IAGA

ISGI is hosted by LATMOS

FAGS

The International Service of Geomagnetic Indices

(I.S.G.I.)

First version prepared by Michel Menvielle (michel.menvielle@latmos.ipsl.fr) and Annick Berthelier (deceased in March 1997); revisions made by M. Menvielle.

The solar wind, including plasma and interplanetary magnetic field, is the source of energy for the Earth's magnetosphere. Solar wind characteristics are highly variable, and they have actually a direct influence on the shape and size of the magnetosphere, on the amount of transferred energy, and on the way this energy is dissipated.

From the Earth surface, distinct signatures of magnetospheric phenomena such as visible aurorae, changes in ionospheric parameters and variations of the Earth magnetic field can be directly observed or measured. Specific interest in geomagnetic variations comes from the following two reasons:

- early magnetic measurements have allowed to build up extensive data bases both temporally (early measurements date back to the beginning of the 19th century) and spatially (more than 200 observatories are distributed all over the world). Moreover, the increasing performances of telecommunication facilities (file transfer) and the use of automated stations and satellite links (e.g. INTERMAGNET) make possible near real-time dissemination of magnetic measurements;

- geomagnetic variations reflect most of the magnetospheric phenomena, in particular the role of electric currents of ionospheric and magnetospheric origins, and of electromagnetic waves in a wide frequency range.

It is clear that the great diversity of sources of magnetic variations give rise to a great complexity in ground magnetic signatures. However, such a complexity is often ignored, probably owing to the simple fact that a single name 'geomagnetic activity' is traditionally attributed to magnetic perturbations of various origin. Also the use of geomagnetic indices, which have been designed to give a global information sometimes as condensed as one digit or so per day is adding to the feeling that geomagnetic activity itself is simple to monitor.

Geomagnetic indices and lists of remarkable geomagnetic events constitute data series aiming at describing at a planetary scale the magnetic activity or some of its components. The data series are homogeneous since 1868 for aa and the list of ssc, 1932 for Kp, 1953 for the list of sfe, 1957 for Dst and 1959 for am (see "The geomagnetic indices: derivation, meaning and availability"; for a presentation of these data). As a result of their unique temporal and spatial coverage, these remarkable data series are widely used in various different research domains:

- they allow for instance statistical studies over long time periods (more than 125 years in the cases of aa and ssc) of the solar wind - magnetosphere coupling. It is then possible to characterise the physical processes driving the coupling, and its dependence on solar wind parameters [Legrand and Simon, Annales Geophysicae, 7, 565, 1989; Simon and Legrand, Annales Geophysicae, 7, 579, 1989; La Sayette and Berthelier, J. Geophys. Res., 101, 10 653, 1996];

- they are mandatory for analysing and processing global magnetic data used to study the geomagnetic field, and to characterise its internal sources and their evolution with time. A striking example of this contribution of geomagnetic indices can be found in the MAGSAT [Mareschal and Menvielle, Phys. Earth Planet. Inter., 43, 199-204, 1986; Cohen and Achache, J. Geophys. Res., 95, 10783-10800, 1990] and forthcoming ?rsted experiments;

- as the result of the efforts, made in particular by I.S.G.I. and I.S.G.I. Collaborating Institutes to circulate within very short delays reliable provisional values of geomagnetic indices these data appear now as basic ones in the development of ?Space weather? research [see e.g., STPW Proceedings].

The International Service of Geomagnetic Indices (I.S.G.I.) is in charge of the elaboration and dissemination of geomagnetic indices, and of lists of remarkable magnetic events, with data provided by geomagnetic observatories. From its foundation until 1987, it was located at the Koninklijk Nederlands Meteorologish Instituut (De Bilt, The Netherlands). During the I.U.G.G. meeting in Vancouver, 1987, it was decided to move I.S.G.I. to France, and to place it under the joint responsibility of M. Menvielle and A. Berthelier. It was first hosted by the Institut de Physique du Globe de Paris (I.P.G.P., Paris, France) then moved to the Centre d?étude des Environnements Terrestre et Planétaires (C.E.T.P., Saint Maur, France) in 1990.

