Surname: Fenoglio-Marc
Firstname: Luciana
Title: Dr.
Organisation: Technical University Darmstadt
Department: Inst. of Physical Geodesy 
Address_1: Petersenstr. 13
Address_2:  
City: 64287
Country: Germany
Email: fenoglio@ipg.tu-darmstadt.de
Phone: +49-6151-163012
Fax: +49-6151-164512

Mass Variation in the Mediterranean Sea from GRACE and its validation by altimetry, steric and hydrologic fields

Luciana Fenoglio-Marc⁽¹⁾ J. Kusche ⁽²⁾ and M. Becker ⁽¹⁾

⁽¹⁾ Institute of Physical Geodesy Darmstadt Technical University, Petersenstrasse 13, D-64287 Darmstadt(fenoglio@ipg.tu-darmstadt.de / Fax-Nr. +49-6151-164512)
⁽²⁾ DEOS Delft University of Technology, Kluyverweg 1 Delft, The Netherlands

Abstract

We use monthly GRACE gravity fields in 2002-2004 to recover water mass variation in the Mediterranean Sea. Time-variable gravity changes measured by GRACE are mainly caused by water mass variations in ocean, land and atmosphere. To minimize both the satellite measurement and the leakage errors in the mass recovery in the selected region, a smoothed spatial averaging kernel is used. The same averaging function as used for GRACE is applied to all the other spatial fields involved.

We estimate both the leakage from surrounding land and the changes in the non-steric sea level change in the Mediterranean Sea,computed as difference between the altimetric Jason and Topex/Poseidon sea level change and the steric sea level change computed from temperature and salinity fields. First results show a good agreement between mass change from GRACE and mass change from the combination of gridded altimetry, steric and land hydrology fields. The seasonal signal has an amplitude of about 4 centimeters and maximum in Winter.

The accuracy is investigated using different hydrologic and oceanographic models as well as different Temperature and Salinity datasets to estimate the steric part. The differences are small and in general not significant. The leakage effect is significant and changes the general seasonal characteristics of the results, causing a change in the phase of the water mass change signal. The seasonal component of the mass variation has a maximum in January-February for GRACE and in October for the non-steric sea level component. The leakage includes a seasonal component that is subtracted from the GRACE averages. This mass change in the Mediterranean Sea water is then compared to the total Mediterranean Sea water content estimated from ECMWF and model data of precipitation, evaporation, river run-off and net inflow from the Gibraltar and Dardanelles straits.