This issue is dedicated to the study of the impact of the loss or addition of satellite altimetry on operational products and systems.

The first news feature by Larnicol et al. is presenting the GODAE OceanView Observing System Evaluation Task Team which primary objective is to support observational agencies by demonstrating the impact of observations on operational forecast and reanalysis systems. Its secondary objective is to improve the performance of operational ocean forecast systems.

The second paper by Labroue et al. is reminding us about the main 2012 events within the satellite altimetry constellation. For the past two decades, we have been used to take for granted the presence of several satellites flying together. The loss of Envisat in April 2012 and the decision to put Jason-1 on its end of life orbit is a crude reminder of this constellation fragility. Hence during 2012, the DUACS and MyOcean Sea Level TAC teams have contributed to secure the altimetry component in the frame of operational oceanography.

The third paper by Labroue et al. is displaying the potential offered by Cryosat-2 for the mesoscale signal. The added value brought by Cryosat-2 as a complement to the existing altimetry constellation is discussed as well as how Cryosat-2 could contribute to secure the altimetry constellation and thus the operational oceanography. Cryosat-2 mission has been introduced into the Near Real Time Sea Level system since February 2012 and has been added to the Delayed Time system in April 2012.

The fourth paper by Remy et al. addresses the impact of the change of the satellite constellation on the French Mercator Ocean analysis and forecasting systems. The impact of the loss of the ENVISAT and Jason1 along track Sea Level Anomaly data in the beginning of the year 2012 in the real time products is studied. A dedicated set of Observing System Experiments (OSEs) is performed and preliminary results are shown. An OSE involves running a copy of an existing assimilation run where some observations are excluded. The difference between this run and the original run assimilating all the observations allows a detailed assessment of the impact the observations have on the assimilation system.

Finally, the fifth paper by Lea et al. is showing a number of Observing System Experiments (OSEs) to assess the impact of the observing network on FOAM, the UK Met Office’s ocean assimilation and forecasting system, as part of GODAE OceanView. A parallel version of the FOAM operational system was run, during April 2011, withholding Jason-2 altimeter observations. Withholding Jason-2 removed 43% of the altimeter data and resulted in a 4% increase in the RMS SSH observation-minus-background differences and around ±2ºC small scale changes in 100m temperature as well as around ±0.2 psu changes in surface salinity.

We will meet again in April 2013 for a joint Mercator Ocean/Coriolis issue displaying the latest news about In Situ Observations. We wish you a pleasant reading.

• GODAE OceanView Observing System Evaluation (OSEval) Task Team news
• Death and birth in the Altimetry constellation
• An eventful year in the Altimetry constellation
• Impact of the loss/addition of satellite altimetry on Mercator Ocean operational products
• Evaluation experiment to test the value of altimetry in FOAM