The gyro-frequency in the ArcticE-layer

Calculation of the gyro-frequency in the E-layer at arctic stations from measurements of critical radio-frequency differences gives a lower magnetic field than that obtained by extrapolation of the terrestrial field measured at ground-level, and, at one station, a large semi-diurnal variation with maxima at 06h and 18h local time. Ray-path deflections which can explain similar effects previously reported for the F-layer cannot be responsible in the E-layer because of the opposite sense of this deviation and because of the small layer-thickness. Moreover, no semi-diurnal variation was found in the F-layer. It is shown that these new E-layer phenomena may be due to a variable concentration of heavy ions rising to over 4,000 times the density of free electrons.