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NCEP Real-time Marine Observations README: 1 April 1997
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1. Introduction
Monthly and weekly files of surface marine data gathered from the Global
Telecommunications System (GTS) by NOAA's National Centers for Environmental
Prediction (NCEP), and provided courtesy of Richard W. Reynolds at NCEP,
become available at NCEP two days after the data month or week.
These are basic observational data (individual marine reports from ships,
buoys, etc.) in a simple ASCII format containing selected weather elements.
The data are largely unedited, although one major change in processing became
effective with March 1997 data (see section 4). Data for the immediately
preceding month and week are available at NCEP; monthly files back to January
1991 are available from NOAA's Environmental Research Laboratories (ERL)
Climate Diagnostics Center (CDC).
The data are also used at CDC to construct monthly summaries for 2-degree
latitude x 2-degree longitude boxes. For additional information about these
summary products, please refer to http://www.cdc.noaa.gov/cgi-bin/CDCData.pl.
Copies of the monthly data, and the 2-degree summaries, become available at
CDC about 2-5 days following each data month.
Section 2 gives detailed information about ftp access to the data at NCEP
or CDC, and Section 3 provides the format description.
2. Availability via anonymous ftp
Although the basic data are in a simple ASCII format (section 3), the files
are stored and transferred via ftp in compressed form. Thus, depending on
the computer type to which you are transferring the data, binary mode should
generally be used for ftp transfers.
The data at NCEP are compressed using the "gzip" utility; to ensure more
widespread availability, the data at CDC have been recompressed using "Z"
compression. (To uncompress "filename.gz" on a Unix system, type "gunzip
filename.gz"; or to uncompress "filename.Z", type "uncompress filename.Z".)
a) To obtain data for the immediately preceding month or week:
ftp nic.fb4.noaa.gov (user: anonymous; password: your e-mail address)
cd /pub/ocean/clim1/gts
The monthly file is "gtsobs.gz" and the weekly file (i.e., Sunday through
Saturday) is "gtswkly.gz". These gzip'd files are overwritten on the second
day of each month and week, respectively. Contact:
Diane Stokes
W/NP24, Room 807
4700 Silver Hill Road
Stop 9910
Washington, DC 20233-9910
(301) 763-8000 x7581
wd01dm@sgi26.wwb.noaa.gov
b) Data back to January 1991 (monthly file "nqYYMM.Z", where YY and MM are
the year and month, e.g., "nq9601.Z"):
ftp ftp.cdc.noaa.gov (user: anonymous; password: your e-mail address)
cd Public/coads/ncep_obs
Contact:
Scott Woodruff
NOAA/ERL (R/E/CD)
325 Broadway
Boulder, CO 80303-3328
(303) 497-6747
sdw@cdc.noaa.gov
3. NCEP GTS surface marine data ASCII format
This is a simple ASCII format with each record 49 characters in length (Table
1). The records are generally sorted by date, but not necessarily by hour
(some variations may exist due to the way the data are gathered). Note that
present weather, complete cloud elements, and various other minor fields have
been omitted from the format.
Table 1. The NCEP GTS surface marine data ASCII format. Report type, BUFR
file type, and the wind speed indicator are defined in Tables 2-4. NOTE:
Distinguishing platform type according to report type or BUFR file type is not
always reliable. The most frequent discrepancies involve moored and drifting
buoys, for which it is best to examine the third digit in the 5-digit (numeric)
buoy ID: a value less than 5 is a moored buoy; a value greater than or equal to
5 is a drifting buoy.
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Column Format Field
from to
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1 2 I2 Year
3 4 I2 Month
5 6 I2 Day
7 10 F4.2 Hour
11 15 F5.2 Latitude (degrees) -- negative = southern hemisphere
16 20 F5.2 Longitude (degrees) -- 0 to 360 West
21 22 I2 or 2I1 Report type; or BUFR file type and wind speed indicator*
23 28 A6 Station ID/ship call sign
29 32 F4.1 Sea level press minus 900.0 (mb) missing=9999
33 35 I3 Wind direction (degs) missing=999
36 38 I3 Wind speed (knots) missing=999
39 42 F4.1 Air temp (deg c) missing=9999
43 45 F3.1 Dew point depression (deg c) missing=999
46 46 A1 Cloud cover** missing=9
47 49 F3.1 Sea surface temp (deg c) missing=999
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* Prior to March 1997, positions 21-22 contain Office Note 124 report type
(Table 2); starting during March 1997 (see section 4), position 21 contains
BUFR file type (Table 3), and position 22 contains the wind speed indicator
(Table 4). Presently, all wind speed indicators are missing=9 (planned for
future addition to the BUFR data).
