For a rough calculation, assume you're walking north, with the horizontal component of Earth's magnetic field decreasing from 50mT to 0mT from the magnetic equator to the magnetic pole, over 10000km = 1.0 \ times 10 ^ { 7 } m.
22.
Radio waves of frequency less than about 7 MHz can become trapped in magnetic field-aligned ionization ducts with L values ( distance from the center of the earth to the field line at the magnetic equator ) less than about 4.
23.
At the magnetic equator, electrons of energies exceeding 500 keV ( resp . 5 MeV ) have omnidirectional fluxes ranging from 1.2?0 6 ( resp . 3.7?0 4 ) up to 9.4?0 9 ( resp . 2?0 7 ) particles per square centimeter per second.
