Trends and inter-annual variability of altimetry-based coastal sea level in the Mediterranean Sea: Comparison with tide gauges and models

The Mediterranean Analysis and Forecasting System operationally produces analyses and 10 days forecasts of the main physical parameters for the entire Mediterranean Sea and its Atlantic Ocean adjacent areas in the framework of the Copernicus Marine Environment Monitoring Service (CMEMS).The system is composed by the hydrodynamic model NEMO (Nucleus for European Modelling of the Ocean) 2-way coupled with the third-generation wave model WW3 (WaveWatchIII) and forced by ECMWF (European Centre for Medium-range Weather Forecasts) atmospheric fields. The forecast initial conditions are produced by the OceanVar, a 3D variational data assimilation system which daily assimilates Sea Level Anomaly, vertical profiles of Temperature and Salinity from ARGO and XBT (upon availbility) observations. Moreover a heat flux correction using satellite SST is imposed.The system has been recently upgraded by including tidal waves, so that the tidal potential is calculated across the domain for the Mediterranean Sea 8 major constituents: M2, S2, N2, K2, K1, O1, P1, Q1. In addition, tidal forcing is applied along the lateral boundaries in the Atlantic Ocean by means of tidal elevation estimated using the FES2014 global tidal model and tidal currents evaluated using TUGO (Toulouse Unstructured Grid Ocean) model. Moreover the data assimilation scheme now accounts for the tidal signal in the altimeter tracks.The system has been validated comparing model results with satellite and in situ observations. A specific harmonic analysis has been performed comparing model sea level amplitudes and phases with respect to: tide gauges, TPXO global tidal model and literature, showing an overall good skill of all the considered tidal constituents. Moreover the ability of the system to predict sea level has been evaluated comparing the model solutions with respect to tide gauges in areas where recent extreme events occurred such as Venice Lagoon &#8220;Acqua Alta&#8221; in November 2019, Western Mediterranean Sea during Gloria storm in January 2020, Ionian Sea during Medicane Ianos in September 2020.

Download Full-text

Estimating Vertical Land Motion in Northern Adriatic Sea with Coastal Altimetry and In Situ Observations

10.5194/egusphere-egu2020-9754 ◽

2020 ◽

Author(s):

Francesco De Biasio ◽

Stefano Vignudelli ◽

Giorgio Baldin

Keyword(s):

Climate Change ◽

Sea Level Rise ◽

Mediterranean Sea ◽

Sea Level ◽

Coastal Zone ◽

Satellite Altimetry ◽

Data Sets ◽

Tide Gauges ◽

The Mediterranean

The European Space Agency, in the framework of the Sea Level Climate Change Initiative (SL_CCI), is developing consistent and long-term satellite-based data-sets to study climate-scale variations of sea level globally and in the coastal zone. Two altimetry data-sets were recently produced. The first product is generated over a grid of 0.25x0.25 degrees, merging and homogenizing the various satellite altimetry missions. The second product that is still experimental is along track over a grid of 0.35 km. An operational production of climate-oriented altimeter sea level products has just started in the framework of the European Copernicus Climate Change Service (C3S) and a daily-mean product is now available over a grid of 0.125x0.125 degrees covering the global ocean since 1993 to present.We made a comparison of the SL_CCI satellite altimetry dataset with sea level time series at selected tide gauges in the Mediterranean Sea, focusing on Venice and Trieste. There, the coast is densely covered by civil settlements and industrial areas with a strongly rooted seaside tourism, and tides and storm-related surges reach higher levels than in most of the Mediterranean Sea, causing damages and casualties as in the recent storm of November 12th, 2019: the second higher water registered in Venice since 1872. Moreover, in the Venice area the ground displacements exhibit clear negative trends which deepen the effects of the absolute sea level rise.Several authors have pointed out the synergy between satellite altimetry and tide gauges to corroborate evidences of ground displacements. Our contribution aims at understanding the role played by subsidence, estimated by the diffence between coastal altimetry and in situ measurements, on the local sea level rise. A partial validation of these estimates has been made against GPS-derived values, in order to distinguish the contributions of subsidence and eustatism. This work will contribute to identify problems and challenges to extend the sea level climate record to the coastal zone with quality comparable to the open ocean, and also to assess the suitability of altimeter-derived absolute sea levels as a tool to estimate subsidence from tide gauge measurement in places where permanent GPS receivers are not available.

Download Full-text