Description and assessment of the OSTIA reanalysis. - Met Office

In order to meet the needs of the users described above, a homogeneous reanalysis using OSTIA
has been produced as part of the MyOcean European project (http://www.myocean.eu.org), covering
the period 1st January 1985 - 31st December 2007. The reanalysis system is based on the NRT
OSTIA system with a number of changes to input data and methods. The OSTIA system provides
an estimate of the foundation SST, which is defined to be the SST free of diurnal warming (Donlon
et al., 2002). The foundation SST is representative of the temperature throughout the mixed layer
just before sunrise measured at a nominal depth of 0.2-1 m.
This report provides a description of the OSTIA reanalysis system as well as a thorough assessment
of the outputs. The production of a level 4 reanalysis relies on a number of external projects
aimed at producing lower level data. The various data inputs provided by these projects are described
in section 2. The method used to produce the reanalysis is described in section 3 with a
focus on the differences to the NRT OSTIA system, together with a description of the additional
quality control performed. Various aspects of the reanalysis data are investigated in section 4, including
an assessment of the accuracy of the reanalysis in various regions, the impact of aerosols
from the Mount Pinatubo eruption on the reanalysis, assessment of the high-latitude regions where
sea-ice is important, comparison with other longer-term SST reanalyses (particularly the HadISST
and Reynolds products), comparison with the NRT OSTIA system, and an assessment of the new
OSTIA climatologies which have also been produced. Section 5 summarises the results and describes
the work which is planned to improve the OSTIA reanalysis in the future.
1.2 OSTIA reanalysis product suite
Several products are available from the OSTIA reanalysis to fulfil different users requirements. Products
are produced in netcdf GHRSST L4 format, see (GHRSST-PP, 2005). High resolution refers to
products on the native 1/20 ◦ OSTIA grid whilst reduced resolution refers to a 1/4 ◦ regular latitudelongitude
grid.
• High resolution daily OSTIA reanalysis. Files contain the foundation SST, SST analysis error,
sea-ice concentration and land/sea/ice mask fields.
• Reduced resolution daily anomaly. Files contain the SST anomaly from the Pathfinder climatology
(REF), foundation SST and the sea-ice concentration fields.
• High resolution daily OSTIA reanalysis climatology. Files contain the daily mean foundation
SST, SST standard deviation, maximum SST, minimum SST, mean sea-ice concentration, sea
ice standard deviation and land/sea/ice mask fields.
• Reduced resolution daily OSTIA reanalysis climatology. Files contain the daily mean foundation
SST, SST standard deviation, maximum SST, minimum SST, mean sea-ice concentration,
sea ice standard deviation and land/sea/ice mask fields.
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