Sea Surface Salinity (SSS) is one of the fundamental variables for which global sustained observations are needed especially in CLIVAR and GOOS programs. SSS measurements are needed to improve our knowledge of the earth's water cycle and climate. SSS has proven to be valuable especially for :
- improving estimates of evaporation minus precipitation (E-P) budgets
- describing and understanding climate variability at seasonal to decadal time scales
- testing physical processes
- assessing numerical model performances
- quantifying the role of salinity on sea level change
- improving El Nino prediction lead time
The Global Ocean Surface Underway Data program is an international programme for the collection, data processing, archiving, and real-time and delayed mode distribution of Sea Surface Salinity (SSS) and other variables collected underway, by research vessels and ship of opportunity.
>> link to GOSUD homepage
The present SSS Observation Service (SO-SSS) represents the French contribution to the GOSUD program. It aims at collecting, validating, archiving and distributing in situ SSS measurements derived from Voluntary Observing Ship programs. The SSS measurements originate from the Ship Of Opportunity Programs (SOOP) operated from Brest, France, and Nouméa, New Caledonia. Additional data are obtained from French research vessels, including the Alis and the Astrolabe. On average, each selected ship provides one to three sections per season along a regular track.
>> link to SO-SSS homepage
The CORIOLIS contribution to the SSS observing network can be detailed in four points :
1. Testing and/or calibration of TSG instruments partly processed by CORIOLIS / SHOM
The SSS measurements are mainly based on SeaBird SBE-21 ThermoSalinoGraph (TSG) instruments fitted with bubble traps, the whole system being located as close as possible to the ship's engine water intake. Since 2002, the Department of Metrology and Chemical Oceanographic SHOM calibrates some TSG instruments and remote temperature sensors fitted to vessels entering through the Coriolis consortium.
2. Data collection on merchant ships and on research vessels
France contributes widely to the SSS network and provide the data to the GOSUD project
- 7 French research vessels acquire thermosalinograph data in a routine mode and transmit their SSS and SST data to the Coriolis data centre (GOSUD GDAC) on a daily basis. Meteorological data are also sent on a daily basis. The following research vessels have been equipped for such a data acquisition and transmission :
- Pourquoi Pas ? (Ifremer)
- L'atalante (Ifremer)
- Le Beautemps Beaupré (Shom)
- Le Suroît (Ifremer)
- Thalassa (Ifremer)
- Marion Dufresne (IPEV)
- L'Europe (Ifremer)
- IRD leads the ORE SSS (Sea Surface Salinity Observing Network). SSS data are collected on board 12 merchant vessels and 2 research vessels. They are checked before any transmission to the GDAC
3. Data management activities
- The real time SSS data collected by the Sea Surface Salinity Observation Service are used to remotely check the on-board TSG systems at LEGOS. LEGOS does not recommend using these data for research purposes since they cannot be properly validated. These data are however made available for operational oceanography from the CORIOLIS data center. Every day, SSS data are sent to Coriolis either by direct submission or through the GTS (Global Telcommunication System) both for research vessels and Merchant vessels.
- Delayed mode processing is performed by IRD/LEGOS for merchant vessels and by Ifremer/LPO and IRD/brest for Research vessels.
4. R&D activities
The R & D activities within the GOSUD project are related to :
- Delayed mode data processing
Taking into account the near real time data, the calibration coefficients of the instruments, the water samples analysis and the neighbouring data (ie Argo data), a method has been developed by IRD within the ORE SSS project. It enables to elaborate a delayed mode data set of higher accuracy
- Gridded fields
An extension of the gridded fields elaborated from vertical profiles to the surface has been done to take into account sea surface salinity data acquired with thermosalinographs
Figure : Latest 30 days of data acquired within GOSUD network from CORIOLIS GDAC
Figure : spatial distribution of real time sea surface salinity data between 1998-2014 (©LEGOS)