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OISST - Frequently Asked Questions

1. Is the the 1/4° daily OISST the same as the Reynolds SST?

The 1/4° daily OISST belongs to a family products that are sometimes referred to as "Reynolds SST" after Richard W. Reynolds. R. W. Reynolds, together with T. Smith, developed methodologies for producing interpolated gridded SSTs when they were working at the National Centers for Environmental Prediction (NCEP). Older Reynolds SST products have been retired, except for the 1° weekly OISST.

2. What is the 1° weekly OISST and how is it different from the 1/4° daily OISST ?

The earliest OISST analyses were at lower spatial and temporal resolution. This includes the NOAA 1° weekly OISST (version 2) available at NCEP, described in Reynolds et al. (2002), and referred to as OI.V2. NCEP also runs a copy of the daily OISST software for their internal use. This and the fact that both weekly and daily analyses are both at version 2 often leads to confusion. The weekly OISST is not a seven-day average of the 1/4° daily OISST. The weekly OISST gets its name because it uses a week of satellite observations averaged onto a 1° grid prior to interpolation; the daily OISST uses a day of satellite observations averaged onto the 1/4° grid. There are other methodological differences between the two products, discussed in the references previously mentioned.

3. What are the inputs to the daily OISST and how are they processed?

The three inputs to the daily OISST require different preparation, as described in Reynolds et al. (2007). The in situ SSTs need to be checked for outliers, and then averaged onto the 1/4° grid, separately for ships and buoys. The ship data are adjusted to the buoys by subtracting a constant 0.14°C. Similarly, satellite temperatures are averaged onto the analysis grid, after which they are bias-adjusted to the in situ data. For the marginal ice zone, where there is little in situ data, proxy SSTs are generated from sea ice concentrations. The interpolation step combines the prepared inputs. Banzon et al. (2016) provides more details on the input datasets used.


OISST processing flowchart.

4. What climatology is used to compute the SST anomalies?

The climatology used to compute the daily OISST anomalies, available from NCEP,represents the 1971–2000 base period and is interpolated to 1/4° daily grid file from the 1° monthly file. The climatology is described in Xue et al. (2003).

5. Is a 30-year climatological mean of the 1/4° daily OISST available?

NOTE: Banzon et al. (2014) computed a new climatology on a 1/4° grid using thirty years (1982-2011) of the AVHRR_ONLY. This climatology, available by ftp, has a higher resolution than the NCEP climatology, but is not yet utilized for the OISST anomaly computation

1971-2000 NCEP SST climatology

Animated loop of NCEP 1971–2000 climatology.