FILE latlonigy VERSION 1.2
CHANGE TIME 89/01/17 10:13:16
ACCESS TIME 89/01/17 10:13:24


				     Wilbur M.L. Spangler/Roy L. Jenne
				     Data Support Section/Computing Division
				     National Center for Atmospheric Research
				     Boulder, Colorado 80307

	   Southern Hemisphere IGY Daily and Monthly Lat-lon Grids
			 (Jun 1957 - Dec 1958)

General Description of Daily 5-degree Lat-lon Grids:
    NCAR has daily sea level pressure grids and 500mb height grids for
    the IGY period, Jun 1957 - Dec 1958. All grids are 5-degree lat-lon
    grids from 15S - 85S and 00E - 355E. There is also a pole value.

General Description of Monthly Mean Grids:
    Monthly mean grids in the same format have been computed for the
    entire period. A count of these daily grids is carried along with
    the mean grid. These grids are maintained on a separate data volume.

Sources of Data for Daily Grids:
    Grids from NOTOS, IGY, Jun 1957 - Dec 1958 :
      This data is printed in volumes 8 and 9 of NOTOS. It was punched
      onto cards by Taljaard's group in the Republic of South Africa.
      The grids were on a diamond lat-lon grid (5-degree lat, 10-degree
      lon), 15S-65S, with fewer points south of this. NCAR used a cubic
      curve fit to four successive data points along a constant latitude
      to calculate missing grid points for 15S-65S. South of this various
      schemes were used because of the sparcity of original points. Cubic
      curve fits were made where possible. In other areas, nearest data
      points in several directions were weighted by distance from the
      missing point and averaged. The grids have no missing points.
      There are pole values.

Format of Grids:
    There is one 273 word (60-bits each) record in binary packed integer
    format for each data grid. Identification is included with each record.
    The format is broken down as follows:

	Word 1, counting bits from left to right
		bits 1-6   format number ( = 10)
		bits 7-17  year, e.g. 1952
		bits 18-21 month, e.g. 11 = NOV
		bits 22-26 day ( = 1 to 31, = 0 for monthly mean)
		bits 27-31 hour ( = 12Z)
		bits 32-41 level ( = 1013 or 500)
		bits 42-50 type ( = 6 for sea level pressure, 1 for heights)
		bits 51-56 source (= 16, for IGY period)
		bits 57-60 grid type ( = 1)

	Word 2, bits 1-15  pole value*
		bits 16-21 number of grids in mean ( = 0 for dailies)
		bits 22-60 not used

	Words 3-272
		1080 binary integer data values in 15-bit bytes.
		Data values are in tenths of millibars and meters.
		The grid of Y(I,J) is dimensioned Y(72,15).
		As I goes from 1 to 72, longitude goes from 00E-355E;
		as J goes from 1 to 15, latitude goes from 15S-85S.



	Word 273,
		60-bit checksum of first 272 words.