NOAA Polar Orbiter Data User's Guide

Section 5.2.3

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5.2.3 SST Monthly Mean Archive

The SST Monthly Mean Archive contains 12 monthly mean SST fields for one year. NESDIS creates this archive tape in January of every year, archiving the monthly mean fields for the previous year. The data on this tape were derived exclusively from satellite data. The field has a 2.5 degree latitude-longitude resolution or 250-km resolution. For each 2.5 degree box in the field, there is a count of the number of observations in the box, the mean SST, and the standard deviation about the mean, σ.

The SST Monthly Mean archive tape contains two files. The first file is a Header File (previously described in Section 5.2) which contains information about the data on tape. The second file has 72 physical records, each containing 12 logical records consisting of satellite SST monthly mean data. For each month of the year and for each point of its geographical grid, the data consists of 1) the month's mean temperature, T; 2) the standard deviation of a single measure, σ; and 3) the number of observations entering into the mean, N. Each of these quantities are stored as 2-byte integers: T as degrees C x 10, σT as degrees C x 100 and N as itself.

The geographical grid establishes a global field of boxes at 2.5 degree resolution. Boxes are bordered by meridians and parallels which are multiples of 2.5 degrees in latitude and longitude. Four of these boxes can be combined to produce boxes centered on intersections of meridians and parallels which are multiples of 5 degrees in latitude and longitude.

The second file contains 12 fields, the first is January, the last is December. Each field has 72 logical records grouped into 12 logical records per physical record or each field has 6 physical records. Each logical record is 876 bytes long with 10,512 bytes in a physical record. The first logical record in each field contains data for the 2.5 degree latitude band with southern boundary at 90.0S. The 72nd logical record for a field has data for the 2.5 degree latitude band with southern boundary at 87.5N. Within a latitude band, the first grid box has a westernmost boundary of 180W. The 144th grid box has a westernmost boundary of 177.5E. Each grid box requires three 16-bit halfwords. In addition, the first 12 bytes of each logical record contains the year, month, and latitude of the latitude band. A detailed format description of a Monthly Mean Data Field is contained in Table 5.2.3-1.

Table 5.2.3-1. Format of Monthly Mean Data Field.
Logical Record # Bytes Content (Integer values indicated)
1 1-4 Year of data (e.g., 1978)
1 5-8 Month of data (e.g., 1)
1 9-12 Latitude of southern edge of this 2.5 degree latitude band (real value)
1 13-14 Number of observations N for 2.5 degree box with southwest corner at 90.0S, 180.0W.
1 15-16 Monthly mean temperature T (degrees C x 10) for same box
1 17-18 Standard deviation σT (degrees C x 100) for same box
1 19-20 N for 2.5 degree box with southwest corner at 90.0S, 177.5W.
1 21-22 T for same box
1 23-24 σT for same box
... ... ...
1 871-872 N for 2.5 degree box with southwest corner at 90.0S, 177.5E.
1 873-874 T for same box
1 875-876 σT for same box
... ... ...
72 10,507-10,508 N for 2.5 degree box with southwest corner at 87.5N, 177.5E.
72 10,509-10,510 T for same box.
72 10,511-10,512 σT for same box.

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