Low attenuation of hydromagnetic waves in the ionosphere and implied characteristics in the magnetosphere for Pc 1 events

Studies of natural hydromagnetic emissions at 0.5 and 1.0 cps, called Pc 1, detected at the conjugately located stations of Baie St. Paul (Quebec), Canada, and Eights Station, Antarctica, indicate an ionospheric attenuation of the signals. In transmission through the daytime ionosphere at 47°N latitude, during the 1964 summer, the signals seem to be reduced to about 0.5–0.7 (at 0.5 cps) and 0.2–0.5 (at 1.0 cps) of their original amplitudes. The higher values corresponded to Kp < 2 and the lower values to Kp of about 3. If some minor assumptions are made concerning the nature of the wave coupling, the measured attenuations appear to be close to predicted values. The magnitudes of energy absorption indicate that significant ionospheric heating does not occur. World station observations, when appropriately translated into the magnetosphere, implied (1) a particle distribution, rather uniform between L values of 7 and 4 with extremal magnitudes in the afternoon and predawn side and (2) a hydromagnetic wave excitation region varying from the noon side at L = 7 to the early morning side at L = 4.