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The Response of the Magnetosphere to Changes in the Solar Wind Dynamic Pressure: 2. Ion and Electron Kappa Distribution Functions.

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Title: The Response of the Magnetosphere to Changes in the Solar Wind Dynamic Pressure: 2. Ion and Electron Kappa Distribution Functions.
Authors: Eyelade, A. V.1 (AUTHOR) adetayo.eyelade@usach.cl, Stepanova, M.2,3 (AUTHOR) marina.stepanova@usach.cl, Espinoza, C. M.2,3 (AUTHOR), Antonova, E. E.4,5 (AUTHOR), Kirpichev, I. P.5 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Jul2024, Vol. 129 Issue 7, p1-18. 18p.
Subject Terms: Dynamic pressure, Solar wind, Wind pressure, Electron distribution, Magnetosphere, Distribution (Probability theory)
Abstract: The Earth's magnetosphere is filled with a collisionless plasma that exhibits non‐Maxwellian particle distributions which are well described by Kappa functions. In contrast to the Maxwellian, the Kappa contains not only density and temperature but also the kappa index that allows us to characterize the energetic tails. In this study, we analyze the response of the ion and electron Kappa distributions, obtained by fitting ion and electron fluxes measured by the five THEMIS satellites, to changes of the solar wind dynamic pressure. It was found that the solar wind dynamic pressure strongly affects the values of the kappa index, and that its impact depends on the magnetic local time (MLT). In particular, there is a significant dawn‐dusk asymmetry for low PSW values which is enhanced in the night side. Further, we observe a narrow partial ring‐shaped structure at different azimuthal extension that divides the plasma into two clearly defined domains. The results obtained reflect the global reconfiguration of the magnetosphere caused by variations of the solar wind dynamic pressure. Kappa distribution parameters and their average values for different ranges of PSW and MLT are provided, which we believe will contribute as realistic inputs to the modeling of the magnetosphere. Plain Language Summary: The Kappa distribution function, which combines the Maxwellian‐type and the power‐law distributions, has been widely used in literature to describe particle populations in space and astrophysical plasmas. In such environments, ions and electrons rarely experience collisions and they are out of thermal equilibrium, which allows us to get insights into the mechanism of energy transfer in these plasmas. The goal is to investigate the roles of non‐thermal particle distributions, and their response to solar wind dynamic pressure in poorly collisional plasma environments such as the Earth magnetosphere. The availability of high cadence Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite data have enabled us to conduct this statistical analysis using THEMIS and OMNI database. Our findings confirm that the ion and electron kappa parameters exhibit distinct behaviors when subjected to the dynamic pressure exerted by the solar wind. Moreover, we find an interesting narrow partial ring shaped structure at different azimuthal extension exhibiting a local minimum for ion kappa parameters, and a local maximum for electron kappa parameters. Key Points: The behavior of Kappa distribution parameters in the Earth magnetosphere in response to the variation of the solar wind dynamic pressure is studiedThe solar wind dynamic pressure strongly influence ion and electron kappa indicesThe core energy (Ec) exhibits a significant dawn‐dusk asymmetry for ions and much weaker for electrons in various range of PSW [ABSTRACT FROM AUTHOR]
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Abstract:The Earth's magnetosphere is filled with a collisionless plasma that exhibits non‐Maxwellian particle distributions which are well described by Kappa functions. In contrast to the Maxwellian, the Kappa contains not only density and temperature but also the kappa index that allows us to characterize the energetic tails. In this study, we analyze the response of the ion and electron Kappa distributions, obtained by fitting ion and electron fluxes measured by the five THEMIS satellites, to changes of the solar wind dynamic pressure. It was found that the solar wind dynamic pressure strongly affects the values of the kappa index, and that its impact depends on the magnetic local time (MLT). In particular, there is a significant dawn‐dusk asymmetry for low PSW values which is enhanced in the night side. Further, we observe a narrow partial ring‐shaped structure at different azimuthal extension that divides the plasma into two clearly defined domains. The results obtained reflect the global reconfiguration of the magnetosphere caused by variations of the solar wind dynamic pressure. Kappa distribution parameters and their average values for different ranges of PSW and MLT are provided, which we believe will contribute as realistic inputs to the modeling of the magnetosphere. Plain Language Summary: The Kappa distribution function, which combines the Maxwellian‐type and the power‐law distributions, has been widely used in literature to describe particle populations in space and astrophysical plasmas. In such environments, ions and electrons rarely experience collisions and they are out of thermal equilibrium, which allows us to get insights into the mechanism of energy transfer in these plasmas. The goal is to investigate the roles of non‐thermal particle distributions, and their response to solar wind dynamic pressure in poorly collisional plasma environments such as the Earth magnetosphere. The availability of high cadence Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite data have enabled us to conduct this statistical analysis using THEMIS and OMNI database. Our findings confirm that the ion and electron kappa parameters exhibit distinct behaviors when subjected to the dynamic pressure exerted by the solar wind. Moreover, we find an interesting narrow partial ring shaped structure at different azimuthal extension exhibiting a local minimum for ion kappa parameters, and a local maximum for electron kappa parameters. Key Points: The behavior of Kappa distribution parameters in the Earth magnetosphere in response to the variation of the solar wind dynamic pressure is studiedThe solar wind dynamic pressure strongly influence ion and electron kappa indicesThe core energy (Ec) exhibits a significant dawn‐dusk asymmetry for ions and much weaker for electrons in various range of PSW [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2023JA031949