Since the closing of the I.U.G.G. Publication Office in 1990, the Service is also in charge of the diffusion of all the IAGA Bulletins relative to geomagnetic indices. The I.S.G.I. Publication Office was then established by A. Berthelier, and located at Saint Maur (same address as I.S.G.I., see Appendix). This paper presents the I.S.G.I. activities, that is the preparation and dissemination of the I.A.G.A. geomagnetic indices and of lists of remarkable magnetic events, in co-operation with the I.S.G.I. Collaborating Institutes.

We think that it is also worth recalling how geomagnetic indices provide global or specific information about very complex underlying phenomena. Basic indication about the geomagnetic field and its variations, and the derivation and meaning of currently used geomagnetic indices, emphasising particularly their specificity and differences are therefore recalled in "The geomagnetic indices: derivation, meaning and availability".

The basic activities of I.S.G.I., and of I.S.G.I. Publication Office are to prepare and circulate magnetic indices and other geomagnetic data, based on the report of magnetic observatories distributed all over the planet, with the help from the following I.S.G.I. Collaborating Institutes (see addresses in Appendix):

- Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS/C.N.R.S.; am, Km, aa; Guyancourt, France);

- WDC-C2 for Geomagnetism (Dst, AE; Kyoto, Japan);

- GeoForschungsZentrum (GFZ) Potsdam (Kp, ap; Potsdam, Germany);

- Observatorio del Ebro (Rapid Variations; Roquetes, Spain).

I.S.G.I. and I.S.G.I. Collaborating Institutes have the responsibility to ensure the homogeneity of the data series.

I.S.G.I. has an Advisory Board, appointed by the Executive Committee of the International Association of Geomagnetism and Aeronomy (C. Barton, Australia, chair; T. Araki, Japan; R. Coles, Canada; M. Menvielle, France, ex officio).

The present derivation scheme of AE, AU, and AL indices (see "The geomagnetic indices: derivation, meaning and availability";) is well suited for producing and circulating provisional values within very short delays. The main challenge is then to have digital data routinely available from all the observatories through electronic networks. At the end of the 1980?s, the situation ranged from no digital data at all, through poor data, to good data but delayed by weeks or months. Connecting the existing digital observatories to the INTERMAGNET network, and replacing progressively analogue observatories by digital ones with automatic data transfer yet allowed to significantly improve the situation. If not perfect, the situation is now far better: all the 12 AE observatories are in principle capable of transferring digital data, but in practice with varying degrees of difficulties in transmitting the data on a reliable routine basis, thanks to the joint efforts of the I.S.G.I. Collaborating Institute (WDC-C2, Kyoto) and of the Institutes ruling the observatories

The AE index is now being made available in three steps. The index in the first of these three steps is a near real-time AE index, or a quick-look AE index, which is made available on line (at the WDC-C2 www homepage) with a 12 hours delay at the present time (summer 1997). The index is derived on an ?available data? basis, and is updated on a daily basis as the missing data are filled. Therefore the derivation of the quick-look AE index is an ?evolving? process, and a due caution is required in using this index, which is primarily meant for uses for diagnostic purposes and not for scientific analyses. The quick-look AE index is plotted on www in colour to indicate the number of observatories that are contributing data to each minute. The maximum number of observatories that can contribute data for the quick-look AE is 8 at the present time. It is worth noting that no quality check is made on the data used for the quick-look AE index. The AE index in the second step is a provisional AE index derived (and published in a Prompt Report) often responding to demands by various projects. The AE index derived by the third step is the final AE index in the form familiar to the scientific community (see description in "The geomagnetic indices: derivation, meaning and availability ").

