Recent Developments to the Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) System
Roberts-Jones, Jonah; Fiedler, Emma; Martin, Matthew; McLaren, Alison; While, James

The Operational Sea surface temperature and Sea Ice Analysis (OSTIA) system was developed at the Met Office, where it is run in near real time on a daily basis. OSTIA produces a global field of foundation sea surface temperature (free of diurnal variability) every day on a 1/20 degree (~6km) grid. The system uses input data from infrared and microwave satellite measurements (currently Met-OpA and NOAA AVHRR, GOES, IASI, NAR, SEVIRI and TMI) together with in-situ data and a sea ice concentration product (from EUMETSAT OSI-SAF). Data assimilation methods are used to combine the different input data, taking into account estimates of the observational error, to produce a gridded analysis. OSTIA is widely used, particularly in numerical weather prediction centres (including the Met Office, ECMWF, Meteo France and others) where it is used as a lower boundary condition in NWP forecast models. The OSTIA system is also being used in the ESA Climate Change Initiative project to produce the filled gridded ('L4') product for the SST essential climate variable.

The OSTIA system is under continual development and recent developments will be discussed together with an assessment of the accuracy of the current near real time OSTIA system. Recent developments include the use of newly calculated background error covariances and an improvement to the numerical scheme which are shown to improve both the accuracy and the feature resolution of the analysis. The loss of AATSR had a significant impact on the accuracy of OSTIA, as AATSR was used as reference data to bias correct the data from other satellites. This will be discussed and also recent improvements to use a subset of MetOP AVHRR data as reference data in the absence of AATSR. Future developments will also be presented, which include extending the current system to produce estimates of diurnally varying sea surface temperature on a global grid.