Magneto-seismology using spacecraft observations

Denton, R. E.

doi:10.1029/169gm20

Cited by 21 publications

(28 citation statements)

References 51 publications

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“…Additional information about ion composition can be determined from the frequencies of toroidal (azimuthally oscillating) Alfvén waves observed in space (Denton 2006) or on the ground (Waters et al 2006). From the frequencies of observed Alfvén waves, the total mass density ρ M can be determined from a solution of the wave equation (Denton 2006).…”

Section: Average Ion Mass From Alfvén Wavesmentioning

confidence: 99%

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Plasmaspheric Density Structures and Dynamics: Properties Observed by the CLUSTER and IMAGE Missions

et al. 2008

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Plasmaspheric density structures have been studied since the discovery of the plasmasphere in the late 1950s. But the advent of the CLUSTER and IMAGE missions in 2000 has added substantially to our knowledge of density structures, thanks to the new 56 F. Darrouzet et al.capabilities of those missions: global imaging with IMAGE and four-point in situ measurements with CLUSTER. The study of plasma sources and losses has given new results on refilling rates and erosion processes. Two-dimensional density images of the plasmasphere have been obtained. The spatial gradient of plasmaspheric density has been computed. The ratios between H + , He + and O + have been deduced from different ion measurements. Plasmaspheric plumes have been studied in detail with new tools, which provide information on their morphology, dynamics and occurrence. Density structures at smaller scales have been revealed with those missions, structures that could not be clearly distinguished before the global images from IMAGE and the four-point measurements by CLUSTER became available. New terms have been given to these structures, like "shoulders", "channels", "fingers" and "crenulations". This paper reviews the most relevant new results about the plasmaspheric plasma obtained since the start of the CLUSTER and IMAGE missions.

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Section: Average Ion Mass From Alfvén Wavesmentioning

confidence: 99%

“…From the frequencies of observed Alfvén waves, the total mass density ρ M can be determined from a solution of the wave equation (Denton 2006). If the electron density n e is independently available, like from plasma wave measurements (LeDocq et al 1994), the average ion mass M can be determined.…”

Section: Average Ion Mass From Alfvén Wavesmentioning

confidence: 99%

Plasmaspheric Density Structures and Dynamics: Properties Observed by the CLUSTER and IMAGE Missions

et al. 2008

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“…For instance, the fundamental mode, with an antinode in the electric field perturbation (radial) and velocity perturbation (azimuthal) at the equator, is slowed down by a concentration of mass density at the magnetic equator, while the second harmonic, with a node for these quantities at the magnetic equator, is not. Thus the ratios of the harmonic frequencies can be used to infer the field line distribution of mass density, determining for instance, the p value for the power law density (5) (Denton 2006). Calculations based on observations by the CRRES and GOES spacecraft indicated that a power law field line variation with p = 2 does a good job of modeling the average field line dependence of mass density (at high altitudes above at least 1 R E ) for L = 4 − 5, p = 1 is best for L = 5 − 6, and at larger L shells there may be an equatorial peak in mass density (nonmonotonic variation between the magnetic equator and the ionosphere) that is largest in the afternoon local time sector at geomagnetically active times (Takahashi et al 2004;Denton et al 2002b;Denton 2006).…”

Section: Field Line Dependence Of Mass Density Based On Spacecraft Obmentioning

confidence: 99%

“…Thus the ratios of the harmonic frequencies can be used to infer the field line distribution of mass density, determining for instance, the p value for the power law density (5) (Denton 2006). Calculations based on observations by the CRRES and GOES spacecraft indicated that a power law field line variation with p = 2 does a good job of modeling the average field line dependence of mass density (at high altitudes above at least 1 R E ) for L = 4 − 5, p = 1 is best for L = 5 − 6, and at larger L shells there may be an equatorial peak in mass density (nonmonotonic variation between the magnetic equator and the ionosphere) that is largest in the afternoon local time sector at geomagnetically active times (Takahashi et al 2004;Denton et al 2002b;Denton 2006). There is evidence from ground-based observations that a larger value of p might be applicable to lower L shells where ionospheric mass loading has a larger effect Price et al 1999;Denton 2006).…”