Similarly, the Equatorial Dst index (Dst) is now prepared and issued in three steps. In the first step, a near real-time Dst, or quick-look Dst, is derived using data from any number of observatories of the five designated Dst observatories (Hermanus, Alibag, Kakioka, Honolulu, San Juan), beginning with a 12-hour delay and updated on a daily basis. As in the case of the quick-look AE index, no quality check is made on the data used for the quick-look Dst index. Therefore it is recommended that the quick-look Dst index is used only for diagnostic purposes; it should not be used for scientific analyses. The second stage product is the provisional Dst index which is now being made available on a monthly basis with approximately 2 months delay. Beginning January 1997 the provisional Dst index is derived using data from 5 observatories including Alibag. The Dst index derived by the third step is the final Dst index published annually, normally with several months delay. To derive this index, the secular change and a model Sq for the year for each of the observatories are removed. The model Sq variation is determined as a function of the local time and season (see "The geomagnetic indices: derivation, meaning and availability "; for a definition of the Sq variation).

The K-derived planetary indices (am, an, as, aa, and Kp; see "The geomagnetic indices: derivation, meaning and availability ";) were traditionally computed on a monthly basis with K-indices hand scaled on analogue magnetograms and provided as hard copies by the observatories. Provisional values were thus circulated with a delay of a few weeks after the end of the month of observation. Definitive values were computed once definitive K values made available by all the observatories.

Provisional and definitive values are still computed with the K values provided by the observatories. In summer 1997, provisional values were circulated on a monthly basis with a few weeks delay for am, an, and as, twice a month with a few weeks delay for Ap, and on a weekly basis with a few days delay for aa. Reducing these delays down to a few days implied to derive provisional K values from digital minute values. Algorithm for computer derivation of Sr (see "The geomagnetic indices: derivation, meaning and availability "; for a definition of the Sr variation), leading to automatic calculation of K indices have then been set up and tested by different research groups. Four of them have been acknowledged by I.A.G.A. and are now available through I.S.G.I. [IAGA News N°32, p. 27, December 1993]. A software which aims at calculating these indices in quasi real time was then developed at the I.S.G.I. Publication Office. It gets automatically on a daily basis digital minute values from geomagnetic observatories through electronic data transfer procedures, and computes K indices using the FMI method. The quick-look values of planetary indices are then computed and circulated once data availability makes it possible. Since the end of 1996, quick-look values of K-derived planetary indices are then made available on the present Web page, with a nominal time delay of a few days (see section 2.2.1). As it is the case for AE and Dst indices, the am and Km quick-look indices are derived on an ?available data? basis, and a due caution is required in using them.

The question of dissemination of geomagnetic indices through electronic network is at present our major concern. There is in fact a strong request from industrial and military communities to have preliminary values of geomagnetic indices available on line within very short delays. Some of them are asking to have them circulated within a one hour delay. On the other hand, it is very easy to make data available through electronic networks, and Institutes which are not part of I.S.G.I. may easily derive and circulate preliminary values of geomagnetic indices. This would be confusing, and would result in a dramatic loss of quality of geomagnetic indices. I.S.G.I. has then to face up two challenges:

- establish a policy of dissemination of geomagnetic indices through electronic networks which prevents any confusing situation;

- ensure a quasi real time derivation and dissemination of reliable provisional I.A.G.A. geomagnetic indices.

As for the first point, discussions between representatives of I.S.G.I. Collaborating Institutes clearly pointed out that the I.S.G.I. label is actually the simplest and the safest way to guarantee the quality of circulated geomagnetic indices. The I.S.G.I. Collaborating Institutes therefore decided to quote their I.S.G.I. membership in all their publications and data bases. During its VIII Scientific Assembly (Uppsala, 1997), the International Association of Geomagnetism and Aeronomy adopted a resolution which recommend geomagnetic indices designed to provide quasi-real time estimates of existing I.A.G.A. indices to be named by adding est to the name of the index (e.g. Kpest for Kp estimates).

As for the second point, the I.S.G.I. Publication Office (for K-derived planetary indices) and the WDC-C2 for Geomagnetism (for Dst and AE indices) are now routinely preparing and circulating quick-look values of geomagnetic indices within delays of the order of a few days.

