NOAA KLM User's Guide

Section 9.1.1

Blue line drawn across page to separate text from document title.
Introduction Page, NOAA KLM TOC, Acronyms,
Previous Section, Next Section

9.1.1 SST Field Format

All of the SST Field products including the 14-km gridded (0.125 degree), 50-km gridded (0.5 degree), and 100-km gridded (1 degree) are derived from the basic 8-km SST observations. An SST Field consists of a specific set of information pertaining to latitude and longitude intersections. The Global-Scale (1 degree resolution) file includes the area from 180W to 179E longitude and from -70S to 70N latitude and is generated daily. The regional scale (0.5 degree) and local scale (0.125 degree) fields are generated twice weekly. All the fields are generated by analyzing all the SST observations obtained during the period since the last analysis.

As mentioned in the previous section, most SST archive cartridges contain a header file which is usually the first file on the cartridge. The remaining files on the cartridge are field accumulation files.

Before September 2001, all field accumulation files (regardless of resolution) consisted of a Directory Record followed by some number of fields. For field data after September 2001, the individual fields are no longer stored in accumulation files. Therefore, the field accumulation Directory Record was eliminated, and multiple field files are no longer bundled into one big file. Field files are now archived as individual fields and thus the rest of the format (field documentation record and field data records) remains the same. Each field consists of a Field Documentation Record, followed by a Field Data Record for each latitude row in the field. The accumulation file Directory Record (which exists prior to September 2001 only) includes, among other things, the starting record number (i.e., the record number of the Field Documentation Record) for each field in the accumulation file. Details of the Directory Record, Field Documentation Record and Field Data Records are contained in Sections 9.1.1.1 , 9.1.1.2 and 9.1.1.3, respectively. Data records (latitude rows) in the fields are ordered from south to north.

The fields will generally be arranged in chronological order. A field for a particular time period may be missing or repeated so one should examine the Field Documentation Record for each field in the file to find that field spanning the time of interest. The Field Documentation Record (the first record of each field) should be used in referencing the data records for the field, since it provides information concerning the organization, size, and time period of the field.

After the Directory Record, there are NFIELDS fields. The first record of each field is a Field Documentation Record which is followed by NRECS Field Data Records, one for each latitudinal row in the field. Each row (logical record) consists of 28 bytes of information for each longitude or column forming a grid intersection, plus 28 bytes at the end of the record (the Latitudinal Row Identifier) containing the row number identification and the date and time of the last analysis made for the field.

The 100-km SST field cartridge is generated monthly (on the second day of the month). The cartridge contains two files: File 1 is the Header File (Table 9.1-1). File 2 is the 100-km SST field accumulation file. In File 2, after the Directory Record, there are 35 fields, 142 logical records per field. These fields are produced daily. Each field contains the Field Documentation Record followed by 141 Field Data Records, one for each 1 degree latitudinal row from -70S to 70N. There are 360 grid intersections in each row, one for each l degree of longitude from -180 W eastward to 179E. Each Field Data Record (logical record) contains 10,108 bytes ((360 x 28) + 28 for row identification).

The 50 km gridded SST field accumulation files are archived to cartridge once a month (on the second day of each month) for the previous month. File 1 is a Header File (Table 9.1-1), while files 2-6 contain the field accumulation files for regions 1 through 5 respectively (one geographic region per file). Each field accumulation file contains 10 fields. These fields are produced twice a week by analyzing all the SST observations obtained since the last analysis. The five regions are defined as follows:

Region 1:

5N through 53N latitude
-100W through -52W longitude

Region 2:

15N through 63N latitude
-145W through -97W longitude

Region 3:

15N through 63N latitude
+170E through -142W longitude

Region 4:

-35S through 20N latitude
-150W through -70W longitude

Region 5:

-35S through 20N latitude
+155E through -145W longitude

The 14-km (0.125 degree) gridded SST fields (Local-Scale Analyses) are archived monthly on two cartridges. There are eight 0.125 degree resolution fields which cover the following areas:

Region 2:

18N through 31N latitude
-98W through -80W longitude

Region 4:

