In situ measurements of transionospheric VLF wave injection

VLF waves at 3.85 kHz from the Siple, Antarctica, transmitter were continuously measured by electric and magnetic receivers on a sounding rocket as the waves propagated through the neutral atmosphere and into the ionosphere. The change from linear to circular polarization was clearly observed along with severe attenuation of the VLF signal in the D region. Interferometric measurements established the index of refraction and provided an independent calibration of the rocket‐borne receivers. An upper bound on the VLF power radiated is estimated to be 1.7×10³ W during a period when the antenna was driven at 115×10³ W. The power estimated to be entering the ionosphere is between 3 W and 12 W and depends on assumptions concerning the geometrical distribution of wave power.