DIGITAL WDC EXCHANGE FORMAT
FOR OBSERVATORY 1.0 MINUTE VALUES
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. 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
1-6 7-12 13-14 15-16 17-18 19 20-21
OBS ORG (Blanks) DATA-1 DATA-60 HRly MEAN
22-24 25 26-34 35-40 389-394 395-400
4. 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 observatory.
ORG is the origin of the data,
e.g. G = US 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
5. 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.
6. Missing data spaces are padded with 99999. No
alteration of logical record length is required
for different types of computers.
7. Positive values of Declination (D) indicate East
Declination and negative values indicate
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 recommended 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)
A = Alaskan meridian magnetometer chain
(includes Canadian sites) for IMS
C = Canadian standard observatory network
O = point samples digitized from analog magnetograms
F = France
G = USGS standard observatory network
(one station operated by NOAA)
J = Japan
K = US AFGL E-W sub-auroral zone magnetometer chain
R = Western Canadian meridian magnetometer chain
operated for IMS
T = Lungping magnetic observatory, Taiwan.
U = E-W mid-latitude magnetometer chain operated for IMS
V = Variations only sent via NOAA GOES satellite relay
W = Eastern Canadian meridian magnetometer chain
operated for IMS