SUCCESSES AND CHALLENGES FOR THE MODERN SEA SURFACE TEMPERATURE OBSERVING SYSTEM C. J. Donlon (1) , K. S Casey (2) , C. Gentemann (3) , P. LeBorgne (4) , I. S. Robinson (5) , R. W Reynolds (6) , C. Merchant (7) , D. Llewellyn-Jones (8) , P. J. Minnett (9) , J. F. Piolle (10) , P. Cornillon (11) , N. Rayner (12) , T. Brandon (2) , J. Vazquez (13) , E. Armstrong (13) , H. Beggs (14) , I. Barton (15) , G. Wick (16) , S. Castro (17) , J. Hoeyer (18) , D. May (19) , O. Arino (20) , D. J. Poulter (5) , R. Evans (9) , C. T. Mutlow (21) , A. W. Bingham (13) and A. Harris (22) . (1) ESA/ESTEC, Noordwijk, The Netherlands, craig.donlon@esa.int (2) NOAA National Oceanographic Data Center (3) Remote Sensing systems, USA (4) Meteo France, France, (5) National Oceanography Centre, Southampton, UK, (6) NOAA National Climate Data Center, USA, (7) University of Edinburgh, UK, (8) University of Leicester, UK (9) University of Miami, USA, (10) IFREMER, Brest, France (11) University of Rhode Island, USA (12) The MetOffice, Exeter, Devon, UK (13) NASA- JPL PODAAC, Pasadena, USA (14) Bureau of Meteorology, Melbourne, Australia (15) CSIRO, Hobart, Tasmania, Australia (16) NOAA ESL, Boulder, Colorado, USA, (17) University of Colorado, Boulder, Colorado, USA (18) Danish Meteorological Institute, Denmark (19) NAVOCEANO, USA, (20) ESA/ESRIN, Frascati, Rome, Italy (21) Rutherford Appleton Laboratory, Oxford, UK (22) University of Maryland, USA 1. INTRODUCTION Sea Surface Temperature (SST) at the ocean- atmosphere interface is a fundamental variable for understanding, monitoring and predicting fluxes of heat, momentum and gas at a variety of scales from local to global climate that determine complex interactions between atmosphere and ocean. This paper has been prepared for those implementing and working with the modern sea surface temperature (SST) observing system. The purpose of the paper is threefold: (1) to highlight key developments of the modern era SST observing system over the last 10 years (2) to discuss the principal challenges for the observing system in the next 10 years and (3) to propose an ideal plan for the global integrated high resolution SST observing system. Each recommendation is fully qualified in a full paper describing the Group for High Resolution SST (GHRSST) Development and Implementation Plan that can be found at http://www.ghrsst- pp.org/modules/documents/documents/OO- ModernEraSST-v3.0.pdf . 2. SST SUCCESSES OF THE LAST DECADE THROUGH THE GHRSST EXPERIENCE The GHRSST project was a significant (but not the only) contribution to progress in SST over the last decade as it nurtured a community of scientists from the scientific and operational agencies and institutions. Ten international workshops were been held to ensure that the SST user-producer community was involved at all stages of GHRSST service and product development. User requirements for all GHRSST activities were defined in five areas: (1) scientific development and applications, (2) operational agency requirements, (3) SST product specifications, (4) programmatic organization of an international SST service and (5) developing and sharing scientific techniques and insight to improve data products and exploit the observing system. These requirements were critical to establishing a GHRSST framework and a work plan. A full discussion of GHRSST success over the last 10 years is reported in [5, 6]. through GHRSST, a large number of users now gain access to a large number of SST products, from a large number of satellite sensors and they are provided with information and tools to understand the strengths, limitations and challenges that