Space environment (natural and artificial) -- Methods for estimation of future geomagnetic activity

This document specifies the methods used for estimating geomagnetic indices for time intervals ranging from short-term (hours to a few months) to long-term (months to years). This document is intended for use to predict future geomagnetic indices and space environment.

Environnement spatial (naturel et artificiel) -- Méthodes d'estimation de l'activité magnétique future

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Publication Date
04-Dec-2019
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6060 - International Standard published
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16-Nov-2019
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05-Dec-2019
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INTERNATIONAL ISO
STANDARD 16698
Second edition
2019-12
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 16698:2019(E)
ISO 2019
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ISO 16698:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Published in Switzerland
ii © ISO 2019 – All rights reserved
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ISO 16698:2019(E)
Contents  Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2  Normative references ...................................................................................................................................................................................... 1

3  Terms and definitions ..................................................................................................................................................................................... 1

4  Symbols and abbreviated terms ........................................................................................................................................................... 1

5  General parameters ........................................................................................................................................................................................... 2

5.1 Geomagnetic field variations ...................................................................................................................................................... 2

5.2 Quiet level and disturbance fields .......................................................................................................................................... 2

5.3 K index (local 3 h range index).................................................................................................................................................. 2

5.4 Kp, ΣKp, ap and Ap indices (planetary indices) .......................................................................................................... 3

5.4.1 General...................................................................................................................................................................................... 3

5.4.2 Kp index (planetary 3 h range index) ............................................................................................................ 3

5.4.3 ΣKp index (planetary daily range index) .................................................................................................... 3

5.4.4 ap index (planetary 3 h equivalent amplitude index)...................................................................... 3

5.4.5 Ap index (planetary daily equivalent amplitude index) ................................................................ 4

5.5 aa index (antipodal amplitude index) ................................................................................................................................. 4

5.6 Dst index (storm time disturbance index) ...................................................................................................................... 4

5.7 ASY and SYM indices (mid-latitude disturbance indices) .................................................................................. 5

5.8 AU, AL, AE and AO indices (auroral electrojet indices) ........................................................................................ 5

5.9 am index........................................................................................................................................................................................................ 6

5.10 PC index ......................................................................................................................................................................................................... 7

5.11 Time lag in the derivation and temporal resolution (sampling) .................................................................. 7

6  Classification of prediction ........................................................................................................................................................................ 8

6.1 General ........................................................................................................................................................................................................... 8

6.2 Short-term prediction ....................................................................................................................................................................... 8

6.3 Middle-term prediction ................................................................................................................................................................... 8

6.4 Long-term prediction ........................................................................................................................................................................ 8

7  Methods of prediction ..................................................................................................................................................................................... 9

7.1 General ........................................................................................................................................................................................................... 9

7.2 Prediction based on statistical models............................................................................................................................... 9

7.2.1 Linear or non-linear prediction filter ............................................................................................................ 9

7.2.2 Machine learning ............................................................................................................................................................. 9

7.2.3 Probabilistic prediction ............................................................................................................................................. 9

7.3 Prediction based on physical principle .............................................................................................................................. 9

8  Evaluation of prediction efficiency .................................................................................................................................................... 9

8.1 Definition of prediction error ..................................................................................................................................................... 9

8.2 Methods of evaluation ...................................................................................................................................................................10

9 Compliance criteria ........................................................................................................................................................................................10

9.1 Rationale....................................................................................................................................................................................................10

9.2 Reporting ..................................................................................................................................................................................................10

9.3 Documenting..........................................................................................................................................................................................10

9.4 Publishing .................................................................................................................................................................................................11

9.5 Archiving ...................................................................................................................................................................................................11

10  Useful Informative Documents ...........................................................................................................................................................11

Annex A (informative) Websites where geomagnetic indices are available .............................................................12

Annex B (informative) Websites where the space weather predictions and/or "now casting"

are presented ........................................................................................................................................................................................................13

Annex C (informative) Definition of various skill scores ..............................................................................................................14

© ISO 2019 – All rights reserved iii
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ISO 16698:2019(E)

Annex D (informative) Useful academic documents related with this document's fields are

presented (These are not cited in the document) ..........................................................................................................15

Bibliography .............................................................................................................................................................................................................................22

iv © ISO 2019 – All rights reserved
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ISO 16698:2019(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.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

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. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,

Subcommittee SC 14, Space systems and operations.

