Unidata Local Data Manager (LDM) World Meteorological Organization (WMO) Surface Meteorological (LDMSFCMETR) Data

1.0 General Description

The Unidata Local Data Manager (LDM) (Unidata, 2002) distributes World Meteorological Organization (WMO) Surface Meteorological data. These data have been converted to columnar ASCII NCAR/EOL surface QC format by the National Center for Atmospheric Research/ Earth Observing Laboratory (NCAR/EOL). The "Nominal" hourly observations for the TREX domain and time period are oncluded in the dataset "LDM Surface METAR Hourly Data (NCAR/EOL surface QC format) [NCAR/EOL). Special records are located in the dataset "LDM Surface METAR Specials Data (NCAR/EOL surface QC format) [NCAR/EOL]". This documentation applies to both.

2.0 Detailed Data Description

This dataset contains ASOS, AWOS, and MANUAL stations. Station ID's are 3 characters long. Some networks use the 4-character ID to refer to these stations. To obtain the 4-character id, prepend a "K". For example, station ABR could also be referred to as station KABR.

2.1 Detailed Format Description

The TREX LDM surface METAR data in NCAR/EOL surface QC format contains ten metadata parameters and 38 data parameters and flags. The metadata parameters describe the station location and time at which the data were collected. The time of observation is reported both in Universal Time Coordinated (UTC) Nominal and UTC actual time. Days begin at UTC 0100 and end at UTC 0000 the following day. The table below details the data parameters in each record. Several data parameters have an associated Quality Control (QC) Flag Code which are assigned by the Joint Office for Science Support (JOSS). For a list of possible QC Flag values see the Quality Control
section 3.0.
    Parameters                              Units
    ----------                              -----
    Date of Observation                     UTC Nominal
    Time of Observation                     UTC Nominal
    Date of Observation                     UTC Actual
    Time of Observation                     UTC Actual
    Network Identifier                      Abbreviation of platform name
    Station Identifier                      Network Dependent
    Latitude                                Decimal degrees, South is negative
    Longitude                               Decimal degrees, West is negative
    Station Occurrence                      Unitless
    Station Elevation                       Meters
    Station Pressure, QC flag               Hectopascals (mb)
    Reported Sea Level Pressure, QC flag    Hectopascals (mb)
    Computed Sea Level Pressure, QC flag    Hectopascals (mb)
    Dry Bulb Temperature, QC flag           Celsius
    Dew Point, QC flag                      Celsius
    Wind Speed, QC flag                     m/s
    Wind Direction, QC flag                 Degrees
    Total Precipitation, QC flag            mm
    Squall/Gust Indicator                   Code Value
    Squall/Gust Value, QC flag              m/s
    Present Weather, QC flag                Code Value
    Visibility, QC flag                     Meters
    Ceiling Height (first layer)            Hundreds of feet
    Ceiling Flag (first layer), QC flag     Code Value
    Cloud Amount (first layer), QC flag     Code Value
    Ceiling Height (second layer)           Hundreds of feet
    Ceiling Flag (second layer), QC flag    Code Value
    Cloud Amount (second layer), QC flag    Code Value
    Ceiling Height (third layer)            Hundreds of feet
    Ceiling Flag (third layer), QC flag     Code Value
    Cloud Amount (third layer), QC flag     Code Value

The list of code values for the Present Weather is too large to reproduce in this document. Refer to WMO, 1988 for a complete list of Present Weather codes.

The code values for the Squall/Gust Indicator are:

    Code      Definition
    ----      ----------
    blank     No Squall or Gust
    S         Squall
    G         Gust
The code values for the ceiling flag Indicator are:
    Code      Definition
    ----      ----------
     0         None
     1         Thin
     2         Clear below 12,000 feet
     3         Estimated
     4         Measured
     5         Indefinite
     6         Balloon
     7         Aircraft
     8         Measured/Variable
     9         Clear below 6,000 feet (AUTOB)
     10        Estimated / Variable
     11        Indefinite / Variable
     12        12-14 reserved
     15        Missing
The code values for the Cloud Amount Indicator are:
     Code      Definition
     ----      ----------
     0         0 ( or clear)
     1         1 okta or less, but not zero or 1/10 or less, but not zero
     2         2 oktas or 2/10-3/10
     3         3 oktas or 4/10
     4         4 oktas or 5/10
     5         5 oktas or 6/10
     6         6 oktas or 7/10-8/10
     7         7 oktas or more, but no 8 oktas or 9/10 or more, but not 10/10
     8         8 oktas or 10/10 (or overcast)
     9         Sky obscured by fog and/or other meteorological phenomena
     10        Sky partially obscured by fog and/or other meteorological
                phenomena
     11        Scattered
     12        Broken
     13        13-14 Reserved
     15        Cloud cover is indiscernible for reasons other than fog or
               other meteorological phenomena, or observation is not made.

2.2 Data Remarks

The "Nominal" hourly observations for the TREX domain and time period are included in the dataset " Surface Meteorological (Hourly) Multi-Network Composite [NCAR/EOL]. Special records are located in the dataset "LDM Surface METAR Specials Data (NCAR/EOL surface QC format) [NCAR/EOL]". This documentation applies to both.

Sea Level Pressure is calculated from station pressure using standard GEMPAK algorithms (Unidata, 2003).

When not present in the raw data, the dewpoint temperature was computed by UCAR/JOSS from temperature and relative humidity using the formula from Bolton (1980).

When not present in the raw data, station pressure is computed by UCAR/JOSS from altimeter and elevation using the formula from the Smithsonian Meteorological Tables, 1949.

3.0 Quality Control Processing

This dataset was not quality controlled by UCAR/JOSS. Possible quality control flags occuring in the data are:
     QC Code   Description
     -------   -----------
     U         Unchecked
     M         Normally recorded but missing.

4.0 References

Bolton, D., 1980: The computation of equivalent potential temperature., Mon. Wea. Rev., 108, pp 1046-1053.

Smithsonian Meteorological Tables, Table No. 65, p.269. Smithsonian Institution Press, Washington, D.C., September, 1949.

Unidata, Cited 2002: Unidata LDM [Available online from http://www.unidata.ucar.edu/packages/ldm/].

Unidata, Cited 2003: Unidata GEMPAK/N-AWIPS [Available online from http://www.unidata.ucar.edu/packages/gempak/].

World Meteorological Organization (WMO), 1988: Manual on Codes Volume I, Part B - Binary Codes. WMO, Geneva, Switzerland.