies by improving the
• standards for sea level recording around the
  world
• Training
• Annual training courses on the techniques of
  tide gauge operations,
• and workshops on special interests e.g.
  measurements in
• environmentally hostile areas

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GLOSS Data Availability

• Data from GLOSS tide gauges
• Permanent Service for Mean Sea Level
• http//www.pol.ac.uk/psmsl/
• University of Hawaii Sea Level Center
• http//www.soest.hawaii.edu/UHSLC/
• National Tidal Facility (Australia) Southern
  Ocean Centre
• http//www.ntf.flinders.edu.au
• GLOSS sea level data and information on each
  gauge in the GCN are also available from PSMSL on
  CD-ROM.

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GLOSS - The Global Sea Level Observing System

• Documentation
• July 1997 Second Implementation Plan for the
  GLOSS Program
• IOC Manuals on Sea Level Measurement and
  Interpretation
• (Manuals and Guides No. 14, 3 volumes)
• Further Information
• GLOSS Technical Secretary Permanent Service for
  Mean Sea LevelIntergovernmental Oceanographic
  Proudman Oceanographic Laboratory
• Commission (IOC), UNESCOemail
  t.aarup_at_unesco.org email psmsl_at_pol.ac.uk

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