Ostende GLOSS Course 2006 GLOSS (and MedGLOSS, GCOS etc.) Philip L. Woodworth Permanent Service for Mean Sea Level

GLOSS The Global Sea Level Observing System Also known as “ Global Level of the Sea Surface”

GLOSS Objectives 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 IOC’s Global Ocean Observing System (GOOS)

Some History GLOSS was initiated in the 1980s with the aim of increasing the quantity and quality of month and annual MSL data to the Permanent Service for Mean Sea Level (PSMSL) A network, now called the GLOSS Core Network, was defined to which all countries would contribute These ideas formed the basis for the first GLOSS Implementation Plan

The GLOSS Core Network

More History By the 1990s there had been many technical developments in sea level measurement: Satellite Altimetry GPS for measuring land movements The second GLOSS Implementation Plan was written to define: GLOSS Core Network A sub-network for Long Term Trends A sub-network for Altimeter Calibration A sub-network for Ocean Circulation

Ways of Measuring Sea Level Changes Tide Gauge (float) Bottom Pressure Gauge Altimeter System

Ways of Measuring Land Level Changes GPS Absolute Gravity

More History continued Another important change was that tide gauge authorities were asked to provide their ‘higher frequency’ sea level data (e.g. hourly values or similar) in addition to MSL values to the PSMSL. Two GLOSS Date Centres defined in addition to PSMSL: GLOSS Fast Centre at Hawaii (where ‘fast’ means data in a few weeks e.g. for altimeter calibration) GLOSS Delayed Mode Centre alongside PSMSL

Real Time Data in 2000’s Most recently there has been a request for as much GLOSS data to be delivered in near real time: 1. Allows data to be provided to a new set of users e.g. tsunami people. 2. Allows faults to be identified and fixed earlier and so also better delayed-mode data eventually. GLOSS Fast Centre at Hawaii also defined to be the GLOSS Real Time Centre

GLOSS Status GLOSS status can be measured by how well the network is providing data to data centres: MSL data available at PSMSL Real-time data available at Real-Time Centre Delayed-mode data available at Delayed-Mode Centre

GLOSS Real-time coverage 22 September 2006

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

Responsibilities of GLOSS Data Providers There are 3 responsibilities of GLOSS data providers: 1.Monthly and annual MSL data to PSMSL by 6 months after the data-year 2.Delayed-mode higher-frequency data (typically hourly values), quality controlled to one of the GLOSS centres (in practice PSMSL again or UHSLC) 4 months after recording 3.‘Fast’ H-F data (not quality controlled) to GLOSS Fast Centre at UHSLC

GLOSS Data Availability Data from GLOSS tide gauges Permanent Service for Mean Sea Level University of Hawaii Sea Level Center Also Regional Centres MedGLOSS

GLOSS and GCOS The Global Climate Observing System has defined a set of approximately 180 tide gauges for long term climate (sea level) monitoring These can to a good approximation be considered the same sites as the GLOSS Core Network In a similar way as the IOTWS has major overlap with the GLOSS Network in the Indian Ocean  Conclusion is that all networks have to be ‘multiple use’.

GLOSS - The Global Sea Level Observing System Further Information GLOSS Technical SecretaryPermanent Service for Mean Sea Level Intergovernmental Oceanographic Proudman Oceanographic Laboratory Commission (IOC), UNESCO