This second edition cancels and replaces the first edition (ISO 16698:2013), which has been technically

revised. The main changes compared to the previous edition are as follows:
— addition of 5.9 and 5.10;
— update of reference lists of Clause 6.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
© ISO 2019 – All rights reserved v
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ISO 16698:2019(E)
Introduction

This document 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. 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.

The accuracy and method of predicting geomagnetic indices depends on the time scale of prediction.

This document 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 a 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 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 document.

vi © ISO 2019 – All rights reserved
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INTERNATIONAL STANDARD  ISO 16698:2019(E)
Space environment (natural and artificial) — Methods for
estimation of future geomagnetic activity
1 Scope

This document specifies the methods used for estimating geomagnetic indices for time intervals

ranging from short-term (hours to a few months) to long-term (months to years). This document is

intended for use to predict future geomagnetic indices and space environment.
2  Normative references
There are no normative references in this document.
3  Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4  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
−22 −2
at the earth's orbit, given in 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
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ISO 16698:2019(E)
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.
[11] [37] [42]
References: Bartels, et al. [1939] , Mayaud [1980] , Menvielle, et al. [2011] .
Table 1 — Permanent conversion scale from R to K for Niemegk observatory
Range (nT) 0–5 5–10 10–20 20–40 40–70 70–120 120–200 200–330 330–500 ≥500
K value 0 1 2 3 4 5 6 7 8 9
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ISO 16698:2019(E)
5.4  Kp, ΣKp, ap and Ap indices (planetary indices)
5.4.1 General

The planetary indices, Kp, ΣKp, ap and Ap, are derived from 13 selected mid-latitude observatories (see

Table 2). The derivation scheme for each index is described in the corresponding subsection.

Table 2 — Thirteen observatories that contributed to the Kp index
Observatory, country Code GLat (°N) GLon (°E) MLat (°) Notes
Meannook, Canada MEA 54,617 246,667 62,5
Sitka, USA SIT 57,058 224,675 60,0
Lerwick, Shetland Is.,UK LER 60,133 358,817 58,9
Ottawa, Canada OTT 45,400 284,450 58,9 Replaced Agincourt in 1969
Uppsala, Sweden UPS 59,903 17,353 58,5 Replaced Lovo in 2004
Eskdalemuir, UK ESK 55,317 356,800 54,3
Brorfelde, Denmark BJE 55,625 11,672 52,7 Replaced Rude Skov in 1984
Fredericksburg, USA FRD 38,205 282,627 51,8 Replaced Cheltenham in 1957
Wingst, Germany WNG 53,743 9,073 50,9
Niemegk, Germany NGK 52,072 12,675 48,8 Replaced Witteveen in 1988
Hartland, UK HAD 50,995 355,517 50,0 Replaced Abinger in 1957
Canberra, Australia CNB −35,317 149,367 −45,2 Replaced Toolangi in 1981
Eyrewell, New Zealand EYR −43,424 172,354 −50,2 Replaced Amberley in 1978
5.4.2  Kp index (planetary 3 h range index)

The Kp index is assigned to successive 3 h UT intervals (0 h to 3 h, 3 h to 6 h, ..., 21 h to 24 h UT), giving

eight values per UT day and ranges in 28 steps from 0 (quiet) to 9 (disturbed) with intermediate values

denoted by −, o, or +, resulting in 0o, 0+, 1−,1o, 1+, 2−, 2o, 2+, ..., 8−, 8o, 8+, 9− and 9o.

Derivation: The K indices at the 13 observatories given in Table 2 are standardized by means of

conversion tables that have been established through the rather complicated procedure introduced by

[10]

Bartels [1949] . The standardized K indices, called the Ks index, are averaged using weighting factors

to derive the Kp index.
[10] [37] [42]
References: Bartels [1949] , Mayaud [1980] , Menvielle, et al. [2011] .
5.4.3  ΣKp index (planetary daily range index)
ΣKp is the sum of the eight Kp values of the day.
5.4.4  ap index (planetary 3 h equivalent amplitude index)

The Kp index is not linearly related to the geomagnetic disturbances measured in the unit of nT. Instead,

the ap index is introduced as it is roughly proportional to the geomagnetic disturbances. One ap unit

corresponds to approximately 2 nT of geomagnetic variations.

