Sources for DS010.0 - Sea Level Pressure, 1899 - current, twice daily

Data in this collections were assembled by the Data Support Section of
the Scientific Computer Division, National Center for Atmospheric Research
from several sources.

PERIOD                  DATA SOURCE

Jan 1899 - Jun 1939     NWS Extended Forecast Division digitized from
			from historical charts and QC work was done
			by NOAA ERL.

Jul 1939 - Nov 1944     Digitized by MIT from historical charts received
			from the Extended Forecast Lab.

Dec 1944 - Dec 1945     no data

Jan 1946 - Mar 1955     Digitized at National Climatic Data Center
			under a Navy contract from historical weather charts.

Apr 1955 - Mar 1960     Points were hand read from historical charts
			by the 433L ESSPO Project.

Apr 1960 - jun 1962     Digitzed under at National Climatic Data Center
			under a Navy contract from historical weather charts.

Jul 1962 - Dec 1993     Operational analyses from US Navy, Monterey
			with a few gaps filled by NCEP analyses.

Jan 1994 - current      NCEP operational final (FNL) analyses.



More details on sources of data.
    Grids from historical maps, Jan 1899 - Jun 1939 (13Z):
      This data, originated at the National Climatic Center, Asheville,
      N.C., was sent to the Extended Forecast Lab; from where a copy
      was sent to the NOAA Environmental Research Laboratories. There,
      Mr. Cotton and others spent about 1.5 man years comparing each
      point to the average of surrounding values. They checked each
      difference over 10 mb with the original maps to see whether a
      correction was necessary. Errors greater than 10 mb were likely
      discovered and corrected by this process. Data are missing where
      historical maps could not be analyzed. Eastern Russia (40-80N,
      35-150E) is missing for 1916-1920, for 3 months in 1921, for one
      month each in 1922 and 1931, and for 6 months each in 1938 and 1939.
      The grids were on a diamond lat-lon grid (5-degree lat, 10-degree
      lon), 20N-80N, with no data at 75N. There are no pole values.

    Grids from MIT, Jul 1939 - Nov 1944 (12Z):
      MIT read values from charts from the Extended Forecast Lab. The
      data are for each 5 degrees of latitude and even 10 degrees of
      longitude for 15N-80N. Data for 85N is present for 10 days.

    Grids from Navy*, Jan 1946 - Mar 1955 (12Z), Apr 1960 - Jun 1962 (12Z),
		      Jul 1962 - current (00Z,12Z):
      The grids from the historical series maps for Jan 1946 - Mar 1955, and
      Apr 1960 - Jun 1962 were digitized with a curve follower at NCC under
      Navy contract. These data were then analyzed by the Navy's operational
      objective analysis program that is used on current data. These grids
      include manual bogus to put in tropical storms. There is no data at 15N.

    * Although the Navy grids are the primary source for updating this set,
      occasionally grids from the National Meteorological Center are used
      until the Navy grids are received.




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    Grids from the 433L ESSPO Project, Apr 1955 - Mar 1960 (00Z,12Z):
      Data for every other point in the NMC octagonal grid were manually
      read from charts for this period. There is no data at 15N.