Illumination of the plasmasphere by terrestrial very low frequency transmitters: Model validation

Abstract

[1] A composite model of wave propagation from terrestrial very low frequency (VLF) transmitters has been constructed to estimate the wave normal angles and fields of whistler mode waves in the plasmasphere. The model combines a simulation of the fields in the Earth-ionosphere waveguide, ionospheric absorption estimates, and geomagnetic field and plasma density models with fully three-dimensional ray tracing that includes refraction, focusing, and resonant damping. The outputs of this model are consistent with those of several previous, simpler simulations, some of which have underlying component models in common. A comparison of the model outputs to wavefield data from five satellites shows that away from the magnetic equator, all of the models systematically overestimate the median field strength in the plasmasphere owing to terrestrial VLF transmitters by about 20 dB at night and at least 10 dB during the day. In addition, wavefield estimates at L < 1.5 in the equatorial region appear to be about 15 dB too low, although measured fields there are extremely variable. Consideration of the models' similarities and differences indicates that this discrepancy originates in or below the ionosphere, where important physics (as yet not conclusively identified) is not being modeled. Adjustment of the low-altitude field estimates downward by constant factors brings the model outputs into closer agreement with satellite observations. It is concluded that past and future use of these widely employed trans-ionospheric VLF propagation models should be reevaluated.

Large-amplitude transmitter-associated and lightning-associated whistler waves in the Earth's inner plasmasphere atL< 2

“…Abel and Thorne [1998] showed that precipitation rates of high-energy electrons, calculated from VLF wave flux model estimates, compared favorably to observed electron precipitation rates. However, Starks et al [2008] found an average of 20 dB less VLF wave power in the inner radiation belt than predicted by ionospheric absorption models and assumed by Abel and Thorne [1998]. More sophisticated absorption models have only increased the discrepancy between required and observed VLF wave fluxes [e.g., Tao et al, 2010].…”

Parametric validations of analytical lifetime estimates for radiation belt electron diffusion by whistler waves

“…At lower energies E < 1 MeV, it is not true anymore if one considers only hiss and lightning-generated waves such that f < 6 kHz as in CRRES spectra from Meredith et al (2007). Nevertheless, VLF waves from ground transmitters are also important at L < 3 (Abel and Thorne, 1998;Starks et al, 2008;Breneman et al, 2011;Cohen et al, 2012), as well as magnetosonic waves at L > 2 (Meredith et al, 2009). Fig.…”

Global lightning distribution and whistlers observed at Dunedin, New Zealand

“…Starks et al (2008) and Lehtinen and Inan (2009) found that signals from terrestrial VLF transmitters measured at LEO were substantially weaker than predicted from sophisticated propagation models. The discrepancies were attributed to the presence of small-scale irregularities in the ionosphere.…”