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

Walsh, Brian M.; Collier, M. R.; Küntz, K. D.; Porter, F. S.; Sibeck, D. G.; Snowden, S. L.; Carter, Jennifer; Collado‐Vega, Y. M.; Connor, H. K.; Cravens, T. E.; Read, A. M.; Sembay, S.; Thomas, Nicholas E.

doi:10.1002/2016ja022348

Cited by 38 publications

(36 citation statements)

References 63 publications

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“…They also showed that peak emissions along lines-of-sight that pass through the subsolar magnetosheath exceed background levels for all but the lowest solar wind plasma fluxes. Walsh et al (2016b) described the process by which realistic global images of soft Xray images from the magnetosheath and cusps can be simulated for wide field-of-view imagers at specified locations. First the magnetospheric contribution is calculated using plasma values from a global magnetohydrodynamic simulation and neutral densities from an exospheric model.…”

Section: Past Modeling Effortsmentioning

confidence: 99%

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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Section: Past Modeling Effortsmentioning

confidence: 99%

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

et al. 2018

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“…Recently, a novel approach was proposed to remotely detect the large‐scale magnetopause: soft X‐ray imaging (Branduardi‐Raymont et al, , ; Collier et al, ; Sibeck et al, ; Walsh et al, ). The basic mechanism for soft X‐ray emissions in the magnetosheath and cusp regions is the solar wind charge exchange (SWCX) process.…”

Section: Introductionmentioning

confidence: 99%

Soft X‐ray Imaging of the Magnetosheath and Cusps Under Different Solar Wind Conditions: MHD Simulations

et al. 2019

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The soft X-ray emissions from the Earth's magnetosheath and cusp regions are simulated under different solar wind conditions, based on the PPMLR-MHD code. The X-ray images observed by a hypothetical telescope are presented, and the basic responses of the magnetopause and cusp regions are discernable in these images. From certain viewing geometries, the magnetopause position in the equatorial plane, as well as the latitudinal scales and azimuthal extent of cusp can be directly extracted from the X-ray images. With these reconstructed positions, the issues we are able to analyze include but are not limited to the compression of magnetopause and widening of the cusp after an enhancement of solar wind flux, as well as the erosion of the magnetopause and equatorward motion of cusp after the southward turning of the interplanetary magnetic field. Hence, the X-ray imaging is an appropriate technique to study the large-scale motion of magnetopause and cusps in response to solar wind variations.Recently, a novel approach was proposed to remotely detect the large-scale magnetopause: soft X-ray imaging (Branduardi-Raymont et al., 2012Collier et al., 2012;Sibeck et al., 2018;Walsh et al., 2016). The basic mechanism for soft X-ray emissions in the magnetosheath and cusp regions is the solar wind charge exchange (SWCX) process. On the one hand, heavy ions in high charge states, such as O 7+ , exist in the ambient solar wind. On the other hand, neutral atoms and molecules, such as the hydrogen, are ubiquitous in the geospace environment due to the Earth's exosphere. When they encounter and interact with each other, an electron can be transferred from the neutral to the ion. As a result of capturing the electron, the solar wind ion is in an electronically excited state, and then emits one or more photons in the extreme ultraviolet or soft X-ray bands while decaying to the lower-energy state. In the magnetosheath, the density of the highly charged ions is enhanced as the solar wind slows down after the bow shock. The solar wind cannot directly penetrate the magnetopause, and thus, the plasma with solar wind origin is quite tenuous inside the magnetosphere. This leads to a sharp boundary at the magnetopause in terms of the soft X-ray emissivity. The cusps are special regions on the magnetopause. The solar wind plasma can enter directly, and thus, the X-ray emissivity is expected to be higher inside of the cusps. With different solar wind fluxes and/or interplanetary magnetic fields (IMF), the X-ray emissivity in the magnetosheath and cusps can be

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“…Because of this discrepancy, MHD models do a poor job of simulating both the size of the emitting region and the emission strength. Walsh et al (2016b) found that the density of the cusp in MHD simulations is usually less than half that of the cusp density as measured by the Polar mission. The observed cusp has an opening angle of ∼ 4 • , which roughly half as wide (in latitude) as the cusp produced by MHD simulations.…”

Section: The Cuspsmentioning

confidence: 90%

“…Were it possible to model SWCX emission for an arbitrary time and look direction, the history of SWCX research would not be over. Remote sensing of the solar wind and direct imaging of the magnetosheath are exciting possibilities for space physicists Walsh et al 2016b). As we will see in the following sections, modeling is still far from successful.…”

Section: Curbing the Chaosmentioning

confidence: 99%

Solar wind charge exchange: an astrophysical nuisance

Küntz

2018

Astron Astrophys Rev

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Solar Wind Charge-Exchange (SWCX) emission is present in every Xray observation of an astrophysical object. The emission is problematic when one cannot remove the foreground by the simultaneous measurement of a nearby field. SWCX emission is a serious impediment to the study of the diffuse hot ISM, including the Galactic halo, as its contribution to diagnostic emission lines is temporally variable. Modeling the SWCX emission, in order to remove it from our observations, has proven to be more difficult than originally anticipated. This work reviews our current understanding of SWCX emission, with special attention to all of the components required for future modeling tools. Since, in the absence of such a tool, observing programs can still be constructed to minimize the effect of SWCX, mitigation strategies are discussed. Although some aspects of SWCX will be very difficult to characterize, progress continues on many fronts.

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

Cited by 38 publications

References 63 publications

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

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

Soft X‐ray Imaging of the Magnetosheath and Cusps Under Different Solar Wind Conditions: MHD Simulations

Solar wind charge exchange: an astrophysical nuisance

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