Quasi-parallel Antisunward-propagating Whistler Waves Associated with the Electron Deficit in the Near-Sun Solar Wind: Particle-in-cell Simulation
In situ observations of the solar wind have shown that the electron velocity distribution function (VDF) consists of a quasi-Maxwellian core, comprising most of the electron population, and two sparser components: the halo, which are suprathermal and quasi-isotropic electrons, and an escaping beam p...
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2025-01-01
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| author | Alfredo Micera Daniel Verscharen Jesse T. Coburn Maria Elena Innocenti |
| author_facet | Alfredo Micera Daniel Verscharen Jesse T. Coburn Maria Elena Innocenti |
| author_sort | Alfredo Micera |
| collection | DOAJ |
| description | In situ observations of the solar wind have shown that the electron velocity distribution function (VDF) consists of a quasi-Maxwellian core, comprising most of the electron population, and two sparser components: the halo, which are suprathermal and quasi-isotropic electrons, and an escaping beam population, the strahl. Recent Parker Solar Probe (PSP) and Solar Orbiter (SO) observations have added one more ingredient to the known nonthermal features, the deficit—a depletion in the sunward region of the VDF, already predicted by exospheric models but never so extensively observed. By employing particle-in-cell simulations, we study electron VDFs that reproduce those typically observed in the inner heliosphere and investigate whether the electron deficit may contribute to the onset of kinetic instabilities. Previous studies and in situ observations show that strahl electrons drive oblique whistler waves unstable, which in turn scatters them. As a result, suprathermal electrons can occupy regions of phase space where they fulfill resonance conditions with the parallel-propagating whistler wave. The suprathermal electrons lose kinetic energy, resulting in the generation of unstable waves. The sunward side of the VDF, initially depleted of electrons, is gradually filled, as this wave−particle interaction process, triggered by the depletion itself, takes place. Our findings are compared and validated against current PSP and SO observations: among others, our study provides a mechanism explaining the presence in the heliosphere of regularly observed parallel antisunward whistler waves, suggests why these waves are frequently observed concomitant with distributions presenting an electron deficit, and describes a noncollisional heat flux regulating process. |
| format | Article |
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| institution | Kabale University |
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| language | English |
| publishDate | 2025-01-01 |
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| spelling | doaj-art-373542aba76f4e4e95fa244ededf88342025-01-29T06:17:37ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01979222610.3847/1538-4357/ada3d7Quasi-parallel Antisunward-propagating Whistler Waves Associated with the Electron Deficit in the Near-Sun Solar Wind: Particle-in-cell SimulationAlfredo Micera0https://orcid.org/0000-0001-9293-174XDaniel Verscharen1https://orcid.org/0000-0002-0497-1096Jesse T. Coburn2https://orcid.org/0000-0002-2576-0992Maria Elena Innocenti3https://orcid.org/0000-0002-5782-0013Institut für Theoretische Physik, Ruhr-Universität Bochum , Bochum, Germany ; alfredo.micera@rub.deMullard Space Science Laboratory, University College London , Dorking, UKMullard Space Science Laboratory, University College London , Dorking, UK; Space Science Institute , Boulder, CO 80301, USAInstitut für Theoretische Physik, Ruhr-Universität Bochum , Bochum, Germany ; alfredo.micera@rub.deIn situ observations of the solar wind have shown that the electron velocity distribution function (VDF) consists of a quasi-Maxwellian core, comprising most of the electron population, and two sparser components: the halo, which are suprathermal and quasi-isotropic electrons, and an escaping beam population, the strahl. Recent Parker Solar Probe (PSP) and Solar Orbiter (SO) observations have added one more ingredient to the known nonthermal features, the deficit—a depletion in the sunward region of the VDF, already predicted by exospheric models but never so extensively observed. By employing particle-in-cell simulations, we study electron VDFs that reproduce those typically observed in the inner heliosphere and investigate whether the electron deficit may contribute to the onset of kinetic instabilities. Previous studies and in situ observations show that strahl electrons drive oblique whistler waves unstable, which in turn scatters them. As a result, suprathermal electrons can occupy regions of phase space where they fulfill resonance conditions with the parallel-propagating whistler wave. The suprathermal electrons lose kinetic energy, resulting in the generation of unstable waves. The sunward side of the VDF, initially depleted of electrons, is gradually filled, as this wave−particle interaction process, triggered by the depletion itself, takes place. Our findings are compared and validated against current PSP and SO observations: among others, our study provides a mechanism explaining the presence in the heliosphere of regularly observed parallel antisunward whistler waves, suggests why these waves are frequently observed concomitant with distributions presenting an electron deficit, and describes a noncollisional heat flux regulating process.https://doi.org/10.3847/1538-4357/ada3d7Plasma astrophysicsSolar windSpace plasmas |
| spellingShingle | Alfredo Micera Daniel Verscharen Jesse T. Coburn Maria Elena Innocenti Quasi-parallel Antisunward-propagating Whistler Waves Associated with the Electron Deficit in the Near-Sun Solar Wind: Particle-in-cell Simulation The Astrophysical Journal Plasma astrophysics Solar wind Space plasmas |
| title | Quasi-parallel Antisunward-propagating Whistler Waves Associated with the Electron Deficit in the Near-Sun Solar Wind: Particle-in-cell Simulation |
| title_full | Quasi-parallel Antisunward-propagating Whistler Waves Associated with the Electron Deficit in the Near-Sun Solar Wind: Particle-in-cell Simulation |
| title_fullStr | Quasi-parallel Antisunward-propagating Whistler Waves Associated with the Electron Deficit in the Near-Sun Solar Wind: Particle-in-cell Simulation |
| title_full_unstemmed | Quasi-parallel Antisunward-propagating Whistler Waves Associated with the Electron Deficit in the Near-Sun Solar Wind: Particle-in-cell Simulation |
| title_short | Quasi-parallel Antisunward-propagating Whistler Waves Associated with the Electron Deficit in the Near-Sun Solar Wind: Particle-in-cell Simulation |
| title_sort | quasi parallel antisunward propagating whistler waves associated with the electron deficit in the near sun solar wind particle in cell simulation |
| topic | Plasma astrophysics Solar wind Space plasmas |
| url | https://doi.org/10.3847/1538-4357/ada3d7 |
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