Motions of particle microstructures in the magnetopause boundary layer

Larson, Nels R.; Parks, G. K.

doi:10.1029/92ja00496

Cited by 12 publications

(6 citation statements)

References 23 publications

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“…The magnetopause boundary layer echoes always show a considerable amount of range (i.e., vertical) spreading indicating that plasma density irregularities are common in this region as has been reported by Larson and Parks [1992] and others. The diffuse nature of the boundary layer echoes in Figure 17 is due to multiple direct reflections, while the rapid drop‐off of the trace at high frequencies provides both the distance to the magnetopause and the maximum density there (as indicated by the plasma frequency).…”

Section: Remote Sounding Of the Magnetopause Demonstrated With Radio supporting

confidence: 76%

Magnetospheric imaging: Promise to reality

Burch

2005

Reviews of Geophysics

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Measurements of the plasmas, energetic particles, and electric and magnetic fields within the Earth's magnetosphere have been made with ever greater coverage and precision throughout the past 46 years; but until recently, no images of this important environment were available. However, for 2 decades or more, theoretical estimates, data from sounding rockets, and background signals from orbiting instruments designed for in situ ion measurements accumulated to show that most of the plasmas contained in the inner magnetosphere could be imaged if new instruments designed for the purpose could be placed in a suitable high‐altitude orbit. With the launch of the NASA IMAGE satellite in March 2000 the promise of magnetospheric imaging began to be realized. IMAGE provides nearly continuous imaging of the inner magnetosphere on a nominal timescale of 2 min. The discoveries made by IMAGE during its first 5 years of operation are reviewed in this paper.

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Section: Remote Sounding Of the Magnetopause Demonstrated With Radio supporting

confidence: 76%

Magnetospheric imaging: Promise to reality

Burch

2005

Reviews of Geophysics

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“…[1989] show some evidence of this patchy structure in their observations of bursts of LH turbulence. Also, Larson and Parks [1992] have pointed out that ISEE 1 and 2 observations indicate that very fine scale structure exists at the magnetopause. They show evidence for large changes in electron fluxes (with energies of a few keV) on timescales of a second or less.…”

Section: Electron Transport Due To Modulational Instabilitymentioning

confidence: 99%

Modulational instability of lower hybrid waves at the magnetopause

Shapiro¹,

Shevchenko²,

Cargill³

et al. 1994

J. Geophys. Res.

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Abstract. The role of lower hybrid waves at the magnetopause is reexamined. It is found that for the maximum observed wave power, the lower hybrid waves are unstable to a modulational instability on the magnetosheath side of the magnetopause. The modulational instability leads to localized field structures , oriented predominantly along the magnetic field. Such patchy lower hybrid turbulence has been observed by some spacecraft. As a result of the large Ti/Te ratio, the waves saturate by ion heating; as a result, unlike other settings (e.g. comets, critical ionization phenomena), energetic electrons are not expected. The stochastic electron transport in the presence of such turbulence is analyzed and results in strongly anisotropic electron diffusion, with the dominant direction across the magnetic field. The diffusion rate exceeds significantly that expected from quasi-linear considerations and, for magnetopause parameters, also exceeds the rate discussed by Sonnerup (1980).

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“…In summary, the phase-coding and spectral-processing techniques that have been used successfully on ionospheric sounders are unlikely to work for magnetospheric sounders. The reason for their inapplicability arises from both the dynamic nature of the magnetopause as identified by Berchern and Russell [ 1982] and Larson and Parks [1992] among others and from the geometrical considerations associated with the large distance between the spacecraft and the magnetopause. These properties of the real magnetopause and the consequences of geometry were not treated by Calvert et al [1995].…”

Section: How Dynamic Is the Magnetopause? Relatively Few High-time-rementioning

confidence: 99%

Comment on “The feasibility of radio sounding of the magnetosphere” by W. Calvert et al.

Greenwald¹

1997

Radio Science

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In a recent paper, Calvert et al. [ 1995] presented the idea of putting a VLF and LF radio wave sounder on a high-altitude satellite to locate and monitor the position of the Earth's magnetopause and plasmapause.Their essential idea was to use the sounder in much the same way as an ionospheric sounder is used to monitor the height and critical frequency of the ionosphere. The sounder would be located outside of the plasmasphere in a region where the local critical frequency is lower than that of either the plasmapause or the magnetopause. Then, by transmitting a series of pulses at stepped frequencies and monitoring the delay time of the returned signals, it should, in principle, be possible to monitor the range to both the magnetopause and plasmapause, as well as the critical frequency of the magnetopause. The concept is quite exciting and has raised interest in the scientific community. It would be of particular value for the detection of the magnetopause, a boundary of considerable importance to solarterrestrial research and one that is not readily detected with other remote sensing techniques. Other groundbased and satellite techniques (e.g., whistlers and EUV imaging) are in use or have been proposed for the detection of the plasmapause.Unfortunately, the proposed measurement is difficult to accomplish for a number of reasons. Two of the most significant are the relatively low powers that will be radiated by the antenna at the frequencies required for magnetopause detection (-50 mW less than the radiated power from a topside sounder and that the range to the magnetospheric reflection point is a factor of 30 greater, accounting for an additional 30 dB of sensitivity loss. To regain some of this sensitivity loss, Calvert et al. [1995] have proposed the use of phase-coded transmissions and spectral integration. They argue that these coherent-integration techniques will increase the sensitivity of their measurements by a combined factor of 21 dB, and they reference Reinisch et al. [1992], who have successfully applied these techniques to ionospheric sounding. Calvert et al. [1995] require this sensitivity enhancement in order to determine the direction of the reflection point on the magnetopause. With it, they claim an angular precision in direction determination of 1 ø (see their equation (35)). If they are unable to achieve this sensitivity enhancement, then their direction determination will be much worse. In fact, it will be worsened by a factor of more than 100.The issue then is to determine whether the magnetopause and plasmapause can be probed with the types of coherent integration that Calvert et al. [1995] have proposed. We note that they have not actually addressed the limitations of these techniques in their paper. We shall examine this issue, devoting particular attention to the magnetopause sounding case. The essential requirement for applying coherent-integration techniques to any radar application is that a measure of phase coherency is maintained in the backscattered or reflected signal thr...

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Motions of particle microstructures in the magnetopause boundary layer

Cited by 12 publications

References 23 publications

Magnetospheric imaging: Promise to reality

Magnetospheric imaging: Promise to reality

Modulational instability of lower hybrid waves at the magnetopause

Comment on “The feasibility of radio sounding of the magnetosphere” by W. Calvert et al.

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