39N through 52N latitude
-136W through -123W longitude

Region 5:

28N through 41N latitude
+155E through -145W longitude

Region 6:

30N through 36N latitude
-82W through -60W longitude

Region 7:

18N through 32N latitude
-85W through -70W longitude

Region 10:

50N through 62N latitude (Seasonal)
-160W through -126W longitude

Region 11:

50N through 70N latitude (Seasonal)
-180W through -157W longitude

Region 12:

20N through 32N latitude
-136W through -105W longitude

The first cartridge of the 14-km gridded SST field data contains Regions 2, 4, 5, 6, and 7 which cover the Gulf of Mexico, Northwest Pacific coast, Southwest Pacific coast, Northeast Atlantic coast, and Southeast Atlantic coast, respectively. This cartridge contains six files, the first file being the Header File. Files two through six contain the 14-km field accumulation files for Regions 2,4,5,6, and 7, respectively. Each accumulation file contains twelve fields (2 per week) ordered chronologically.

The second cartridge of the 14-km gridded SST data contains Regions 10, 11 and 12 which cover the Gulf of Alaska, Bering Sea and the Gulf of California, respectively. This cartridge contains four files, the first file being the Header File (Table 9.1-1). The second, third and fourth files contain the 14-km field accumulation files for Regions 10,11 and 12, respectively. Each accumulation file contains twelve fields (2 per week) ordered chronologically.

Beginning with data from NOAA-16 on February 21, 2001, a new 14-km SST Field encompasses all but Regions 10 and 11, listed above. This is considered the new North American field (14 km NA ETA Field). This region corresponds to the ETA model's grid for North America and should be very useful for modeling and climatological purposes. The region itself consists of an area that extends from 15N to 60N and 50W to 140W. This field is produced on odd days of the year by analyzing all the SST observations obtained in the previous two days. The 14 km NA ETA Field contains 18 files organized chronologically. The first physical record of the file is a directory record pointing to the beginning of each of the 18 fields. Each field of the file contains 1+(18 x 361)=6499 logical records blocked into 6499 physical records in the file.

The original SST field formats were not Year 2000 (Y2K) compliant, but have been changed to meet the four-digit year requirement. These changes are noted in the appropriate locations in the format records.

Starting with data generated on or about September 2, 2001, all the field accumulation files will be discontinued. They will be replaced by individual field data files (as opposed to bundling several field files into accumulation files). Specifically: the 100-km field accumulation file that is archived monthly will be replaced by a 100-km field file archived daily; the 50-km field accumulation Regional files that are archived monthly will be replaced by the new 50-km global field file which will be archived twice weekly; the 14-km field accumulation data for Regions 10 and 11 that are archived monthly will be replaced by 14-km field data including a new Hawaii region (between 10N and 30N latitude and 170W and 150W longitude) archived twice weekly; and the 14-km field accumulation data for Region 12 that are archived monthly will be replaced (encompassed) by 14-km field data archived every 48 hours or on all odd Julian days.

9.1.1.1 Directory Record Format

A Directory Record is always the first record of each SST Field Accumulation File (not counting the Header File and for data generated after September 2001 which are not accumulation files but are individual field files). It has a variable length with zero fill to the logical record size of the type of field, and serves as a pointer to the beginning of each field. Table 9.1.1.1-1 contains the format of the Directory Record.

Table 9.1.1.1-1. Format of the Directory Record for any SST Field Accumulation File.
Full Word # Content
1 Number of records in the data set
2 Number of records in each field (NRECS)
3 Number of fields in the accumulation file (NFIELDS)
4 Field number of latest field entered in accumulation file
5 Record number of first record of Field #1
6 Record number of first record of Field #2
... ...
4+NFIELDS Record number of first record of Field #NFIELDS

9.1.1.2 Field Documentation Record Format

The format of the Field Documentation Record is described in this section. There are 158 words of information in the Field Documentation Record with blank fill to the end of the logical record (logical record size is dependent on number of longitude columns in the field). The minimum size is 158 words (632 bytes) and the maximum size is 2,527 words (10,108 bytes). Table 9.1.1.2-1 contains the format (where R or I indicate real or integer words, respectively) of the Field Documentation Record.