Section: Field Line Dependence Of Mass Density Based On Spacecraft Obmentioning

confidence: 99%

Augmented Empirical Models of Plasmaspheric Density and Electric Field Using IMAGE and CLUSTER Data

et al. 2009

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Empirical models for the plasma densities in the inner magnetosphere, including plasmasphere and polar magnetosphere, have been in the past derived from in situ measurements. Such empirical models, however, are still in their initial phase compared to magnetospheric magnetic field models. Recent studies using data from CRRES, POLAR, and IMAGE have significantly improved empirical models for inner-magnetospheric plasma and mass densities. Comprehensive electric field models in the magnetosphere have been developed using radar and in situ observations at low altitude orbits. To use these models at high altitudes one needs to rely strongly on the assumption of equipotential magnetic field lines. 232 B.W. Reinisch et al.Direct measurements of the electric field by the CLUSTER mission have been used to derive an equatorial electric field model in which reliance on the equipotential assumption is less. In this paper we review the recent progress in developing empirical models of plasma densities and electric fields in the inner magnetosphere with emphasis on the achievements from the IMAGE and CLUSTER missions. Recent results from other satellites are also discussed when they are relevant.

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“…Here we used to convert R to MLAT, and we used α = 1.5, a value intermediate between 1, characteristic of the plasmasphere, and 2–3, characteristic of the plasmatrough for n e [ Denton et al , , ]. Note that the field line dependence for n e is statistically different than that of ρ m [ Denton , ] and n MPA,i is closer to n e than to ρ m ; that is why we do not use here. These two adjustments were relatively minor, because the LANL spacecraft were at geostationary orbit close to L dip =6.8 and were near equatorial with MLAT close to 8°.…”

Section: Lanl Mpa Ion Densitymentioning

confidence: 99%

Evolution of mass density and O+ concentration at geostationary orbit during storm and quiet events

et al. 2014

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We investigated mass density ρm and O+ concentration ηO+≡nO+/ne (where nO+ and ne are the O+ and electron density, respectively) during two events, one active and one more quiet. We found ρm from observations of Alfvén wave frequencies measured by the GOES, and we investigated composition by combining measurements of ρm with measurements of ion density nMPA,i from the Magnetospheric Plasma Analyzer (MPA) instrument on Los Alamos National Laboratory spacecraft or ne from the Radio Plasma Imager instrument on the Imager for Magnetopause‐to‐Aurora Global Exploration spacecraft. Using a simple assumption for the He+ density at solar maximum based on a statistical study, we found ηO+ values ranging from near zero to close to unity. For geostationary spacecraft that corotate with the Earth, sudden changes in density for both ρm and ne often appear between dusk and midnight magnetic local time, especially when Kp is significantly above zero. This probably indicates that the bulk (total) ions have energy below a few keV and that the satellites are crossing from closed or previously closed to open drift paths. During long periods that are geomagnetically quiet, the mass density varies little, but ne gradually refills leading to a gradual change in composition from low‐density plasma that is relatively cold and heavy (high‐average ion mass M ≡ ρm/ne) to high‐density plasma that is relatively cold and light (low M) plasmasphere‐like plasma. During active periods we observe a similar daily oscillation in plasma properties from the dayside to the nightside, with cold and light high‐density plasma (more plasmasphere‐like) on the dayside and hotter and more heavy low‐density plasma (more plasma sheet‐like) on the nightside. The value of ne is very dependent on whether it is measured inside or outside a plasmaspheric plume, while ρm is not. All of our results were found at solar maximum; previous results suggest that there will be much less O+ at solar minimum under all conditions.

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Magneto-seismology using spacecraft observations

Cited by 21 publications

References 51 publications

Plasmaspheric Density Structures and Dynamics: Properties Observed by the CLUSTER and IMAGE Missions

Plasmaspheric Density Structures and Dynamics: Properties Observed by the CLUSTER and IMAGE Missions

Augmented Empirical Models of Plasmaspheric Density and Electric Field Using IMAGE and CLUSTER Data

Evolution of mass density and O+ concentration at geostationary orbit during storm and quiet events

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