Instructions and Format

   The data offered in the SCRAM mixing height data files are comprised of data
provided by the National Climatic Data Center in their 'Twice Daily Mixing
Height Data' format (TD9689).  The format of the records has been modified to
correspond to that required by the RAMMET and PCRAMMET preprocessor programs.
Also, the first and last records of each file have been added to conform to the
requirements of these preprocessor programs.  RAMMET and PCRAMMET also require
that the meteorological input data sets contain no missing values.  Since
missing data values are found within the original data sets, the missing values
have been filled as prescribed in "Procedures for Substituting Values for
Missing NWS Meteorological Data for Use in Regulatory Air Quality Models".  The
filled data values can be identified by a type code of "3" or "4", in column 12
(for morning mixing height values) or column 30 (for afternoon mixing height
values).  See the format description below.

   The individual files are in .TXT format, however all files for a single
state are zipped into a single zipped file which can be downloaded.
The parameters and the format of the records in these files are as follows:

       Field        Parameter                    
      Position        Name

        1-5       National Weather Service
                  Station Number
        6-7       Year
        8-9       Month
       10-11      Day
        12        AM Type
                    1 = No Precipitation.
                    2 = Precipitation occurred at two or more
                        observation times with the intensity of
                        light, or at one observation time with
                        the intensity of moderate or heavy during
                        the hours 1000-2100 LST for the afternoon
                        or during the hours 2200 (previous day)-
                        0900 LST for the morning.
                    3 = (afternoon) The maximum temperature selected
                        between 1200-1600 LST is less than the sur-
                        face temperature of the 1200Z RAOB temperature.
                        (morning) The minimum temperature selected
                        between 0200-0600 LST plus 5 degrees Celsius
                        is less than the surface temperature of the
                        1200Z RAOB temperature.
                    4 = Missing
        13        Blank
       14-17      AM Mixing Height above surface (whole meters).
       18-21      Wind Speed in meters per second averaged through
                    the mixing depth (surface wind only if mixing
                    depth < 150 meters).
                  The average is determined from the 1200Z RAWIN.
                  The average of the hourly surface wind speeds
                  during 2200-0600 LST was used in place of the
                  surface wind speed in the RAWIN.
                  For Type 3, wind speeds were averaged from the
                  surface through 4000 meters.
       22-25      Average surface wind speed (meters per second).
       26-29      Blank
        30        PM Type (see AM Type)
        31        Blank
       32-35      PM Mixing Height above surface (whole meters).
       36-39      Wind Speed in meters per second averaged through
                    the mixing depth (See AM Wind Speed).
       40-43      Average surface wind speed (meters per second).

   Note that RAMMET and PCRAMMET only use the data in columns 1-11, 14-17, and
32-35.

   It should be noted that the computation of mixing height requires both an
upper air sounding and hourly surface temperature values.  Most National
Weather Service upper air sites coexist with an hourly surface site.  However,
when this is not the case, the closest hourly surface site has been chosen for
the mixing height computations.  If the sites do not coexist, the state
download menus of mixing height data list both the site of the upper air
sounding (labeled "UA") and the site of the surface temperature data
(labeled "SFC T").