WDC-A Digital Exchange Format for One-Minute Geomagnetic Data (Update August 1993) 1. The logical record length is 400 coded characters containing header information, blank spaces, and data for one element for one hour. Twelve such logical records, containing a total of 4800 coded characters, are combined into a single data block on magnetic media. There are 12 hours of data for one component for one station in each block. The data are sequenced according to positions 1-24 of each record. Therefore, 24 hours of D are followed by 24 hours of the next element for the same OBS, YR, MO, DA. 2. Each observatory month is written as one file on the media. 3. Blocks are padded with (9's) internally to fill missing data segments and to complete a data set. 4. Each logical record contains header information and data in the following format: North polar distance, longitude, year, month, day, hour, element, observatory code, blank spaces, 60 data values, and an hourly mean. NPD LONG YR MO DA E HR OBS ORG BLANK DATA-1 DATA-60 HR MEAN 1-6 7-12 13-14 15-16 17-18 19 20-21 22-24 25 26-34 35-40 389-394 395-400 5. NPD is the observatory's North Polar Distance (0 to 180) from the north geographic pole in thousandths of a degree and is allotted 6 characters. A decimal point is implied between positions 3 an 4. LONG is the geographic longitude (0 to 360) measured east from Greenwich in thousandths of a degree and also has a 6 character field. A decimal points is implied between positions 9 and 10. YR, MO, DA, HR are each 2-digit numbers giving the year, month, day and hour (GMT). E is the element symbol in 1 character; it may be D, F, H, P, R, X, Y, or Z. OBS is the 2 or 3 letter abbreviation for the observatory. ORG is the origin of the data. A = Alaska Chain. C = Canadian Standard Network. D = Digitized from analog records. F = France G = U.S.G.S. Network. K = AFGL Chain. M = McClay Chain. R = Rostoker Chain. S = S.U.N.Y. Chain. T = Tiawan U = U.C.L.A. Chain. V = Variation Values via SMS-GOES Satellite. W = Walker Chain. BLANK are 10 character spaces reserved for future additions. DATA-1..DATA-60 are one-minute values of the given element for that data hour. H, Z, X, Y, or F to the nearest nanotesla and D in the tenth-minutes (e.g. 612 = 1 degree 1.2 minutes), each in a six character field. HR MEAN is the average of the proceeding 60 one-minute values. 6. Each element value and the hourly mean is given a six-digit field including a minus sign for negative values or a blank for positive values. 7. Missing data-value spaces are padded with 99999. No alteration of logical record length is required for different computer types. 8. Data on this CD are written in monthly ASCII files as (code)YYMM (i.e. BOU9003 would be Boulder for March 1990).