Derivation: The ap index is derived directly from the Kp index by using the conversion table shown in

Table 3.
[12] [37] [42]

References: Bartels and Veldkamp [1954] , Mayaud [1980] , Menvielle, et al. [2011] .

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ISO 16698:2019(E)
Table 3 — Conversion table from the Kp index to the ap index
Kp 0o 0+ 1− 1o 1+ 2− 2o 2+ 3− 3o 3+ 4− 4o 4+
ap 0 2 3 4 5 6 7 9 12 15 18 22 27 32
Kp 5− 5o 5+ 6− 6o 6+ 7− 7o 7+ 8− 8o 8+ 9− 9o
ap 39 48 56 67 80 94 111 132 154 179 207 236 300 400
5.4.5  Ap index (planetary daily equivalent amplitude index)
The Ap index is the average of the eight values of the ap index in a UT day.
5.5  aa index (antipodal amplitude index)

The aa index is a simple measure of global geomagnetic activity, which can be traced back continuously

to 1868.

Derivation: The aa index is produced from the K indices of two nearly antipodal magnetic observatories

in England and Australia, which are listed in Table 4. The K indices at the two observatories are

converted back to amplitudes using Table 5. The aa index is computed as an average of the northern and

southern values of amplitude using the weighting factors, λ, shown in Table 4.
[36]
References: Mayaud [1971] .
Table 4 — Observatories in England and Australia contributing to the aa index
Observatory, country Code Period GLat (°N) GLon (°E) MLat (°) λ
Greenwich, England 1868–1925 1,007
Ablinger, England ABN 1926–1956 51,18 359,62 53,4 0,934
Hartland, England HAD 1957– 50,97 355,52 54,0 1,059
Melbourne, Australia 1868–1919 0,967
Toolangi, Australia TOO 1920–1979 −37,53 145,47 −45,6 1,033
Canberra, Australia CNB 1979– −35,30 149,00 −42,9 1,084

Table 5 — Conversion table from the K index at the aa observatories to amplitudes

K index 0 1 2 3 4 5 6 7 8 9
Amplitude 2,3 7,3 15 30 55 95 160 265 415 667
5.6  Dst index (storm time disturbance index)

The Dst index is a measure of the axially symmetric part of the H component along the geomagnetic

equator on the ground and the main physical source is a combination of the equatorial ring current, the

plasma sheet current and the magnetopause current.

Derivation: The Dst index is defined as the average of the disturbance variations of the H component,

D , at the four observatories (i = 1 to 4) listed in Table 6, divided by the average of the cosines of the

dipole latitudes at the observatories for normalization to the dipole equator. Dst is computed for each

UT hourly interval from the four observatories.
[54] [55]
References: Sugiura [1964] , Sugiura and Kamei [1991] .
Table 6 — Four observatories contributing to the Dst index
Observatory, country Code GLat (°N) GLon (°E) Dipole Lat (°)
Kakioka, Japan KAK 36,230 140,190 26,0
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ISO 16698:2019(E)
Table 6 (continued)
Observatory, country Code GLat (°N) GLon (°E) Dipole Lat (°)
San Juan, USA SJG 18,113 293,850 29,6
Honolulu, USA HON 21,320 201,998 21,1
Hermanus, South Africa HER −34,425 19,225 −33,3
5.7  ASY and SYM indices (mid-latitude disturbance indices)

The disturbance fields in mid- and low latitudes are generally not axially symmetric, in particular in the

developing phase of a magnetic storm. To describe the asymmetric and symmetric disturbance fields

in mid-latitudes with a high time resolution of 1 min, longitudinally asymmetric (ASY) and symmetric

(SYM) disturbance indices were introduced and derived for both the H and D components. The SYM-H

index is approximately the same as the Dst index, while its time resolution is 1 min.

