Figure 1:
Locations of Regional Warning Centres (RWCs) of the
World Space Weather Service (from Thompson et al., 1993).
Abstract. The planet Earth is unique in the solar system as the only planet supporting the existence of life. Space as the medium connecting the solar system has weather whose variations have tremendous consequences for life on Earth. In the early fifties only a few countries monitored space weather from ground-based observatories. Recently the study of the origin, propagation and impact of a space weather event was carried out by 20 spacecraft owned by 12 countries, and by 30 ground-based observatories. The advances in space weather monitoring and the resultant ability to predict and prepare for the violent perturbations to the near-Earth space environment are examined in the light of the disruption of life-supporting technological systems on Earth.
Sommaire. La planète Terre est unique dans le système solaire: c'est la seule planète sur laquelle la vie est présente. L'espace, en tant que milieu baignant le système solaire, a un climat dont les variations ont de terribles conséquences sur la vie sur Terre. Dans les années cinquante seuls quelques pays faisaient un suivi du climat spatial à partir d'observatoires au sol. Récemment, l'étude de l'origine, de la propagation et de l'impact d'un disfonctionnement du climat spatial a été menée par 20 engins spatiaux appartenant à 12 pays, et par 30 observatoires au sol. Les progrès réalisés dans le suivi du climat spatial et la capacité qu'il en résulte à prédire les violentes perturbations dans le proche environnement de la Terre et à s'y préparer, sont examinés à la lumière des troubles causés à la vie courante par la perturbation des systèmes technologiques.
The 150 million kilometres of space between the Sun and the Earth's orbit, which the solar wind traverses in 30 hours, provides ample room to position several space weather stations for monitoring the solar wind. The stations should contribute data about the origin, development and propagation of coronal mass ejections (CMEs), which is the largest single information gap in space weather monitoring system.
The level of disturbance in the geomagnetic field serves as a convenient proxy that characterizes the level of disturbance of the near-Earth space environment, namely, the magnetosphere and the ionosphere. Extraordinary levels of geomagnetic disturbances known as ``magnetic storms'' characterize sp-ace weather. Magnetic storms denote variations in the Earth's magnetic field intensity, which may be as large as the several percent of the undisturbed value measured at the Earth's surface. Particle, electromagnetic, and ionospheric disturbances resulting from solar storms, coronal mass ejections, fast solar wind streams and ionospheric instabilities pose several costly hazards.
A particular advantage of geomagnetic data is that beginning with the earliest scientific records, the data have been characterized, or indexed by the level of disturbance. The Space Environmental Laboratory (SEL) of the National Oceanic and Atmospheric Administration (NOAA) has a Space Environment Service Center (SESC) which works around the clock to monitor more than 1400 separate data streams, which sense solar, magnetospheric and ionospheric parameters (Joselyn, 1995).
The origin of solar-terrestrial physics is generally traced to Sabine's recognition in 1852 that geomagnetic activity paralleled the recently discovered sunspot cycle. Geomagnetic storms can have two distinct solar sources: recurrent high-speed wind streams from around coronal holes and CMEs asso-ciated with eruptive solar flares and disappearing solar filaments (DSFs) (Cliver, 1994). Alexander von Humboldt in Germany and Arago in France made early studies of magnetic storms, which were rapid variations of the geomagnetic field, during the first part of the 19th century. The first set of British observatories was set up by Sabine in 1840 at Toronto, Hobart (Tasmania), the Cape of Good Hope and St Helena. In 1826 Heinrich Schwabe, an amateur astronomer, began observing the Sun and making counts of sunspots at least partly in the hope of discovering intra-Mercurical planets.
Ten regional warning centres (RWCs) of the International Ursigram and World Days Service (IUWDS) monitor and predict solar terrestrial activity and provide space weather forecasts andwarnings forusers who plan to conduct activities sensitive to solar-terrestrial conditions. The IUWDS is a joint service of the International Union of Radio Science (URSI), the International Astronomical Union (IAU) and the International Union of Geodesy and Geophysics (IUGG) and is a permanent service of the Federation of Astronomical and Geophysical Data Services. The RWCs have the responsibility for collecting data from their geographical areas and exchanging these data through the IUWDS network.
The ten regional warning centres (Fig. 1) are in Beijing (China), Boulder (U.S.A.), Moscow (Russia), Paris (France), New Delhi (India), Ottawa (Canada), Prague (Czechoslovakia), Tokyo (Japan), Sydney (Australia), and Warsaw (Poland). The center in Boulder plays a special role as ``World Warning Agency,'' acting as a hub for data exchange and forecast (Thompson et al., 1993).
The users of the services of RWCs include high frequency (HF) radio communications, mineral surveyors using geophysical techniques, power line and pipeline authorities, operators of satellites and global positioning systems and a host of commercial and scientific users. The increasing sophistication and sensitivity of modern technology has resulted in a rapidly expanding range of applications where knowledge of the solar-terrestrial environment is important.
Figure 1:
Locations of Regional Warning Centres (RWCs) of the
World Space Weather Service (from Thompson et al., 1993).