Unfortunately, the SST fields were developed when the format for IBM real numbers were thought to be the standard. Many platforms cannot read IBM real numbers and so the following variables in the Field Documentation Record: SMGLAT, AXLAT, SMLONG, ASLONG, RES, SMHOUR, HOURS, TIMGAP, SMREL, AXREL, SORC, OBTYPE, GRDWTS, MKM, H, EXP, FDX, XCLASS, DEL, BDEL and FCWT (defined in Table 9.1.1.2-1) will be unavailable without conversions. The values of the most used parameters for the 14 km NA ETA field are listed specifically in Table 9.1.1.2-1. The general user will not need the rest of the values, but for the advanced user a conversion program from IBM real numbers to IEEE real numbers is included in Appendix N.

Table 9.1.1.2-1. Format of the Field Documentation Record.
Word # Parameter R or I Description
1 LDBGN I Record number of the first row of the field (currently 2 for all fields since the documentation record requires only one record).
2 SMGLAT R Minimum latitude included in field which is the bottom edge and first row of field (-South; + North). 15.0 for 14 km NA ETA field.
3 AXLAT R Maximum latitude included in field which is the top edge and last row of field (-South; + North). 60.0 for 14 km NA ETA field.
4 SMLONG R Minimum longitude included in field which is the left edge and first column of field (-West; + East). -140.0 for 14 km NA ETA field.
5 AXLONG R Maximum longitude included in field which is the right edge and last column of field (excluding the I.D. column) (-West;+East). -50.0 for 14 km NA ETA field.
6 RES R Number of latitude-longitude degrees between each grid point. 0.125 for 14 km NA ETA field.
7 SMHOUR R Youngest time, in hours of the year, of observations used during last analysis, which becomes the oldest time allowed for the next analysis.
8 HOURS R Oldest time, in hours of the year, of observations used during last analysis.
9 TIMGAP R Number of hours between youngest and oldest times of observations used in analysis.
10 MAXDAT I Maximum number of hours allowed in time period for observation times to be included in analysis.
11 SMREL R Minimum reliability of observations to be used in analysis.
12 AXREL R Maximum reliability of observations to be used in analysis.
13-22 SORC(10) R List of source codes of observations to be used in analysis. (See Table 9.1.2-5)
23-32 OBTYPE (10) R List of observation types allowed to be used in analysis. (See Table 9.1.2-4)
33 NROWS I Number of rows (latitudinal parallels) included in field, excluding documentation record.
34 NCOLS I Number of columns (longitudinal meridians) in field, including the I.D. column.
35 IBLK I Number of rows or logical records per physical block.
36 NWRDS I Number of full words (32 bits) allocated to each grid point.
37 ISZ I Number of rows to be maintained in an array in core for temperature analysis and calculation of gradients.
38 ICENT I Center line within the array of ISZ rows upon which calculations will be performed.
39-41 LWT, LNT, LBT I Word number, length in bits, and starting bit location of analysis temperature within a grid intersection information unit of an SST field.
42-44 LWG, LNG,LBG I Word number, length in bits, and starting bit location of average gradient.
45-47 LWGXP, LNGXP, LBGXP I Word number, length in bits, and starting LBGXP bit location of gradient X+ direction.
48-50 LWGXN, LNGXN, LBGXN I Word number, length of bits, and starting LBGXN bit location of gradient X- direction.
51-53 LWGYP, LNGYP, LBGYP I Word number, length in bits, and starting LBGYP bit location of gradient Y+ direction.
