The National Geophysical Data Center provides the observations here with no re- strictions on their use. Please contact us at the address below with your com- ments and questions about the form and the content of this information product or about the measurements themselves. NATIONAL GEOPHYSICAL DATA CENTER 325 Broadway Mail Code E/GC2 Boulder, Colorado 80303-3328 USA Telephone: (303) 497-6475 email: info@ngdc.noaa.gov FAX: (303) 497-6513 WWW: www.ngdc.noaa.gov ------------------------------------------------------------------------------- SELECTED GEOMAGNETIC AND SOLAR ACTIVITY INDICES ------------------------------------------------------------------------------- WORLDWIDE INDICES The subscript "p" means planetary and designates a global magnetic activity in- dex. The following 13 observatories, which lie between 46 and 63 degrees north and south geomagnetic latitude, now contribute to the planetary indices: Ler- wick (UK), Eskdalemuir (UK), Hartland (UK), Ottawa (Canada), Fredericksburg (USA), Meannook (Canada), Sitka (USA), Eyrewell (New Zealand), Canberra (Aus- tralia), Lovo (Sweden), Brorfelde (Denmark), Wingst (Germany), and Niemegk (Germany). ------------------------------------------------------------------------------- EQUIVALENT AMPLITUDE The a-index ranges from 0 to 400 and represents a K-value converted to a linear scale in gammas (nanoTeslas)--a scale that measures equivalent disturbance am- plitude of a station at which K=9 has a lower limit of 400 gammas. ------------------------------------------------------------------------------- FORMAT FOR MONTHLY MEANS OF SELECTED GEOMAGNETIC INDICES ------------------------------------------------------------------------------- COLUMNS FMT DESCRIPTION ------------------------------------------------------------------------------- 1- 4 I4 YEAR 5- 6 I2 MONTH 7-10 I4 Monthly mean Ap PLANETARY EQUIVALENT DAILY AMPLITUDE 11-12 2X Blank 13-16 I4 Monthly mean ap or PLANETARY EQUIVALENT AMPLITUDE for 00-03 UT. 17-20 I4 Monthly mean ap or PLANETARY EQUIVALENT AMPLITUDE for 03-06 UT. 21-24 I4 Monthly mean ap or PLANETARY EQUIVALENT AMPLITUDE for 06-09 UT. 25-28 I4 Monthly mean ap or PLANETARY EQUIVALENT AMPLITUDE for 09-12 UT. 29-32 I4 Monthly mean ap or PLANETARY EQUIVALENT AMPLITUDE for 12-15 UT. 33-36 I4 Monthly mean ap or PLANETARY EQUIVALENT AMPLITUDE for 15-18 UT. 37-40 I4 Monthly mean ap or PLANETARY EQUIVALENT AMPLITUDE for 18-21 UT. 41-44 I4 Monthly mean ap or PLANETARY EQUIVALENT AMPLITUDE for 21-24 UT. 45-50 F6.2 Monthly mean Cp or PLANETARY DAILY CHARACTER FIGURE--a qualitative estimate of overall level of magnetic activity for the day determined from the sum of the eight ap amplitudes. Cp ranges, in steps of one-tenth, from 0 (quiet) to 2.5 (highly disturbed). 51-53 I3 Monthly mean C9--a conversion of the 0-to-2.5 range of the Cp index to one digit between 0 and 9. -------------------------------------------------------------------------------