Density variations in the Earth's magnetospheric cusps

Walsh, Brian M.; Niehof, J. T.; Collier, M. R.; Welling, D. T.; Sibeck, D. G.; Mozer, F. S.; Fritz, T. A.; Küntz, K. D.

doi:10.1002/2015ja022095

Cited by 14 publications

(29 citation statements)

References 71 publications

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“…To conclude, as shown in Figures , the coupled MFLFM‐IPWM test simulation suggests that at a radial distance of 5 R E (and above), ionospheric populations have relatively small contributions to the total plasma pressure and the simulated ratio of N cusp / N sw especially during quiet periods, which is consistent with Walsh et al (). At radial distances smaller than 3.5 R E , the ionospheric populations are important in order to make the N cusp / N sw ratio in agreement with observations.…”

Section: Effect Of Ionospheric Outflowsupporting

confidence: 87%

“…As shown in Figure 2a, in the Northern Hemisphere, the average number density in the high-altitude cusp region increases approximately linearly with the solar wind number density with a correlation coefficient of 0.91, which indicates the efficient direct entry of solar wind plasma into the high-altitude cusp region in the simulation. The ratio between the cusp number density and SW number density is 0.78 in the global simulation, which agrees well with the ratio of 0.8 in the observations of Walsh et al (2016), which is averaged over all seasons and dipole tilt conditions. Note that since the Polar's orbit passes through the noon-midnight meridian twice per year (once with perigee toward noon and once with apogee toward noon), the condition of being within 1.5 h of local noon is met during two periods each year, one in March-April and the other in September-October.…”

Section: Cusp Density Versus Sw Density 311 the Equinox Casementioning

confidence: 92%

“…In this study, we investigate the relationship between solar wind conditions and cusp number density at high-altitude (radial distance of 5 R E ) using the Lyon-Fedder-Mobarry (LFM) global magnetosphere model based on two event simulations near March equinox and December solstice, respectively. The simulated relationship between solar wind number density and cusp number density is in agreement with the statistical results derived by Walsh et al (2016). With the implementation of a direct-entry cusp electron precipitation model, the effectiveness of various SW coupling functions are tested using the simulated number flux and energy flux of cusp soft electron, for both the equinox and the solstice cases.…”

Section: Introductionmentioning

confidence: 99%

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On the Relation Between Soft Electron Precipitations in the Cusp Region and Solar Wind Coupling Functions

et al. 2018

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In this study, the correlations between the fluxes of precipitating soft electrons in the cusp region and solar wind coupling functions are investigated utilizing the Lyon‐Fedder‐Mobarry global magnetosphere model simulations. We conduct two simulation runs during periods from 20 March 2008 to 16 April 2008 and from 15 to 24 December 2014, which are referred as “Equinox Case” and “Solstice Case,” respectively. The simulation results of Equinox Case show that the plasma number density in the high‐latitude cusp region scales well with the solar wind number density (ncusp/nsw=0.78), which agrees well with the statistical results from the Polar spacecraft measurements. For the Solstice Case, the plasma number density of high‐latitude cusp in both hemispheres increases approximately linearly with upstream solar wind number density with prominent hemispheric asymmetry. Due to the dipole tilt effect, the average number density ratio ncusp/nsw in the Southern (summer) Hemisphere is nearly 3 times that in the Northern (winter) Hemisphere. In addition to the solar wind number density, 20 solar wind coupling functions are tested for the linear correlation with the fluxes of precipitating cusp soft electrons. The statistical results indicate that the solar wind dynamic pressure p exhibits the highest linear correlation with the cusp electron fluxes for both equinox and solstice conditions, with correlation coefficients greater than 0.75. The linear regression relations for equinox and solstice cases may provide an empirical calculation for the fluxes of cusp soft electron precipitation based on the upstream solar wind driving conditions.

