Ionospheric Plasma Fluctuations Induced by the NWC Very Low Frequency Signal Transmitter

• Published in: Journal of geophysical research. Space physics Vol. 126; no. 5
• Main Authors: Ivarsen, Magnus F., Park, Jaeheung, Jin, Yaqi, Clausen, Lasse B. N.
• Format: Journal Article
• Language: English
• Published: 01.05.2021
• Subjects: ionosphere; plasma; plasma fluctuations; Swarm; turbulence; VLF signal
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2021JA029213

The Australian NWC (North West Cape) signal transmitter is known to strongly interfere with the topside ionosphere. We analyze 456 conjunctions between Swarm A, B and NWC, in addition to 58 conjunctions between NorSat‐1 and NWC. The in‐situ measurements provided by these satellites include the 16 Hz Swarm Advanced Plasma Density data set, and the novel 1,000 Hz plasma density measurements from the m‐NLP system aboard NorSat‐1. We subject the data to a detailed PSD analysis and subsequent superposed epoch analysis. This allows us to present comprehensive statistics of the NWC‐induced plasma fluctuations, both their scale‐dependency, and their climatology. The result should be seen in the context of VLF signal transmitter‐induced plasma density fluctuations, where we find counter‐evidence for the existence of turbulent structuring induced by the NWC transmitter. Plain Language Summary Plasma turbulence is an elusive concept, but vital to understanding the ionosphere. Previous studies have posited that a powerful naval radio transmitter on the coast of Australia is producing turbulence in the ionosphere just north of the transmitter location. We investigate the effect caused by the radio transmitter on ionospheric plasma, and present a comprehensive statistical analysis. We find counter‐evidence for the existence of actual turbulence, and go on to briefly discuss the difference between fluctuations in plasma and turbulence. Key Points The NWC transmitter produces clearly observable plasma density fluctuations in the topside F‐region ionosphere The scale sizes associated with the strongest plasma fluctuations are between 1 and 10 km The NWC‐induced plasma fluctuations are most visible during a tenuous ionosphere, and during magnetic midnight