54-56 LWGYN, LNGYN, LBGYN I Word number, length in bits, and starting LBGYN bit location of gradient Y- direction.
57-59 LWPD, LNPD, LBPD I Word number, length in bits, and starting LBPD bit location of Physiographic Description.
60-62 LWNO, LNN, OLBNO I Word number, length in bits, and starting LBNO bit location of Number Observations.
63-65 LWAGE, LNAGE, LBAGE I Word number, length in bits, and starting LBAGE bit location of Age of most Recent Observations.
66-68 LWREL, LNREL, LBREL I Word number, length in bits, and starting LBREL bit location of Reliability.
69-71 LWCLS, LNCLS, LBCLS I Word number, length in bits, and starting LBCLS bit location of Class 1 coverage.
72-74 LWSXP, LNSXP, LBSXP I Word number, length in bits, and starting LBSXP bit location of Spatial Covariance X+.
75-77 LWSXN, LNSXN, LBSXN I Word number, length in bits, and starting LBSXN bit location of Spatial Covariance X-.
78-80 LWSYP, LNSYP, LBSYP I Word number, length in bits, and starting LBSYP bit location of Spatial Covariance Y+.
81-83 LWSYN, LNSYN, LBSYN I Word number, length of bits, and starting LBSYN bit location of Spatial Covariance Y-.
84-86 LWIND, LNIND, LBIND I Word number, length in bits, and starting LBIND bit location of Independent Temperature.
87-96 GRDWTS (10) R Weight assigned to each grid unit, according to its distance from the grid intersection for which gradients are being calculated.
97 NP I Number of grid points to be used in calculation of gradients.
98-117 KMDST (10,2) I Look up table of gradient values and corresponding distances to be used in determining the search area for analysis.
118 MKM R Number of paired entries in KMDST.
119-138 H(10,2) R Look up table of gradient values and corresponding factors to be used in determining the new weight assigned to the observation temperature analysis.
139 MH I Number of paired entries in H.
140 EXP R Exponent used in temperature analysis.
141 FDX R Factor used in determining new weight assigned to the observation temperature for analysis.
142 XCLASS R Factor used to place gradients into a class for Gradient Class Summary.
143 DEL R Maximum number of degrees centigrade (x 10) that the new analysis temperature may differ from the previous SST field temperature.
144 MF I Factor applied to the previous field temperature and reliability to determine the final analysis temperature and its reliability.
145 MSTAR I Factor applied to the combined observation temperature and weight in determining the new analysis temperature.
146 MNSRCH I Minimum distance in kilometers to be searched for analysis observations.
147 MXSRCH I Maximum distance in kilometers to be searched for analysis observations.
148 BDEL R Maximum distance in kilometers to be searched for analysis observations. Maximum difference allowed between new analysis temperature and the previous one for Class 1 coverage bit to be set to 1.
149 FCWT R Maximum value that can be assigned as the reliability of the new analysis temperature.
150 IYYY I Year of youngest time of observation data used (0-99).
151 IYMM I Month of youngest time of observation data used (1-12).
152 IYDD I Day of youngest time of observation data used (1-31).
153 IYHH I Hour of youngest time of observation data used (0-23).
154 IOYY I Year of oldest time of observation data used (0-99).
155 IOMM I Month of oldest time of observation data used (1-12).
156 IODD I Day of oldest time of observation data used (1-31).
157 IOHH I Hour of oldest time of observation data used (0-23).
158 ICURTM I Last time used in analysis (in Julian days from Jan. 1, 4713 BC).

