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S6: Applications II - Sea Level and Extreme Events (cont'd)
14:00 - 14:40
Session Chair: P David Cotton Session Chair: Kaoru Ichikawa Session Chair: Clara Lázaro Session Chair: Luciana Fenoglio-Marc
14:00 - 14:20
Accurately Measuring Sea Level Change from Space in the Coastal Zone: an ESA Climate Change Initiative
Anny Cazenave1, Jean-François Legeais2, Michael Ablain2, Gilles Larnicol2, Johnny Johannessen3, Martin Scharffenberg4, Gary Timms5, Ole Baltazar Andersen6, Paolo Cipollini7, Mònica Roca8, Serguei Rudenko9, Joana Fernandes10, Magdalena Balmaseda11, Graham Quartly12, Luciana Fenoglio13, Américo Ambrózio14, Marco Restano15, Jérôme Benveniste16
1LEGOS; 2CLS; 3NERSC; 4University of Hamburg; 5CGI; 6DTU; 7NOC; 8isardSAT; 9GFZ; 10University of Porto; 11ECMWF; 12PML; 13University of Bonn; 14DEIMOS/ESRIN; 15SERCO/ESRIN; 16ESA-ESRIN
Sea level is a major climate index because it integrates the response of oceans, mountain glaciers, ice sheets and land waters to external forcing factors and internal climate variability. Understanding sea level variability and changes implies an accurate monitoring of sea surface height variations at different spatio-temporal scales. This is why the 'Sea Level' Essential Climate Variable (ECV) was selected in the frame of the ESA Climate Change Initiative (CCI) programme. The main objective of this initiative was to provide long-term sea level time series at global and regional scales, with regular updates, as is required for climate studies.
The CCI is now in its 3 year long second phase, following a first phase that spanned 2011 to 2013. It has contributed to the reinforcement of collaboration of the European sea level community, refined their needs, and collected their feedback about product quality. It has also served to develop, test and select the best algorithms and standards needed to generate an improved sea level time series. This has led to the production of the Sea Level ECV that now covers the period 1993-2014.
The efforts conducted during the Sea Level CCI project will be extremely useful for future developments of sea level products in specific regions (e.g., the Arctic) and in coastal zones. Because sea level rise will aggravate the vulnerability of low-lying, highly-populated coastal regions of the world, providing accurate coastal sea level products is now a major goal and a scientific challenge. In coastal zones, 'absolute' sea level variations are the combination of the global mean rise, regional variability and short-scale oceanographic processes. Improvement of the first two factors in the open ocean has been the main objective of the Sea Level CCI project. In addition to summarizing what has been learnt during the project, the presentation will also address future needs, focusing especially on coastal issues.
14:20 - 14:40
Combining Tide Gauge and Satellite Altimetry Data: Towards Monitoring Vertical Land Motion at the Coast
Guy Wöppelmann1, Marta Marcos2
1University of La Rochelle, France; 2IMEDEA - UIB, Spain
Vertical land motions are a key element in understanding how sea levels have changed over the past century and how future sea levels may impact coastal areas. Ideally, to be useful in long-term sea level studies, vertical land motion should be determined with standard errors that are one order of magnitude lower than the contemporary climate signals of 2-3 mm/year observed on average in sea level records, either using tide gauges or satellites. This metrological requirement constitutes a challenge in geodesy.
Here we review the use of the combination of satellite radar altimetry with tide gauge data to derive vertical land motion data. This method is independent from GPS, and enables to overcome some limitations associated with the use of GPS (number of stations and data availability, local leveling).We update previous data analyses and assess the quality of global satellite altimetry products available to the users for coastal applications. In particular, we carefully examine the uncertainties. Various satellite altimetry products are considered from the major data suppliers (Archiving, Validation, and Interpretation of Satellite Oceanographic data (AVISO), Climate Change Initiative (CCI), Commonwealth Scientific and Industrial Research Organization (CSIRO), Colorado University, Goddard Space Flight Center (GSFC)). The time span covered by the satellite altimetry data considered here extends at maximum from 1993 to 2016, although the final year depends on the particular data set. We investigate the linearity of the differenced (satellite minus tide gauge data) time series and evaluate their noise content. Finally, we use the new combined satellite altimetry and tide gauge data set to estimate vertical land motion at nearly500 coastal sites around the world and compare the results with the a GPS solution dedicated to tide gauge monitoring.