Tuesday 23 August 2005

GP2

PT0090
Inter-decadal sea level variability in the 20th century from tide gauges and altimetry
Knudsen, Per¹, Andersen, Ole¹, Kjaer, Niels¹
1 Geodetic Department, Danish National Space Center, Denmark
Author email: pk@spacecenter.dk
An objective of the European Sea Level Service - Research Infrastructure (ESEAS-RI) project, is to develop an empirical model for sea level variability over the past century based on data from both altimetry and especially tide gauges, covering the European Seas but also globally, at a low spatial and temporal resolution. Here we will present some of the approaches taken to initiate such a simple model based on a robust regression method, where the link between tide gauge data and altimetry data plays an important role. Tide gauge data have an uneven coverage in both space and time, somewhat limiting their ability to capture changes over the open ocean and with a decreasing number of records going back in time. Therefore the inclusion of climatic indices with long time series, such as the North Atlantic Oscillation (NAO) or the Southern Oscillation Index (SOI), which are effectively pressure differences and thereby linked to sea level variability, have been considered. We have also looked at, how the use of Empirical Orthogonal Functions (EOFs) could improve the emphasis on the dominant spatial variability, and finally how filtering in time, using different intervals to focus more closely on variability with longer periods, can be useful. Tide gauge data have been tied to open ocean sea level through a combination of two hydrodynamic models incorporating altimetric data; the SODA (Simple Ocean Data Assimilation - run at the University of Hawaii) and MICOM (Miami Isopycnic Coordinate Ocean Model - run at the Nansen Environmental and Remote Sensing Center in Bergen, Norway) models both utilize the meteorological reanalysis fields (from NCEP and ECMWF) in order to describe the sea level variations from 1950 to 2002, and this period forms the basis of our simple centennial model.

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