11. Aircraft flying polar routes near the geomagnetic poles are at particular risk. 12. The frequency of geomagnetic storms increases and decreases with the sunspot cycle. 13. A geomagnetic storm has three phases : initial, main and recovery. 14. Transmitting and receiving stations should be nearly equidistant from the geomagnetic equator. 15. Effects on Schumann resonances have been reported following geomagnetic and ionospheric disturbances. 16. Skywave propagation is usually degraded sometimes seriously during geomagnetic storms. 17. The geomagnetic polarity time scale was calibrated largely using K Ar dating. 18. Brief disruptions that do not result in reversal are called geomagnetic excursions. 19. :Geomagnetic reversal # Future of the present field has some information. 20. A G4 ( severe ) geomagnetic storm was reported on September 26.
