NWC Transmitter Effects on the Nightside Upper Ionosphere Observed by a Low‐Altitude Satellite

Abstract

AbstractNWC is an extremely powerful very low frequency (19.8 kHz) transmitter located in the north‐west Australia. Although the transmitter typically operates continuously, it was off during the second half of 2007. This allows for a direct comparison of an ionospheric situation at the times when the transmitter is on with the times when the transmitter is off. We use electromagnetic wave and plasma measurements performed by the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions spacecraft at an altitude of about 660 km. Given that the transmitter signal is significantly attenuated in lower ionospheric layers during the daytime and, moreover, the dayside ionosphere is controlled primarily by the solar radiation, concealing possible transmitter‐related effects, we focus exclusively on the nightside. We show that although the NWC transmitter signal does not significantly change the mean plasma density and only slightly increases the electron temperature, it causes significant perturbations of both these quantities at distances up to about 200 km. The wave intensity is considerably enhanced in the same spatial region close to the transmitter in a large range of frequencies above about 14 kHz. Finally, clear signatures of transmitter induced electron precipitation are detected to the east of the transmitter at somewhat larger L‐shells, consistent with a gyroresonance condition.