Research objectives and content
long-term monitoring of sea-level variability by applying the most advanced geodetic techniques, including satellite altimetry and airborne laser;
b) to provide additional sea-level related constraints for the validation of climate models;
c) to study past sea-levels in the Mediterranean in order to further our understanding of the current processes;
d) to assess the potential hazards in coastal areas in the Mediterranean and to provide a basis for developing strategies to mitigate these hazards. The Mediterranean is dominantly affected by processes related to the semi-enclosed body of ocean water. Sea level as the upper boundary of the oceanic body carries a wealth of information related to the state of the sea as well as to the forces acting on it. Therefore, studying the physical interactions of the ocean, the atmosphere and the Earth's crust provides a basis for a better understanding of the changes in both the forcing atmospheric dynamics and in the responding ocean, which is mandatory for the design of statistical or physical models with predictive power. To study the physical (mechanical) interactions of the ocean with the atmosphere and solid Earth thus is complementary to those projects focusing on chemical or biological interactions. The recent realization of global and regional projects to connect well established tide gauges on a global well defined reference system made it possible to determine the Tide Gauge BenchMark (TGBM) heights at the one centimeter level of accuracy or even better. In order to be able to understand true sea-level variations it is necessary to determine vertical crustal movements of the TGBMs to an accuracy of one mm/yr or better. Within SELF II, the most appropriate strategy, will be defined and implemented in order to assess the capability to achieve a reliable knowledge of the vertical rates of the TGBMs, within limited time intervals. Dualfrequency Water Vapor Radiometer (WVR) observations will be performed simultaneously with the GPS observations. Absolute gravity observations with an accuracy of 2 microgal can be used to detect vertical crustal movements of the order of I cm. It is expected that GPS observations with the simultaneous collection of WVR data and absolute gravity measurements will provide the capability to assess vertical crustal rates in the Mediterranean and Black Sea regions over limited intervals of time. With the present availability of the Topex/Poseidon mission it is now possible to measure the spatial variability of sea level. Within SELF II, the complementary nature of the tide gauge and altimetry information will be used in an integrated way to provide a better understanding of the spatial pattern of the temporal variability of the sea level. It is recognized that a substantial fraction of the seasonal to multidecadal sea-level fluctuations is due to atmospheric forcing . Therefore, sea level can be expected to record climate variability on these time scales. On the basis of statistical analyses as well as mathematical and physical models the interaction of the atmosphere and ocean will be studied to achieve a better understanding of the momentum transfer from atmosphere to ocean and the climate variability in the Mediterranean with some emphasis on the detection of rapid changes in the atmospheric forcing. Futhermore, these studies will allow an assessment of the usefulness of the sea-level variability in the validation of climate models. In the most active regions of the Mediterranean, sites separated by only 10-20 km can show different direction and rates of vertical movements. Within SELF II, selected areas in the Mediterranean will be studied to infer former sea levels as well as related paleoclimatic conditions. It is expected that the geological observations and the petrographic and mineralogical analysis of coastal deposits will allow to derive paleo-climatic and depositional information which, in connection with the paleo-morphology results could be related to paleo sea levels. The immediate hazards for sinking areas (e.g. Venice) come from extreme surges driven by the meteorology. Statistical techniques have been developed for finding the distribution of extremes and to estimate the return periods for flooding events. These techniques will be applied to the available hourly tide gauge data for the Mediterranean and a search for trends in extreme sea levels will be performed. In addition to the study of the past extremes, models of the atmospherically forced sea level variability in conjunction with climate models will be used to provide further estimates of the developments of future potential hazards.