The ISGI Publication Office started circulating geomagnetic indices through a mail interface which allowed users on remote computers to obtain geomagnetic indices from the ISGI data base by simply sending messages to the internet address ISGI.DATA@latmos.ipsl.fr. This service, named IMAGINE (Interface for Mailing Automatically Geomagnetic INdices via Electronic networks) has been established on the model of the automatic e_mail running at the INTERMAGNET GIN of Edinburgh, thanks to the kind collaboration of Simon Flower. The IMAGINE server is presented in notes which appeared in the IAGA News N°35 [pp. 45-46, July 1996] and N°36 [pp. 16-17, February 1997].

The ISGI Web homepage is open since Mars 1999, and replaces the server IMAGINE.

Similar efforts are being made by the for Geomagnetism (Kyoto University, Kyoto, Japan), as has already been mentioned in section 2.1. The on-line service for a quick-look Dst index was begun in the summer of 1996, and now the quick look Dst index and the quick-look AE index are both on line on the Web. An early version of the Kyoto on line facilities was presented in a note which appeared in the IAGA News N°35 [pp. 47-48, July 1996].

The GeoForschungsZentrum Potsdam offers several presentations of Kp and associated indices via Internet. Its Web homepage can be found from the homepage of the GeoForschungsZentrum Potsdam or the Adolf-Schmidt Observatory Niemegk. Besides several descriptions the actual Kp table and the musical diagram can be displayed. The whole Kp series beginning in 1932 is available, as well as the derived indices and the quietest and most disturbed days of every month. All data can be inquired via ftp from the ftp server of the GeoForschungsZentrum Potsdam.

In parallel with the development of the on-line facilities described in the previous section, the I.S.G.I. Publication Office and the I.S.G.I. Collaborating Institutes continue to issue printed bulletins. Therefore they ensure the circulation of data primarily through both printed bulletins and electronic network facilities. It is worth being underlined that these services are complementary. The on-line services ensures a rapid dissemination of provisional values of geomagnetic indices, while the printed bulletins make these basic data available to all the laboratories, even if they have no computer facilities for transferring data from World Data Centres. In order to help local digital access, diskettes at the PC format are now associated to each copy of the IAGA Bulletin 32.

All the printed bulletins described hereafter are available on request (see Appendix for the I.S.G.I. Collaborating Institutes addresses). Copies of former Bulletins relative to indices, coming from the former I.U.G.G. Publication Office in Paris and from De Bilt are gathered at the I.S.G.I. Publication Office. A list of still available Bulletins can be found in IAGA News N°32 [p. 41, December 1993]

The provisional values of geomagnetic indices are also sent to H. Coffey for publication in the Solar Geophysical Data NOAA/NGDC reports, and in Journal of Geophysical Research. The final values of geomagnetic indices are sent to World Data Centers from where they are also available.

The I.S.G.I. Publication Office circulates a monthly bulletin and the yearly IAGA Bulletin 32 series:

- the monthly bulletin contains the provisional values of planetary magnetic indices (am, aa, Kp, and Dst), the list of the quiet magnetic days of the month and a preliminary report on remarkable magnetic events. The regular publication of the monthly bulletin resumed in 1994, after updating the bulletin contents and presentation. It is normally sent six to eight weeks after the end of the current month.

- the yearly IAGA Bulletin 32 series contain the definitive values of the I.A.G.A. indices and the list of remarkable magnetic events for the year. These bulletins are aimed to be published within a delay of about two years after the end of the year. Free copies are sent to contributing institutes; about 50 copies are kept at the I.S.G.I. Publication Office in Saint Maur for distribution to subscribers and for sale. In order to facilitate local digital access to the geomagnetic indices published in the IAGA Bulletin 32 series, we now add to each copy a floppy containing all the data published in the Bulletin. The IAGA Bulletin 32r (1987) and the followings were thus circulated with the corresponding floppy, and the floppies for the years 1981 to 1986 were also prepared. They are now available at the I.S.G.I. Publication Office.

The Analysis Centre for Geomagnetism and Spacemagnetism, Kyoto University, publishes and distributes the provisional Dst index on a monthly basis, the provisional AE index in Prompt Reports, and the final AE index in Data Books.

