Oceanography
sors, also with in situ data [see for example [3, 4, 5, 6, 7, 8, 9, 10, 11, 12], collaborating with many different groups inside and outside Europe (among others, Rosenstiel School of Marine and Atmospheric Science (RSMAS), University ‘Parthenope’ of Napoli, Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), National Oceanography Centre Southampton (NOCS), Agenzia nazionale per le nuove tecnologie, l’energia e lo sviluppo economico sostenibile (ENEA)). This work gives an overview of GOS activity summarizing the main results of the two most recent GOS works, namely Volpe et al. [1] and Rinaldi et al. [2]. The first describes the analysis of the relation between physical and biological processes affecting the Mediterranean surface layer in the period 1998-2006 (Section 3.1). The second is a study of the Tyrrhenian Sea surface circulation from the combination of surface drifters and altimeter data between December 2001 and February 2004 (Section 3.2). The paper is organized as follows: Section 2 describes the data used and the methodologies adopted within the two works. Section 3 discusses the main results while conclusions are drawn in Section 4.
2 2.1
Data and Methods MADT Dataset
The altimeter data used here are produced by Ssalto/Duacs and distributed by Aviso, with support from Cnes (http://www.aviso.oceanobs.com/duacs/). The 2001-2004 altimeter data time series is the Mediterranean Absolute Dynamic Topography (MADT) built from four altimetric satellites: Jason-1, Envisat or ERS2, Topex/Poseidon and Geosat Follow-On 1408
GFO. Standard corrections have been applied to data by Ssalto/DUACS [13]. Data were merged and interpolated on a weekly basis over a regular 1/8° grid using an optimal interpolation [14]. Finally, the mean dynamic topography (MDT) was added to the sea level anomalies (SLA), as detailed in Rio et al. [15].
2.2
The SST Dataset
The SST time series is the optimally interpolated re-analysis product [OISST, [6]], widened to include the 2006 measurements. The re-analysis is based on Pathfinder SST time series. The data span from January 1998 to December 2006 and they cover the Mediterranean area at 1/16° resolution. To match the MADT spatial domain the northern Adriatic Sea was masked out (because of its shallowness). The daily SST time series were averaged over 8-day “week” intervals of which there are 45 in a year of 360 days.
2.3
The Chlorophyll Dataset
SeaWiFS ocean colour data were acquired and processed by the receiving station HROM at GOS from 1998 to 2006, The MedOC4 [5] algorithm for chlorophyll (CHL) retrieval in case-1 waters was applied to the remote sensing reflectance. CHL maps were remapped at the spatial resolution of 1.1x1.1 km over an equirectangular grid covering the Mediterranean Sea. The 1/16° resolution grid map was achieved by averaging the base-10 logtransformed chlorophyll values (LCHL, to differentiate from CHL), to account for chlorophyll lognormal distribution [16]. This spatial resolution matches the resolution of the SST OI maps developed in