Derivation: The ASY/SYM indices are derived from six selected mid-latitude observatories (see Table 7)

in the following four steps: (1) subtraction of the geomagnetic main field and the Sq field to obtain the

disturbance field component, (2) coordinate transformation to a dipole coordinate system by using a

rotation angle that is an angle between the geomagnetic dipole pole position and local geomagnetic

direction, (3) calculation of the longitudinally symmetric indices, SYM-H and SYM-D, by taking averages

of disturbance fields of the six stations and (4) calculation of the asymmetric disturbance indices, ASY-H

and ASY-D, by computing the range between the maximum and the minimum asymmetric fields.

[26] [42]
References: Iyemori, et al. [1992] , Menvielle, et al. [2011] .
Table 7 — Six observatories contributing to the SYM/ASY indices

Observatory, country Code GLat (°N) GLon (°E) MLat (°) MLon (°E) Rotation angle (°)

Memambetsu, Japan MMB 43,9 144,2 34,6 210,2 −16,0
Honolulu, USA HON 21,3 202,0 21,5 268,6 −0,6
Tuscon, USA TUC 32,3 249,2 40,4 314,6 2,02
Fredericksburg, USA FRD 38,2 282,6 49,1 352,2 11,8
Hermanus, South Africa HER −34,4 19,2 −33,7 82,7 −12,7
Alma Ata AAA 43,3 76,9 34,5 153,0 11,0
5.8  AU, AL, AE and AO indices (auroral electrojet indices)

The auroral electrojet indices are measures of the intensity of the auroral electrojets and consist of

four indices, AU, AL, AE and AO. The AU and AL indices are intended to express the strongest current

intensity of the eastward and westward auroral electrojets, respectively. The AE index represents the

overall activity of the electrojets and the AO index provides a measure of the equivalent zonal current.

Derivation: The auroral electrojet indices are derived from geomagnetic variations in the H component

observed at 12 selected observatories along the auroral zone in the northern hemisphere (see Table 8).

The AU and AL indices are respectively defined by the largest and the smallest values thus selected. The

symbols, AU and AL, derive from the fact that these values form the upper and lower envelopes of the

superposed plots of all the data from these stations as functions of UT. The difference, AU minus AL,

defines the AE index and the mean value of the AU and AL, i.e. (AU+AL)/2, defines the AO index.

[42] [30]
References: Davis and Sugiura [1966] , Kamei and Maeda [1981] .
Table 8 — Twelve (and obsolete three) observatories contributing to the AE index
Observatory, country Code GLat (°N) GLon (°E) MLat (°) MLon (°E) Notes
Abisko, Sweden ABK 68,36 18,82 66,06 114,66
Dixon Island, Russia DIK 73,55 80,57 64,04 162,53
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ISO 16698:2019(E)
Table 8 (continued)
Observatory, country Code GLat (°N) GLon (°E) MLat (°) MLon (°E) Notes
Cape Chelyuskin, Russia CCS 77,72 104,28 67,48 177,82
Tixie Bay, Russia TIK 71,58 129,00 61,76 193,71
Pebek, Russia PBK 70,09 170,93 63,82 223,31 Opened in 2001/04
Barrow, USA BRW 71,30 203,25 69,57 246,18
College, USA CMO 64,87 212,17 65,38 261,18
Yellowknife, Canada YKC 62,40 245,60 68,87 299,53
Fort Churchill, Canada FCC 58,80 265,90 67,98 328,36
Sanikiluaq, Canada SNK 56,5 280,8 66,6 349,7 Opened in 2007/12
Narssarssuaq, Denmark NAQ 61,20 314,16 69,96 37,95
Leirvogur, Iceland LRV 64,18 338,30 69,32 71,04
Cape Wellen, Russia CWE 66,17 190,17 62,88 241,36 Closed in 1996
Great Whale River, Russia GWR 55,27 282,22 65,45 351,77 Closed in 1984/07
Opened in 1984/09
Poste-de-la-Baleine, Canada PBQ 55,27 282,22 65,45 351,77
Closed in 2007/11
5.9 am index

The am index is designed to measure global geomagnetic activity using a large set of stations

representing all longitudes and possible hemispheric discrepancies. Time resolution of the am index

is 3 h (0 h to 3 h, 3 h to 6 h, ..., 21 h to 24 h UT), giving eight values per UT day, same as

...

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