Global images of trapped ring current ions during main phase of 17 March 2015 geomagnetic storm as observed by TWINS

Perez, J. D.; Goldstein, J.; McComas, D. J.; Valek, P. W.; Fok, M. C. H.; Hwang, Kyoung‐Joo

doi:10.1002/2016ja022375

Cited by 18 publications

(32 citation statements)

References 44 publications

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“…Orbits/locations of RBSP (A and B) and THEMIS (a, d, and e) are overplotted together. Added to Figure c is a map of TWINS 1 ion flux, obtained via numerical inversion [ Perez et al , , ] from the nearest‐in‐time (1645 UT) ENA image. The TWINS inversion map shows 15 keV pitch angle‐averaged equatorial flux in units of

\underset{10}{\log} {({normalcm}^{2} normalsr normals normaleV)}^{- 1}

, as given by the colorbar at the bottom right.…”

Section: Ring Current Dynamicsmentioning

confidence: 99%

“…Indeed, fluxes measured by a different instrument (Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE)) on the same spacecraft (RBSP A), obtained during the same 17 March storm, are significantly lower than those measured simultaneously by HOPE. For example, between 1700 and 1715 UT RBSPICE A measured a peak 30 keV flux of ∼300 (cm 2 srseV) −1 [ Perez et al , ]. In the same interval, HOPE A recorded a mean 30 keV flux of 6 × 10 3 (cm 2 srseV) −1 , i.e., >20 times higher flux.…”

Section: Ring Current Dynamicsmentioning

confidence: 99%

“…Another aspect of the observations that we do not herein consider is pitch angle distribution. The TWINS global observations at this time indicate a PAD that is more pancake than isotropic [ Perez et al , ], which might influence the flux of energetic neutrals reaching an imager viewing from above the SM equatorial plane.…”

Section: Ring Current Dynamicsmentioning

confidence: 99%

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Cross‐scale observations of the 2015 St. Patrick's day storm: THEMIS, Van Allen Probes, and TWINS

et al. 2017

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We present cross‐scale magnetospheric observations of the 17 March 2015 (St. Patrick's Day) storm, by Time History of Events and Macroscale Interactions during Substorms (THEMIS), Van Allen Probes (Radiation Belt Storm Probes), and Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS), plus upstream ACE/Wind solar wind data. THEMIS crossed the bow shock or magnetopause 22 times and observed the magnetospheric compression that initiated the storm. Empirical models reproduce these boundary locations within 0.7 RE. Van Allen Probes crossed the plasmapause 13 times; test particle simulations reproduce these encounters within 0.5 RE. Before the storm, Van Allen Probes measured quiet double‐nose proton spectra in the region of corotating cold plasma. About 15 min after a 0605 UT dayside southward turning, Van Allen Probes captured the onset of inner magnetospheric convection, as a density decrease at the moving corotation‐convection boundary (CCB) and a steep increase in ring current (RC) proton flux. During the first several hours of the storm, Van Allen Probes measured highly dynamic ion signatures (numerous injections and multiple spectral peaks). Sustained convection after ∼1200 UT initiated a major buildup of the midnight‐sector ring current (measured by RBSP A), with much weaker duskside fluxes (measured by RBSP B, THEMIS a and THEMIS d). A close conjunction of THEMIS d, RBSP A, and TWINS 1 at 1631 UT shows good three‐way agreement in the shapes of two‐peak spectra from the center of the partial RC. A midstorm injection, observed by Van Allen Probes and TWINS at 1740 UT, brought in fresh ions with lower average energies (leading to globally less energetic spectra in precipitating ions) but increased the total pressure. The cross‐scale measurements of 17 March 2015 contain significant spatial, spectral, and temporal structure.

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\underset{10}{\log} {({normalcm}^{2} normalsr normals normaleV)}^{- 1}

, as given by the colorbar at the bottom right.…”

Section: Ring Current Dynamicsmentioning

confidence: 99%

Section: Ring Current Dynamicsmentioning

confidence: 99%

See 1 more Smart Citation

Cross‐scale observations of the 2015 St. Patrick's day storm: THEMIS, Van Allen Probes, and TWINS

et al. 2017

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“…Regarding the global‐local agreement in Figure b, Perez et al () had demonstrated that stereo imaging more accurately resolves flux peaks. The newer result by Perez et al (), using only TWINS 1, shows how single‐point inversions can still achieve reasonable agreement—in both flux and PAD—with in situ data.…”

