ISO 16698:2019 pdf download

ISO 16698:2019 pdf download.Space environment (natural and artificial) — Methods for estimation of future geomagnetic activity
5  General parameters
5.1  Geomagnetic field variations
The geomagnetic field consists of internal and external magnetic fields. The internal (main) magnetic field is produced by source currents that are mostly inside the Earth’s core and by induced currents present in the solid Earth and the ocean, caused by the temporal variation of external magnetic fields. The external magnetic field is produced by magnetospheric and ionospheric currents. The magnetosphere is highly dynamic with time scales ranging from minutes to days. Solar wind is the ultimate source of magnetospheric dynamics. The role played by the IMF north-south component, Bz, is particularly important and its southward component, Bs, plays a fundamental role in substorm and magnetic storm activity through the process of magnetic field line reconnection. Solar wind speed also plays an essential role in these dynamics.
5.2  Quiet level and disturbance fields
Five days of every month are selected as the Five International Quietest Days using the Kp index (see 5.4.2). Note that the five quietest days are selected regardless of the absolute level of quietness. Thus, in a disturbed month, the quietest days may not be very quiet. Derivation: The quietest days (Q-days) of each month are selected using the Kp indices based on three criteria for each day: (1) the sum of the eight Kp values, (2) the sum of squares of the eight Kp values and (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 then averaged and the days with the first to fifth lowest mean order numbers are selected as the five international quietest days. Reference: Website of the Deutsches GeoForschungsZentrum (http:// www -app3 .gfz -potsdam .de/ kp _index/ qddescription .html). Once the quiet level is determined using the Five International Quietest Days, disturbance fields can be obtained as deviations from the quiet level of geomagnetic field.
5.3  K index (local 3 h range index)
The K index is a number in the range of 0 (quiet) to 9 (disturbed) that provides a local classification of the variations of the geomagnetic field observed after subtraction of the regular daily variation (Sq). Each activity level relates almost logarithmically to the corresponding disturbance amplitude of the horizontal field component during a 3 h UT interval. In a day, eight K indices are given in successive 3 h UT (universal time) intervals (0 h to 3 h, 3 h to 6 h, …, 21 h to 24 h UT). Derivation: The ranges R for the H and D (or X and Y) components are defined as the expected difference between the highest and lowest deviation, within the three-hour interval, from a smooth curve (a regular daily variation) for that element on a magnetically quiet day. Only the larger value of R, i.e. R for the most disturbed element, is taken as the basis of K. To convert from R to K, a permanent scale prepared for each observatory is used. Table 1 is an example of the permanent scale for the Niemegk observatory.