9.1.1.3 Field Data Record Format

Each Field Data Record (latitudinal row) consists of a series of grid intersection points. These points are 28 bytes in length. Each longitude (column) reflects one grid intersection. At the end of the data record (i.e., immediately following the last column) is the 28-byte Latitudinal Row Identifier. All parameters in the grid intersection are stored as integer values and have the format shown in Table 9.1.1.3-1.

Table 9.1.1.3-1. Format of the parameters in the grid intersection.
Word # Byte # Description Units Range
1 1-2 Analysis Temperature C x 10 -850 to +610
1 3-4 Average Gradient C/100 km (x 10) 0 to 300
2 5-6 Gradient X+ C/100 km (x 10) 0 to 300
2 7-8 Gradient X- C/100 km (x 10) 0 to 300
3 9-10 Gradient Y+ C/100 km (x 10) 0 to 300
3 11-12 Gradient Y- C/100 km (x 10) 0 to 300
4 13 Physiographic Descriptor 0 = sea; 1=land 0 to 15
4 14 Ice Field Percent sea ice for 50 km SST field. Otherwise, undefined. 0 to 100 for 50 km SST Field. Set to 100 for all other fields.
4 15 Number of Observations Integer 0 to 255
4 16 Age of Most Recent Observation Hours 0 to 255
5 17-18 Reliability Integer 0 to 32767
5 19-20 Class 1 Coverage Bits 0 or 1
6 21 Spatial Covariance X+ Grid units 0 to 10
6 22 Spatial Covariance X- Grid units 0 to 10
6 23 Spatial Covariance Y+ Grid units 0 to 10
6 24 Spatial Covariance Y- Grid units 0 to 10
25-26 Climatological Temperature (for 100 km field file only) C (x 10) -850 to +610  
7 27-28 Spare Undefined Blank

The format of the Latitudinal Row Identifier (last 28 bytes of a row) is contained in Table 9.1.1.3-2. All parameters in the table are stored as integer values.

Table 9.1.1.3-2. Format of the Latitudinal Row Identifier.
Word # # Bytes Description Units Range
1 4 Row Integer 1-141
2 4 Spare Undefined 0 to 32767
3 4 Spare Undefined 0 to 32767
4 1 Physiographic Descriptor Integer Always 255
4 3 Spare Undefined 0 to 32767
Date and time at which analysis was performed:
5 4 Hour of Day, Minutes of hour 100 x hours + minutes 100 x (0-23) + (0-59)
6 4 Day of Year Days 1-366
7 4 Year (2-digits before 3/3/99; 4-digits after 3/3/99) Years 0-99 (1999-2100 after 3/3/1999)

The terms used to describe the grid intersection points are defined as follows:

ANALYSIS TEMPERATURE - The latest sea surface temperature calculated based on the previous analysis temperature, weighted according to its reliability, combined with a weighted average of current observations within a surrounding area of the gridpoint. The surrounding area is determined according to the gradient in each direction .

AVERAGE GRADIENT - The average of the gradients in all four directions (N, S, E, W) from the grid intersection.

GRADIENT IN X+ DIRECTION - Change in temperature between the grid point and neighbor points within the field in the positive direction along the X axis.

GRADIENT IN X- DIRECTION - Change in temperature in the negative direction along the X axis.

GRADIENT IN Y+ DIRECTION - Change in temperature in the positive direction along the Y axis.

GRADIENT IN Y- DIRECTION - Change in temperature in the negative direction along the Y axis.

PHYSIOGRAPHIC DESCRIPTOR - The land/sea tag indicating whether a grid intersection is a land or sea point.

SPARE - Unused parameter.

NUMBER OF OBSERVATIONS - The total number of current observations used in the analysis of the new temperature for the grid intersection.

AGE OF MOST RECENT OBSERVATION - The age, in hours before the time of the analysis, of the most recent observation used to determine the new temperature for a grid intersection.

RELIABILITY - New reliability associated with the new temperature, based on the previous reliability combined with the weighted reliability of all observations used in the last analysis. Larger values are more reliable.

CLASS 1 TEMPORAL COVERAGE - Set of bits (0-15) of which Bit 1 is set to 1 for each analysis which included observations with a reliability greater than or equal to a specific minimum reliability considered as Class 1. Bit 0 always remains a 0, and all bits are shifted right during each analysis leaving Bit 1 to 0 when no Class 1 reliability observations are used for a grid intersection.

SPATIAL COVARIANCE X+ - The distance in grid units from the grid intersection to the nearest land mass in the positive direction along the X axis.

SPATIAL COVARIANCE X- - The distance in grid units from the grid intersection to the nearest land mass in the negative direction along the X axis.

SPATIAL COVARIANCE Y+ - The distance in grid units from the grid intersection to the nearest land mass in the positive direction along the Y axis.

SPATIAL COVARIANCE Y- - The distance in grid units from the grid intersection to the nearest land mass in the negative direction along the Y axis.

CLIMATOLOGICAL GRID TEMPERATURE - The average sea surface temperature of a grid intersection for a particular month over a number of years, taken from the global climatology file (for 100 km field file only).

Amended September 5, 2001


Previous Section Top of Page Next Section