As power systems interlink and grow more complex to meet increased demand, the vulnerability of satellites to shutdowns by space storms increases. Accurate monitoring and specific space weather forecasts would allow commercial and other customers of the space weather service to take evasive actions to reduce hazards, disruptions, losses and errors.
Figure 2:
Projection of the Advance Composition Explorer's (ACE)
orbit in the ecliptic plane (from Zwickl and Joselyn, 1994).
However, a crucial input for magnetospheric and ionospheric forecasting is missing and that is upstream measurement of solar wind parameters including the Interplanetary Magnetic Field (IMF). In the interest of space weather forecasting, NOAA, NASA and the Department of Defense have reached an agreement to secure the capability of receiving quasi-continuous, real-time solar wind and IMF data from NASA's WIND and Advance Composition Explorer (ACE) spacecraft.
A quality-of-life benefit to society would be the NSWS forecast that reduces disruptions in services from industries sensitive to space weather. Avoiding a major grid failure has considerable strategic value. One of the most crucial needs for short-term alerts of geomagnetic activity is early-warning of the arrival of solar wind carrying intense southward directed interplanetary magnetic fields Bz. A good location for a sentry space craft measuring Bz as well as other important parameters, such as the solar wind velocity and density, is the L1 libration point between the Sun and the Earth, which is about 0.01 AU (4 times the distance of the moon) upstream. Solar wind passing this point and travelling towards Earth arrives within 30 to 60 minutes offering enough time for concerned customers, such as electric utilities and spacecraft operations, to take mitigating actions. The ACE is stationed at L1.
Figure 2 shows the projection of the ACE orbit in the ecliptic plane. The scientific focus of ACE includes both comparative studies of the origin and evolution of interplanetary populations of matter from the solar system and the galaxy, and studies of the acceleration process occuring in different plasma environments. ACE will measure elemental and isotopic composition of accelerated nuclei spanning six decades in energy per nucleon, from the low energy solar wind to galactic cosmic-rays (Zwickl and Joselyn, 1994).
In 1997 the first observation of a space weather event from start to finish was recorded. On January 6, 1997, a coronal mass ejection (CME) left the surface of the Sun into the solar wind and moved towards Earth; by January 10, a cloud of charged particles buffeted the face of the Earth. This event (Fig. 3) is the first true success story of the four-year-old International Solar-Terrestrial Physics (ISTP) programme, which includes NASA's WIND and POLAR spacecraft, the joint Solar and Heliospheric Observatory (SOHO) mission of NASA and the European Space Agency (ESA), the joint Geotail mission of NASA and Japan's Institute of Space and Aeronautical Science and Russia's Interball satellites (Carlowicz, 1997). The magnetic cloud that left the Sun as a CME and crossed paths with Earth presented a unique opportunity to study the origin, propagation and impact of a space weather event. Scientists from at least 12 countries, using 20 spacecraft and 30 ground-based observatories were able topredict and prepare for this ``violent perturbation to the near-Earth space environment.''
Figure 3:
The satellites of the ISTP constellation were in position to view
the space weather event
of January 6-11, 1997, from several different
angles (from Carlowicz, 1997).
As the magnetic cloud reached Earth's magnetosphere, films from POLAR spacecraft revealed strong reactions in the auroral zones. The particle flux of Earth's radiation belts increased more than 100 times over previous levels: satellite and ground-based instruments detected impulse heating, substorm activity, moderate to high spacecraft charging, and intense upflowing of auroral ions. The ILE-IFE geo-magnetic observatory (a low-latitude observatory), in Nigeria, was one of the ground-based observatories which recorded the features of the magnetic storm, which hit the Earth in the early hours of January 10, 1997 (Fig. 4). The magnetograms show the horizontal components Bx, By, and the vertical component Bz. Fig. 4a shows the disturbed magnetic field components for January 10, 1997, while Fig. 4b shows those for January 11, 1997. Fig. 4c shows the magnetogram for a quiet day on January 3, 1997, before the beginning of the magnetic storm event. It is seen that the horizontal component Bx on a quiet day shows a maximum about midday local time. This is characteristic of the effect of the Equatorial Electrojet on Bx at low latitudes (Ogunade, 1995). In Fig. 4a, the figures 970109 and 235900 on the time axis indicate the date and time, respectively. Hence the record for January 10, 1997, started at 23:59:00 UT on January 9, 1997, and ended at 23:59:00 UT on January 10, 1997.
Figure 4:
Magnetic field components at Ile-Ife showing: (a) the arrival on
the Earth's surface of the
magnetic storm of January 10, 1997, at about
04.30 UT, (b) the full-blown storm on January 11, 1997,
(c) a quiet day on
January 3, 1997, before the beginning of the magnetic storm event.
Acknowledgement
I wish to acknowledge the regular supply of the International STEP Newsletter by the SCOSTEP Secretariat. The material for this paper was put together during a re-invitation to Germany by the Alexander von Humboldt Foundation.
References
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