Format Documentation of kpyymm.wdc Files


The most recent kpyymm.wdc (yymm stands for year and month, each expressed with two digits) files are distributed per e-mail half-monthly by
Dr. H.-J. Linthe,
Both recent and past tables (since 1932) are supplied as an archive on the FTP servers
WWW access:
Note: FTP sites sometimes refuse connections due to excessive traffic.
Your mileage may vary with a different FTP program or the WWW access alternative.

Background information on geomagnetic indices and the classification of days is supplied at the WWW startpage


For the intermediate data transfer between the calculation and plot programs the Institut fuer Geophysik (Goettingen) has decided to use the standard format as published by the National Geophysical Data Center (NGDC) in Boulder, Colorado.


The following scientific and format documentation is adapted from

Selected Geomagnetic and Solar Activity Indices

Worldwide Indices

The subscript p means planetary and designates a global magnetic activity index. The following 13 observatories, which lie between 46 and 63 degrees north and south geomagnetic latitude, now contribute to the planetary indices: Lerwick (UK), Eskdalemuir (UK), Hartland (UK), Ottawa (Canada), Fredericksburg (USA), Meanook (Canada), Sitka (USA), Eyrewell (New Zealand), Canberra (Australia), Lovo (Sweden), Brorfelde (Denmark), Wingst and Niemegk (Germany).

Three-hour-range Index Kp

Ks indices isolate solar particle effects on the earth's magnetic field; over a 3-hour period, they classify into disturbance levels the range of variation of the more unsettled horizontal field component. Each activity level relates almost logarithmically to its corresponding disturbance amplitude. Three-hour indices discriminate conservatively between true magnetic field perturbations and the quiet-day variations produced by ionospheric currents.

Ks indices range in 28 steps from 0 (quiet) to 9 (greatly disturbed) with fractional parts expressed in thirds of a unit. A Ks-value equal to 27, for example, means 2 and 2/3 or 3-; a Ks-value equal to 30 means 3 and 0/3 or 3 exactly; and a Ks-value equal to 33 means 3 and 1/3 or 3+. The arithmetic mean of the Ks values scaled at the 13 observatories listed above gives Kp.

Equivalent Amplitude ap

The ap-index ranges from 0 to 400 and represents a Kp-value converted to a linear scale in nT (nanoTesla) - a scale that measures equivalent disturbance amplitude of a station at which K=9 has a lower limit of 400 nT.

Format Description

Column  Format  Description
======  ======  ===========
 1- 2     i2    yy, last two digits of year
 3- 4     i2    mm, month (1-12)
 5- 6     i2    dd, day of month (1-31)

 7-10     i4    Bartels solar rotation number - a sequence of 27-day
                  intervals counted continuously from February 8, 1832
11-12     i2    Number of day within the Bartels 27-day cycle

13-28    8i2    3-hourly Kp indices (0-3, 3-6, 6-9, 9-12, 12-15,
                                     15-18, 18-21, 21-24 UT)
29-31     i3    Daily Kp sum, expressed to the nearest third of a unit
                (supplied only for tradition, use Ap scientific purposes!)

32-55    8i3    3-hourly ap indices (0-3, 3-6, 6-9, 9-12, 12-15,
                                     15-18, 18-21, 21-24 UT)
56-58     i3    Ap equivalent daily amplitude - the arithmetic mean
                  of the day's eight ap values

59-61     f3.1  Cp or Planetary Daily Character Figure - a qualitative estimate
                  of overall level of magnetic activity for the day determined
                  from the sum of the eight ap amplitudes.  Cp ranges, in steps
                  of one-tenth, from 0 (quiet) to 2.5 (highly disturbed)

62-62     i1    C9 - a conversion of the 0 to 2.5 range of the Cp index to one
                  digit between 0 and 9

63-65     i3    International Sunspot Number. Records contain
                  * Zurich number through December 31, 1980
                  * International Brussels number thereafter

66-70     f5.1  Ottawa 10.7 cm Solar Radio Flux adjusted to 1 AU - measured
                  at 1700 UT daily and expressed in units of 10^-22 W/m^2/Hz.
                  Observations began on February 14, 1947. From that date
                  through December 31, 1973, the fluxes given here do not
                  reflect the revisions Ottawa made in 1966.

71-71     i1    Flux Qualifier
                  0: indicates flux required no adjustment;
                  1: indicates flux required adjustment for burst
                     in progress at time of measurement;
                  2: indicates a flux approximated by either
                     interpolation or extrapolation;
                  3: indicates no observation.

For questions concerning specific data or the contents of this page, please contact:
Dr. H.-J. Linthe,
Last modified: Jul 5 2000