1. The logical record length is 400 coded characters containing header information, blank spaces, and data for one element for one hour.

  2. Blocks are padded with nines (9s) internally to fill missing data segments and to complete a data set.

  3. nks)
  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.

    1-67-1213-1415-16 17-181920-2122-2425 26-3435-40389-394395-400

  5. NPD is the observatory's North Polar Distance (0 to 180 degrees) from the north geographic pole in thousandths of a degree and is alloted 6 characters. Decimal point is implied between positions 3 and 4.

    LONG is the geographic longitude (0 to 360 degrees) measured EAST from Greenwich in thousandths of a degree and also has a 6-character field. Decimal point is implied between posilions 9 and 10.

    YR, MO, DA, and HR are each 2-digit numbers giving the date and time in GMT. E is the element symbol in 1 character: it may be D, H, X, Y, Z, or F.

    OBS is the 3-letter code (abbreviation) assigned by IAGA for the obser- vatory. ORG is the origin of the data, e.g. G = U.5. Geological Survey.

    Blanks are spaces for 9 characters reserved for future additions.

    DATA-1 ... DATA-60 are 1-minute values of the given element for that hour. H, X, Y, Z, or F are given to the nearest nanoTesla (gamma). D is given to the nearest tenth-minute of arc (612 = l degree + 01.2 minutes East). Each value is in a 6-character field.

    HRly MEAN is the average of the preceding 60 1-minute values.

  6. Each element value and the hourly mean is given in a six-digit field including a minus sign for negative values, or a blank for positive values.

  7. Missing data spaces are padded with 99999. No alteration of logical record length is required for different types of computers.

  8. Positive values of Declination (D) indicate East Declination and negative values indicate West Declination.

Codes for sources of digital magnetometer data in the WDC system not only indicate the source organization, but also show whether the data are average values or point data. For example, 1-minute point values scaled from analog magnetograms for the production of AE indices are coded with a "D" because they are "digitized". Typically, digital 1-minute values received by WDCs from organizations operating automatic magnetic observatory instruments are averages of more frequendy sampled values, e.g. 10-second point samples. Different organizations process their higher time resolution observations in different ways. Some may filter and smooth the observations. Some follow the practice recom- mended by IAGA of averaging higher time resolution samples from before and after the minute to obtain a 1-minute value centered exactly on the minute. Others average values from the beginning of a given minute to the beginning of the next minute, effectively centering the mean on the half-minute, in similar fashion to the processing of 1-minute values to obtain hourly means. If the method used to obtain 1-minute average values is important to a user, the WDC will assist in determining the exact procedure applied.

In general, digital values from national networks are "absolute" and are tied to baselines determined by are operating institutions. Often only timely variations data are needed to support special research campaigns and digital values may be transmitted from regular observatory sites via satellite relay platforms. Such values are "flagged" with a "V" as noted below and eventually are replaced by the standard digital observatory output. Values from special networks such as the IMS chains are variations only. Attempts are made to check the absolute output of these instruments but usually no systematic absolute observations are possible or they are later replaced by adopted standard observatory digital values.

ORG (data origin codes)

AAlaskan meridian magnetometer chain (includes Canadian sites) for lMS
CCanadian standard observatory network
Opoint samples digitized from analog magnetograms
GUSGS standard observatory network (one station operated by NOAA)
KUS AFGL E-W sub-auroral zone magnetometer chain
RWestern Canadian meridian magnetometer chain operated for IMS
TLungping magnetic observatory, Taiwan.
UE-W mid-latitude magnetometer chain operated for IMS
VVariations only sent via NOAA GOES satellite relay
WEastern Canadian meridian magnetometer chain operated for IMS