Most middle-size and large countries of the world operate permanent observatories where measurements of magnetic field changes are preserved in digital (electronic number storage) or analog (amplitude-time recording) form. Today, there are about 100 major magnetic observatories worldwide that share information (Figure 5.12).
Special calibration techniques verify the record accuracy before distribution. By international agreement, duplicate records are archived at six World Data Centers, so that scientists and students can use the global magnetic information for field modeling, chart preparation, and solar-terrestrial disturbance investigation. Approximately 70 world observatories cooperate in an advanced observatory system called INTERMAGNET, which uses satellites for relaying 1-minute digitized magnetic field values in "real-time" (delayed by less than 1 hr) to several special, globally distributed collection points.
DAR GNA DYW CTA TCK
DAR GNA DYW CTA TCK
10 20 30 40 50 60 70 80 Hours from start of storm day
FIGURE 5.10 ► For a geomagnetic storm recorded at nine magnetic field observatories, consisting of five along a longitude line through central Australia from Darwin to Port Augusta and four standard observatories near the corners of the country (see station code letters at the upper right of the figure), field differences were determined. These differences represent the H field components (from which the Sq quiet fields were removed) minus the Dst index values (adjusted for the observatory latitude with the division by the cosine of that latitude). Note the similarity of the overlaid station values and their significant amplitudes with respect to the Dst (plotted below the group).
Three World Data Centers are particularly active in collecting geomagnetic data from the observatories in Figure 5.12 and in providing convenient methods for user access to the archives:
• In the United States: World Data Center A, NGDC/NOAA, mailstop EGC2, 325 Broadway, Boulder, Colorado 80305-3328, USA; tel: 1303-297-6761; fax: 1-303-497-6513; e-mail: [email protected]
• In Russia: World Data Center B, Academy of Sciences of Russia, Molodezhnaya 3, Moscow 117 296, RUSSIA; tel: 7-095-930-1762 or -5619, fax: 7-095-930-5509
• In Japan: World Data Center C2, Data Analysis Center for Geomagnetism and Space Magnetism Graduate School of Science, Kyoto University, Kyoto 606-8502, JAPAN; tel: 81-75-753-3929, fax: 81-75-7227884.
^ 0 Jcm<adaj . „ tlSaiijl.i------ (J-----, , ...
0 —I------—■ ■■ m-tr -m fir- - ---:---——~
75° West Meridian Time
FIGURE 5.11 ► The field pulsation similarity at the conjugate high-latitude observatories of Baie St. Paul, Quebec, Canada, and Eights Station, Antarctica. Spectral displays for Pc pulsations (dark regions of limited frequency content) are illustrated. Local background noise appears as full vertical grey lines. Calibration harmonics near 1130 at Quebec appear on the record. The frequency scale is given to the left in cycles per second (Hz). The horizontal axis shows midnight to midday hours (0 to 13) at 75° West Meridian Time.
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