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Probing the Magnetosheath Boundaries Using Interstellar Boundary Explorer (IBEX) Orbital Encounters.

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Title: Probing the Magnetosheath Boundaries Using Interstellar Boundary Explorer (IBEX) Orbital Encounters.
Authors: Hart, S. T.1,2 samuel.hart@contractor.swri.org, Dayeh, M. A.1,2, Reisenfeld, D. B.3, Janzen, P. H.4, McComas, D. J.5, Allegrini, F.1,2, Fuselier, S. A.1,2, Ogasawara, K.1, Szalay, J. R.5, Funsten, H. O.3, Petrinec, S. M.6
Source: Journal of Geophysical Research. Space Physics. Jul2021, Vol. 126 Issue 7, p1-14. 14p.
Subject Terms: *Ionosphere, *Solar activity, Heliosphere (Ionosphere), Heliospheric current sheet, Solar wind
Abstract: Inside the magnetosheath, the IBEX‐Hi energetic neutral atom (ENA) imager measures a distinct background count rate that is more than 10 times the typical heliospheric ENA emissions observed when IBEX is outside the magnetosheath. The source of this enhancement is magnetosheath ions of solar wind (SW) origin that deflect around the Earth's magnetopause (MP), scatter and neutralize from the anti‐sunward part of the IBEX‐Hi sunshade, and continue into the instrument as neutral atoms, behaving indistinguishably from ENAs emitted from distant plasma sources. While this background pollutes observations of outer heliospheric ENAs, it provides a clear signature of IBEX crossings over the magnetospheric boundaries. In this study, we investigate IBEX encounters with the magnetosheath boundaries using ∼8 yr of orbital data, and we determine the MP and bow shock (BS) locations derived from this background signal. We find 280 BS crossings from XGSE ∼ 11 Re to XGSE ∼ −36 Re and 241 MP crossings from XGSE ∼ 6 Re to XGSE ∼ −48 Re. We compare IBEX BS and MP crossing locations to those from IMP‐8, Geotail, Cluster, Magion‐4, ISEE, and Magnetospheric Multiscale Mission, and we find that IBEX crossing locations overlap with the BS and MP locations inferred from these other data sets. In this paper, we demonstrate how IBEX can be used to identify magnetosheath crossings, and extend boundary observations well past the terminator, thus further constraining future models of magnetosheath boundaries. Furthermore, we use the IBEX data set to show observational evidence of near‐Earth magnetotail squeezing during periods of strong interplanetary magnetic field By. Plain Language Summary: The Interstellar Boundary Explorer (IBEX) spacecraft is designed to use remote‐sensing to examine the outer reaches of the solar system, yet it has been shown to have many magnetospheric applications as well. The primary interaction between the SW and the Earth's magnetosphere is the creation of a comet‐tail like structure known as the magnetosheath. The magnetosheath is highly dynamic, and its size and shape changes in response to changing SW conditions, with the exact details presently unknown. In this paper, we demonstrate how the IBEX's highly eccentric orbit allows for hundreds of encounters with both the inner and outer magnetosheath boundaries, and we use these crossings to create a new magnetosheath boundary data set. We then compare our new data set with data sets from previous magnetospheric missions. Finally, we use our new data set to provide observational evidence for a poorly understood phenomenon known as magnetotail squeezing. Key Points: We demonstrate a technique for producing both Bow Shock and Magnetopause data sets using the Interstellar Boundary ExplorerWe introduce new boundary crossings further tailward than previously used data sets into underexplored magnetosheath regionsWe provide observational evidence of magnetotail squeezing during periods when the interplanetary magnetic field has a strong y‐component [ABSTRACT FROM AUTHOR]
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Abstract:Inside the magnetosheath, the IBEX‐Hi energetic neutral atom (ENA) imager measures a distinct background count rate that is more than 10 times the typical heliospheric ENA emissions observed when IBEX is outside the magnetosheath. The source of this enhancement is magnetosheath ions of solar wind (SW) origin that deflect around the Earth's magnetopause (MP), scatter and neutralize from the anti‐sunward part of the IBEX‐Hi sunshade, and continue into the instrument as neutral atoms, behaving indistinguishably from ENAs emitted from distant plasma sources. While this background pollutes observations of outer heliospheric ENAs, it provides a clear signature of IBEX crossings over the magnetospheric boundaries. In this study, we investigate IBEX encounters with the magnetosheath boundaries using ∼8 yr of orbital data, and we determine the MP and bow shock (BS) locations derived from this background signal. We find 280 BS crossings from XGSE ∼ 11 Re to XGSE ∼ −36 Re and 241 MP crossings from XGSE ∼ 6 Re to XGSE ∼ −48 Re. We compare IBEX BS and MP crossing locations to those from IMP‐8, Geotail, Cluster, Magion‐4, ISEE, and Magnetospheric Multiscale Mission, and we find that IBEX crossing locations overlap with the BS and MP locations inferred from these other data sets. In this paper, we demonstrate how IBEX can be used to identify magnetosheath crossings, and extend boundary observations well past the terminator, thus further constraining future models of magnetosheath boundaries. Furthermore, we use the IBEX data set to show observational evidence of near‐Earth magnetotail squeezing during periods of strong interplanetary magnetic field By. Plain Language Summary: The Interstellar Boundary Explorer (IBEX) spacecraft is designed to use remote‐sensing to examine the outer reaches of the solar system, yet it has been shown to have many magnetospheric applications as well. The primary interaction between the SW and the Earth's magnetosphere is the creation of a comet‐tail like structure known as the magnetosheath. The magnetosheath is highly dynamic, and its size and shape changes in response to changing SW conditions, with the exact details presently unknown. In this paper, we demonstrate how the IBEX's highly eccentric orbit allows for hundreds of encounters with both the inner and outer magnetosheath boundaries, and we use these crossings to create a new magnetosheath boundary data set. We then compare our new data set with data sets from previous magnetospheric missions. Finally, we use our new data set to provide observational evidence for a poorly understood phenomenon known as magnetotail squeezing. Key Points: We demonstrate a technique for producing both Bow Shock and Magnetopause data sets using the Interstellar Boundary ExplorerWe introduce new boundary crossings further tailward than previously used data sets into underexplored magnetosheath regionsWe provide observational evidence of magnetotail squeezing during periods when the interplanetary magnetic field has a strong y‐component [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2021JA029278