Magnetospheric properties deduced from OGO 1 observations of ducted and nonducted whistlers

Abstract

The OGO 1 satellite has yielded evidence for both ducted and nonducted modes of whistler propagation in the magnetosphere. Two new types of nonducted whistlers have been identified: the ‘magnetospherically reflected’ whistler and the ‘Nu’ whistler. These whistlers have never been observed on the ground. Their unique properties result in part from the presence of ions that permit reflection of whistler‐mode energy in the magnetosphere. These phenomena provide a new tool for study of the distribution of ionization in the magnetosphere. Ducted whistlers from OGO 1 have provided the first in situ observations of whistler ducts. Near L = 3, the equatorial separations between ducts ranged from 50 to 500 km, and the equatorial thicknesses were about 400 km. The analysis yielded independent experimental support for the diffusive equilibrium model of distribution of ionization along the field lines in the plasmasphere. Some evidence was found of distortion of the magnetic field on the nightside at L ∼ 3, possibly due to oblique incidence of the solar wind on the earth's field.

Characteristic properties of Nu whistlers as inferred from observations and numerical modelling

“…An unexpected possibility for whistler-wave reflection when the ions are taken into account in the dispersion relation, and the visualisation of this effect by ray tracing, were first demonstrated by Kimura (1966). In a sense, this finding predicted magnetospherically reflected (MR) whistlers, which were found in the spectrograms of wave data from OGO 1 and 3 (Smith and Angerami, 1968). In their study, mainly devoted to MR whistlers, Smith and Angerami also pointed out that the spectrogram of an MR whistler observed far from the equator may have the shape of the Greek letter ν.…”

“…The main focus of the present study is Nu whistlers, which were first reported by Smith and Angerami (1968). We have presented many examples of Nu whistlers from MA-GION 5 measurements, using numerical simulations as a tool for understanding their main features.…”

“…Although the close relation between MR whistlers and Nu whistlers was established in the initial work by Smith and Angerami (1968), in later work MR whistlers were studied much more than Nu whistlers; see, for instance, Sonwalkar and Inan (1989), Draganov et al (1992), Thorne and Horne (1994), and Jasna et al (1990). Some comments on these studies may be found in the paper by Shklyar and Jiȓícek (2000), where an analysis of MR whistlers observed by MAGION 4 and 5 was supplemented by an extensive numerical simulation of MR-whistler spectrograms.…”

Assigning the causative lightning to the whistlers observed on satellites

“…After an initial rapid rise in frequency, these waves asymptotically approach the proton cyclotron frequency. Smith and Angerami (1968), using measurements on OGO 1 and OGO 3 satellites, first reported Magnetospherically Reflected (MR) whistlers predicted by Kimura (1966). The MR whistlers are highly oblique (with respect to magnetic field lines) propagating waves that undergo a reflection in the region where their frequency is close to the local Lower Hybrid Resonance (LHR) frequency.…”

Constraints on Jovian plasma properties from a dispersion analysis of unducted whistlers in the warm Io torus

“…Lightning-generated whistlers were detected by the plasma wave instrument on Voyager I in three distinct The dispersion of whistlers was initially used as a remote probe for plasma properties in the Earth's inner magnetosphere [Helliwell, 1965;Smith and Angerami, 1968]. Subsequently, the dispersion of Jovian whistlers was analyzed to estimate the electron and light ion (H +) densities along field-aligned propagation paths between the Jovian ionosphere and the Io torus [Tokar et al, 1982a, b].…”