ISO 16698:2013

INTERNATIONAL ISO
STANDARD 16698
First edition
2013-05-01
Space environment (natural and
artificial) — Methods for estimation of
future geomagnetic activity
Environnement spatial (naturel et artificiel) — Méthodes
d’estimation de l’activité magnétique future
Reference number
©
ISO 2013
ISO 16698:2013(E)
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ii © ISO 2013 – All rights reserved

ISO 16698:2013(E)
Contents  Page
Foreword .iv
Introduction .v
1 Scope . 1
2  Symbols and abbreviated terms . 1
3  General parameters . 1
3.1 Geomagnetic field variations . 1
3.2 Quiet level and disturbance fields . 2
3.3 K index (local 3 h range index). 2
3.4 Kp, ΣKp, ap, and Ap indices (planetary indices). 2
3.5 aa index (antipodal amplitude index) . 4
3.6 Dst index (storm time disturbance index) . 4
3.7 ASY and SYM indices (mid-latitude disturbance indices) . 5
3.8 AU, AL, AE, and AO indices (auroral electrojet indices) . 5
3.9 Time lag in the derivation and temporal resolution (sampling) . 6
4  Classification of prediction . 6
4.1 Short-term prediction . 6
4.2 Middle-term prediction . 8
4.3 Long-term prediction . 8
5  Methods of prediction . 9
5.1 Prediction based on statistical models. 9
5.2 Prediction based on physical principle . 9
6  Evaluation of prediction efficiency . 9
6.1 Definition of prediction error . 9
6.2 Methods of evaluation . 9
7 Compliance criteria .10
7.1 Rationale.10
7.2 Reporting .10
7.3 Documenting.10
7.4 Publishing .10
7.5 Archiving .10
Annex A (informative) Websites where geomagnetic indices are available .11
Annex B (informative) Websites where the space weather predictions and/or “now casting”
are presented .12
Annex C (informative) Definition of various skill scores .13
Bibliography .14
ISO 16698:2013(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International
Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies
casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 16698 was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 14, Space systems and operations.
iv © ISO 2013 – All rights reserved

ISO 16698:2013(E)
Introduction
This International Standard provides guidelines for specifying the process of estimating future
geomagnetic activity. Geomagnetic indices describe the variation of the geomagnetic field over a certain
time period and provide a measure of the disturbance of the magnetosphere.
The accuracy and method of predicting geomagnetic indices depends on the time scale of prediction.
This International Standard presents existing works based on three categories of time scale:
a) short-term prediction (1 h to a few days);
b) middle-term prediction (a few weeks to a few months);
c) long-term prediction (half year to one solar cycle).
These are required as input parameters for the magnetospheric magnetic field (ISO 22009), upper
atmosphere (ISO 14222), ionosphere, plasmasphere (ISO/TS 16457), magnetosphere charged particles,
and other models of the near-Earth space environment. They also serve as the input parameters for
orbital lifetime prediction and worst-case environment analysis of electrostatic charging.
Three International Standards deal with the Earth’s magnetic field, including ISO 16695 on the internal
magnetic field, ISO 22009 on the magnetospheric magnetic field, and this International Standard.
INTERNATIONAL STANDARD  ISO 16698:2013(E)
Space environment (natural and artificial) — Methods for
estimation of future geomagnetic activity
1 Scope
This International Standard specifies the methods used for estimating geomagnetic indices for time
intervals ranging from the short-term (hours to a few months) to the long-term (months to years).
Geomagnetic indices are used to describe the activity levels of the disturbance of the geomagnetic field.
These indices can be used to estimate upper atmospheric and plasmaspheric densities and many other
space environment models. They are also used as the input parameters for orbital lifetime prediction
and worst-case environment analysis of electrostatic charging.
This International Standard is intended for use to predict future geomagnetic indices and space environment.
2  Symbols and abbreviated terms
Bs Southward component of the interplanetary field (Bs = 0 when Bz ≥ 0 and Bs = Bz when
Bz < 0)
Bz North-south component of the interplanetary field
F10.7 flux Measure of the solar radio flux at a wavelength of 10,7 cm at the earth’s orbit, given in
−22 −2
units of 10 W·m
GLat Geographic latitude
GLon Geographic longitude
IMF Interplanetary magnetic field
MLat Geomagnetic latitude
MLon Geomagnetic longitude
MHD Magnetohydrodynamics
Sq Daily geomagnetic field variations during quiet conditions (Solar quiet)
UT Universal time
3  General parameters
3.1  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 (interplanetary magnetic
field) north–south component, Bz, is particularly important, and its southward component, Bs, plays a
ISO 16698:2013(E)
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.
3.2  Quiet level and disturbance fields
Five days of every month are selected as the Five International Quietest Days using the Kp index
(see 3.4.1). 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.
3.3  K index (local 3 h range index)
The K index is a number in the range 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
d
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