The Kp and Kp-related geomagnetic indices (ap, Cp, C9; see "The geomagnetic indices: derivation, meaning and availability "; for further details) are distributed on tables edited half-monthly. The definitive values of these indices are circulated on monthly tables, together with musical diagrams of Kp, semi graphic tables of C9, and lists of the quietest and most disturbed days of the month.

Given the new facilities for data transfer, related to the increasing development of both digital magnetometers and electronic networks, the basic charges of I.S.G.I. and I.S.G.I. Collaborating Institutes could be at present set out as follows:

- to prepare and to circulate provisional values of magnetic indices and other geomagnetic data within delays as short as possible, of the order of, and if possible smaller than a few days, while carrying on the traditional dissemination of provisional values on a monthly basis;

- to publish the definitive values of these data, using traditional reference booklets (IAGA Bulletin 32 series) or any other new solution insuring the same reliability and durability as printed materials;

- to advise the other I.A.G.A. members as far as geomagnetic indices and related data are concerned. This latter part of the I.S.G.I. missions is at present very important, because of the profound changes induced by the already mentioned new data transfer facilities.

The future developments of I.S.G.I. will be managed according to these three basic requirements. It order to illustrate what we want it to be, in the line of the tradition and tuned in to the present challenges, let us conclude in emphasising on three examples already presented in this paper:

- the I.S.G.I. Publication Office (for K derived planetary indices) and the WDC-C2 for Geomagnetism (for Dst and AE indices) started preparing and circulating quick look values of geomagnetic indices within a delay of a few days. In a second step, the same institutes have the project to decrease the delay down to a few hours. They aim to achieve this objective during the next few years;

- it was decided with the I.S.G.I. Advisory body that the publication of the IAGA Bulletin 32 series is worth being pursued because it constitutes now a long and unbroken series of reference documents (the first bulletin of the series, the IAGA Bulletin 32a, corresponds to 1970), while investigating the possibilities of replacing printed Bulletins by other equivalent, but less expansive products;

- the I.S.G.I. Collaborating Institutes and the I.S.G.I. Publication Office are more and more present in the scientific programs of interest for the whole I.A.G.A. community, such as the INTERMAGNET network of geomagnetic observatories or new programs of magnetic satellites. In particular, the I.S.G.I. Collaborating Institutes will directly provide the ?rsted data centre with classical geomagnetic indices, and the I.S.G.I. Publication Office will provide it with longitude sector indices allowing a better characterisation of the magnetic recordings made onboard the satellite (?rsted is a Danish magnetic satellite, launched in February 1999);

Thanks are due to M. Sugiura and T. Kamei for their help in writing this I.S.G.I. presentation, and to C. Barton for his fruitful comments on this manuscript.. Thanks are also due to the I.S.G.I. Advisory Board, chaired by C. Barton for its contribution to I.S.G.I. policy definition.

ISGI/LATMOS (ex C.E.T.P.)
4, Avenue de Neptune
F-94107 SAINT MAUR DES FOSSES CEDEX
FRANCE
e_mail: michel.menvielle@latmos.ipsl.fr

GeoForschungsZentrum (GFZ) Potsdam
Adolf-Schmidt observatorium für Geomagnetismus
Lindenstr., 7
D-14823 NIEMEGK
GERMANY
e_mail: linthe@gfz-postdam.de

Observatorio del Ebro
C. Horta Alta, 38
E-43520 ROQUETES
SPAIN
e_mail:: ebre.jjcurto@readysoft.es

WDC-C2 for Geomagnetism
Faculty of Sciences
Kyoto University
KYOTO 606-01
JAPAN
e_mail:: Toyo@kugi.kyoto-u.ac.jp

WDC for Geomagnetism
Geomagnetism and Space Physics
Danish Meteorological Institute
Lyngbyvej 100
DK-2100, Copenhagen, DENMARK

Arctic and Antarctic Research Institute
Department of Geophysics
38 Bering str.
St. Petersburg, Russia, 199397
e_mail::vikkorn@aari.nw.ru