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Discussion papers | Copyright
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 13 Jul 2018

Research article | 13 Jul 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Ocean Science (OS).

Synergy between in situ and altimetry data to observe and study the Northern Current variations (NW Mediterranean Sea)

Alice Carret1, Florence Birol1, Claude Estournel2, Bruno Zakardjian3, and Pierre Testor4 Alice Carret et al.
  • 1LEGOS, Université de Toulouse-CNES-CNRS-IRD, OMP, 14 Av. E. Belin, 31400 Toulouse, France
  • 2L.A. Université de Toulouse-CNRS, OMP, 14 Av. E. Belin, 31400 Toulouse, France
  • 3Université de Toulon, CNRS/INSU, IRD, Mediterranean Institute of Oceanography (MIO), UM 110, 83957 La Garde, France
  • 4LOCEAN, Sorbonne Université-CNRS-IRD-MNHN, Paris, France

Abstract. During the last 15 years, substantial progress has been achieved in altimetry data processing, providing now data with enough accuracy to illustrate the potential of these observations for coastal applications. In parallel, new altimetry techniques improve the data quality by reducing the land contamination and by enhancing the signal-to-noise ratio. Satellite altimetry provides ever more robust and accurate measurements ever closer to the coast and resolve ever shorter ocean signals. An important issue is now to learn how to use altimetry data in conjunction with the other coastal observing techniques.

Here, we demonstrate the ability of satellite altimetry to observe part of the Northern Current variability. We cross-compare and combine the currents provided by large data sets of ship-mounted ADCPs, gliders, HF radars and altimetry. We analyze how the different available observing techniques capture the current variability at different time-scales. We also study the coherence/divergence/complementarity of the informations derived from the different instruments considered. Two generation of altimetry missions are used: Jason 2 (nadir Ku-band radar) and SARAL/AltiKa (nadir Ka-band altimetry); their performances are compared.

In terms of mean speed of the Northern Current, a very good spatial continuity and coherence is observed at regional scale, showing the complementarity between all the types of current measurements. In terms of current variability, there is still a good spatial coherence but the amplitude of the seasonal variations is underestimated by ~50% in altimetry, compared to both gliders and ADCPs, because of a too low spatial resolution. For individual dates this number varies a lot as a function of the distance to the coast and width of the Northern Current. Compared to Jason 2, the SARAL/AltiKa data tend to give estimations of the NC characteristics that are closer to in situ data in a number of cases. Satellite altimetry obviously provides a synoptic view of the Northern Current circulation system and variability which helps to interpret the other current observations. Its regular sampling allows the observation of many features that may be missed by in situ measurements.

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Short summary
This study uses different in-situ and satellite measurements to investigate the ocean circulation in the NW Mediterranean Sea. We analyze how the different instruments (satellite altimetry, HF radars, gliders, ADCPs) capture the current variability and how they complement each other. We demonstrate the ability of satellite altimetry to capture the fluctuations of the narrow coastal Northern Current at different time-scales. This study provides an integrated approach to a coastal dynamics study.
This study uses different in-situ and satellite measurements to investigate the ocean...