Section: Scientific Results From 2013 To 2017mentioning

confidence: 93%

The Big Picture: Imaging of the Global Geospace Environment by the TWINS Mission

Goldstein

McComas

2018

Reviews of Geophysics

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Encircling our planet at distances of 2.5 to 8 Earth radii is a dynamic plasma population known as the ring current (RC). During geomagnetic storms, the solar wind's interaction with Earth's magnetic field pumps petaJoules of energy into the RC, energizing and transporting particles. To measure the global geospace response, RC imaging is performed by capturing energetic neutral atoms (ENAs) created by charge exchange between geospace ions and the neutral exosphere. The H exosphere is itself imaged via its geocoronal Lyman‐α glow. Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS) is a stereoscopic ENA and Lyman‐α imaging mission that has recorded the deep minimum of solar cycle (SC) 23 and the moderate maximum of SC 24, observing geospace conditions ranging from utterly quiet to major storms. This review covers TWINS studies of the geospace response published during 2013 to 2017. Stereo ENA imaging has revealed new dimensionality and structure of RC ions. Continuous coverage by two imagers has allowed monitoring storms from start to finish. Deconvolution of the low‐altitude signal has extended ENA analysis and revealed causal connections between the trapped and precipitating ion populations. ENA‐based temperature and composition analyses have been refined, validated, and applied to an unprecedented sequence of solar activity changes in SC 23 and SC 24. Geocoronal imaging has revealed a surprising amount of time variability and structure in the neutral H exosphere, driven by both Sun and solar wind. Global models have been measurably improved. Routine availability of simultaneous in situ measurements has fostered huge leaps forward in the areas of ENA validation and cross‐scale studies.

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“…Current inversion and forward modeling techniques from ENA images do not fully utilize LAE signatures and MCCIs effects (Brandt et al, ; Perez et al, ; Roelof & Skinner, ; Vallat et al, ). These midlatitude to high‐latitude LAEs (dominant ENA signatures from prestorm through main phase (i.e., Valek et al, , )) include plasma sheet particles mapping farther down into the magnetotail, as shown in Perez et al (). Our model allows us to apply these findings to interpret observations where MCCIs are involved, maximizing the particle information that can be retrieved by global ENA images.…”

Section: Discussionmentioning

confidence: 99%

Low‐Altitude Emission of Energetic Neutral Atoms: Multiple Interactions and Energy Loss

et al. 2017

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Low‐altitude emissions (LAEs) are the energetic neutral atom (ENA) signature of ring current ions precipitating along the magnetic field to an altitude of 200–800 km. This altitude region is considered to be “optically thick” because ring current ions undergo multiple charge changing interactions (MCCIs) with Earth's dense oxygen exosphere. While each interaction involves an energy loss of ~36 eV, no prior study has determined the accumulated energy lost by 1–100 keV H+ emerging as LAEs. We have developed a 2‐D model with a geomagnetic dipole that captures the net effects in energy loss and pitch angle evolution as a result of MCCIs without the computational requirements of a full Monte Carlo simulation. Dependent on the amount of latitudinal migration, the energy loss is greater than 20% for ions below 60 keV for equatorward moving particles (30 keV for poleward). Since the ENA travels ballistically across a geomagnetic dipole, upon reionization, ion velocity along the local field increases (antiparallel in the northern hemisphere). Redirecting the particle upward through MCCIs is most effective during poleward ENA motion. The net effect is to redirect precipitating ions (below 2,500 km) to eventually emerge from the optically thick region either as an ion or ENA. Precipitation is a joint ion‐neutral process, affecting both the energy and pitch angle distribution through the transverse motion of ENA segments in a converging field. For particles that enter the MCCI regime, the energy loss and evolution of the pitch angle distribution must be considered within a realistic magnetic field.

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Global images of trapped ring current ions during main phase of 17 March 2015 geomagnetic storm as observed by TWINS

Cited by 18 publications

References 44 publications

Cross‐scale observations of the 2015 St. Patrick's day storm: THEMIS, Van Allen Probes, and TWINS

Cross‐scale observations of the 2015 St. Patrick's day storm: THEMIS, Van Allen Probes, and TWINS

The Big Picture: Imaging of the Global Geospace Environment by the TWINS Mission

Low‐Altitude Emission of Energetic Neutral Atoms: Multiple Interactions and Energy Loss

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