North-East Atlantic current systems from 10 years of multi-mission satellite altimetry
Clara Lázaro(1) , M. Joana Fernandes(1) , and Mário Alves(2)
Faculty of Science, University of Porto,
Rua do Campo Alegre, 687 ,
(2) Laboratory of Marine Environment and Technology, Edifícios da Marina, 9760 Praia da Vitória, Portugal
Satellite altimetry data provide a quasi-synoptically description of the sea level anomaly (SLA) field, which can be the base to ocean circulation variability studies. Although continuous single mission analysis can now be performed for a series of 13-years of Topex/Poseidon (T/P) data it has been recognised that merged multi-mission data sets allow the observation of the ocean at better spatial and temporal resolutions, leading to an improved understanding of the ocean circulation at higher scales, in particular the mesoscale, and its seasonal and interannual variability.
ERS-2 and Topex/Poseidon (T/P) data continuity was provided by the launch of Envisat and Jason 1 missions, in 2002 and 2001, respectively. From these missions a ten year continuous and homogenous data set of merged data from the NASA/CNES 10-day missions T/P and Jason-1 and the ESA 35-day missions ERS-2 and Envisat can be derived.
At the Faculty of Science, University of Porto (FCUP) data from several altimeter missions are regularly reprocessed using state-of-art geophysical corrections and merged data sets are derived.
In this study a 10 year series (from June 1995 to June 2005) of merged data of T/P/Jason-1 with ERS-2/Envisat has been used to characterise the SLA field in the NE Atlantic (3º – 50ºN, 50º – 5ºW). From early-2003 onwards, Envisat, T/P and Jason-1 SLA data sets have also been merged and analysed.
This paper presents the analysis of the surface current systems for two main sub-regions: the eastern tropical Atlantic and the region of the Azores-Portugal current systems. The seasonal and interannual variability of the oceanic processes present in each region have been analysed from monthly maps of various computed oceanographic variables: SLA, ADT, geostrophic currents and eddy kinetic energy. The advances in the determination of oceanographic variables from the merged two-mission data set are discussed and compared with the information derived by the unique combination presently provided by T/P, Jason-1 and Envisat.