Description of the OI.v2 (v2 indicates version 2) Weekly SST Analysis

The optimum interpolation (OI) sea surface temperature (SST) analysis is produced weekly on a one-degree grid. The analysis uses in situ and satellite SST's plus SST's simulated by sea-ice cover. Before the analysis is computed, the satellite data is adjusted for biases using the method of Reynolds (1988) and Reynolds and Marsico (1993).

The OI.v2 analysis is described in Reynolds, R.W., N.A. Rayner, T.M. Smith, D.C. Stokes, and W. Wang, 2002: An Improved In Situ and Satellite SST Analysis for Climate. J. Climate, 15, 1609-1625.

From 1990 onward the weeks are centered on Wednesday. For the 1980's the weeks are centered on Sunday because the best satellite data available to us for that period are weekly fields centered on Sunday.

The ice field shows the weekly median ice concentration values input to the SST analysis. Ice concentration is stored as the percentage of area covered. For the ice fields, the value 122 represents land or coast. Note, the ice land mask is a function of the ice analysis and may change periodically.

The sst, error and ice fields are on a 1-degree (360 lon by 180 lat) grid. The first gridbox of each array is centered on 0.5E, 89.5S. The points move eastward to 359.5E, then northward to 89.5N.

The OI analysis is done over all ocean areas and the Great Lakes. There is no analysis over land. The land values are filled by a Cressman interpolation to produce a complete grid for possible interpolation to other grids. The ocean and land areas are defined by a land sea mask. This data set is a binary, direct access file, lstags.ondeg.dat, which is included in the same directory. The spatial grid is defined identically to the grid for the SST arrays.

Please note, a new climatology based on these fields was derived by Yan Xue of NCEPs Climate Prediction Center following the technique of Reynolds and Smith (1995) and Smith and Reynolds (1998). The new climatology is available in:

For further information, contact:

Diane C. Stokes

Voice: (301) 763-8000 extension 7581
FAX: (301) 763-8125

Postal Address:
Climate Modeling Branch W/NP24
Environmental Modeling Center
National Centers for Environmental Prediction
World Weather Building, Room 807
5200 Auth Road
Camp Springs, MD 20746 USA

UPDATED: 20 December 2001