** Prior to 4 August 1991 this contains low cloud amount; starting then it
contains total cloud amount.
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Table 2. Office Note 124 report types. Until March 1997 (see section 4),
positions 21-22 contain report type minus 500 (this field may be unreliable
as an indicator of platform type; see Table 1).
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Code Type of Report
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---------Ocean Station-------
521 Fixed (OWS)
522 Moving ship with name
523 Moving ship without name
---------Marine reporting station (MARS)---------
531 Fixed (Stationary)
532 Moving
---------Quality control data---------
551 By latitude-longitude*
---------Buoy---------
561 Moored
562 Drifting
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* This is listed as a valid "report type" in NCEP documentation, but no reports
of this type have ever been encountered.
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Table 3. BUFR file type. Starting in March 1997 (see section 4), position 21
contains the type of BUFR file from which the report was obtained (this field
may be unreliable as an indicator of platform type; see Table 1).
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Code BUFR file type
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1 ship
2 drifting buoy
3 moored buoy
4 Coastal-Marine Automated Network (C-MAN)
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Table 4. The wind speed indicator (starting in March 1997), showing the units
in which and the method by which wind speed was originally recorded (WMO code
1855). All winds are stored in this format in knots.
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Code
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0 meter per second, estimated
1 meter per second, measured (obtained from anemometer)
3 knot, estimated
4 knot, measured (obtained from anemometer)
9 missing
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4. Technical notes
a) Original weekly files that existed in some of the earlier years have been
consolidated into single monthly files for retention at CDC.
b) The original files for January-12 February 1991 were supplemented with some
ATLAS buoy data that may be unavailable in the regular NCEP archives for that
time period.
c) During ftp, a small amount of data was truncated from the original January
1991 file "nq9101.Z," which was also used for construction of the existing
2-degree summary files. Missing data, except possibly the supplementary
ATLAS data noted above, have been recovered in the file "nq9101_complete.Z."
Similarly, days 1-8 were inadvertently omitted, and days 9-16 duplicated,
from the original June 1991 file "nq9106.Z," also used for construction of the
existing 2-degree summary files. Missing data have been recovered in the file
"nq9106_complete.Z."
d) Starting 1 March 1997, data are available processed by NCEP into the BUFR
format (file "nq9103_bufr.Z"). In addition, overlapping data were processed
into NCEP's previous Office Note (ON) 124 format until 31 March ("nq9703.Z").
Due to concerns about temperature biases in initially available BUFR data, the
ON file was used to construct the 2-degree summaries for March 1997.
e) In March 1997 we became aware that ON data from moored buoy 52312 reported
close to 180 longitude were sporadically impacted by a change in the latitude
sign, such that latitudes ~2S were changed to ~2N. Data for March 1997 were
manually edited (only in the "nq9703.Z" file; not in the original "gtsobs.gz"
file) by changing positive latitudes to negative with the same magnitude. No
previous data were corrected, and the scope of the problem is not fully known.
File "nq9703_52312" contains all reports from 52312 (edited plus unedited).
f) "Dup/merge" software is used at NCEP in processing the BUFR data to combine
partially complete duplicate reports. Duplicate reports were not merged in the
ON data; only the most recent report was kept.
g) Delayed data that are not retained in these files, and marine reports
containing the full suite of observed weather elements, eventually become
available in the full NCEP GTS archives stored at the National Climatic Data
Center (NCDC) in Asheville, and at the National Center for Atmospheric Research
(NCAR) in Boulder. The full marine reports, plus a variety of delayed data,
are merged into the Comprehensive Ocean-Atmosphere Data Set (COADS). For more
information about COADS including current data availability, please see our
COADS homepage (http://www.cdc.noaa.gov/coads/).