International Q-Days and D-Days

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Classification of Days (deduced from Kp indices)

The selection of the quietest days (Q-days) and most disturbed days (D-days)
of each month is deduced from the Kp indices on the basis of three criteria
for each day:

  1. The sum of the eight Kp values.
  2. The sum of squares of the eight Kp values.
  3. The maximum of the eight Kp values.

According to each of these criteria, a relative order number is assigned to
each day of the month, the three order numbers are averaged and the days
with the lowest and the highest mean order numbers are selected as the five
(respectively ten) quietest and the five most disturbed days.

Refined Classification

It should be noted that these selection criteria give only a relative
indication of the character of the selected days with respect to the other
days of the same month. As the general disturbance level may be quite
different for different years and also for different months of the same
year, the selected quietest days of a month may sometimes be rather
disturbed or vice versa.

In order to indicate such a situation, selected days which do not satisfy
certain absolute criteria are marked as follows.

   * A selected quiet day is considered not really quiet and is marked by
     the letter A if Ap greater than 6, or marked by the letter K if Ap less
     or equal 6 and either one Kp value greater than 3 or two Kp values
     greater than 2+.
   * A selected disturbed day is considered not really disturbed and marked
     by an asterisk (*) if Ap less than 20.

Classification Tables

   * This year
   * January 1990 - recent
   * January 1980 - December 1989
   * January 1970 - December 1979
   * January 1960 - December 1969
   * January 1950 - December 1959
   * January 1940 - December 1949
   * January 1932 - December 1939

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For questions concerning specific data or the contents of this page, please
contact:

     Dr. H.-J. Linthe, mailto:kp_index@gfz-potsdam.de