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Section: Effect Of Ionospheric Outflowsupporting

confidence: 87%

Section: Cusp Density Versus Sw Density 311 the Equinox Casementioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

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On the Relation Between Soft Electron Precipitations in the Cusp Region and Solar Wind Coupling Functions

et al. 2018

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“…Plasma densities on these cusp magnetic field lines are slightly less than those in the magnetosheath, but far greater than those in the adjacent magnetosphere (Lavraud et al 2004;Walsh et al 2016a). Furthermore, the cusps extend deep into regions of the exosphere where neutral densities are very high.…”

Section: The Earth's Cuspsmentioning

confidence: 88%

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

et al. 2018

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Both heliophysics and planetary physics seek to understand the complex nature of the solar wind's interaction with solar system obstacles like Earth's magnetosphere, the ionospheres of Venus and Mars, and comets. Studies with this objective are frequently conducted with the help of single or multipoint in situ electromagnetic field and particle observations, guided by the predictions of both local and global numerical simulations, and placed in con- text by observations from far and extreme ultraviolet (FUV, EUV), hard X-ray, and energetic neutral atom imagers (ENA). Each proposed interaction mechanism (e.g., steady or transient magnetic reconnection, local or global magnetic reconnection, ion pick-up, or the KelvinHelmholtz instability) generates diagnostic plasma density structures. The significance of each mechanism to the overall interaction (as measured in terms of atmospheric/ionospheric loss at comets, Venus, and Mars or global magnetospheric/ionospheric convection at Earth) remains to be determined but can be evaluated on the basis of how often the density signatures that it generates are observed as a function of solar wind conditions. This paper reviews efforts to image the diagnostic plasma density structures in the soft (low energy, 0.1-2.0 keV) X-rays produced when high charge state solar wind ions exchange electrons with the exospheric neutrals surrounding solar system obstacles. The introduction notes that theory, local, and global simulations predict the characteristics of plasma boundaries such the bow shock and magnetopause (including location, density gradient, and motion) and regions such as the magnetosheath (including density and width) as a function of location, solar wind conditions, and the particular mechanism operating. In situ measurements confirm the existence of time-and spatial-dependent plasma density structures like the bow shock, magnetosheath, and magnetopause/ionopause at Venus, Mars, comets, and the Earth. However, in situ measurements rarely suffice to determine the global extent of these density structures or their global variation as a function of solar wind conditions, except in the form of empirical studies based on observations from many different times and solar wind conditions. Remote sensing observations provide global information about auroral ovals (FUV and hard X-ray), the terrestrial plasmasphere (EUV), and the terrestrial ring current (ENA). ENA instruments with low energy thresholds (∼ 1 keV) have recently been used to obtain important information concerning the magnetosheaths of Venus, Mars, and the Earth. Recent technological developments make these magnetosheaths valuable potential targets for high-cadence wide-field-of-view soft X-ray imagers.Section 2 describes proposed dayside interaction mechanisms, including reconnection, the Kelvin-Helmholtz instability, and other processes in greater detail with an emphasis on the plasma density structures that they generate. It focuses upon the questions that remain as yet unanswered, such as the significanc...

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“…The magnetic topology of the magnetospheric cusps allows solar wind plasma to enter deep into the magnetosphere where the exospheric density is high [Kremser et al, 1995;Perry et al, 2000;Walsh et al, 2016]. Fujimoto et al [2007] monitored emissions along a line of sight passing through the northern cusp from the low-altitude Suzaku spacecraft and attributed enhancements to a significant charge exchange in the cusp.…”

Section: Introductionmentioning

confidence: 99%

Wide field‐of‐view soft X‐ray imaging for solar wind‐magnetosphere interactions

et al. 2016

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Soft X‐ray imagers can be used to study the mesoscale and macroscale density structures that occur whenever and wherever the solar wind encounters neutral atoms at comets, the Moon, and both magnetized and unmagnetized planets. Charge exchange between high charge state solar wind ions and exospheric neutrals results in the isotropic emission of soft X‐ray photons with energies from 0.1 to 2.0 keV. At Earth, this process occurs primarily within the magnetosheath and cusps. Through providing a global view, wide field‐of‐view imaging can determine the significance of the various proposed solar wind‐magnetosphere interaction mechanisms by evaluating their global extent and occurrence patterns. A summary of wide field‐of‐view (several to tens of degrees) soft X‐ray imaging is provided including slumped micropore microchannel reflectors, simulated images, and recent flight results.

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Density variations in the Earth's magnetospheric cusps

Cited by 14 publications

References 71 publications

On the Relation Between Soft Electron Precipitations in the Cusp Region and Solar Wind Coupling Functions

On the Relation Between Soft Electron Precipitations in the Cusp Region and Solar Wind Coupling Functions

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

Wide field‐of‐view soft X‐ray imaging for solar wind‐magnetosphere interactions

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