Investigating propagation characteristics of ground transmitter signals in the magnetosphere and magnetospheric conditions of the associated triggered emissions
Abstract
Ground-based very low frequency (VLF) transmitters have been utilized for long distance communication and geo-location in past few decades (Watt 1967, Swanson 1983). Despite that the signals are primarily confined within the Earth-ionosphere wave-guide (Helliwell 1965), part of the transmitter wave power can penetrate through the ionosphere and into the magnetosphere. These signals have been demonstrated to produce precipitation of radiation belt electrons (e..g, Inan et al., 2007); recent observation also reveals that sharp radial gradients of the outer radiation belt electron fluxes (Baker et al., 2014, 2016) were spatially coincident with the region of ground VLF transmitter wave enhancement (Foster et al., 2016). Because the radiation belt electrons directly impact spacecraft through accumulated dose, internal charging, and electronic upsets and significantly affect astronauts in the space station, it is of great interest to understand anthropogenic effects on the radiation belts. However, the assessment of such anthropogenic effects, which depends on propagation modes (ducted and nonducted) inside the magnetosphere, still remains a subject of uncertainty because of very limited wave observations inside the magnetosphere, especially near the equator where most of wave-particle interaction is expected to occur. We propose to investigate the magnetospheric condition for different propagation modes and quantify the contribution of different propagation modes to transmitter wave power in the magnetosphere. To study wave-particle interaction in the Earth s magnetosphere, controlled experiments have also done previously by injecting VLF waves from the ground into near-Earth space (See Golkowshi et al., 2019 review). A large database of observations has successfully been generated (e.g., Gołkowski et al., 2008). However, the observation of the amplified and triggered waves due to the controlled experiment were primarily made on the ground, with little information on corresponding plasma conditions in the magnetosphere, where wave-particle interactions take place. Thanks to the Van Allen Probes mission that is capable of detecting the waveforms of triggered emissions associated with the Alpha transmitter signals, we propose to examine the magnetospheric conditions that favors the triggered emissions.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 07, 2024
- Source ID
- FA95502310568
Entities
People
- Lunjin Chen
Organizations
- Air Force Office of Scientific Research
- United States Air Force
- University of Texas at Dallas