The Contribution of a Geophysical Data Service: The International Service of Geomagnetic Indices

Abstract

Geomagnetic indices are basic data in Solar-Terrestrial physics and in operational Space Weather activities. The International Service of Geomagnetic Indices (ISGI) is in charge of the derivation and dissemination of the geomagnetic indices that are acknowledged by the International Association of Geomagnetism and Aeronomy (IAGA, an IUGG association) INTRODUCTIONGeomagnetic activity corresponds to that part of the transient variations of the geomagnetic field observed at the surface of the Earth, which bears the magnetic signature of currents flowing in the ionized environment of the Earth, the dynamics of which is driven by the solar wind. Since the beginning of systematic geomagnetic field observations more than one hundred years ago, efforts to characterize geomagnetic activity led to the definition of a few geomagnetic indices that are widely used by the scientific community and officially recognized by the International Association of Geomagnetism and Aeronomy (IAGA). These quantities are hereafter referred to as IAGA geomagnetic indices.Since the dynamics of currents flowing in the ionized environment of the Earth are driven by the solar wind, geomagnetic indices are basic data in Solar-Terrestrial physics, and there is accordingly a need for long homogeneous data series. It is worth being noted that, although geomagnetic indices are thus widely used in magnetospheric physics, as, e.g., indicators of the magnetosphere-ionosphere system activity or input parameters in the models, ignorance of their real physical meaning often leads to using them as black boxes. The International Service of Geomagnetic Indices (ISGI) has the mission to make reference values for the IAGA geomagnetic indices available to the scientific community and to maintain archives of these data series.Magnetospheric activity may otherwise cause disturbance -which can be severe -in the functioning and behaviour of satellites and space systems: geomagnetic indices are also basic data for operational Space Weather activities, and this requires the shortest possible dissemination delay. Early in the Internet age, many institutions that are not part of ISGI started to derive and disseminate online preliminary values (also called quick-look values) of IAGA geomagnetic indices, without any control by IAGA bodies on the quality of their products. This resulted in a very confusing situation and could have resulted in a dramatic loss of user confidence in the quality of geomagnetic indices made available through the Internet.ISGI had then to face up to two challenges: -establish a policy for on-line dissemination of indices; -ensure a quasi real time on-line dissemination of reliable quick-look values of IAGA geomagnetic indices.ISGI decided to routinely make available on-line preliminary values for almost all IAGA geomagnetic indices. ISGI also drove discussions in the frame of IAGA. They resulted in an IAGA resolution urging the producers of estimated indices to make clear by a specific label that they are not official IAGA indices. The...